Flaky Carbon-Supported NiCo Nanoparticles Enable Efficient Water Splitting Catalysis

Hydrogen has long been touted as a clean fuel of the future, but producing it at industrial scale still depends heavily on electricity, catalysts, and economics. A research team in China has now reported a catalyst made entirely from abundant, inexpensive elements that matches precious-metal benchmarks in the laboratory and, more importantly, survives punishing industrial-like operating conditions. The work, published in Catalysis Letters, describes flaky carbon-supported nickel-cobalt nanoparticles that function as dual-purpose electrocatalysts, efficiently driving both halves of the water-splitting reaction and holding steady for more than 200 hours at near-industrial current densities.

Electrolyzers split water into hydrogen and oxygen using two complementary half-reactions: the hydrogen evolution reaction (HER) at the cathode, where protons or water molecules are reduced to hydrogen gas, and the oxygen evolution reaction (OER) at the anode, a slower, more energy-demanding four-electron process that liberates oxygen. The efficiency losses in a practical electrolyzer stem largely from the overpotentials—excess voltage beyond thermodynamic minimum—needed to push these reactions at useful rates. Platinum and iridium oxide are the standard benchmarks for HER and OER respectively, but their scarcity and cost make them poor candidates for gigawatt-scale hydrogen production. Bifunctional catalysts that can perform both reactions allow a single material to serve as both the cathode and the anode in a two-electrode cell, simplifying device design and cutting costs dramatically.

The new material, designated Ni₁Co₃@CN-sh, was synthesized through a straightforward pyrolysis route. The researchers, led by Muxi Wang, Wenwen Luo, Guang Li, and Qingfeng Yi of Hunan University of Science and Technology, together with Ruowei Yi of Xiangtan University, modulated two key variables: the nickel-to-cobalt ratio in the metallic nanoparticles and the choice of organic compound used as the carbon source. By carefully tuning these parameters, they produced a catalyst in which NiCo alloy nanoparticles are dispersed on flaky, nitrogen-containing carbon sheets that assemble into a three-dimensional hierarchical porous architecture. This porous structure is not merely cosmetic; it provides an abundance of electrochemically accessible active sites, channels for rapid electrolyte penetration, and interconnected pathways for the electrons that must shuttle between the metal particles and the external circuit during catalysis.

The performance numbers reported for the optimal composition are striking. For the oxygen evolution reaction—widely considered the bottleneck of water electrolysis—the Ni₁Co₃@CN-sh catalyst required an overpotential of just 191 millivolts to reach a current density of 100 milliamperes per square centimeter, a figure that places it on par with commercial iridium dioxide, the noble-metal reference catalyst for OER. On the hydrogen side, the same material needed only 194 millivolts of overpotential, comparable to what commercial platinum-on-carbon delivers. Achieving such balanced performance from a single non-noble-metal catalyst is rare, because the atomic-scale requirements for the two reactions differ: HER favors surfaces with optimal hydrogen adsorption energy, while OER depends on the energetics of oxygen-containing intermediates and often benefits from in-situ surface reconstruction into higher-valent oxyhydroxide species.

Nickel and cobalt, as neighboring transition metals, offer a productive synergy that the authors exploited through composition control. Cobalt-rich compositions appear to optimize the electronic structure of the alloy nanoparticles, modulating the d-band position and thereby tuning adsorption energies for reaction intermediates on both catalyst surfaces. The nitrogen-doped carbon support contributes in its own right: graphitic and pyridinic nitrogen sites can tune the electronic structure of adjacent metal atoms, enhance charge transfer, and themselves contribute catalytic activity, while the flaky morphology of the carbon provides mechanical robustness and good electrical connectivity to the metal nanoparticles. The team characterized the material using a comprehensive suite of techniques including X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller surface area analysis, building a structural picture consistent with well-dispersed alloy particles anchored within the conductive carbon framework.

The true test of any electrolysis catalyst comes when it is assembled into a working device, and here the results were particularly compelling. In a two-electrode alkaline electrolyzer with identical Ni₁Co₃@CN-sh electrodes serving as both cathode and anode, the cell required a voltage of only 1.796 volts to sustain a current density of 100 milliamperes per square centimeter. That figure outperformed a reference electrolyzer built from the noble-metal combination of platinum-on-carbon and iridium dioxide, a benchmark pairing that has defined the state of the art for decades. In the economics of water electrolysis, every hundredth of a volt saved at high current density translates directly into lower electricity consumption per kilogram of hydrogen, so an earth-abundant catalyst beating the noble-metal standard at this level is a meaningful milestone.

Perhaps the most industrially relevant finding concerns durability. Alkaline water electrolysis (AWE) is the most mature electrolysis technology, but pushing it toward industrial relevance requires operation at elevated temperatures and very high current densities—conditions that corrode, dissolve, or delaminate most laboratory catalysts within hours. The Hunan team subjected their electrolyzer to 80 degrees Celsius and a current density of 500 milliamperes per square centimeter, a regime approaching that of commercial alkaline electrolyzers. The cell held a voltage of approximately 1.84 volts for more than 200 hours of continuous operation without significant degradation. Sustained stability at 500 milliamperes per square centimeter is a demanding criterion that many highly active catalysts fail, as high current densities accelerate gas bubble formation, catalyst dissolution, and mechanical stress. Surviving this treatment suggests the carbon-supported architecture provides genuine structural resilience rather than just transient high activity.

The design strategy behind the material may prove as important as the catalyst itself. Rather than relying on complex multi-step syntheses or exotic compositions, the researchers demonstrated that systematically varying the bimetallic ratio and carbon precursor in a single pyrolysis step can systematically optimize the three-dimensional pore structure and, with it, catalytic performance. This gives the approach a clear route toward scale-up: pyrolysis of organic-metal precursors is among the simplest and most manufacturable methods for producing carbon-supported nanoparticle catalysts, and the use of nickel and cobalt—both produced in enormous quantities for batteries and steels—avoids the supply-chain fragility associated with platinum-group metals. The study also aligns with a broader trend in electrocatalysis research, where single materials must serve multiple functions, whether HER and OER in electrolyzers or the oxygen reduction and oxygen evolution reactions in rechargeable metal-air batteries.

There remain, of course, gaps between a laboratory electrode and a commercial electrolyzer stack. The researchers evaluated the catalyst on laboratory-scale electrodes in alkaline solution; industrial devices must maintain such performance over months and years, across thousands of start-stop cycles, and at even higher current densities with efficient gas separation. Faradaic efficiency, turnover frequency, and the precise identity of the active sites under operating conditions—particularly the surface species formed during OER—will require further study. The authors also note that no datasets beyond those in the paper were generated, meaning the conclusions rest on the experimental characterization presented. Still, the combination of noble-metal-matching activity, single-material bifunctionality, and demonstrated stability under elevated-temperature, high-current operation places this catalyst among the more practically oriented non-precious systems reported to date.

The work was supported by the National Natural Science Foundation of China under grant number 22379042, and the authors declare no competing interests. As governments worldwide commit to green hydrogen targets and electrolyzer manufacturing ramps up, the search for catalysts that are cheap, active, and durable intensifies. This study offers a promising answer on all three fronts: a nickel-cobalt alloy on flaky nitrogen-doped carbon that splits water as efficiently as precious metals and keeps doing so where it matters—at high current density, high temperature, and for hundreds of hours on end. If the design strategy transfers from alkaline laboratory cells to industrial electrolyzer hardware, earth-abundant catalysts of this kind could play a significant role in making hydrogen a genuinely affordable clean energy carrier.