Laser written high entropy oxide electrodes with tree like nanoarrays integrate structure and chemistry to achieve efficient and durable hydrogen production under industrial electrolysis conditions.
(Nanowerk Spotlight) Producing hydrogen without fossil fuels is often described as one of the missing pieces in the clean energy puzzle. The gas could power factories, trucks, and even entire power plants, and unlike oil or coal it leaves only water behind when used. The simplest way to make it is to split water with electricity. Yet what looks neat in a classroom diagram becomes far more stubborn in practice. Pushing large amounts of current through water wears out electrodes, wastes energy, and creates bottlenecks where gases and liquids collide. These obstacles have slowed the vision of hydrogen as a widely used sustainable fuel.
The difficulty is not only chemical. Electrodes must carry enormous currents without overheating, resist corrosion in harsh solutions, and let bubbles of gas escape instead of sticking and blocking the surface. Existing materials either work well but cost too much, or they are affordable but fall apart under stress. Engineers have been stuck in this trade off for decades.
A research team in China has now tried a different approach. Inspired by the way trees work together in a forest, they designed electrodes with supporting trunks and catalytic leaves, each serving a role that strengthens the whole system. Using nanosecond bursts of laser light, they carved titanium into cone shaped structures and decorated them with mixed metal oxides.
Laser pulses carve titanium foam into cone shaped “trunks” decorated with clusters of mixed metal oxide nanoparticles, forming tree like arrays. This architecture combines micro and nanoscale roughness that changes how the surface interacts with liquids and gases, making it both strongly water attracting and resistant to bubble buildup. Elemental mapping confirms the even distribution of the five metals across the structure, showing that the process produces a stable high entropy oxide material directly on the titanium support. (Image: Adapted and reprinted with permission from Wiley-VCH Verlag) (click on image to enlarge)
High entropy oxides are central to this story. They are mixtures of several different metal oxides in nearly equal proportions. By combining multiple elements, the material stabilizes itself in ways that no single oxide can achieve. The mixture can resist corrosion, adapt its electronic properties, and create a broad range of sites where chemical reactions can occur. In theory this makes them excellent catalysts.
In practice they have been difficult to use because conventional synthesis methods produce powders with little control over shape. When those powders are glued to supports with binders, the result is fragile and inefficient.
The team set out to change that by uniting chemistry and architecture in a single manufacturing step. They coated titanium foam with a solution of salts containing iron, cobalt, nickel, molybdenum, and chromium. Then they exposed the surface to extremely short laser pulses. Each pulse deposited energy so quickly that the titanium melted locally while the salts decomposed. The surface then cooled in microseconds, too fast for the atoms to separate into stable phases. Instead, nanoparticles of mixed oxides froze in place, firmly anchored to the titanium. At the same time, flows within the molten metal sculpted cone shaped protrusions. What emerged was a landscape of tiny trunks supporting dense foliage of nanoparticles.
This forest like architecture is not just visually appealing. It gives the electrode properties that directly address the obstacles of water electrolysis. The cones act as channels that pull in liquid through capillary action, ensuring that fresh electrolyte reaches every active site. The oxide nanoparticles provide the catalytic activity, while the rough surface prevents bubbles from sticking. Water spreads instantly across the surface, while gas bubbles slide off as if repelled. Because the catalyst is grown directly from the substrate rather than glued on, it remains firmly in place even when bubbles form and burst.
Performance tests showed the benefits of this design. In alkaline solution, the electrode needed only 188 millivolts of extra voltage to drive the oxygen evolution reaction at a standard current density of 10 milliamperes per square centimeter. More importantly for industrial use, it reached 1 ampere per square centimeter at 1.82 volts when operated in a full electrolyzer with an anion exchange membrane.
This outperformed commercial titanium mesh coated with iridium oxide, a benchmark material. The electrode also proved durable, maintaining steady performance for 600 hours at 500 milliamperes per square centimeter with only a minimal increase in required voltage.
The team also investigated why this combination of elements and architecture worked so well. Using density functional theory, a computational method for modeling atomic interactions, they analyzed how electrons were distributed in the mixed oxide. The calculations showed that nickel atoms acted as the main active sites for oxygen evolution. Their behavior, however, was tuned by the presence of molybdenum and chromium. These elements donated charge through the network of metal and oxygen bonds, adjusting the electronic structure of nickel.
This subtle shift made the nickel sites bind oxygen intermediates less tightly, which helped the reaction proceed more smoothly. The models also confirmed that the rapid cooling produced an amorphous structure with a wide variety of bond lengths. This structural diversity increased the likelihood of having sites that were close to ideal for catalysis.
The researchers did not arrive at this design by chance. They used high throughput experiments to explore how laser parameters affected performance. By varying scanning speeds and energy densities across titanium plates, they created dozens of samples in a single run and measured their activity quickly. This allowed them to map out a window of processing conditions that consistently produced the desired microcone nanoparticle structure.
Too little energy left the surface largely unchanged. Too much energy created irregular and unstable features. Intermediate settings yielded ordered arrays with excellent catalytic properties. This method linked process, structure, and function in a way that can guide scaling to larger systems.
Microscopy and spectroscopy provided further detail. Transmission electron images showed nanoparticles about 20 nanometers in diameter, bonded together in tight clusters. Elemental mapping confirmed that the five metals were evenly distributed, meeting the definition of a high entropy material. High resolution analysis revealed crystalline titanium domains embedded in an amorphous oxide matrix. This dual phase structure offered both conductivity and a high density of active sites.
X-ray spectroscopy revealed high oxidation states of molybdenum and chromium, known to aid charge transfer and resist corrosion. Even after prolonged testing, the electrode largely retained its amorphous character, with only partial dissolution of molybdenum and chromium. That dissolution may have played a beneficial role by releasing soluble species into the electrolyte that enhance the oxygen evolution reaction.
What makes this study notable is not only the performance numbers, though they are impressive. It is the design philosophy it illustrates. Rather than focusing on a single parameter, the team created a system where chemical composition, structural hierarchy, and interfacial properties reinforce one another. The forest analogy captures this well. Just as trunks, branches, and leaves each serve a purpose in a living system, cones, nanoparticles, and surface textures each play a role in this electrode. The result is more than the sum of its parts.
There are still challenges ahead. Extending the method to meter sized electrodes will require careful control of heat flow, uniformity, and precursor evaporation. Yet laser systems are already widely used in industry for cutting, welding, and surface treatment, which makes the technique more compatible with scaling than many laboratory methods. The approach could also be adapted to other combinations of metals, opening the door to new families of catalysts.
The broader lesson is that progress in hydrogen technology may come not only from new materials but also from new ways of thinking about structure. By designing electrodes that behave more like integrated systems than collections of particles, researchers can overcome the intertwined problems of efficiency, stability, and transport. Lin and colleagues call their creation a morphological high entropy catalyst, emphasizing that shape matters as much as composition.
If clean hydrogen is to play the role many hope for in a low carbon future, electrolysis must become cheaper, more efficient, and more durable at scale. This work offers a vision of how that might be achieved. It shows that an electrode can be sculpted into a forest of microscopic trunks and leaves, where each level of structure supports the next. By blending chemistry with architecture, the researchers demonstrate a path toward electrodes that can withstand industrial demands and bring sustainable hydrogen a step closer to reality.
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Yonggang Yao (Beijing National Laboratory for Molecular Science)
, 0000-0002-9191-2982 corresponding author
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