conclusion of reflection of light experiment

Investigating Reflection ( Cambridge O Level Physics )

Revision note.

Investigating Reflection

Aims of the experiment.

• To investigate reflection by a plane mirror
• Independent variable = angle of incidence, i
• Dependent variable = angle of reflection, r
• Distance of ray box from mirror
• Width of the light beam
• Same frequency / wavelength of the light

Apparatus to investigate reflection

• Set up the apparatus as shown in the diagram
• In the middle of the paper use a ruler to mark a straight line of about 10 cm long
• Use a protractor to draw a 90° line that bisects (cuts in half) the 10 cm line
• Place the mirror on the first line as shown in the diagram above
• Switch on the ray box and aim a beam of light at the point where the two drawn lines cross at an angle
• A point just after leaving the ray box
• The point on the reflected beam about 10 cm away from the mirror
• Remove the ray box and mirror
• Use a ruler to join the two marked positions to the point where the originally drawn lines crossed
• Use the protractor to measure the two angles from the 90° line. The angle for the ray towards the mirror is the angle of incidence, and the other is the angle of reflection
• Repeat the experiment three times with the beam of light aimed at different angles
• An example of the data collection table is shown below:

Example Results Table

Analysis of Results

• The law of reflection states:
• i = angle of incidence in degrees (°)
• r = angle of reflection in degrees (°)
• If the experiment was carried out correctly, the angles should be the same, as shown below:

Correct Results of the Experiment

Law of reflection demonstrated correctly

Evaluating the Experiment

Systematic Errors:

• Use a set square to draw perpendicular lines
• If the mirror is distorted, this could affect the reflection angle, so make sure there are little to no blemishes on it

Random Errors:

• Use a sharpened pencil and mark in the middle of the beam
• Use a protractor with a higher resolution

Safety Considerations

• Run burns under cold running water for at least five minute
• Avoid looking directly at the light
• Stand behind the ray box during the experiment
• Keep all liquids away from the electrical equipment and paper
• Damages on the mirror can affect the outcome of the reflection experiment

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Dan graduated with a First-class Masters degree in Physics at Durham University, specialising in cell membrane biophysics. After being awarded an Institute of Physics Teacher Training Scholarship, Dan taught physics in secondary schools in the North of England before moving to SME. Here, he carries on his passion for writing enjoyable physics questions and helping young people to love physics.

Law of Reflection Lab

↘︎ Apr 18, 2010 … 6′ … download ⇠ | skip ⇢

To develop an understanding of the Law of Reflection, to apply the Law of Reflection to finding images formed by plane and spherical mirrors, and to learn to draw ray diagrams to assist in predicting the locations of images formed by spherical concave mirrors.

According to the Law of Reflection, the angle of incidence will equal the angle of reflection when light is shone off a flat reflecting surface. When light is shone off a spherical mirror, it will converge at a focal point. Light will converge at a real focal point in front the concave mirror, and light will converge at a virtual focal point somewhere behind the convex mirror. An object placed beyond the curvature of a mirror will cast an inverted, shrunken, real image. An object placed at the curvature of a mirror will project and inverted, true to size, real image. Finally, an object placed between the curvature and focal point will project an inverted, magnified, real image.

Labeled Diagrams

See attached sheet.

Focal length of mirror f = 5.5 cm

1. What statement can you make regarding the relative positioning of the normal, the incident ray and the reflected ray?

The angle between the incident ray and the normal is equal to the angle between the reflected ray and the normal.

2. Do your observations validate the Law of Reflection?

Yes, the observations validate the Law of Reflection as θ i = θ r or the values are extremely close in all trials.

3. Using your data above, create a graph in Graphical Analysis of pq vs. p + q. Your graph should appear linear. Perform a linear fit on the graph.

See graphs section.

4. There is an equation in geometrical optics called the mirror equation. It relates the object distance p and the image distance q to the focal length of the mirror f: 1/p + 1/q = 1/f. The mirror equation can be used to determine a mirror’s focal length. Solve the above equation algebraically for f.

In the instance of case 1, for trial 1 f = 4.0 cm, for trial 2 f = 4.1 cm, and for trial 3 f = 3.8 cm. In the instance of case 2, for trial 1 f = 4.1 cm. In the instance of case 3, for trial 1 f = 4.0 cm, for trial 2 f = 4.2 cm, and for trial 3 f = 4.3 cm. The average value for f is 4.1 cm.

5. How is your answer to Question 4 related to the slope of your graph from Question 3?

The slope of the graph from Question 3 is 4.0 cm, so these values are strikingly similar.

6. What is the percent difference between your slope and the focal length of the mirror that you measured?

The percent difference between the slope, 4.0 cm, and the focal length of the mirror that was measured, 5.5 cm, is 32%.

7. The magnification of the image of an object from a spherical mirror can also be expressed as the ratio –q/p. Calculate this ratio for each of your object and image distances and record in your data table.

See data table.

8. How does the ratio of –q/p compare to your calculated magnifications h i /h o for each entry? What is the percent difference?

In regards to case 1, the values for both h i /h o and –q/p are negative, but the values for h i /h o are more negative than that of –q/p. The percent difference for trial 1 is 126%, for trial 2 is 132%, and for trial 3 is 153%.

Case 2 shares the same characteristics of case 1. The percent difference is 112%.

In regards to case 3, the values are quite dissimilar because all h i /h o values are positive while all –q/p values are negative. The percent difference for trial 1 is 1200%, trial 2 is 700%, and trial 3 is 569%. It is thought that the images were recorded as upright when they were really inverted, which caused this error, but it cannot be validated by repeating the laboratory procedure at this time.

9. Do your data verify the prediction from your ray diagrams?

In regards to case 1, the values for –q/p verify the predictions made from the ray diagram, as when the object was moved further away from the mirror, the images became smaller. The values for h i /h o dot not support this claim however, as they say that the image way magnified, but in reality the projected image was smaller. The images were also inverted as told by the negative sign.

In regards to case 2, neither the value for –q/p nor h i /h o verifies the prediction made from the ray diagram. The magnification should have been 0.

In regards to case 3, the values for –q/p do verify the predictions made from the ray diagram, as when the object was moved closer to f, the images became more magnified. The images were recorded as being upright, but in reality were probably inverted as suggested by theory and the negative sign the –q/p value carries.

For part 1 of the experiment, the reflection of light from a plane mirror was measured. Equipment was set up on the optics bench so that light shone through a slit plate and slit mask onto a plane mirror. A ray table was used to measure the angle at which the line hit and reflected off the mirror. The ray table was rotated from 0 o to 90 o at 10 o intervals. The angle of incidence and angle of reflection were measured for each trial. The measured angles were identical or nearly identical in all trials, which seem to confirm the Law of Reflection. Any discrepancy in the measurements may be attributed to the ray optics mirror not being perfectly aligned on the ray table; without any way to secure it in place, it may have shifted slightly during some of the trials. This would have caused a difference in the angles of incidence and reflection.

For part 2 of the experiment, the focal points of a concave and convex mirror were measured. Equipment was set up on the optics bench so that light shone through a parallel ray lens and then through a slit plate and then onto the concave or convex mirror situated on a ray table. The parallel ray lens had to be adjusted to make the light rays project in a parallel fashion onto the mirror. Once parallel, the mirror was situated so that the centermost light ray would hit the center of the mirror perpendicularly. The light rays converged at a focal point which was measured and recorded. In the case of the convex mirror, a piece of paper was place underneath the mirror and the projected light rays were draw onto the piece of paper. The paper was then removed and the lines were extended to find the focal point which was located behind the mirror. In the case of the concave mirror, the focal point was in front of the mirror. The focal length of the concave mirror was 0.060 m and the focal point of the convex mirror was 0.058 m. This slight discrepancy could be attributed to difficulty tracing the lines projected by the convex mirror, but these values are rather close in value, which is expected.

For part 3 of the experiment, the cases of 3 ray diagrams were tested. Equipment was set up on the optics bench so that light shone through a crossed arrow target onto an angled spherical mirror which then reflected an image onto a viewing holder. The focal length of the mirror was first determined by placing the mirror as far away from the crossed arrow as target as possible. The viewing screen was moved to locate the point where the image of the target was focused, and that was designated as the focal point. In the case of this experiment, the focal length was 5.5 cm. The target was then placed at three positions beyond the curvature, directly on the curvature, and then at three positions between the curvature and the focal length. The viewing screen was situated in each trial to find the point where the projected image was focused. The distance from object to mirror, distance from image to mirror, height of the object, and height of the image were measured in each trial.

The results from this part of the experiment are not very consistent. In case 1, the values for both h i /h o and –q/p were both negative, but the values for h i /h o were more negative than that of –q/p. The percent difference for trial 1 was 126%, for trial 2 was 132%, and for trial 3 was 153%. The values for –q/p seems most reasonable as they predict that the image was shrunken and inverted, which was actually the case. The values for h i /h o suggest that the images were magnified and inverted, which was not what was observed. Case 2 shares the same characteristics of case 1, in that the value for both h i /h o and –q/p was negative, but the value for h i /h o was more negative than that of –q/p. The percent difference was 112%. During this case, it was predicted that the image would be inverted, but would be life size; not magnified or shrunken. In regards to case 3, the values were quite dissimilar because all h i /h o values were positive while all –q/p values were negative. The percent difference for trial 1 was 1200%, trial 2 was 700%, and trial 3 was 569%. It is thought that the images were recorded as upright when they were really inverted, which caused this discrepancy, but it cannot be validated by repeating the laboratory procedure at this time. The values for –q/p are most logical, as they suggest that the image was inverted and magnify, which is also what theory suggests.

The error from this part of the experiment came from the inability to distinguish when the image on the viewing screen was focused. Many times it was thought that the image was focused, but may not have truly been focused; there was not way to tell with certainty if it was focused or not. The viewing screen could be moved a few centimeters in either direction and the image would look about the same. All measurements for the height of the image are in question as well. The spherical mirror was placed at an angle in order to view the image, but this angle was never taken into consideration in any of the equations. The undoubtedly is what caused all the h i /h o values have such a stark difference from the –q/p values. It was not stated in the lab manual how to take that angle into consideration, and thus those values should most likely be thrown out. The –q/p values are most representative of the projected image, though the values for –q/p and h i /h o should have been equal.

1/p + 1/q = 1/f

Magnification = -q/p = h i /h o

Percent Difference = |x 1 – x 2 | / (x 1 + x 2 )/2 x 100%

circa 2008 (20 y/o)

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GCSE Physics Required Practical: Investigating Reflection and Refraction of Light

• 1.1 Meaning
• 1.2.1 Method
• 1.2.2 Improving Accuracy
• 1.3.1 Method
• 1.3.2 Improving Accuracy

Key Stage 4

Investigate the reflection and refraction of light .

Experiment 1: Reflection from a Plane Mirror

• Place a plane mirror in the centre of a piece of paper and draw a pencil line along its reflective side.
• Use a ray box and a slit to allow a single beam of light to be incident on the surface of the mirror at an angle less than 90°.
• Place a pair of x's on the incident ray and along the reflected ray .
• Remove the ray box and mirror .
• Use a ruler to join the x's with a pair of lines leading to the mirror to show the direction of the incident and reflected rays.
• Use a protractor and ruler to draw a normal line at right angles to the surface of the mirror at the point the light rays meet the mirror .
• Use the protractor to measure the 'i' the angle of incidence and 'r' the angle of reflection .
• Repeat this procedure for a number of different angles of incidence .

Improving Accuracy

Experiment 2: refraction from a rectangular glass block.

• Place a rectangular glass block in the centre of a piece of paper and draw a pencil line around the outside.
• Use a ray box and a slit to allow a single beam of light to be incident on the surface of the glass block at an angle less than 90°.
• Place a pair of x's on the incident ray and along the emergent ray .
• Remove the ray box and glass block.
• Use a ruler to join the x's with a pair of lines leading to the glass block to show the direction of the incident and emergent rays.
• Join the emergent ray and the incident ray with a line to represent the refracted ray .
• Use a protractor and ruler to draw a normal line at right angles to the surface of the glass block at the point the light rays meet the glass block.
• Use the protractor to measure the 'i' the angle of incidence and 'r' the angle of refraction .

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Reflection and refraction

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Light rays change direction when they reflect off a surface, move from one transparent medium into another, or travel through a medium whose composition is continuously changing. The law of reflection states that, on reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray. (By convention, all angles in geometrical optics are measured with respect to the normal to the surface—that is, to a line perpendicular to the surface.) The reflected ray is always in the plane defined by the incident ray and the normal to the surface. The law of reflection can be used to understand the images produced by plane and curved mirrors. Unlike mirrors, most natural surfaces are rough on the scale of the wavelength of light, and, as a consequence, parallel incident light rays are reflected in many different directions, or diffusely. Diffuse reflection is responsible for the ability to see most illuminated surfaces from any position—rays reach the eyes after reflecting off every portion of the surface.

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When light traveling in one transparent medium encounters a boundary with a second transparent medium (e.g., air and glass), a portion of the light is reflected and a portion is transmitted into the second medium. As the transmitted light moves into the second medium, it changes its direction of travel; that is, it is refracted. The law of refraction, also known as Snell’s law , describes the relationship between the angle of incidence (θ 1 ) and the angle of refraction (θ 2 ), measured with respect to the normal (“perpendicular line”) to the surface, in mathematical terms: n 1 sin θ 1 = n 2 sin θ 2 , where n 1 and n 2 are the index of refraction of the first and second media, respectively. The index of refraction for any medium is a dimensionless constant equal to the ratio of the speed of light in a vacuum to its speed in that medium.

By definition, the index of refraction for a vacuum is exactly 1. Because the speed of light in any transparent medium is always less than the speed of light in a vacuum, the indices of refraction of all media are greater than one, with indices for typical transparent materials between one and two. For example, the index of refraction of air at standard conditions is 1.0003, water is 1.33, and glass is about 1.5.

The basic features of refraction are easily derived from Snell’s law. The amount of bending of a light ray as it crosses a boundary between two media is dictated by the difference in the two indices of refraction. When light passes into a denser medium, the ray is bent toward the normal. Conversely, light emerging obliquely from a denser medium is bent away from the normal. In the special case where the incident beam is perpendicular to the boundary (that is, equal to the normal), there is no change in the direction of the light as it enters the second medium.

Snell’s law governs the imaging properties of lenses . Light rays passing through a lens are bent at both surfaces of the lens. With proper design of the curvatures of the surfaces, various focusing effects can be realized. For example, rays initially diverging from a point source of light can be redirected by a lens to converge at a point in space, forming a focused image. The optics of the human eye is centred around the focusing properties of the cornea and the crystalline lens . Light rays from distant objects pass through these two components and are focused into a sharp image on the light-sensitive retina . Other optical imaging systems range from simple single-lens applications, such as the magnifying glass, the eyeglass, and the contact lens , to complex configurations of multiple lenses. It is not unusual for a modern camera to have a half dozen or more separate lens elements, chosen to produce specific magnifications, minimize light losses via unwanted reflections, and minimize image distortion caused by lens aberrations .

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Science project, plane mirror reflection experiment.

Plane (flat) mirrors have a reflective surface that bounces back light within 180 degrees of the mirror's face. We use these mirrors every day in our bathrooms, bedrooms, and cars. When you look in a plane mirror, you see a mirror image  that is flipped backwards and opposite to the objects it is reflecting.

You’ve been tasked with projecting a line of text onto a glass screen for a magic show. However, the projector can’t be on stage, and is instead around a corner, and it’s too bright for the trick. You only have two mirrors. How can you project an image of the text on the glass screen that is dim but readable? Let’s do a mirror physics experiment and see if you can use what you learn to think of a clever solution!

How does the angle of two mirrors change the reflection of an object?

• Two identical, small plane mirrors
• Modeling clay
• Small object (coin, small figure, etc.)
• Strip of paper
• Plastic packing tape
• Tape your mirrors together so that they can be opened and closed like a hinge. You want to leave a slight gap between the two edges (around 1/16th of an inch) to do this.

• Mark angles of 30, 36, 45, 60, 90, 120 and 180 degrees on a piece of paper using your protractor.
• Place the hinge of your mirrors at the vertex of your marked angles.
• The first angle you will test will be 180 degrees.
• Place your object (you can embed it in modeling clay if it won’t stand up on its own) in the middle of the mirrors and look at the reflection. How many objects do you see, including both reflected and real?
• Keeping the object equally between the two mirrors, move the mirrors together into the other angles you marked out with your protractor. How many objects do you see at each angle? Is there something about the angle can help you predict how many objects you will see? Is every reflected image the same brightness?

• Write a word on a piece of paper, and place it in between the mirrors at 60 degrees. Look closely at the second reflection (the reflection of the reflection). Can you read the text? Why do you think this is happening?

You will see an ever-increasing number of objects as you move the mirrors closer together (reducing the angle between them). Whenever you can see a whole number of images reflected, the angle of the mirrors will perfectly divide into 360 degrees. When you look at the reflection of a reflection you will be able to read the text in the mirror, as if you pointed a camera at the object. The reflections should get dimmer (more silvery) as the number of times they are reflected increases

The mirrors reflect the reflections of other mirrors within 180 degrees of the mirror’s face. When mirrors reflect, the reflected image will be backwards, but if you reflect something twice, it will look normal.

Because light is traveling in a straight line to and from each mirror, the light will bounce a number of times back and forth between the mirrors before it travels from the object to your eye. The number of times the light bounces (and the number of objects that you see) will correlate to the number of times the angle divides into 360. As the mirrors get closer and closer to having zero angle between them, more and more images appear. At an angle of 0 degrees, or when the two mirrors are facing each other, there are an infinite number of reflections.

So, how are you going to accomplish your trick? You can make the text appear by lining up your mirrors and your projector so that the light bounces an even number of times before it gets to your eyes. Using multiple mirrors will also dim the image before it hits the glass plate for the trick.

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Light Refraction Experiment

March 30, 2020 By Emma Vanstone Leave a Comment

This light refraction experiment might be one of the most simple to set up science experiments we’ve ever tried. It is a bit tricky to explain, but impressive even if you can’t quite get your head around it!

If you like this activity don’t forget to check out out our other easy science experiments for kids .

Materials for Light Refraction Experiment

Paper or card

Instructions

Fill the glass almost to the top.

Draw arrows on one piece of of card or paper. Place the paper behind the glass and watch as the arrow points the other way.

Now try to think of a word that still makes sense if you put it behind the glass.

We tried bud , the green ( badly drawn ) plant is on the opposite side when the paper is not behind the glass.

NOW works well too 🙂

How does this work?

Refraction ( bending of light ) happens when light travels between two mediums. In the refraction experiment above light travels from the arrow through the air, through the glass, the water, the glass again and air again before reaching your eyes.

The light reaching your eye (or in this case our camera) coming from the arrow is refracted through the glass of water. In fact the glass of water acts like a convex lens (like you might have in a magnifying glass). Convex lenses bend light to a focal point . This is the point at which the light from an object crosses.

The light that was at the tip of the arrow is now on the right side and the light on the right side is now on the left as far as your eye is concerned (assuming you are further away from the glass than the focal point.

If you move the arrow image closer to the glass than the focal point it will be the way around you expect it to be!

More Refraction experiments

Create an Alice in Wonderland themed version of this too!

Find out how to make your own magnifying glass .

We’ve also got a fun disappearing coin trick .

Or try our light maze to learn about reflection .

Last Updated on February 22, 2021 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

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Effect of ion-specific water structures at metal surfaces on hydrogen production

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• Scanning probe microscopy
• Surface assembly

Water structures at electrolyte/electrode interfaces play a crucial role in determining the selectivity and kinetics of electrochemical reactions. Despite extensive experimental and theoretical efforts, atomic-level details of ion-specific water structures on metal surfaces remain unclear. Here we show, using scanning tunneling microscopy and noncontact atomic force microscopy, that we can visualize water layers containing alkali metal cations on a charged Au(111) surface with atomic resolution. Our results reveal that Li + cations are elevated from the surface, facilitating the formation of an ice-like water layer between the Li + cations and the surface. In contrast, K + and Cs + cations are in direct contact with the surface. We observe that the water network structure transitions from a hexagonal arrangement with Li + to a distorted hydrogen-bonding configuration with Cs + . These observations are consistent with surface-enhanced infrared absorption spectroscopy data and suggest that alkali metal cations significantly impact hydrogen evolution reaction kinetics and efficiency. Our findings provide insights into ion-specific water structures on metal surfaces and underscore the critical role of spectator ions in electrochemical processes.

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Introduction.

The microscopic structure of electrical double layer (EDL) between the electrode and electrolyte underpins a great importance, influencing both the selectivity and kinetics of numerous electrochemical reaction processes 1 , 2 , 3 , 4 , 5 . The Gouy–Chapman–Stern (GCS) model has served as the predominant framework for describing the EDL, which encompasses a Stern layer and a diffuse layer 6 . The Stern layer characterizes the arrangement/packing of water and ions on the surface, critically influencing mass transport to/from the interface and charge transfer processes 7 , 8 , 9 , 10 , 11 . However, this model, rooted in classical mean-field theory, overlooks the specific water orientation and ion arrangement at the molecular scale. Therefore, it struggles to interpret phenomena such as ion-specific effects 12 , 13 , 14 , 15 , 16 , overcharging 17 , 18 and water orientational asymmetry 19 , 20 . Furthermore, alkali metal cations have been found to alter the interfacial solvation environment and electrochemically active sites. These modifications in turn impact the proton-coupled electron-transfer (PCET) barrier in hydrogen evolution reaction (HER)/hydrogen oxidation reaction (HOR) and the mass transport processes of oxidation reactions, varying with the different cations present 7 , 13 , 21 , 22 .

Exploring molecular-level details of an EDL, from both experiment and theory, remains a formidable challenge. Various vibrational spectroscopy 23 , 24 , 25 , 26 , 27 and diffraction techniques 28 , 29 have been employed to identify the EDL structure at electrode/electrolyte interfaces. In particular, advancements in surface enhanced vibrational spectroscopy, including surface enhanced Raman spectroscopy (SERS) 26 , 30 and surface enhanced infrared absorption spectroscopy (SEIRAS) 24 , 31 , 32 , have enabled researchers to discern the dipole orientation and H-bonding structure of water molecules near the electrified interface. However, these techniques endure poor spatial resolution and the difficulty of spectral assignment. Recently, individual Na + hydrates, hydronium-water layers and alkali ion-water chains were successfully visualized by noncontact atomic force microscopy (AFM) with a carbon monoxide (CO)-terminated tip. This development opens up the possibility of probing interfacial ion-water interactions with atomic precision 33 , 34 , 35 , 36 .

In this work, we investigated the extended network formed by different alkali metal cations and water molecules on a charged Au(111) surface in real space, which constitutes an ideal model system to understand the atomic structure at electrolyte/electrode interface. We were able to fabricate a sample with an ion concentration of ~10 M at the surface, corresponding to an effective bulk ion concentration of ~0.1 M 37 and resulting in a Stern layer thickness of ~6 Å 38 . Combining high-resolution scanning tunnelling microscopy (STM), AFM with CO-functionalized tips, and density functional theory (DFT) calculations, we deciphered the atomic structures of the cation-water networks on the Au(111) surface. These results showed that the water molecules were able to lift the Li + cations from the substrate, with the underlying water molecules forming an ordered hexagonal structure. In contrast, the Cs + and K + cations tend to adsorb on the substrate directly, disrupting the water structure. We also used SEIRAS to discern the water structure at the electrochemical solution/Au interface with varied cation species, which share similar features with our STM/AFM findings. Additionally, our HER analyzes suggest that the reaction efficiency is influenced by the cation species due to their impact on the interfacial water structure.

Cs + -water monolayer with distorted H-bonding network

The diverse cation-water structures were grown on the Au(111) surface by depositing alkali metal atoms at room temperature, followed by dosing water molecules at ~120 K. Since the alkali metal atoms have smaller work functions than the Au(111) surface, electrons will transfer from the alkali metal atoms to the Au substrate. This causes the alkali metal atoms to become cations and renders the Au(111) surface negatively charged, leading to electrostatic and dispersion interactions between the alkali metal cations and the Au substrate (Supplementary Text  1 , Supplementary Figs.  1 , 2 ). Additionally, owing to the Fermi-level nature of metal substrate, the charge transfer process from alkali metal atoms to the metal surfaces is a widely used method to simulate electrified interfaces with a net charge 26 , 39 . Figure  1a shows STM images of a 2D Cs + -water island acquired at 5 K with a CO-terminated tip, which reveals that the Cs + and water molecules could form a periodic 1D array structure. The height profile analysis across the layer indicates that the cations display larger apparent heights than the water molecules due to the larger ion radius of Cs + . Additionally, the height of the water region highlights the monolayer nature of the complex structure (Fig.  1a , lower-right panel). High-resolution STM image illustrates that the 2D Cs + -water layer consists of single-stranded zigzag Cs + chains interconnected via water ring structures (Fig.  1a , lower-left panel). Although STM could resolve the position of Cs + cations, it is still challenging to identify the actual hydration shell and hydrogen(H)-bonding structure of the network.

a Constant-current STM images of 2D Cs + -water layer on Au(111). Upper: The 2D Cs + -water layer is composed of single-stranded zigzag Cs + chains. Lower left: The zoomed-in STM image of a 2D cation-water layer. Lower right: The line profile across the edge showing the heights of the layers, 1.7 (water molecules)−2.2 Å (Cs + cations). b Constant-height AFM (Δf) images at the tip heights of 70 pm (left) and −140 pm (right). c Simulated AFM images at the tip heights of 12.45 Å (left) and 11.00 Å (right). d , e Top ( d ) and side ( e ) views of the structural model of 2D Cs + -water structure on the Au(111) surface. Au, Cs, H, and O atoms are denoted as yellow, cyan, white, and red spheres, respectively. The bridging water molecules are indicated by black (white) arrows in d ( b and c ). The flat-lying water molecules are indicated by red arrows in b – d . The water hexagons are indicated by black (red) dashed lines in d ( b and c ). The tip heights in b are referenced to the STM set point on the Au substrate (100 mV, 10 pA). The tip heights in c are defined as the vertical distance between the apex atom of the metal tip and the outmost atom of Au substrate. The oscillation amplitude of experimental and simulated images is 100 pm.

To gain more details of the cation-water structure, a series of AFM investigations were conducted at varying tip heights (Fig.  1b and Supplementary Fig.  3 ) 34 , 40 . At a large tip height, the AFM image is predominantly shaped by high-order electrostatic force, revealing a dark depression of the positively charged Cs + , a consequence of its electrostatic attraction with the negatively charged CO-tip apex (Fig.  1b , left panel) 34 . Conversely, the water molecule was resolved as a bright feature, which is attributed to the negatively charged O atom (Supplementary Fig.  3 ). At a lower tip height, the Pauli repulsion force significantly influences the AFM signals, and the feature of cation turns to a bright protrusion (Fig.  1b , right panel). Moreover, the H bonds within the water molecules network were imaged as sharp-line features, resulting from the lateral relaxation of the CO-tip 41 , 42 . As shown in Fig.  1b , the AFM imaging could facilitate the discernment of the precise location of both cations and water molecules, indicating the alignment of Cs + ions in a zigzag pattern within a network of distorted hexagonal water rings.

Based on the insights from the high-resolution AFM images, a detailed atomic model for 2D Cs + -water structure was proposed. This model, characterized by a 1:7 cation-water ratio, approximating 8 M concentration, was validated for structural stability using ab-initio DFT calculation (Fig.  1d ). The theoretical AFM simulations indicated images in quantitative agreement with the experimental results (Fig.  1c , Supplementary Fig.  3 and Supplementary Table  1 ). Notably, each Cs + cation is hydrated by five water molecules, and two water molecules act as bridge between adjacent cations [indicated by white (black) arrows in Figs.  1b, c (d) ]. The negatively charged surface preferentially orients most water molecules into an H-down configuration. But, some of the water molecules adopt a flat-lying configuration, critically influencing the formation of water hexagon structures between the neighbouring Cs + chains. Due to their weaker interaction with the surface, flat-lying water molecules are situated at a higher plane relative to the H-down ones, rendering them discernible as bright protrusions in the AFM images (Figs.  1b, c , left panel). Although the water molecules could form hexagonal water rings between the Cs + chains, the H-bonding network of water molecules exhibits high distortions, evidenced by variations in bond angles and the O-O distances ranging from 93° to 136° and 265 pm to 300 pm, respectively. (Supplementary Table  1 )

Li + -water monolayer with structured H-bonding network

To further explore the ion-specific effect on the water structure, we prepared a water overlayer on Au(111) surface mixed with Li + cations, which have much stronger interaction with water molecules than Cs + cation. The high-resolution STM image reveals that the 2D Li + -water layer is composed of double-stranded Li + chains that are interconnected via a honeycomb water structure (Fig.  2a ). The height and surface corrugation of the Li + -water layer are more distinct than those observed in the Cs + -water layer (Fig.  2a , lower-right panel). This pronounced height difference, together with the significantly smaller ion radius of Li + compared to Cs + , suggest a 3D hydration structure of Li + cation. The AFM images provide further insight into the structure of the Li + -water layer (Fig.  2b ). At large and medium tip heights, AFM images reveal a bright protrusion (Fig.  2b ) and a “Y”-shape feature at the Li + site (Supplementary Fig.  4 ), implying the presence of an addition water molecule adsorbed on the top of Li + , causing a large height corrugation. The additional water molecules exhibit different orientations: H-up and flat, which could be distinguished by AFM images (indicated by red and yellow arrows respectively in Figs.  2b, c and Supplementary Fig.  4 ). The H-up configuration may become kinetically trapped during sample preparation (Supplementrary Text  2 ). It is worth noting that imaging the water molecules between the Li + chains proved challenging due to their much smaller height. We developed a varying-height AFM imaging technique and captured the information of water molecules at different heights in the same image (Fig.  2b , right panel and Methods), showing that there is a hexagonal ice-like water structure between the Li + chains.

a Constant-current STM images of 2D Li + -water layer on Au(111). Upper: The 2D Li + -water layer is composed of double-stranded Li + chains. Lower left: The zoomed-in STM image of a 2D cation-water layer. Lower right: The line profile across the edge showing the heights of the layers, 1.8 (water molecules)−2.4 Å (water molecule on the top of Li + cation). b Constant-height AFM (Δf) image at 150 pm and varying-height AFM image with the original tip height of 150 pm, the threshold current of 7.6 pA and the height offset of −200 pm. c Simulated AFM images at the tip heights of 12.50 Å, and 11.10 Å. The brightness of the protrusions in AFM image at the large tip height is sensitive to the orientation of water molecule adsorbed on the top of Li + . d , e Top ( d ) and side ( e ) views of the structural model of 2D Li + -water structure on the Au(111) surface. Au, Li, H, and O atoms are denoted as yellow, green, white, and red spheres, respectively. The water hexagons are indicated by black (red) lines in d ( b and c ). The additional water molecules exhibit different orientations: H-up and flat, indicated by red and yellow arrows in b and c . The tip heights in b are referenced to the STM set point on the Au substrate (100 mV, 10 pA). The tip heights in c are defined as the vertical distance between the apex atom of the metal tip and the outmost atom of Au substrate. The oscillation amplitude of experimental and simulated images is 100 pm.

Based on our detailed AFM analysis, we propose an atomic structural model to describe the Li + -water layer, characterized by a cation-water ratio of 1:12 ( ~ 5 M) (Fig.  2d ). In this model, the water molecules form a hexagonal ice-like structure on the Au(111) surface, and the Li + cations adsorb at the bridge sites between two water molecules with a slight disturbance to the water network. An additional water monomer, exhibiting two orientations, is adsorbed on the top of Li + , contributing to the large height corrugation shown in the STM/AFM images. Each Li + cation in this configuration is hydrated with three water molecules and elevated away from the surface (Supplementary Fig.  5 ). The model’s accuracy is substantiated by the simulating AFM images (Fig.  2c , Supplementary Fig.  4 and Supplementary Table  2 ) that mirror our experimental results. Similar to the Cs + -water layer, we note that the water molecules tend to adopt the H-down configuration, arising from the presence of negative charge distribution on the Au(111) surface (Supplementary Fig.  1 ).

Comparison of cation-water structure among Li + , K + and Cs +

We also investigated the 2D K + -water layer with a cation-water ratio of approximately 1:6 ( ~ 9 M) on Au(111), whose properties fall in between Cs + - and Li + -water structures due to the interaction strength of K + with water molecules is stronger than Cs + and weaker than Li + . The K + cations are hydrated with four water molecules and could form a compact chain through sharing water molecules like Cs + cations do (Supplementary Fig.  6 ). However, the K + and water could only assemble into short chains with random orientations, likely because the K + -water and water-water interactions are comparable, resulting in the competitive structural arrangement. Meanwhile, the K + chains are interconnected by a honeycomb H-bonding network of water molecules, similar to the ice-like structure observed in the Li + -water layer.

Based on the observations above, we can conclude three main features of cation-water layers along with the sequence of Li + -K + -Cs + . Firstly, there is a sequential increase in the number of water molecules in the first hydration shell of each cation: three for Li + , four for K + , and five for Cs + . Secondly, the cation-surface separation is decreased by removing the water layer between the cations and the surface, which indicates that the K + and Cs + cations would absorb the surface directly, potentially resulting in a site-blocking effect. Thirdly, the disturbance of cations on the H-bonding network of water increases. The Li + cation shows a structure-making effect, while the Cs + plays a structure-breaker role and the K + presents intermediate behavior. We also explore the double-layer alkali cation-water structures at diluted ion concentrations, which show similar properties to the single-layer structures (Supplementary Fig.  7 ). While our STM/AFM experiments were performed under high vacuum and low temperature, it is possible that those findings may have some relevance to the liquid/solid interface under ambient conditions considering the strong interaction between the cation-water layers and the charged surface 43 , 44 . Although the thermal fluctuations may suppress the lifetime of those structures, it is conceivable that certain intrinsic properties of ion-specific water structures could persist under ambient conditions. To support this, we employed in situ SEIRAS to probe interfacial water structure on the Au substrate immersed in alkaline (Fig.  3 and Supplementary Fig.  8 ), near neutral (Supplementary Fig.  9 ) and acidic (Supplementary Fig.  10 ) electrolytes containing different alkali metal cations.

a – c The potential-dependent OH stretching features of in situ SEIRAS spectra at pH13 in a H 2 -saturated aqueous solution of 0.1 M of LiOH, KOH, and CsOH, respectively, where the reference spectrum was taken at 1.1 V RHE . Full spectra before and after subtracting by reference spectrum (at 1.1 V RHE ) are available in Supplementary Fig.  8 . d The deconvolution of the OH stretching peak of spectra acquired at −0.6 V RHE , where OH stretching peak was deconvoluted into three components: 1) 3600 cm −1 with width=160 cm −1 (isolated water), 2) 3450 cm −1 with width=260 cm −1 (asymmetrically H-bonded water), and 3) 3240 cm −1 with width=250 cm −1 (symmetrically H-bonded water). The deconvolution of OH stretching peak at other potentials is shown in Supplementary Fig.  12 . e – g The potential- and cation-dependence of the relative fraction of peaks at 3600 cm −1 , 3450 cm −1 , and 3240 cm −1 . h A schematic showing that Li + promotes symmetric H-bonded water at the interface while Cs + tends to form isolated water molecules at the Au surface.

Cation-dependent water structure at the electrolyte/electrode interface using in situ SEIRAS

In situ SEIRAS experiments were performed from the potential of zero charge (PZC) of polycrystalline Au (0.5 V RHE at pH1 and 1.2 V RHE at pH13) to HER relevant potential region (−0.3 V RHE at pH1 and −0.6 V RHE at pH13) 45 , 46 , 47 , where the Au electrode surface is negatively charged. It should be noted that the PZC of Au does not change drastically with different facets (Supplementary Text  3 ). In addition, the negative surface charge density of Au(111) surface at the conditions of STM/AFM measurements was −0.15 (Li + -water layer)~−0.20 (Cs + -water layer) As m −2 as suggested by ab initio DFT calculations. Thus, the surface potential of Au(111) surface at STM/AFM conditions can be estimated at −0.45 V versus PZC for Li + and −0.3 V versus PZC for Cs + by using the Gouy-Chapman-Stern model (Supplementary Fig.  11 and Supplementary Text  4 ), which correlate with pre-HER relevant potential in SEIRAS and electrochemical measurements.

To investigate the impact of alkali cations on the interfacial water structure, we examined the OH stretching modes ( ~ 3600-3200 cm −1 ) of water molecules at the Au/electrolyte interface. Figure  3a–c displays the SEIRAS spectra of OH stretching at pH13 in aqueous electrolytes of 0.1 M hydroxide of Li + , K + and Cs + . At potentials below PZC, the Au surface was negatively charged. Moving to low electrode potentials could increase the negative surface charge, which could enhance the interaction between the water dipole and the electrified interface. Consequently, the intensity of OH stretching peak increases as the potential decreases from 1 to −0.6 V RHE .

We further deconvoluted the OH stretching band by three peaks at 3600, 3450, and 3240 cm −1 , representing weakly H-bonded (isolated) water molecules, asymmetrically H-bonded water molecules within the hydration shell, and symmetrically H-bonded ice-like water molecules on Au, respectively, as shown in Fig.  3d for −0.6 V RHE (Supplementary Fig.  12 for other potentials) 24 . The potential-dependent relative fractions of deconvoluted peaks for isolated water, asymmetrically and symmetrically H-bonded water molecules are shown in Figs.  3e–g . By comparing the relative fractions of different peaks for different cations, we found that the Cs + promotes weakly H-bonded (isolated) water molecules at negatively charged Au/electrolyte interface, whereas the Li + predominantly promotes symmetric H-bonded ones, which suggests that the Li + reinforces the H-bonding network of interfacial water, rendering it more structured than that of Cs + and K + . These observations qualitatively agree with the results obtained from AFM/STM experiments (Figs.  1 , 2 and Supplementary Fig.  6 ). Similar cation-dependent interfacial water features were observed at pH6-7 and pH1 (Supplementary Figs.  9 , 10 ).

Cation- and pH-dependent HER kinetics

In order to further explore the effect of alkali cations on the actual electrochemical reaction, we evaluated HER experiments at different pH values and analyzed the reaction kinetics to obtain insights into the microscopic mechanism. The cation- and pH-dependent HER polarization curves on Au rotating disk electrode (RDE) are shown in Figs.  4a–c (Supplementary Fig.  13 ). The HER exchange current density decreases in the order of Li + > Na + > K + > Cs + in acidic, neutral and alkaline electrolytes (Fig.  4d ). The cation-dependence of HER kinetics on polycrystalline Au surface can be attributed to the accumulation of cations at electrified interface, namely weakly hydrated cations (K + and Cs + ) show higher near-surface concentration in comparison to a strongly hydrated cation (Li + ), which is also evidenced in our STM/AFM results. The higher near-surface concentration of weakly hydrated cations could inhibit HER kinetics on Au surface by blocking the active sites 44 and altering the interfacial hydrogen bonding network 13 . Furthermore, consistent with the observation by Monteiro et al. 44 , we found that weakly hydrated cations (K + and Cs + ) favour HER on gold only at low overpotentials compared to strongly hydrated cations (Li + ) (Supplementary Fig.  13c ), whereas at high overpotentials a lower HER activity has been observed in the electrolytes containing weakly hydrated cations (K + and Cs + ) (Fig.  4c ). The promotion (at lower overpotentials) and inhibition (at higher overpotentials) of HER on Au surfaces has been attributed to cation concentration effect on Volmer step. Due to the low solubility of perchlorate salt of Cs + , we employed 0.1 M chloride salts of Li + , K + and Cs + to confirm the cation-dependence of HER kinetics on Au in 0.1 M HClO 4 at pH1 (Supplementary Fig.  14 ), observing a similar cation trend but with a more pronounced effect for chloride salts compared to perchlorate salts. On the other hand, HER kinetics on polycrystalline Au was shown to be pH dependent. Specifically, the HER kinetics in acidic electrolytes (pH1) exhibited a higher j 0 than that in alkaline electrolytes (pH13). The pH dependence of HER kinetics on Au is similar to the trend of HER/HOR kinetics on Pt group metal surfaces in previous studies 48 , 49 , 50 , which can be attributed to the pH-dependent interfacial water structure rather than pH-dependent hydrogen-binding energy (HBE) 12 , 13 , 51 . The HER kinetics in 0.05 M perchlorate salt at near-neutral condition (pH6-7) showed the lowest j 0 among all the three pH, due to proton transport limitation at near-neutral pH 52 .

a – c HER polarization curves on Au surface in acidic, neutral and alkaline electrolytes, respectively, measured at 10 mV s −1 and 2500 rpm in H 2 -saturated aqueous electrolytes of 0.1 M HClO 4 and 0.1 M perchlorate salt of Li, Na, K or 0.05 M perchlorate salt of Cs (pH1), aqueous solutions of 0.05–0.1 M MClO 4 (M=Li, Na, K and Cs) (pH6-7), and aqueous electrolytes of 0.1 M hydroxide of Li, Na, K and Cs (pH13). The zoom-in of low overpotential region can be found in Supplementary Fig.  13 . d The exchange current density extracted by MHC formalism (Supplementary Fig.  15 ). e The reorganization energy extracted by MHC formalism and interfacial static dielectric constant extracted via Born model of reorganization energy. f The reorganization energy of HER on Au RDE as a function of the relative fraction of isolated water in OH stretching peak at −0.2 V RHE for acidic, neutral and alkaline electrolytes. All CV data has been iR corrected. The non-iR corrected HER polarization curves are shown in Supplementary Fig.  16 . Error bars were obtained from the standard deviation of 2–3 independent measurements.

Based on our investigations, we further established a correlation between HER kinetics and the solvation environment at the electrified interface. Employing Marcus-Hush-Chidsey (MHC) formalism and Born model, we revealed that the HER exchange current density decreased, while the reorganization energy and the interfacial dielectric constant increased with an increasing trend of alkali metal cation from Li + to Cs + (Figs.  4d–f , Supplementary Fig.  15 and Supplementary Text  5 ). Our SEIRAS and STM/AFM experiments (Figs.  1 – 3 and Supplementary Figs.  8 to 10 ) converge on the finding that structure-breaking cations (such as Cs + ) could interact strongly with negatively charged Au surface, consequently, displace interfacial water molecules and suppress the interfacial H-bonding network, leading to isolated or weakly H-bonded water molecules on the Au surface. Conversely, structure-making cations (such as Li + ) could retain their solvation structure and migrate from the substrate through water molecules, promoting a more structured interfacial water layer with a more abundant ice-like H-bonding network. These results potentially offer atomic-level insight into the kinetic properties. The structured H-bonding network at the interface demonstrates enhanced structural stability, exhibits diminished responsiveness to the change of electrode potential, and consequently, shows a lower interfacial dielectric constant (Fig.  4e ). The interfacial solvation environment exhibits a weakly H-bonded network with distorted H-bonding angles and varied bonding lengths. These irregularities yield a larger interfacial dielectric constant and increased reorganization energy, which impedes proton transfer during electrochemical reactions and leads to an increase in the PECT barrier in the Volmer and the Heyrovsky steps in HER kinetics. In contrast, the strongly H-bonded interface could facilitate PCET processes on Pt 13 and Au (this work) surfaces.

We carefully fabricated and systematically characterized the 2D network of water molecules and alkali metal cations (Li + , K + and Cs + ) on a charged Au(111) surface. The STM/AFM results contribute real-space insights into the ion-specific water structures on metal surfaces, which are qualitatively aligned with the SEIRAS experiments of electrolyte/electrode interfaces under ambient conditions. These results not only provide a further understanding of the atomic structure at liquid/solid interfaces but also reveal the important role of ions in the electrochemical reactions at the atomic scale. We expect that our methods can be further applied to a large variety of cations and anions, to construct different model systems for studying various ion-water structures at different electrode surfaces. Recently, the atomic structures of the bulk insulating ice Ih surface have been observed using qPlus AFM technique 53 . Additionally, by integrating nanosecond laser transient heating and rapidly re-freezing technology 54 into the AFM system, it is possible to capture the liquid-like states and the dynamics of water and ions. These technological advancements could present an opportunity for future exploration into ion-specific water multilayer structures.

STM/AFM experiments

All the STM and non-contact AFM experiments were performed using Createc (Germany) and CASAcme (China) instruments. These investigations were conducted at a cryogenic temperature of 5 K, utilizing a custom-made qPlus sensor equipped with a tungsten (W) tip, featuring a spring constant (k0) of approximately 1800 N·m −1 , a resonance frequency (f 0 ) of around 28.7 kHz, and a high-quality factor (Q) in the order of 100,000. The bias voltage is defined relative to the potential difference between the sample and the probe tip. The CO-terminated tips were employed to acquire both STM topographic images and AFM frequency shift (Δf) images, using constant-current and constant-height modes, respectively, except for those specified in the text. The process for creating a CO-terminated tip involves precisely aligning the metallic tip above a CO molecule residing on the Au(111) surface—initially set at a voltage of 100 mV and current of 10 pA—and incrementally increasing the tunnelling current to 400 pA to facilitate the tip’s termination.

In order to verify the precise 3D structure of Li + -water layer, we used a varying-height AFM method, in which the tip was approached to the surface by a height offset as long as the detected current value was smaller than the set threshold value, so that the H-bonding skeleton of lower water molecules surrounding the higher water molecules could be clearly resolved.

Sample preparation

The Au(111) single crystal employed in this studies was purchased from MaTeck and underwent a cleaning process, fllowing repeated Ar + ion sputtering at 1 keV and annealing at about 700 K for multiple cycles. The SAES alkali-metal dispensers were used to deposite alkali metal atoms. The dispensers were degassed, with regulated currents set for the evaporation of lithium (I Li  = 8.5 A), potassium (I K  = 6.5 A), and cesium (I Cs  = 5.5 A) over a duration of 2 min. The alkali metal atoms were deposited on the Au(111) surface at room temperature, with deposition current I Li  = 8.3 A, I K  = 6.3 A, I Cs  = 5.2 A, duration of 1 min. The ultrapure H 2 O was purchased from Sigma Aldrich, with a maximum deuterium content limited to 1 ppm. The water was subjected to additional purification under vacuum by 3–5 freeze-and-pump cycles to remove remaining gas impurities.

DFT calculations

DFT calculations were conducted employing the Vienna ab initio simulation package (VASP) 55 , 56 . The calculations used projector augmented wave pseudopotentials with a cut-off energy of 550 eV for the description of the electronic wave functions 57 . To address the van der Waals interactions for dispersion forces, were considered by using the optB86b-vdW exchange-correlation functional was employed 58 , 59 . In modeling the Au(111) surface, a slab comprising four layers was constructed, with all but the topmost layer fixed to emulate the bulk-like properties of the substrate. The gold lattice constant was set to be 4.073 Å. For Li + system, a ( \(2\sqrt{3}\times \sqrt{57}\) ) supercell and a ( \(2\times 1\times 1\) ) Monkhorst–Pack (MP) grid were used for the Brillouin zone sampling. For K + system, a ( \(5\times \sqrt{3}\) ) supercell and a ( \(2\times 7\times 1\) ) MP grid were implemented. For Cs + system, a ( \(\sqrt{97}\times 2\sqrt{3}\) ) supercell and a ( \(1\times 3\times 1\) )) MP grid were applied. A vacuum layer thickness exceeding 16 Å was instituted to preclude spurious interactions between periodic images, with dipole corrections being applied along the surface normal direction 60 , 61 . The procedure of geometry optimization was performed with a force criterion of 0.01 eV  · Å −1 . To provide an incisive assessment of charge distribution on the optimized geometries, Bader charge analysis was performed 62 .

AFM Simulations

To simulate the frequency shift (Δf) images, a molecular mechanics model encapsulating electrostatic forces was used, based on the methods described in ref. 63 . The flexible probe-particle tip model was used. This model assigns an effective lateral stiffness k   =  0.75 N‧m −1 and defines the effective atomic radius R c   =  1.661 Å. To mimic the characteristics of a CO-terminated tip, a quadrupole-like ( \({{{{{\rm{d}}}}}}_{{{{{{\rm{z}}}}}}^{{2}}}\) ) charge distribution was prescribed at the tip apex, with an inherent charge q = –0.1 e. Electrostatic potentials from DFT calculations were employed in AFM simulations. The Lennard-Jones potential parameters for element interactions are detailed Supplementary Table  3 . The tip height is defined as the vertical distance from the tip apex to the substrate’s top atomic layer. The oscillation amplitude of the simulated AFM images was 100 pm.

Electrochemical measurements and electrolyte preparation

For all electrochemical measurements, a three-electrode electrochemical system and a Biologic SP-300 potentiostat were employed 13 . A polycrystalline Au rotating disk electrode (RDE) (E3PK series fixed-disk, Pine instrument) was used as the working electrode. Before each measurement, the electrode surface was polished with successively finer-grade diamond slurries down to 0.25 μm. A gold foil (thickness 0.1 mm, Sigma-Aldrich 99.99%) was used counter electrodes. Potentials were recorded versus a mercury sulfate (Hg/HgSO 4 ) reference electrode in acidic and neutral solutions and to a mercury oxide (Hg/HgO) reference electrode in alkaline electrolytes. The mercury sulfate (Hg/HgSO 4 ) reference electrode was calibrated in H 2 -saturated 0.1 M HClO 4 elelctrolyte using a polycristalline Pt RDE, with a potential value of 0.355 V SHE . The mercury oxide (Hg/HgO) reference electrode was calibrated in H 2 -saturated 0.1 M KOH elelctrolyte using a polycristalline Pt RDE, with a potential value of 0.867 V SHE . All potentials were converted to the RHE scale using E RHE  =  E meas  + E RE  + 0.059×pH. A standard glass electrochemical cell with a water jacket (150 mL, Pine research instrument) was used for the measurements in acidic and neutral electrolytes. For experiemnts in alkaline electrolytes, an alkaline-resistant PTFE cell (175 mL, Pine research instrument) was utilized.

The effects of pH and cations on the kinetics of HER were examined by CV measurements at a scan rate of 10 mV s −1 at 2500 rpm in H 2 saturated solutions at 293 K. The normalized current density was obtained using the geometric surface area of RDE (0.196 cm 2 ) and the reported potentials were iR corrected. The ohmic resistance value of each experiment was summarized in Supplementary Table  7 . The pH of the electrolytes was measured using a digital desktop laboratory pH-meter (PHS-3C, Puchun). The pH values of all electrolytes were summarized in Supplementary Table  8 . Neutral solutions, acidic and alkaline electrolytes were prepared from deionized water (Millipore, > 18.2 MΩ.cm). For cation-dependent measurements, 0.05–0.1 M perchlorate salt of Li + , Na + , K + and Cs + (LiClO 4 , Sigma-Aldrich 99.99%; NaClO 4 , Sigma-Aldrich 99.9%; KClO 4 , Sigma-Aldrich 99.99%; CsClO 4 , Sigma-Aldrich 99.9%) were added to 0.1 M HClO 4 (Sigma-Aldrich 70 wt% and 99.999% trace metal basis) at pH1. 0.05–0.1 M perchlorate salts of Li + , Na + , K + and Cs + (LiClO 4 , Sigma-Aldrich 99.99%; NaClO 4 , Sigma-Aldrich 99.9%; KClO 4 , Sigma-Aldrich 99.99%; CsClO 4 , Sigma-Aldrich 99.9%) were used to prepare electrolytes at neutral pH. Alkaline electrolytes at pH13 were prepared with aqueous solutions of 0.1 M hydroxides of Li + , Na + , K + and Cs + (LiOH, Sigma-Aldrich 99.99%; NaOH, Sigma-Aldrich 99.9%; KOH, Sigma-Aldrich 99.95%; CsOH, Sigma-Aldrich 99.95%). The electrolyes were prepared and stored at ambient conditions, and were used for experiements within 1–2 h of preparation.

In situ Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS)

The reflecting plane of the hemispherical Si prism (radius 22 mm, Pier optics) on which gold thin film is deposited was polished with successively finer grade diamond slurries down to 0.25 μm. Then the surface was contacted with 40% NH 4 F for 90 s to remove oxide layer on the Si surface and to terminate it with hydrogen. Deposition of Au was performed at 60 °C simply by dropping a mixture of a plating solution and 2% HF (1:1 in volume) onto the hydrogen-terminated Si surface. The composition of the plating solution was 0.0075 M NaAuCl 2 , 0.075 M Na 2 SO 3 , 0.025 M Na 2 SO 3 and 0.025 M NH 4 Cl. At 60–90 s after dropping the plating solution, the prism was rinsed with Milli-Q water to finish the deposition.

The Au-deposited hemispherical Si prism was mounted in a spectro-electrochemical three-electrode system (Supplementary Fig.  17 ). A mercury oxide electrode (Hg/HgO) and a gold foil (thickness 0.1 mm, Sigma-Aldrich 99.99%) were used as the reference and counter electrodes. Prior to measurements, the Au surface was cleaned electrochemically in 0.1 M HClO 4 by repeating potential scans between 0 and 1.3 V RHE . The SEIRAS measurements were performed using a Bruker Vertex 70 Fourier-Transform Infrared (FTIR) spectrometer, equipped with a MCT detector. The optical path was fully replaced with N 2 gas. The SEIRAS spectra were recorded with a resolution of 4 cm –1 at a scan velocity of 7.5 kHz covering the 500−4000 cm –1 spectral range; with an average of 64 scans. A single reflection ATR (Attenuated Total Reflection) accessory (Pike Vee-Max II, Pike Technologies) with a Au deposited Si prism at an incident angle of 68° was used. The enhanced region was estimated to be around 10 nm of the surface 64 (Supplementary Text  6 ). For in situ SEIRAS measurements during HER in electrolytes at pH1 in 0.1 M HClO 4 (Sigma-Aldrich 70 wt% and 99.999% trace metal basis) and 0.05–0.1 M perchlorate salt of Li + , K + and Cs + (LiClO 4 , Sigma-Aldrich 99.99%; NaClO 4 , Sigma-Aldrich 99.9%; KClO 4 , Sigma-Aldrich 99.99%; CsClO 4 , Sigma-Aldrich 99.9%); at neutral pH in 0.05 M perchlorate salt of Li + , K + and Cs + (LiClO 4 , Sigma-Aldrich 99.99%; NaClO 4 , Sigma-Aldrich 99.9%; KClO 4 , Sigma-Aldrich 99.99%; CsClO 4 , Sigma-Aldrich 99.9%); at pH13 in 0.1 M of hydroxide of Li + , K + and Cs + (LiOH, Sigma-Aldrich 99.99%; NaOH, Sigma-Aldrich 99.9%; KOH, Sigma-Aldrich 99.99%; CsOH, Sigma-Aldrich 99.9%) were saturated with H 2 by purging H 2 gas. Before conducting in situ SEIRAS experiments, the Au-deposited Si prism surface was cleaned by cycling the potential between 0.05 and 1.1 V RHE . SEIRAS spectra were then collected at potentials ranging from 1.1 V RHE to HER relevant potential region. The reference spectrum, I 0 , was recorded at 1.1 V RHE . All spectra are presented in absorbance units, defined as log(I 0 /I), where I 0 and I correspond to the reference and sample spectra, respectively. The same Au surface was used for measurements at a given pH to ensure similar surface enhancement effects.

Data availability

The tabulated data used to create the figures have been deposited at Zenodo ( https://doi.org/10.5281/zenodo.13634826 ) 65 . All data needed to evaluate the conclusions in the paper are present in the paper or the  Supplementary Information .  Source data are provided in this paper.

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Acknowledgements

This work was supported by the National Key R&D Program of China under grants 2021YFA1400500; the National Natural Science Foundation of China under grants 92361302, 12250001, U22A20260, 11935002; the Strategic Priority Research Program of Chinese Academy of Sciences under grants XDB28000000 and XDB33000000; the Key R&D Program of Guangdong Province under grants 2020B010189001; the China Postdoctoral Science Foundation under grants 2022M720003 and 2023T160011; the Broad Agency Announcement (BAA) for Basic and Applied Scientific Research funded by the U.S. Army Research Laboratory (ARL); the U.S. Department of Defense (DoD); under Award Number W911NF1920065, by a grant from MISTI-China (Project No. 2244703). Y.J. acknowledges support from the New Cornerstone Science Foundation through the New Cornerstone Investigator Program and the XPLORER PRIZE. We are grateful for the computational resources provided by the TianHe-1A, TianHe II supercomputer, High-performance Computing Platform of Peking University.

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These authors contributed equally: Ye Tian, Botao Huang, Yizhi Song, Yirui Zhang.

Authors and Affiliations

International Center for Quantum Materials, School of Physics, Peking University, Beijing, P. R. China

Ye Tian, Yizhi Song, Dong Guan, Jiani Hong, Duanyun Cao, Enge Wang, Limei Xu & Ying Jiang

Electrochemical Energy Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA

Botao Huang, Yirui Zhang & Yang Shao-Horn

Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA

Botao Huang

Department of Physics, Temple University, Philadelphia, Pennsylvania, USA

Collaborative Innovation Center of Quantum Matter, Beijing, P. R. China

Enge Wang, Limei Xu & Ying Jiang

Songshan Lake Materials Lab, Institute of Physics, CAS and School of Physics, Liaoning University, Shenyang, P. R. China

Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials, Peking University, Beijing, P. R. China

Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA

Yang Shao-Horn

Department of Material Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA

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Contributions

Y.J. and Y.S.H. designed and supervised the project. Y.T. performed the STM/AFM measurements with D.G., J.H., B.H., and Y.Z. performed the SEIRAS and HER experiments. Y.S., D.C. and L.-M.X. performed ab initio DFT calculations and theoretical simulations of the AFM images. Y.T., B.H., Y.S., Y.Z., L.-M.X., E.-G.W., Y.S.H., and Y.J. analyzed the data. Y.T., B.H., Y.S., Y.Z., Y.S.H., and Y.J. wrote the manuscript with the inputs from all other authors. The manuscript reflects the contributions of all authors.

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Correspondence to Ye Tian , Limei Xu , Yang Shao-Horn or Ying Jiang .

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Tian, Y., Huang, B., Song, Y. et al. Effect of ion-specific water structures at metal surfaces on hydrogen production. Nat Commun 15 , 7834 (2024). https://doi.org/10.1038/s41467-024-52131-w

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DOI : https://doi.org/10.1038/s41467-024-52131-w

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