Hydrogenation, the addition of hydrogen atoms to molecules, underpins the production of an enormous range of everyday goods, from pharmaceuticals and agrochemicals to plastics and fine chemicals. In conventional industrial practice, the reaction relies on hydrogen gas, usually generated from fossil fuels and handled under pressure with metal catalysts. Electrocatalytic hydrogenation offers a fundamentally different route: instead of using molecular hydrogen, the process generates hydrogen equivalents directly from water at the surface of an electrode, driven by electricity. When that electricity comes from renewable sources, the approach promises a far more sustainable way to carry out reductive chemical transformations, one of the workhorse reaction classes of modern synthesis.

The difficulty has always been the catalyst. Platinum, rhodium, palladium and their relatives are superb hydrogenation catalysts, but they are scarce, costly and geopolitically concentrated. Finding cheaper alternatives that match their activity and, crucially, their selectivity has proved stubbornly hard. A major challenge in electrocatalytic hydrogenation is replacing scarce platinum-group metals with earth-abundant catalysts without sacrificing activity or selectivity, said Mahito Atobe, professor at Yokohama National University’s Faculty of Engineering and a corresponding author of the study. Selectivity matters enormously in this context, because hydrogenation reactions can follow multiple pathways, and unwanted byproducts translate directly into wasted energy, wasted material and costly purification steps.

The Yokohama team, co-led by Naoki Shida, associate professor in the same faculty, turned to cobalt, an abundant and comparatively inexpensive transition metal that has attracted growing interest as a catalytic workhorse for electrochemistry. But rather than simply testing cobalt in one fixed form, the researchers asked a more subtle question: what happens to the oxidation state of cobalt while the catalyst is actually operating, and could the balance between metallic cobalt and cobalt oxide be the real determinant of performance? We wanted to understand how the oxidation state of cobalt changes under operating conditions and whether controlling the balance between metallic cobalt and cobalt oxide could provide an effective catalyst, Shida explained.

To build the catalyst, the researchers started from cobalt sulfate and calcined the material at 750 degrees Celsius, producing cobalt species supported on carbon. They then deployed the catalyst in an anion-exchange membrane electrolyzer, a device in which an electric current drives hydrogenation reactions at the cathode, with water serving as the ultimate hydrogen source. Under ambient electrolysis conditions, the optimized catalyst converted pyridine, a simple nitrogen-containing aromatic ring, into piperidine, its fully saturated counterpart, with a yield exceeding 99 percent. That figure means almost every molecule of pyridine that reacted emerged as the desired product rather than as partially hydrogenated or over-reduced byproducts. Piperidine itself is far from a trivial target: the saturated nitrogen heterocycle is a fundamental building block in synthetic and medicinal chemistry, appearing in the scaffolds of numerous drugs, which makes the reaction a demanding and practically relevant benchmark of catalytic selectivity.

What the team discovered next is the conceptual heart of the paper. The catalytic performance of cobalt is determined not simply by its elemental composition, but by its dynamic oxidation state during electrolysis, Atobe said. During operation, cobalt does not sit still chemically. It shuttles between metallic Co(0) and cobalt oxide, denoted CoOx, as electrons flow and the local chemical environment shifts. The researchers found that catalysts containing too much of either form performed poorly. Purely metallic cobalt and heavily oxidized cobalt each fell short of the activity and selectivity achieved by an intermediate mixture. The optimum lay at a specific ratio of metallic Co to CoOx, a chemical middle ground that neither extreme could match.

To understand why this balance matters, the team combined experimental characterization with in situ X-ray spectroscopy, which allowed them to track the catalyst’s chemical state while it was actually working, and with theoretical calculations of the reaction energetics. The results point to a cooperative mechanism: the coexistence of metallic cobalt and residual cobalt oxide creates a favorable environment for adsorbing pyridine and delivering hydrogen to it. In other words, the two cobalt phases are not competing with each other but complementing each other, with each providing part of the chemical functionality needed to bind the substrate and hydrogenate it cleanly. Maintaining an appropriate balance between metallic Co and residual CoOx enables highly selective hydrogenation, Atobe said. This picture reframes catalyst design in an important way. Instead of treating a catalyst as a static material whose identity is fixed at synthesis, the study shows that the operating state of the catalyst, continuously shaped by the electrochemical conditions, can be the decisive variable.

The generality of the approach was tested across a wide chemical landscape. The catalyst selectively hydrogenated a broad range of nitrogen-containing compounds, including pyridines, quinolines, pyrazines, nitriles and nitroarenes, spanning several important families of substrates in pharmaceutical and agrochemical synthesis. Notably, the cobalt system also suppressed undesired hydrogenation pathways that are commonly observed with rhodium-based catalysts, which are among the most capable but least sustainable options available. In effect, the earth-abundant metal not only matched the precious-metal benchmark on yield but avoided some of its characteristic side reactions, a combination that could make the cobalt platform genuinely attractive for practical synthesis rather than merely a laboratory curiosity.

One practical obstacle remained. During prolonged electrolysis, the catalyst tends to be over-reduced, drifting away from its optimal mixed oxidation state and losing performance over time. The team’s solution was elegantly simple: intermittent electrolysis, in which the current is switched on and off in a controlled pattern, allows the catalyst to recover and maintain the appropriate Co(0)/CoOx balance throughout the reaction. With this strategy, the researchers achieved gram-scale conversion of pyridine to piperidine with an 89 percent yield while keeping the cell voltage stable, demonstrating that the concept can operate at quantities relevant to real synthetic work rather than only in trace-scale demonstrations. The result highlights a broader principle for catalyst design: controlling a catalyst’s chemical state while it operates can be as important as choosing the catalyst itself.

Looking ahead, the team plans to extend the oxidation-state-control strategy to other earth-abundant transition-metal catalysts and to a broader range of synthetically important reactions, potentially opening a general playbook for replacing precious metals across electrochemical manufacturing. Our ultimate goal is to develop scalable electrochemical processes in which catalyst states can be actively controlled under operating conditions, Shida said. This could enable selective chemical manufacturing without relying on scarce precious metals. If that vision is realized, the humble tuning of a metal’s oxidation state, monitored and adjusted in real time by nothing more than the rhythm of an electric current, could become a standard tool of green chemistry, turning one of the most abundant metals on Earth into a precision instrument for building the molecules modern life depends on.

Subject of Research: Oxidation-state control of cobalt electrocatalysts for selective hydrogenation of nitrogen-containing aromatic compounds

Article Title: Fine-tuning cobalt for cleaner chemical transformations

Article References: Fine-tuning cobalt for cleaner chemical transformations. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: cobalt catalyst, electrocatalytic hydrogenation, oxidation state, pyridine, piperidine, electrolysis, sustainable chemistry, earth-abundant metals, nitrogen heterocycles, anion-exchange membrane electrolyzer, catalyst selectivity, green chemistry

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

Previous research had already hinted that something like this preferential sorting was taking place, but only in objects that formed between two and four million years after the solar system’s origin. Among carbonaceous chondrites, the primitive stony meteorites that contain organic compounds and water within their silicate minerals, those that formed earlier consistently contained a higher percentage of chondrules and a lower percentage of matrix. This pattern suggested that in the regions where the first planetesimals were coalescing, the icy, volatile-rich dust was already being squeezed out in favor of the heat-forged rocky beads. What was missing was direct evidence from the very earliest epoch, the first million years, when the first generation of solid bodies came together. No undifferentiated bodies from that period survive intact today, leaving a critical gap in the record of how the solar system’s construction began.

Damanveer Grewal, an assistant professor of Earth and planetary sciences in Yale’s Faculty of Arts and Sciences and first author of the study, set out to close that gap with an unconventional approach. Rather than searching for preserved early bodies, which do not exist, he turned to iron meteorites whose parent bodies formed in the outer solar system during that missing first million years. These parent bodies had accumulated so much of the radioactive isotope aluminum-26 that they melted completely, destroying every physical trace of their original chondrule-to-matrix composition. On the surface, that total melting would seem to erase all useful information. But Grewal and his colleagues realized that the chemical fingerprints of the original ingredients would survive the melting, locked into the metallic cores of these differentiated bodies.

The team identified two independent chemical tracers, both tied specifically to the matrix component. The first is sulfur, which exists in concentrated form within matrix material. The amount of sulfur preserved in the iron meteorites therefore reveals how much fine-grained, volatile-rich dust the original parent body had incorporated before it melted. The second tracer is the oxidation state of iron, which reflects how much water ice and oxidized dust the original body contained. Because matrix is the component that carries water ice and oxidized material, a low oxidation state in the surviving metal indicates that very little icy dust was present when the body assembled. By measuring both tracers in the same set of meteorites, the researchers could reconstruct the original composition of bodies that had otherwise lost all physical memory of their building blocks.

The results were striking. Using the paired tracers, the researchers calculated that matrix made up only 8 to 17 percent of the original bodies sampled by these iron meteorites. That range is lower than the matrix fraction found in any known chondrite, meaning the earliest planetesimals of the outer solar system were more chondrule-dominated than any primitive meteorite ever recovered on Earth. In other words, the first solid bodies ever built in the solar system were constructed from 83 to 92 percent chondrules, with only a small admixture of the icy, volatile-rich dust that dominates objects that formed later. The two tracers, measured independently, converged on the same answer, giving the team confidence that the reconstruction was robust rather than an artifact of any single measurement.

Both tracers independently tell the same story: these early planetesimals were remarkably matrix-poor, Grewal explained. That convergence is what makes the result robust. The finding demonstrates that the assembly process was remarkably selective from the very beginning, sorting heat-forged chondrules into the first generation of solid bodies while excluding most of the cold, volatile-bearing dust. This selectivity implies that physical processes in the young protoplanetary disk, such as aerodynamic sorting of particles by size and density, were already operating efficiently within the first million years, concentrating the millimeter-sized chondrules and winnowing away the finer matrix grains before the first planetesimals accreted.

The discovery also resolves a long-standing puzzle about the meteorite record itself. Chondrules from the earliest epoch are scarce among the meteorites collected on Earth, and the new study explains why. The bodies that incorporated those oldest chondrules were the same bodies that accumulated enough radioactive aluminum-26 to melt completely, and that melting erased the physical evidence of their chondrule-rich composition. The oldest chondrules were not absent from the early solar system; they were simply swallowed by bodies that later transformed beyond recognition, leaving only their chemical ghosts in the iron meteorites that survive today. The scarcity of ancient chondrules in chondrites is thus a consequence of planetary differentiation, not of their original rarity.

Beyond solving that puzzle, the findings carry broader implications for understanding how the planets themselves came to be. Chondrules are the ubiquitous little beads of rock that served as the basic building blocks from which the planets were eventually assembled, and the new work shows that they were already being sorted and incorporated into the first generation of solid bodies from the very start. If the earliest planetesimals were so strongly enriched in chondrules and so depleted in volatile-rich matrix, then the seeds of the planets began their lives chemically dry and rocky, with the water and organic material arriving later or in different proportions than many models had assumed. This has consequences for theories of how Earth acquired its water and for understanding the volatile budgets of the outer solar system’s icy bodies.

The study was co-authored by Zhongtian Zhang of Princeton University and Joanna Drążkowska of the Max Planck Institute for Solar System Research in Germany, and the research was funded by Yale University. For Grewal, the work also carries a sense of deep connection to the deep past. Chondrules are found inside chondrites, the most primitive meteorites in geological collections, and holding one in your hand means holding a fragment of a process that started billions of years ago, a timescale that is hard to wrap your head around. By reading the chemical memory preserved in melted iron cores, the team has recovered a chapter of solar system history that physical evidence alone could never provide, revealing that when the solar system first began to build, it chose fire over ice.

Subject of Research: Geochemical reconstruction of the chondrule-to-matrix composition of the solar system's first planetesimals

Article Title: From the start, the solar system chose fire over ice to build its first bodies

Article References: From the start, the solar system chose fire over ice to build its first bodies. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: chondrules, matrix, planetesimals, iron meteorites, carbonaceous chondrites, solar system formation, aluminum-26, protoplanetary disk, Yale University, Nature Astronomy, oxidation state, volatile-rich dust