Anchoring single metal atoms on ultrathin supports improves catalyst efficiency and stability, making hydrogen production cleaner, more scalable, and less dependent on scarce metals.
(Nanowerk Spotlight) Producing clean hydrogen from water using electricity sounds simple enough. Run a current through water, collect the hydrogen at one end and the oxygen at the other. No carbon emissions, no fossil fuels, no pollution. In principle, the basic chemistry of electrolysis has been understood for over a century. In practice, it remains costly, inefficient, and dependent on metals that are scarce, expensive, and not easily replaced.
The problem lies with the catalysts, the materials that help drive the chemical reactions by making them faster and less energy-intensive. The most effective catalysts for water electrolysis contain elements like platinum and iridium. These metals have just the right electronic properties to break apart water molecules and steer the resulting reactions in the right direction. But they are among the rarest elements in the Earth’s crust. Their supply is limited, mining them is expensive, and the costs make up a large share of the total price of a hydrogen production system.
Even when these metals are used, most of the atoms never come into contact with the reactants. In traditional catalyst designs, metal particles are clumped together in small clusters, and only the atoms on the outer surface are available to participate in the reaction. The rest sit idle inside the structure, contributing to cost without contributing to performance. Over time, these clusters tend to merge, losing surface area and becoming less effective.
This has led researchers to ask a simple but far-reaching question: what if every single atom in a catalyst could be used? That idea has given rise to single-atom catalysts, materials that spread metal atoms one at a time across a surface, each acting as an independent reaction site. This approach makes far better use of expensive materials and opens the door to finely tuning how the catalyst behaves. But it also introduces a new problem. Isolated atoms are unstable. They do not stay put. They move, combine, or detach from the surface unless carefully anchored in place.
That anchoring role is played by a support material, and the nature of that support turns out to matter as much as the metal itself. Recent attention has turned to atomically thin materials, substances just one or two atoms thick, with properties that make them ideally suited to hosting and stabilizing single atoms. These ultrathin supports not only hold atoms in place but also influence their reactivity by changing how electrons flow around them. New materials like graphene, MXenes, and transition metal dichalcogenides offer a highly tunable platform for building catalysts with unprecedented precision.
A recent review paper published in Advanced Powder Materials (“Single-atom catalysts supported on atomically thin materials for water splitting”), explores this convergence of atomic-scale engineering and clean energy chemistry. It examines how single atoms interact with atomically thin supports, how these systems are made and studied, and how they perform in splitting water into hydrogen and oxygen.
Schematic illustration of the synthetic strategies, characterization techniques, and mechanism insights of water electrolysis based on single-atom catalysts supported on atomically thin materials (SACs@ATMs). (Image: reprinted from DOI:10.1016/j.apmate.2025.100330, CC BY) (click on image to enlarge)
The authors make the case that combining isolated catalytic atoms with ultrathin support materials offers a promising route toward more efficient, durable, and affordable hydrogen production.
At the center of this approach is the interaction between the single metal atom and the surface that holds it. This interaction determines how tightly the atom is bound to the support, how it responds to incoming molecules, and how electrons move during the reaction. Supports with specific surface features such as defects, vacancies, or added atoms can be designed to form stable bonds with metal atoms while also shaping their electronic behavior. These modifications allow scientists to control how easily hydrogen or oxygen is formed during electrolysis and how much energy is required to start the reaction.
In many cases, the support does more than just hold the atom in place. It actively influences the reaction. For instance, by creating titanium vacancies on the surface of a layered material known as MXene, researchers were able to anchor nickel atoms in specific positions that enhanced hydrogen production. The nickel atoms bonded with surrounding carbon atoms, improving the efficiency of key reaction steps. Another study used a layered structure made from molybdenum and titanium to confine platinum atoms between sheets, holding them in a specific atomic arrangement that improved their stability under operating conditions.
To take advantage of these effects, researchers have developed several methods to produce single-atom catalysts on atomically thin supports. Each method involves trade-offs between precision, cost, and scalability.
One common technique is wet impregnation, where a solution containing metal ions is applied to the support material, allowing the atoms to attach to surface sites. Heating then locks them in place. This method is straightforward and scalable but often results in uneven distribution and low metal loading. More advanced versions use controlled heating steps or special atmospheres to improve atom placement and achieve higher loadings.
Chemical vapor deposition, or CVD, offers greater precision by delivering metal atoms as a gas onto the surface. This approach can fine-tune the atomic structure of the catalyst and create highly uniform systems. In some cases, plasma energy is used to generate defects on the support that help trap the metal atoms in place. However, CVD requires complex equipment and is expensive to scale.
Mechanical ball milling is a simpler method. It uses physical force to embed metal atoms into the support surface. While environmentally friendly and low in cost, the method can damage the structure of delicate materials and often yields less control over atom placement.
Photochemical methods use ultraviolet light to activate the support and reduce the metal ions onto its surface. These approaches are useful for creating well-defined atomic environments but are typically limited to laboratory settings due to their complexity and low throughput.
The performance of these systems depends not only on how well the atoms are anchored but also on how their electronic structure is tuned. The interaction between the support and the metal atom can change the atom’s charge, alter how it binds to intermediate molecules, and affect the energy needed to complete each step of the reaction. In water electrolysis, this kind of tuning can reduce the energy losses that make current systems inefficient.
Some examples show just how much of a difference these combinations can make. A platinum-based catalyst anchored on a molybdenum titanium MXene achieved a remarkably low overpotential of 30 millivolts at a current density of 10 milliamperes per square centimeter, a key benchmark for hydrogen evolution. Another system using crumpled MXene sheets with platinum clusters reached a mass activity of 1,847 milliamperes per milligram of platinum, reducing the amount of precious metal needed without sacrificing performance.
For oxygen evolution, a cobalt-based single-atom catalyst on a graphene support achieved a high loading of over 10 percent by weight and delivered strong activity and stability. A ruthenium-based catalyst supported on a layered hydroxide maintained stable performance at very high current densities, even after more than one thousand hours of operation.
These results underscore the central importance of the metal-support interaction. It is not just about placing atoms on a surface but about shaping their chemical environment in ways that optimize performance. Electron transfer between the atom and the support can adjust how the catalyst binds to water, hydrogen, or oxygen. Nearby atoms in the support can also participate directly in the reaction, helping to stabilize intermediate molecules or promote the movement of protons and electrons.
Looking ahead, researchers are beginning to explore more complex configurations. Some are designing catalysts with two different metal atoms placed side by side. These dual-atom systems can handle different parts of the reaction more efficiently than a single atom could on its own. Others are combining single atoms with tiny metal clusters to exploit both the high efficiency of atomic sites and the robustness of larger structures.
New tools are also helping guide the design process. Techniques like X-ray absorption spectroscopy and high-resolution electron microscopy can reveal how atoms are arranged and how they behave during the reaction. Meanwhile, computer modeling and machine learning are being used to predict which combinations of metals and supports will offer the best performance before they are built in the lab.
The review by Chen and colleagues provides a clear picture of how this field is developing. It shows that the key to improving water electrolysis is not just finding better materials but learning how to control matter at the atomic level. By combining isolated catalytic atoms with ultrathin, carefully engineered supports, researchers are building systems that use fewer resources, produce more hydrogen, and remain stable under demanding conditions.
As the need for clean energy grows, these advances in catalyst design may help make hydrogen a more practical and widely available fuel. The challenge now is to move from laboratory success to industrial application. That will require not only new materials but also new ways of making them at scale. Still, the principles are now well understood. With careful design and continued innovation, single-atom catalysts on atomically thin supports could play a central role in the next generation of energy technologies.
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Yuhai Dou (University of Shanghai for Science and Technology,)
, 0000-0003-2549-1400 corresponding author
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