The study, published in Discover Electrochemistry by Prince Gollapalli, Santu Biswas, Leeor Meir, Nofar Refaeli and Maytal Caspary Toroker, tackles a question that has lingered because of an experimental catch. The catalysis does not happen on the stable nickel hydroxide phase that is easy to characterize in the lab. Instead, water oxidation occurs on a metastable nickel oxyhydroxide (β-NiOOH) surface that forms only under operating potentials of roughly 1.3 to 1.5 volts versus the reversible hydrogen electrode, when the material sheds protons and nickel transitions from the +2 to the +3 oxidation state. Capturing that fleeting phase at the atomic scale requires demanding in situ experiments, so most studies have settled for characterizing the stable precursor. Density functional theory (DFT) offers a way around the problem, letting researchers build atomistic models of the active phase and watch the reaction unfold electron by electron.

To make the model as realistic as possible, the team anchored it in experiment. Transmission electron microscopy studies of nickel hydroxide consistently reveal hexagonal, plate-like nanoparticles, so the researchers carved a hexagonal nanocrystal out of the unit cell of staggered β-NiOOH, a structural variant predicted to be stable in earlier first-principles work. The cluster measures roughly one nanometer across in width and length, closely matching the approximately 2.5-nanometer particles synthesized and imaged in a combined experimental and theoretical study the team used as a benchmark. They then built two versions of the particle: a three-layer stack about 1.35 nanometers tall, and a single layer just 0.38 nanometers thick. Crucially, the top layer is identical in both, so any difference in catalytic performance could be attributed purely to what lies beneath.

On that shared top surface, the researchers identified three chemically distinct places where the reaction could begin. At the edge of the particle, an undercoordinated nickel atom bonded to only five oxygens offers a natural docking point for water, with no vacancy needed. In the interior, the surface alternates between oxygen-terminated and hydroxyl-terminated triangular sites, and the team created vacancies at each, removing an oxygen atom in one case and an oxygen plus a hydrogen atom in the other, to open adsorption sites. This choice of locations matters because the conventional wisdom in nanocatalysis holds that edges are the hot spots of reactivity. The simulations were set to test whether that wisdom survives on a particle this small.

The answer, at least for thermodynamics, is a resounding no. Running the full four-step OER mechanism, in which water adsorbs and then loses four proton-electron pairs through *OH2, *OH, *O and *OOH intermediates, the team computed Gibbs free energies for every step on every site of both particle sizes. The overpotential, the extra voltage beyond thermodynamic requirement needed to make every step proceed downhill, dropped consistently when the particle was thinned from three layers to one. On the hydroxyl-terminated site, the overpotential fell from 0.78 volts to 0.57 volts; on the oxygen-terminated site, from 0.98 to 0.75 volts; and on the edge site, from 1.62 to 1.11 volts. The single-layer hydroxyl-terminated configuration, at 0.57 volts, matched or beat values reported in the literature for extended surfaces of the same material.

Two mechanisms appear to explain the advantage of going thin. First, shrinking the particle raises the catalytically active surface area per unit volume, a straightforward geometric effect. Second, and more subtly, a single layer has no neighboring layer above it for protons to migrate into or to hydrogen-bond with. Previous work had shown that hydrogen desorption is easier by about half an electron-volt in monolayers precisely because interlayer hydrogen bonding is absent, and that adding protons to β-NiOOH is otherwise spontaneous. Without a second layer to hold protons back, deprotonation steps become easier, and the tallest energy barrier on the reaction coordinate shrinks. The team confirmed this with an implicit solvation model, which raised the best-case overpotential only modestly, by 0.06 to 0.1 volts, leaving the single-layer advantage intact.

The identity of the potential determining step, the slowest rung on the energetic ladder, also depended on where the reaction happened. At the edge site, where the reacting intermediate touches only a single nickel atom, the hardest step was the second deprotonation, converting *OH to *O. At both interior sites, where three nickel atoms surround the adsorbate, the bottleneck shifted to the third deprotonation, from *O to *OOH, and the overpotential dropped by roughly a factor of two. In every configuration, the *O intermediate turned out to be the pivotal species, appearing either as the product or the reactant of the rate-limiting step, underscoring its central role in limiting oxygen evolution on this catalyst.

Because nickel can access multiple oxidation states, the team could use magnetism as a fingerprint of electronic change. Assigning magnetic moments of roughly 1.7, 1.2 and 0.2 Bohr magnetons to nickel in the +2, +3 and +4 states, they found that at the edge site only one nickel atom oxidizes from +3 to +4 during the reaction, while at the oxygen-terminated site none do, and at the hydroxyl-terminated site two of the three supporting nickel atoms make the jump to +4. Robustness checks with different values of the DFT+U correction parameter and with the hybrid HSE06 functional confirmed the assignments. The hydroxyl-terminated site, with its more oxidized nickel atoms, sits closest to the highly oxidized state the material is expected to adopt during real oxygen evolution, marking it as the genuinely active reaction center.

The final piece was dynamics rather than thermodynamics. Each reaction step ejects a proton-electron pair, leaving behind a hole in the valence band that must travel to the active site to drive oxidation. The team propagated quantum wave packets through the electrostatic potential landscapes of each intermediate, using a split-operator algorithm to solve the time-dependent Schrödinger equation on a femtosecond timescale, and measured the cumulative hole flux crossing a barrier near the adsorbate. The results tracked the thermodynamics beautifully: the edge site showed the lowest hole flux and the highest electrostatic barriers, while the hydroxyl-terminated site showed the highest flux, with a cumulative probability of 0.83 for its potential determining reactant compared with just 0.37 at the edge. More nickel atoms sharing the load and a more oxidized surface mean more holes available to do chemistry.

Taken together, the study rewrites a piece of nanocatalyst intuition. On β-NiOOH nanoparticles, the bulk-like hydroxyl-terminated site outperforms the edge, contradicting the general rule that edges are more active, and the thinnest possible particle delivers the lowest overpotential. For engineers designing anode materials for green hydrogen electrolyzers, the prescription is concrete: maximize surface-to-volume ratio by exfoliating the catalyst toward single layers, and engineer hydroxyl-terminated, vacancy-rich surfaces where multiple nickel atoms can participate and change oxidation state. The work also suggests magnetism itself could serve as a control handle, since spin-polarized band structures mean the number of available states at the Fermi level differs for spin-up and spin-down carriers. As the hydrogen economy scales up, such atomistic design rules, extracted from simulations that can finally see the metastable phase where the real chemistry happens, may prove as valuable as any new material discovery.

Subject of Research: Computational study of how nanoparticle size and active site location govern the thermodynamics and hole transport dynamics of β-NiOOH catalysts for the oxygen evolution reaction

Article Title: Effect of nanoparticle size and active site position on the thermodynamics and charge dynamics of NiOOH catalyst for oxygen evolution reaction

Article References: Gollapalli, P., Biswas, S., Meir, L., Refaeli, N., & Caspary Toroker, M. (2026). Effect of nanoparticle size and active site position on the thermodynamics and charge dynamics of NiOOH catalyst for oxygen evolution reaction. Discover Electrochemistry, 3(1), Article 50. https://doi.org/10.1007/s44373-026-00135-0

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00135-0

Keywords: oxygen evolution reaction, NiOOH, water splitting, green hydrogen, density functional theory, electrocatalysis, nanoparticles, overpotential, hole transport, oxidation state, nickel oxyhydroxide, DFT+U

The core insight concerns a mechanism that electrochemists have courted for a decade: lattice-oxygen redox. In conventional metal oxide and oxyhydroxide catalysts, oxygen atoms in the crystal framework sit passively as spectators; every bond made and broken during water oxidation happens at adsorbed intermediates such as *OH and *O. That is safe but slow, because the adsorption energies of these intermediates are locked together by rigid scaling relationships. Make *OH binding stronger to speed up one step, and *O binding strengthens too, penalizing another. The scaling relations impose a theoretical floor on the overpotential, a tax every conventional catalyst must pay. Lattice-oxygen redox breaks that tax. When framework oxygen atoms themselves participate in the redox chemistry, oxygen-oxygen bonds can form through direct coupling of lattice oxygen, sidestepping the adsorbate scaling conundrum entirely.

The catch is stability, and it has been brutal. Oxidizing lattice oxygen means ripping electrons from the very orbitals that hold the crystal together. Once activated indiscriminately, that oxidation delocalizes across the lattice, holes accumulate on framework oxygen, metal-oxygen bonds soften and break, and the material dissolves or amorphizes. Many catalysts that unlock lattice oxygen in the laboratory die within hours under the punishing polarization of a real electrolyzer. The literature is littered with tantalizing activity reports that collapse under accelerated ageing. The Singapore-led team, whose senior authors include Junmin Xue, Haoyin Zhong, Bin Tian and Xiaopeng Wang, asked a different question: what if lattice oxygen could be activated not all at once, but in a spatially ordered, electronically programmed sequence?

Their answer begins with an unlikely precursor: a composite of chromium(III) oxide and nickel diselenide, Cr2O3/NiSe2. When the electrode is held under anodic polarization in alkaline electrolyte, the reconstruction unfolds in two chemically distinct stages, and the order matters enormously. In the first stage, selenium leaches out of the NiSe2 phase. Losing the chalcogen opens up the nickel 3d band manifold, specifically broadening the antibonding eg band, the orbital set that overlaps with oxygen 2p states. A broader eg band strengthens nickel-oxygen covalency, and stronger covalency does two things at once: it accelerates the deprotonation of *OH intermediates, a known rate-limiting step on nickel oxyhydroxide surfaces, and it begins to tilt the electronic structure toward oxygen participation.

Then comes the second, decisive stage. Chromium begins to leach from the oxide component, and crucially, the chromium departure selectively depletes oxygen atoms that were coordinated to nickel across the composite interface. What remains is a modified nickel oxyhydroxide, SRA-NiOOH, in which oxygen non-bonding states, oxygen 2p orbitals stripped of their bonding partners, are generated not randomly across the lattice but in spatially confined pockets. This is the heart of the strategy. Confined non-bonding states act as local redox reservoirs for lattice oxygen, close enough to the surface to join the catalytic cycle, yet electronically quarantined so that oxidation holes cannot wander freely through the framework. Destructive redox delocalization, the killer mechanism of lattice-oxygen catalysts, is suppressed by construction. The oxygen-redox activity and the lattice stability, usually two ends of a seesaw, are decoupled.

The experimental evidence for this picture is layered across multiple structural and spectroscopic probes. X-ray absorption spectroscopy traces the changes in nickel coordination and oxidation state as reconstruction proceeds, while synchrotron-based measurements carried out at the Singapore Synchrotron Light Source document the emergence of the modified oxyhydroxide phase. Density functional theory calculations, performed with the ASTAR Computational Resource Centre and the National Supercomputing Centre in Singapore, complement the experiments, showing how the broadened eg* band and the confined oxygen non-bonding states reshape the energy landscape of the oxygen evolution mechanism. The team further demonstrates that the approach generalizes: the sequential-reconstruction activation paradigm is not a one-off trick of one composition but a design framework that can be exported to related systems, a claim their fourth figure addresses directly.

The device-level performance is where the work will command the most attention. Anion-exchange-membrane water electrolyzers are the commercial sweet spot for many of these nickel-based catalysts, because AEM technology can use earth-abundant transition metals instead of the iridium that proton-exchange-membrane electrolyzers demand. But AEM electrolyzers still need to run at high current density, above 2 amperes per square centimeter, to reach the cost targets that would make green hydrogen competitive with fossil-derived hydrogen. At 4.1 A cm-2 at 1.8 V in 1 M KOH at 80 degrees Celsius, the SRA-NiOOH anode sits squarely in industrially relevant territory, and the nearly 3,500-hour stability test under accelerated ageing at 60 degrees Celsius suggests the catalyst does not merely sprint; it runs a marathon. Sustained oxygen-redox operation at high current density, the authors argue, is precisely what the sequential electronic reconstruction buys: a durable oxygen-redox window that stays open under demanding polarization.

The conceptual contribution may outlast the specific numbers. For years, the field has treated catalyst reconstruction as something to minimize, a necessary evil on the path to stable operation, or at best a one-shot activation. This work reframes reconstruction as something to choreograph. By choosing a precursor whose constituents leach in a controlled order, selenium first, chromium second, the researchers wrote the electronic structure of the final catalyst as a timed sequence rather than a static composition. Each leaching event performed a specific electronic function, band broadening here, oxygen non-bonding state generation there, and the final NiOOH inherited the benefits of both without the instability that an uncontrolled surface transformation would bring. It is a programming philosophy applied to surfaces, and it echoes a broader shift in electrocatalysis toward operando-informed precatalyst design, in which the working electrode is understood as a dynamic, self-assembling entity rather than a fixed material.

There are, of course, caveats and open questions. The reported metrics come from laboratory-scale AEM cells and accelerated ageing protocols, and the road from such benchmarks to kilowatt-scale stacks involves membrane durability, flow uniformity, and cost questions that no single anode catalyst can answer alone. The precise atomic-scale geography of the confined non-bonding states, and how far the confinement holds as reconstruction continues over thousands of hours, will reward further study. But the bar the paper clears is a meaningful one: it shows that the activity-stability trade-off, long treated as a law of nature for lattice-oxygen catalysis, can be suspended by electronic design. If sequential reconstruction proves as general as the authors suggest, the oxygen evolution bottleneck that has constrained green hydrogen may finally have an engineering-grade exit, built not from a miracle material but from a catalyst taught to rebuild itself in the right order.

Subject of Research: Sequential electronic reconstruction of a Cr2O3/NiSe2 precursor to enable durable lattice-oxygen redox in anion-exchange-membrane water electrolysis

Article Title: Sequential electronic reconstruction enables durable oxygen redox in water electrolysis

Article References: Yu, J., Zhong, H., Zhang, Q., Zhang, X., Ye, Y., Diao, C., Yu, Z. G., Xi, S., Tian, B., Wang, X., & Xue, J. (2026). Sequential electronic reconstruction enables durable oxygen redox in water electrolysis. Nature Sustainability. https://doi.org/10.1038/s41893-026-01940-6

Image Credits: AI Generated

DOI: 10.1038/s41893-026-01940-6

Keywords: water electrolysis, oxygen evolution reaction, lattice oxygen redox, nickel oxyhydroxide, green hydrogen, anion-exchange membrane, electrocatalysis, catalyst reconstruction, eg band, catalyst stability, nickel selenide, Nature Sustainability