The elegance of the approach lies in what the researchers did not do. There is no multi-step synthesis, no high-temperature calcination, no hydrothermal autoclave, and no template removal. Instead, the team applied a direct current to a copper electrode immersed in a plating bath containing nickel salts, and they tuned the chemistry of that bath with two familiar ions: nitrate and chloride. Each ion plays a distinct role. Nitrate is known in electroplating circles for its ability to modify deposit morphology and even darken nickel films by altering how the metal nucleates and grows on the surface. Chloride, meanwhile, influences particle size and film compactness. By adjusting the balance between the two, the researchers could jointly control two things that usually fight each other in catalyst design: the ratio of metallic nickel to nickel hydroxide in the final film, and the mesoporous architecture that determines how much of the catalyst surface is actually reachable by electrolyte.

Why does that dual control matter so much? The answer lies in the complementary weaknesses of the two phases. Metallic nickel is an excellent electrical conductor, but on its own it is a mediocre oxygen evolution catalyst; the reaction intermediates bind to its surface with the wrong energetics, and the kinetics stall. Nickel hydroxide, by contrast, offers far more favorable adsorption sites for the oxygen-containing intermediates that form during water oxidation, but it is a poor conductor and, in many preparations, suffers from structural reconstruction during operation, gradually converting into other phases whose activity can drift over time. The hybrid electrode sidesteps both problems. Metallic nickel domains act as an internal electron highway, shuttling charge to and from the catalytically active hydroxide regions, while the low-crystallinity nickel hydroxide provides the reactive interface where water molecules are oxidized. The result is a composite in which each phase covers for the other’s deficiencies.

The performance numbers back up this design logic. At the benchmark current density of 10 milliamperes per square centimeter, the Ni/Ni(OH)2 electrode required an overpotential of just 254 millivolts, meaning the researchers had to apply only that much extra voltage beyond the thermodynamic minimum to get water oxidation underway at a useful rate. Equally telling is the Tafel slope, a measure of how quickly current rises as additional voltage is applied. The hybrid electrode delivered a Tafel slope of 50.3 millivolts per decade, indicating markedly accelerated reaction kinetics compared with conventional nickel-based catalysts. In practical terms, a lower Tafel slope means the catalyst does not need ever-larger voltage penalties as the electrolyzer is pushed toward industrial current densities, which is precisely where energy efficiency is won or lost.

Durability, the quiet killer of promising electrocatalysts, was also addressed head-on. Many laboratory catalysts post impressive initial numbers only to degrade within hours as their active layers dissolve, delaminate, or restructure. The Jingdezhen team subjected their electrode to a 100-hour chronopotentiometry test at a demanding 50 milliamperes per square centimeter, a current density far closer to real electrolyzer operation than the standard 10-milliamp benchmark. The electrode held its performance throughout, a result the researchers attribute to the in-situ nature of the fabrication: because the hybrid film is grown directly on the copper substrate rather than deposited as a powder and glued on with a polymer binder, the catalyst-substrate interface is intimate and mechanically robust, resisting the bubble evolution and mechanical stress that peel weaker electrodes apart.

Mechanistic analysis of the composite revealed why the interface between metallic nickel and low-crystallinity nickel hydroxide is so productive. The two phases form a coupled system in which electrons generated during the oxidation of hydroxide species can transfer efficiently across the phase boundary into the metallic network, avoiding the charge accumulation that throttles pure hydroxide electrodes. The low crystallinity of the hydroxide component is itself an asset rather than a defect: disordered structures typically expose a higher density of under-coordinated metal sites, edges, and defects that serve as active centers for the four-electron water oxidation sequence. Meanwhile, the anion-regulated deposition produced a mesoporous morphology with finely dispersed particles, maximizing the electrochemically accessible surface area and ensuring that bubbles generated during operation can escape easily rather than blanketing the surface.

The choice of copper as the substrate deserves its own note. Copper is cheap, conductive, and mechanically robust, and it is increasingly favored in the electrocatalysis literature as a support that can even participate chemically in the catalysis, promoting the transformation of nickel hydroxide into higher-valent nickel species that are considered the true active phase for oxygen evolution. By growing the catalyst directly on copper foil or mesh in a single electrochemical step, the researchers eliminated the need for expensive conductive additives, binders, and the energy-intensive processing steps that inflate the cost of conventional electrode manufacturing. For an industry trying to drive down the capital cost of alkaline water electrolyzers, a fabrication route that is essentially room-temperature electroplating is a genuinely attractive proposition.

The broader context makes the result more than a laboratory curiosity. Alkaline water electrolysis is the most mature hydrogen production technology, but its efficiency is capped by the large overpotential of the oxygen evolution reaction at the anode, which can waste hundreds of millivolts of electrical energy per cell. Every millivolt saved translates directly into kilowatt-hours saved per kilogram of hydrogen produced. Nickel-based catalysts have long been the workhorse candidates for replacing precious metals in this role, and recent years have seen an explosion of strategies, from nickel-iron layered double hydroxides to doped nitrides and oxyhydroxides, aimed at squeezing more activity out of earth-abundant elements. What distinguishes the new work is its emphasis on process simplicity: rather than adding complexity, it uses the intrinsic chemistry of two common anions to achieve phase control, morphology control, and interface engineering in a single deposition bath.

The anion-regulation concept also opens a tunable design space that other groups can explore. Because nitrate and chloride each exert distinct effects on nucleation density, particle size, and phase composition, varying their relative concentrations offers a continuous dial for optimizing the catalyst, rather than a discrete choice between recipes. The same principle could plausibly extend to other transition metal systems, including nickel-iron and nickel-cobalt chemistries, where anion-directed electrodeposition might similarly couple conductive metallic phases with active hydroxide phases. The researchers suggest that their work offers a facile route to low-cost, high-performance non-noble-metal OER electrodes with direct implications for industrial alkaline water electrolysis, and the combination of a 254-millivolt overpotential, a 50.3-millivolt-per-decade Tafel slope, and 100 hours of stable operation at 50 milliamperes per square centimeter gives that claim real weight.

Challenges remain before such electrodes see service inside a commercial electrolyzer stack. Long-term testing at even higher current densities, in flowing industrial electrolyte, and under the intermittent loads characteristic of renewable-powered hydrogen plants will be needed to confirm that the hybrid structure survives years rather than days. Scaling from small copper substrates to meter-scale electrode plates will test whether the anion-regulated deposition remains uniform across large areas. Still, the study is a reminder that some of the most consequential advances in clean energy chemistry come not from exotic new materials but from smarter control of the ones we already have. Two cheap ions, one electric current, and a copper plate may turn out to be an unlikely recipe for making green hydrogen a little more affordable.

Subject of Research: Anion-regulated one-step electrodeposition of Ni/Ni(OH)2 hybrid electrocatalysts for the alkaline oxygen evolution reaction

Article Title: NO₃⁻/Cl⁻-regulated one-step electrodeposition for in-situ fabrication of Ni/Ni(OH)₂ hybrid structures toward high-efficiency alkaline oxygen evolution reaction

Article References: Shi, J., Fan, J., Xv, J., Sun, L., Gong, Q., Huang, Y., Zhang, K., & Zhang, H. (2026). NO₃⁻/Cl⁻-regulated one-step electrodeposition for in-situ fabrication of Ni/Ni(OH)₂ hybrid structures toward high-efficiency alkaline oxygen evolution reaction. Ionics. https://doi.org/10.1007/s11581-026-07490-3

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07490-3

Keywords: oxygen evolution reaction, water electrolysis, green hydrogen, electrodeposition, nickel catalyst, nickel hydroxide, nitrate regulation, chloride regulation, copper substrate, Tafel slope, electrocatalyst durability, alkaline media

The device, which the authors call a hydroxide exchange membrane carbon capture cell, or HEMCC, belongs to a growing family of electrochemical approaches to direct air capture. Unlike conventional solid sorbent systems that swing between hot and cold temperatures to grab and release CO2, electrochemical cells use renewable electricity to drive the capture chemistry, promising lower energy costs, modular scaling, and compatibility with intermittent power sources. The problem, the researchers note, is that few proposed electrochemical devices have simultaneously delivered low energy cost, high durability, and full purification of the captured CO2, and almost none have addressed the practical realities of scale-up and pressure drop that matter enormously when you are pushing enormous volumes of air through a machine.

The core of the new design is a pair of identical nickel hydroxide electrodes, the same kind of material that has served for decades as the positive electrode in nickel-metal hydride batteries. Nickel hydroxide cycles reversibly between Ni(OH)2 and nickel oxyhydroxide, NiOOH, in alkaline conditions, and it is this pH-swinging battery chemistry that the team exploits. When one electrode is discharged, it consumes hydroxide ions and acidifies its local environment, releasing CO2 from bicarbonate and carbonate; the opposite electrode charges and generates hydroxide, which converts CO2 in the incoming air into carbonate and bicarbonate, effectively capturing it. A hydroxide exchange membrane, an 80-micrometre-thick PiperION membrane supplied by Versogen, separates the two sides while allowing hydroxide ions to shuttle between them.

In operation, ambient air flows past the charging electrode, where its CO2 is stripped out and chemically bound, and the depleted air exits the cell. During the discharge half of the cycle, the roles reverse: the previously charged electrode now releases its stored CO2 as a concentrated stream that can be collected, purified, and sequestered or utilized. Because the cell is symmetric, with identical electrodes on either side of the membrane, the air feed and product collection lines simply switch sides each cycle, allowing continuous operation without any change in hardware. The team’s laboratory-scale device used 25-square-centimetre electrodes made by electrochemically precipitating nickel hydroxide onto nickel foam, a process in which the working electrode gained 0.83 grams of material while counter electrodes sacrificed nickel from a nickel chloride bath.

Before testing, the electrodes underwent a careful break-in protocol in 1 molar potassium hydroxide, cycling at low current densities to stabilize their capacity, which settled at roughly 2.1 to 2.4 milliampere-hours per square centimetre. Cyclic voltammetry revealed the key electrochemical signatures: an oxidation peak at 1.44 volts versus the reversible hydrogen electrode corresponding to the Ni(OH)2 to NiOOH conversion, a reduction peak at 1.28 volts for the reverse reaction, and the onset of parasitic oxygen evolution at 1.52 volts. That narrow window between the useful battery reaction and the wasteful oxygen evolution reaction is central to the cell’s efficiency, and at 2 milliamperes per square centimetre the kinetic overpotential for the battery reaction averaged just 0.09 volts.

The durability results are among the most striking in the study. The 25-square-centimetre laboratory cell ran for 5,000 hours, more than half a year of continuous operation, without catastrophic degradation, addressing one of the most persistent doubts about electrochemical capture devices, which often show rapid performance decay. Transient analysis of the cycling behaviour showed that electron efficiency, the fraction of electrical charge that goes into useful CO2 capture rather than side reactions, peaked at 0.32 during optimal portions of the cycle, with an average of 0.25, and that flux and efficiency were tightly coupled to the phase of the battery cycle. The researchers used these insights to design an operating strategy with dedicated capture and regeneration phases for each electrode.

Perhaps most importantly, the team did not stop at the laboratory bench. Working with RepAir DAC, they built a pilot-scale electrochemical stack of nine cells, each with 300 square centimetres of active area, and ran it for 48 hours. The stack achieved the same headline figures, 132 kilojoules per mole of CO2 and a flux of 0.19 moles of CO2 per square metre per hour, equivalent to 75 kilograms of CO2 captured per square metre per year, while meeting the demanding 300-pascal pressure drop requirement that direct air capture systems must satisfy to keep fan energy manageable. Pressure drop is a frequently ignored constraint in academic capture studies, yet it can dominate the total energy budget of a real-world plant handling vast volumes of air, so demonstrating compliance at pilot scale is a significant step toward commercial credibility.

On the strength of these results, the authors present a techno-economic pathway to capturing CO2 for less than 100 US dollars per tonne, a threshold widely regarded as the price point at which direct air capture becomes viable at climate-relevant scale. Their projection rests on energy technology learning rates, the well-documented tendency of manufacturing costs for electrochemical and energy hardware to fall steadily as production volumes grow, a pattern seen in solar panels, lithium-ion batteries, and fuel cells. Because the HEMCC borrows mature manufacturing concepts from batteries and fuel cells, including membrane electrode assemblies and porous electrode architectures grounded in decades of theory dating back to Newman’s classic analyses, the researchers argue that its cost trajectory could follow those successful technologies rather than the steeper curves typical of bespoke chemical plants.

The work was supported by the US Department of Energy’s National Energy Technology Laboratory and the US Department of Defense Army Research Laboratory, and it arrives at a moment when governments and companies are racing to build gigatonne-scale carbon removal capacity. The Intergovernmental Panel on Climate Change and the International Energy Agency both count direct air capture among the tools likely needed to reach net-zero emissions by mid-century, particularly for offsetting hard-to-abate sectors such as aviation and agriculture. If the Delaware and RepAir teams’ durability and cost projections hold up as the technology scales beyond the pilot stage, the humble nickel hydroxide electrode, a workhorse of twentieth-century batteries, may find itself pressed into service as a cornerstone of twenty-first-century climate repair, quietly scrubbing the sky one reversible charge cycle at a time.

Subject of Research: A nickel hydroxide symmetric battery cell with a hydroxide exchange membrane for electrochemical direct air capture of carbon dioxide.

Article Title: A Ni(OH)2 symmetric battery cell for hydroxide exchange membrane-based direct air capture of CO2

Article References: Buchen, J. R., Wang, T., Geiger, B. K., Gluz, N. Y., Artoul, M., Hiegel, J.-P., Achrai, B., Setzler, B. P., & Yan, Y. (2026). A Ni(OH)2 symmetric battery cell for hydroxide exchange membrane-based direct air capture of CO2. Nature Energy. https://doi.org/10.1038/s41560-026-02129-z

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02129-z

Keywords: direct air capture, carbon dioxide removal, nickel hydroxide, hydroxide exchange membrane, electrochemical carbon capture, battery cell, climate change, Nature Energy, energy cost, carbon capture and storage, electrochemistry, pilot-scale stack

The research team set out to answer a deceptively simple question: when hydrogen gas bubbles off a nickel electrode in an alkaline solution, which of the surface species that form on nickel is actually doing the catalytic work? Nickel electrodes in alkaline media are never chemically naked. Depending on the applied potential and local conditions, their surfaces can host nickel oxide, nickel hydroxide, and nickel hydride phases, each with distinct electronic structures and bonding geometries. For decades, researchers have debated whether these species are innocent bystanders, harmful blockers, or hidden active sites. Because real electrodes present a patchwork of all three, isolating their individual contributions has been extraordinarily difficult.

The breakthrough of the new work lies in its systematic approach to well-defined nickel surfaces. Rather than studying polycrystalline foams or nanoparticles, where grain boundaries and defects confound interpretation, the researchers prepared carefully controlled nickel surfaces and deliberately generated each candidate species under known conditions. By systematically varying the presence and coverage of nickel oxide, nickel hydride, and nickel hydroxide, and then measuring the hydrogen evolution activity of each configuration, they could assign catalytic roles with a clarity that previous ensemble measurements could not achieve. The strategy echoes a classic theme in surface electrochemistry: only when a surface is well defined can the link between structure and function be drawn unambiguously.

What emerged is a picture in which no single species can claim sole credit. Nickel oxide species, the team found, contribute to the reaction in ways that depend sensitively on their exact chemical state and distribution on the metallic surface. Nickel hydroxide, which forms readily in alkaline environments and has often been invoked as the key promoter of alkaline hydrogen evolution, plays a role that must be carefully separated from the contributions of the oxide and hydride phases. Meanwhile, nickel hydride, the species formed when adsorbed hydrogen penetrates the metal lattice or binds in hydride-like configurations, emerges as a central participant in the hydrogen formation chemistry itself. The study’s central achievement is showing how these three species interact and divide the labor of the reaction rather than acting in isolation.

The distinction matters enormously for the alkaline hydrogen evolution reaction because its mechanism differs fundamentally from the one that operates in acid. In acidic media, the reaction proceeds through adsorbed hydrogen atoms that form directly on the metal surface and combine into hydrogen molecules. In alkaline electrolytes, however, water itself is the proton source, so every hydrogen molecule produced requires a water molecule to dissociate on the surface, cleaving an O-H bond and liberating a hydroxide ion. This initial water dissociation step is widely regarded as the kinetic bottleneck on pure metals, and it is precisely where adjacent oxide or hydroxide species have been proposed to help, by offering oxygen-affine sites that cleave water while neighboring metallic sites assemble the hydrogen. The new results put this bifunctional picture on a much firmer experimental footing for nickel.

For the electrolyser industry, the implications are immediate. Alkaline water electrolysis is the most mature and lowest-cost electrolysis technology on the market, but its cathodes and anodes still trail the performance achievable with platinum-group catalysts. Nickel is already the workhorse electrode material in commercial alkaline electrolysers, prized for its corrosion resistance in concentrated potassium hydroxide and its reasonable activity. If engineers can now identify which surface species to stabilize—and in what proportion—they can rationally tune electrode preparation protocols, whether through surface oxidation treatments, controlled potential cycling, or the deliberate engineering of oxide-hydride interfaces, instead of relying on empirical trial and error. The study effectively converts a long-standing controversy into an engineering design principle.

The findings also carry weight for the broader search for precious-metal-free catalysts. Earth-abundant transition metals such as nickel, cobalt, iron, and molybdenum have all been explored as hydrogen evolution catalysts, and many of the most successful candidates are not pure metals at all but composites in which metallic domains coexist with oxide or hydroxide phases. The nickel study provides a conceptual template for deconvoluting such systems: prepare well-defined versions of each phase, measure their individual kinetics, and then interrogate their combinations. Applied across the periodic table, this methodology could accelerate the discovery of catalysts that match platinum’s performance at a fraction of the cost, a goal that would ripple through green hydrogen production, fuel cells, and carbon-neutral synthesis of fuels and chemicals.

There are also cautionary lessons in the results. Because nickel hydride participates directly in the reaction, the subsurface and bulk hydride chemistry of nickel electrodes deserves renewed attention, particularly under the strongly reducing potentials of cathodic operation where hydride formation is thermodynamically favored. Hydride formation can induce lattice strain, alter electronic properties, and even degrade electrode morphology over time, so understanding its catalytic role may simultaneously illuminate pathways to more durable electrodes. Similarly, the finding that oxide and hydroxide species make separable, state-dependent contributions suggests that the dynamic potential-dependent evolution of surface chemistry during electrolyser start-up, shutdown, and fluctuating renewable power input could shift which species dominates, with consequences for both efficiency and lifetime.

The study arrives at a moment when green hydrogen is scaling from demonstration projects to gigawatt deployments, and every millivolt saved at the cathode translates into real energy and cost savings at industrial scale. By systematically dissecting the individual roles of nickel oxide, nickel hydride, and nickel hydroxide on well-defined nickel surfaces, the researchers have replaced a murky, contested narrative with a mechanistically grounded one. The work does not end the search for better alkaline hydrogen evolution catalysts, but it decisively sharpens it: the target is no longer simply nickel, or nickel oxide, or nickel hydroxide, but the precisely engineered coexistence of all three. For a field racing to strip precious metals out of the hydrogen economy, that clarity may prove as valuable as any single catalyst.

Subject of Research: The individual roles of nickel oxide, nickel hydride, and nickel hydroxide surface species in the alkaline hydrogen evolution reaction on nickel electrodes.

Article Title: The role of individual nickel surface species in the hydrogen evolution reaction on nickel in alkaline electrolytes

Article References: Kozlica, D. K., Finšgar, M., Farinazzo Bergamo Dias Martins, P., Huš, M., Genorio, B., Connell, J. G., Martins, M., Hývl, M., Žibert, T., Andrina Varda, K., Osmić, A., Bele, M., Likozar, B., Tomc, B., Gaberšček, M., & Strmčnik, D. (2026). The role of individual nickel surface species in the hydrogen evolution reaction on nickel in alkaline electrolytes. Nature Catalysis. https://doi.org/10.1038/s41929-026-01605-9

Image Credits: AI Generated

DOI: 10.1038/s41929-026-01605-9

Keywords: hydrogen evolution reaction, nickel, alkaline electrolytes, water electrolysis, nickel oxide, nickel hydride, nickel hydroxide, electrocatalysis, green hydrogen, surface chemistry, precious-metal-free catalysts, Nature Catalysis