The core problem the review tackles lies in the chemistry of water electrolysis itself. Splitting water into hydrogen and oxygen involves two half-reactions: the hydrogen evolution reaction, which produces hydrogen gas at one electrode, and the oxygen evolution reaction, which releases oxygen at the other. Of the two, oxygen evolution is by far the more sluggish. Its kinetics are slow, demanding a large extra voltage, called an overpotential, beyond the thermodynamic minimum required to split water. That wasted energy translates directly into higher electricity bills and lower overall system efficiency, and it has been a persistent bottleneck for every electrolyzer design on the market.

Compounding the problem, the catalysts that currently tame the oxygen evolution reaction are precious. Conventional proton exchange membrane electrolyzers depend on noble metal catalysts, typically iridium and platinum group materials, which are scarce, expensive, and geographically concentrated. The review also points to a second vulnerability: these systems degrade under the intermittent, fluctuating power inputs that come hand in hand with wind and solar generation. An electrolyzer that only performs well when fed perfectly steady current is a poor match for a renewable grid, so cost and durability problems reinforce one another.

Transition metal chalcogenides offer a way around both constraints. These are compounds of transition metals, such as nickel, cobalt, iron, or molybdenum, combined with chalcogen elements like sulfur, selenium, or tellurium. Because their constituent elements are abundant in the Earth’s crust, they sidestep the supply chain risks and price volatility that plague noble metal catalysts. More importantly, their electronic structure gives them genuine catalytic talent. The review emphasizes that partially filled d-orbitals in these materials enable optimized adsorption of the reaction intermediates that form and vanish in the course of both the hydrogen and oxygen evolution reactions. Getting that adsorption energy right is the central art of electrocatalysis, because intermediates that bind too weakly never react, while those that bind too strongly poison the surface. Chalcogenides hit a favorable middle ground, lowering both the kinetic and thermodynamic barriers for the two half-reactions.

The most consequential property highlighted in the review is bifunctionality. Most electrolyzers to date have required different catalysts at the anode and the cathode, each optimized for its own half-reaction. A bifunctional transition metal chalcogenide can catalyze both the hydrogen evolution reaction and the oxygen evolution reaction within a single material system. That simplifies electrolyzer design considerably, reduces the number of distinct materials that must be synthesized, tested, and manufactured at scale, and opens the door to symmetric or reversible cell architectures in which the same electrode can switch roles. For a technology trying to drive down capital costs, collapsing two catalyst systems into one is a meaningful engineering advantage.

Conductivity is the third pillar of the case. Many abundant catalyst candidates fail not because they lack catalytic activity but because they are poor conductors, so electrons cannot reach the active sites efficiently. The review notes that transition metal chalcogenides possess metallic or semi-metallic conductivity, which improves charge transfer kinetics at the electrode surface. Faster charge transfer means less resistive loss inside the cell, which matters enormously when the goal is operation at high current density, the regime commercial electrolyzers must reach to produce hydrogen at scale. The materials also show enhanced resistance to corrosion, a critical trait in the harsh oxidative environment of the oxygen evolution electrode, where many otherwise promising compounds dissolve or crumble within hours.

Structurally, the review frames these advantages as arising from tunable electronic structures. Because the metal and chalcogen identities, stoichiometry, and crystal phase can all be varied, researchers have a broad design space in which to optimize adsorption energies and electronic properties. This tunability is what separates chalcogenides from a simple substitution story: rather than merely replacing iridium with something cheaper, designers can engineer the catalyst’s electronic landscape to suit specific operating conditions, electrolyzer configurations, and current density targets. The review consolidates synthesis strategies reported in recent literature and evaluates how the resulting catalysts perform across various electrolyzer configurations, providing a map of which approaches have delivered the strongest results so far.

The authors are candid that the field is not yet ready for prime time. Three challenges dominate their assessment: catalyst stability, scalability, and integration into commercial systems. Stability remains the hardest test, since laboratory measurements are often taken over hours while commercial electrolyzers must run for tens of thousands of hours under fluctuating load. Scalability raises the question of whether synthesis routes that work on milligram quantities in a beaker can be translated to the square meters of electrode area a commercial stack requires, without losing the nanostructured features that give the catalysts their activity. Integration, meanwhile, encompasses everything from electrode fabrication and membrane compatibility to how bifunctional catalysts behave in full devices rather than half-cell tests.

The significance of the review lies in its attempt to bridge these knowledge gaps and channel them into rational design principles. By systematically connecting synthesis strategies, electronic structure, and measured performance, it aims to give researchers a framework for designing cost-effective, high-performance bifunctional electrocatalysts rather than discovering them by trial and error. The timing is pointed. As nations commit to net-zero emission targets, demand for low-carbon hydrogen is projected to grow sharply, and the economics of production will determine whether that demand is met with genuinely green hydrogen or with fossil-derived alternatives. Catalyst cost is one of the levers that most directly shapes those economics.

The work also carries a regional dimension. The research team, based at De La Salle University in Manila and supported by a grant from the Philippine Department of Science and Technology through its Council for Industry, Energy, and Emerging Technology Research and Development, reflects growing scientific engagement with the hydrogen economy in Southeast Asia, a region whose island geography and renewable potential make energy storage and clean fuels particularly salient. If bifunctional transition metal chalcogenides can clear the stability and scalability hurdles the review identifies, the payoff would be electrolyzers that run at high current density, tolerate the stop-and-go rhythm of renewable power, and cost a fraction of today’s noble metal systems. That combination, the authors argue, is what it will take to move green hydrogen from a promising cornerstone to a load-bearing one.

Subject of Research: Bifunctional transition metal chalcogenide electrocatalysts for high current density water electrolysis and green hydrogen production

Article Title: Harnessing bifunctional transition metal chalcogenides for high current density sustainable electrolyzer technologies

Article References: Owogowog, M. B. B., Flaviano, A. L., Morente, P. R. O., & Ortenero, J. R. (2026). Harnessing bifunctional transition metal chalcogenides for high current density sustainable electrolyzer technologies. Discover Sustainability. https://doi.org/10.1007/s43621-026-04758-6

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04758-6

Keywords: green hydrogen, water electrolysis, electrocatalysis, transition metal chalcogenides, oxygen evolution reaction, hydrogen evolution reaction, bifunctional catalysts, proton exchange membrane, overpotential, catalyst stability, renewable energy, electrolyzer technology

The case for better catalysts is straightforward. Water electrolysers split water into hydrogen and oxygen through two paired reactions: the hydrogen evolution reaction at the cathode and the oxygen evolution reaction at the anode. Platinum-based catalysts perform these transformations with exceptional efficiency, but their cost and scarcity limit any realistic path to large-scale deployment. Earlier alternatives built from metal oxides, sulfides, and nitrides brought their own problems, including toxicity and limited stability. That gap has pushed researchers toward organic polymer semiconductors whose delocalized pi-conjugated systems allow rapid charge transfer while remaining cheap, lightweight, and chemically robust.

What makes polymers so attractive is molecular-level design freedom. Chemists can tune pore structures, graft functional groups, and position active sites with a precision that is nearly impossible in conventional inorganic catalysts. The review catalogues the major classes now under investigation: polymers of intrinsic microporosity, hypercrosslinked polymers, conjugated microporous polymers, covalent organic frameworks, covalent triazine frameworks, and porous aromatic frameworks. Built from light elements joined by strong covalent bonds, these materials combine high specific surface areas with tunable pore architectures and, critically, long-term chemical stability in harsh electrolytic environments.

Covalent organic frameworks, or COFs, are the crystalline stars of this lineup. Their periodically ordered channels and predictable active-site distributions make them ideal platforms for hydrogen evolution. The most common preparation route is solvothermal synthesis, in which boronic acid or catechol derivatives condense in mixed solvents at around 120 degrees Celsius over several days, often with metalloporphyrin or bipyridine units incorporated as catalytic centers. A standout example is TpPAM, a metal-free porphyrin-based covalent organic polymer made by Schiff base condensation. It achieved a Faradaic efficiency of 98 percent and retained 91 percent of its initial current density after 1000 catalytic cycles—remarkable numbers for a catalyst containing no metal at all.

Alternative synthetic routes expand the toolbox further. Ionothermal synthesis, using molten zinc chloride as both solvent and catalyst at 400 to 600 degrees Celsius, produces highly stable triazine-based frameworks with strong hydrogen evolution activity. Mechanochemical ball milling offers a solvent-free route in under an hour, though at the cost of lower crystallinity. For conjugated microporous polymers, palladium-catalyzed Sonogashira-Hagihara coupling yields networks with pore sizes from 0.5 to 2 nanometers and surface areas up to 1000 square meters per gram, while Suzuki and Yamamoto couplings provide routes to heteroatom-doped, highly conjugated networks with excellent charge transport.

The classic conducting polymers—polyaniline, polypyrrole, and polythiophene—have also been revived for catalysis. Electrochemical polymerization can grow these films directly onto electrodes such as glassy carbon or carbon cloth, giving precise control over thickness and morphology, while chemical oxidative polymerization produces powders that can be coated onto electrode surfaces. Doping with nitrogen or sulfur during synthesis significantly boosts catalytic activity. Perhaps most impressive are the donor-acceptor polymers, whose alternating electron-rich and electron-poor units drive efficient intramolecular charge transfer, and which can be post-metalated with earth-abundant cobalt, nickel, or iron to introduce catalytic metal centers.

Metal-containing polymers are where performance numbers get dramatic. A bimetallic cobalt and nickel porphyrin two-dimensional polymer, synthesized by condensing metallated octahydroxyporphyrin with fumaric acid, delivered an overpotential of just 105 millivolts at 10 milliamperes per square centimeter, a Tafel slope of 74.1 millivolts per decade, and 97 percent Faradaic efficiency. The researchers attributed this to a polar porous structure that gives protons easy access to active sites, with nickel incorporation improving conductivity and lowering adsorption energy barriers. Even better, an imidazole-based porous organic polymer loaded with platinum nanoparticles of roughly 2.28 nanometers reached an overpotential of only 56 millivolts and stayed stable for 4000 cycles, because the polymer scaffold prevented the nanoparticles from clumping and aided electron transfer through pi-pi interactions.

The review also emphasizes that polymers can do far more than serve as catalysts in their own right. They can act as conductive supports, fixing agents, adsorption sites for reaction intermediates, proton trapping agents, hydrophilic surface modifiers, porous scaffolds, and even templates for synthesizing other catalysts. An efficient hydrogen evolution catalyst needs a large specific surface area, minimal overpotential, high exchange current density, and durability—and the review argues that conductive polymers, despite rigorous evaluation of their properties, remain underappreciated in the hydrogen evolution field relative to their potential.

Significant obstacles remain before polymer catalysts can graduate from laboratory glassware to industrial electrolyzers. Most high-performing systems still lean on platinum or ruthenium as active centers, undermining the cost argument. The relationship between polymer structure and active site density is poorly mapped, and the mechanistic link between porosity, conjugation length, heteroatom doping, and performance remains incompletely understood. Performance demonstrated on small three-electrode cells rarely survives translation to the high current densities, scalable electrode fabrication, and acidic or alkaline abuse of commercial membrane electrode assembly electrolyzers.

The path forward, according to the review, lies in designing donor-acceptor polymers to sharpen intramolecular charge transfer, engineering porosity and substituents to expose more active sites, and compositing polymers with carbon nanotubes, graphene, or carbon cloth to boost conductivity. Crosslinking and protective carbon coatings could extend durability, while in situ Raman, X-ray photoelectron, and X-ray absorption spectroscopies combined with density functional theory can reveal how hydrogen intermediates bind and how active sites evolve under operating conditions. If those strategies succeed, polymer cathodes could deliver the low-cost, durable hydrogen production that global carbon neutrality goals demand—and the same design principles may ripple outward into carbon dioxide, oxygen, and nitrate reduction catalysis.

Subject of Research: Polymer-based electrocatalysts for the hydrogen evolution reaction in water splitting

Article Title: Research progress on polymer electrochemical hydrogen evolution

Article References: Emin, A. (2026). Research progress on polymer electrochemical hydrogen evolution. Frontiers in Membrane Science and Technology, 5, Article 1823653. https://doi.org/10.3389/frmst.2026.1823653

Image Credits: AI Generated

DOI: 10.3389/frmst.2026.1823653

Keywords: hydrogen evolution reaction, electrocatalysis, covalent organic frameworks, conjugated polymers, water splitting, green hydrogen, porous organic polymers, donor-acceptor polymers, platinum-free catalysts, renewable energy, Faradaic efficiency, overpotential

The research team developed an interpenetrated RuO2/Co3O4 heterostructure in which the two oxide phases are not simply juxtaposed but woven together at the atomic level. At the boundaries where the two lattices meet, the metal centers are connected through bridging oxygen atoms in asymmetric Ru–O–Co configurations. These interfacial bridges are short, with a Ru–Co distance below 2.4 angstroms, a geometry that turns out to be the decisive factor in unlocking a reaction pathway that conventional RuO2 cannot access. The work was made available online on 1 July 2026.

To appreciate why that short distance matters, it helps to understand the two mechanistic regimes at play. For decades, acidic OER on ruthenium and iridium oxides has been described by the adsorbate evolution mechanism, or AEM. In the AEM, the catalyst surface accumulates hydroxyl and oxo intermediates in a strict four-step sequence, and the final O–O bond forms between a surface oxo species and an oxygen-containing adsorbate. The problem with this route is the well-known scaling relationship: the binding energies of the various intermediates are linearly coupled to one another, so improving the adsorption strength of one intermediate inevitably worsens another. The result is a theoretical minimum overpotential of roughly 0.3 to 0.4 volts that no AEM catalyst, however optimized, can undercut.

The alternative is the oxide pathway mechanism, or OPM. In the OPM, two adjacent oxo species couple directly with each other to form the O–O bond, bypassing the adsorbate-mediated step and thereby escaping the scaling relationship. Lattice oxygen participates directly in the bond-forming event, which is why the OPM is sometimes discussed alongside lattice oxygen evolution chemistry. The catch for ruthenium dioxide is geometric. In the RuO2 rutile lattice, neighboring ruthenium centers are separated by more than 3.1 angstroms, a distance too long for two surface oxo species to couple efficiently. Activating the OPM on RuO2 has therefore been impeded by the very structure of the material itself.

The interpenetrated heterostructure solves this geometric problem at the interface. Where a ruthenium center and a cobalt center share a bridging oxygen, the short Ru–O–Co bridge brings the reactive oxo species into a configuration that permits low-energy O–O coupling. In other words, the interface acts as a structural template that compresses the effective metal–metal spacing below the threshold needed for direct oxo–oxo coupling. According to the study, these asymmetric Ru–O–Co sites selectively trigger the OPM, while the sites away from the interface, the ordinary Ru–O–Ru and Co–O–Co environments, continue to operate through the traditional AEM.

This spatial division of labor is what makes the design conceptually elegant. Rather than converting the entire catalyst surface to a single new mechanism, the heterostructure runs both pathways in parallel: OPM at the interface, AEM everywhere else. The synergy breaks the single-mechanism limit that has constrained RuO2-based catalysts, accelerates deprotonation steps in the catalytic cycle, and enhances the antioxidant capacity of the ruthenium centers. That last point is critical, because ruthenium’s Achilles’ heel in acidic OER is over-oxidation. At the high potentials required for water oxidation, Ru atoms can be oxidized beyond their stable valence states and dissolve into the electrolyte, degrading the catalyst. Coupling ruthenium to cobalt oxide through short interfacial bridges appears to stabilize the Ru centers against this oxidative dissolution, extending the lifetime of the active phase.

The performance numbers reported for the interpenetrated catalyst are striking. The catalyst achieves an overpotential of only 196 millivolts at a current density of 10 milliamperes per square centimeter, the standard benchmark for comparing OER catalysts, and maintains an overpotential of 370 millivolts even at a demanding 500 milliamperes per square centimeter, a current density relevant to industrial electrolysis. Its mass activity is 7.1 times higher than that of commercial RuO2. Perhaps most importantly for real-world deployment, the catalyst operates steadily for more than 100 hours at 500 milliamperes per square centimeter in acidic conditions, demonstrating that the dual-mechanism design is not a fleeting laboratory curiosity but a durable electrocatalytic system.

For context, commercial RuO2 and IrO2 catalysts typically exhibit overpotentials in the range of 250 to 350 millivolts at 10 milliamperes per square centimeter, and their stability at industrial current densities in acid remains a persistent challenge. A 196-millivolt overpotential at benchmark current density, sustained operation at 500 milliamperes per square centimeter for over 100 hours, and a sevenfold gain in mass activity together represent the kind of combined activity-and-stability improvement that the field has been pursuing through strategies including alloying, doping, and support engineering. What distinguishes this approach is that the improvement comes not from adding new elements in bulk but from a precise interfacial architecture that changes the reaction mechanism itself.

The implications extend beyond this particular material pair. The authors describe their work as providing a general interfacial design strategy for activating complementary reaction pathways. If the principle holds, other oxide heterostructures could be engineered so that short interfacial metal–oxygen–metal bridges trigger OPM chemistry while the surrounding lattice handles AEM chemistry, a design motif that could in principle be applied to catalyst systems beyond the ruthenium–cobalt combination. Because cobalt is far more abundant and less expensive than iridium, and because the strategy reduces the amount of precious ruthenium needed per unit of catalytic output, the approach also carries economic weight for the hydrogen economy, where the cost and supply of platinum-group metals are significant constraints on electrolyzer scale-up.

The study, titled “Asymmetric Ru–O–Co sites Coupled Adsorbate Evolution and Oxide Pathway Mechanisms for Enhanced Acidic Water Oxidation,” was published in Advanced Powder Materials, a peer-reviewed journal focused on powder and materials chemistry research. As proton exchange membrane electrolyzers move toward gigawatt-scale deployment, the anode remains the most punishing environment in the entire water-splitting device, and catalysts that can simultaneously deliver low overpotential, high current density, and long operational lifetimes in acid are the field’s most sought-after commodity. By showing that the mechanistic ceiling of RuO2 is not an intrinsic property of ruthenium but a consequence of its lattice geometry, and that a short interfacial bridge to a cheaper transition metal oxide can rewrite that geometry, this work offers a concrete and potentially transferable route to acidic OER catalysts that are both more active and more durable than the commercial benchmarks they aim to replace.

Subject of Research: Dual-mechanism RuO2/Co3O4 heterostructure electrocatalysts for acidic oxygen evolution in water splitting

Article Title: Asymmetric Ru–O–Co sites coupled adsorbate evolution and oxide pathway mechanisms for enhanced acidic water oxidation

Article References: Asymmetric Ru–O–Co sites coupled adsorbate evolution and oxide pathway mechanisms for enhanced acidic water oxidation. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: oxygen evolution reaction, water oxidation, acidic electrolysis, RuO2, Co3O4, heterostructure, adsorbate evolution mechanism, oxide pathway mechanism, green hydrogen, electrocatalysis, overpotential, ruthenium catalysts

The appeal of the design lies in the marriage of two inexpensive components with complementary strengths. Spinel oxides, named for the crystal structure in which metal cations occupy tetrahedral and octahedral sites within a close-packed oxygen lattice, are prized in electrocatalysis for their robust frameworks and tunable electronic configurations. CuAl2O4 in particular brings a distinctive arrangement of copper and aluminum cations that, according to the authors, boosts OER activity by virtue of its unique electronic structure. On its own, however, a spinel oxide powder suffers from limited electrical conductivity and a tendency for particles to clump together, burying many of the active sites where the four-electron oxygen chemistry actually takes place. That is where the carbon nitride scaffold comes in.

Graphitic carbon nitride is a layered, graphite-like material made of carbon and nitrogen, typically produced by simply heating inexpensive nitrogen-rich precursors. It is chemically stable in both acids and bases, and its nitrogen-rich surface offers abundant anchoring points for metal species. In the new composite, the g-CN serves several roles at once. The researchers found that its incorporation increased the electrical conductivity of the hybrid, promoted rapid electron mobility between the oxide particles and the conductive support, and enlarged the electrochemically active surface area by encouraging the uniform dispersion of CuAl2O4. In practical terms, the carbon nitride keeps the spinel nanoparticles spread out and electrically wired, so that more of the catalyst surface participates in the reaction rather than sitting idle inside aggregates.

The synthesis itself is part of the story. The team used a hydrothermal method, a technique in which the reaction mixture is sealed in an autoclave and heated in water above its normal boiling point, allowing crystals and hybrid structures to grow under controlled conditions. Hydrothermal processing is economical, scalable and accessible to ordinary laboratories, which matters enormously for any catalyst hoping to compete with the incumbent technology. Today’s best OER catalysts are based on iridium and ruthenium, precious metals so scarce and expensive that they are widely viewed as impractical for the gigawatt-scale electrolyzers a hydrogen economy would require. A catalyst assembled from copper, aluminum and carbon nitride, all abundant and cheap, sidesteps that supply problem entirely.

The performance metrics reported in the study are worth unpacking for what they reveal about the catalyst’s behavior. The overpotential of 235 millivolts is the extra voltage beyond the thermodynamic requirement needed to drive a meaningful oxygen-evolving current; lower values translate directly into less wasted electricity and better energy efficiency for an electrolyzer. The Tafel slope of 47 millivolts per decade describes how quickly the current grows as voltage is increased, and it offers a window into the reaction mechanism, with smaller slopes generally indicating faster electron-transfer kinetics. A low solution resistance of 1.0495 ohms further indicates that the electrode and electrolyte impose little ohmic penalty, meaning less of the applied voltage is lost to internal resistance before it ever reaches the catalytic sites.

Perhaps the most striking number is the electrochemically active surface area, which the team measured at 587.5 square centimeters. ECSA, as it is abbreviated, estimates the true interfacial area where electrolyte, electrons and catalyst meet, and it is a key predictor of how much current a given mass of catalyst can deliver. The large value reflects the successful dispersion of the spinel phase on the carbon nitride support, confirming the morphological benefits the authors set out to achieve. The researchers characterized their samples thoroughly to establish these morphological, structural and textural features, building the case that the nanohybrid’s performance stems from genuine structural advantages rather than measurement artifacts.

Durability, the quiet killer of many promising electrocatalysts, also fared well. Alkaline water electrolysis is a punishing environment: the catalyst must withstand concentrated hydroxide solutions, continuous gas evolution that mechanically stresses the surface, and potential-driven reconstruction that can dissolve or transform active phases over time. The CuAl2O4/g-CN nanohybrid demonstrated extraordinary durability over 35 hours of continuous operation, according to the study, a result that suggests the carbon nitride support does more than boost activity; it also stabilizes the spinel particles against degradation. Long-term stability is precisely the property that separates laboratory curiosities from materials that could plausibly be engineered into real electrolyzer electrodes.

The work fits into a broader and rapidly growing effort to replace noble-metal OER catalysts with earth-abundant alternatives. Recent literature has explored perovskite oxides, transition-metal sulfides, layered double hydroxides and metal-organic framework derivatives, often coupled with carbon supports such as reduced graphene oxide or carbon nanotubes. Graphitic carbon nitride has emerged as a particularly versatile platform in this landscape, having been paired with nickel oxide, cobalt ferrite, ruthenium dioxide, cerium oxide and many other catalytic phases. The new study extends that strategy to a copper aluminate spinel, a combination that had received comparatively little attention as an OER catalyst, and demonstrates that the spinel-plus-carbon-nitride architecture can hold its own in alkaline media.

There are, of course, caveats that temper any immediate industrial claims. The reported measurements come from laboratory-scale three-electrode testing, and translating a powder catalyst into a full water-splitting device requires integrating it with a hydrogen-evolving cathode, optimizing catalyst loading and binder chemistry, and proving performance at the current densities commercial electrolyzers demand. The authors position their material as a viable catalyst for a variety of purposes, and the data support its promise as a sustainable alternative to rare noble-metal electrocatalysts, but scale-up studies and device-level demonstrations remain the necessary next steps. The team notes that the datasets generated in the work are available upon reasonable request, which should help other groups reproduce and build on the results.

Even so, the significance of the finding is easy to appreciate. Green hydrogen depends on splitting water with minimal energy loss, and every millivolt shaved off the oxygen evolution overpotential reduces the electricity bill of the entire process. By showing that a simple hydrothermal recipe can produce a durable, conductive, high-surface-area catalyst from copper, aluminum and carbon nitride, the researchers have added a compelling entry to the catalogue of non-precious OER catalysts. If follow-up work confirms the performance at scale, the humble combination of a spinel oxide and a carbon-based scaffold could move from the pages of Ionics toward the heart of the clean-energy infrastructure that the hydrogen economy will require.

Subject of Research: Development of a CuAl2O4/graphitic carbon nitride nanocomposite electrocatalyst for the oxygen evolution reaction in water splitting

Article Title: Spinel CuAl2O4 nanomaterials anchored on g-CN as an effective catalyst for water splitting

Article References: Qasim, M., Alsalhi, S. A., El-Rayyes, A., & Ullah, W. (2026). Spinel CuAl2O4 nanomaterials anchored on g-CN as an effective catalyst for water splitting. Ionics. https://doi.org/10.1007/s11581-026-07551-7

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07551-7

Keywords: water splitting, oxygen evolution reaction, electrocatalyst, CuAl2O4 spinel, graphitic carbon nitride, hydrothermal synthesis, green hydrogen, nanocomposite, alkaline electrolysis, overpotential, electrochemically active surface area, non-precious metal catalyst

The appeal of MoS2 begins with its structure. It is a layered transition-metal dichalcogenide in which sheets of molybdenum sandwiched between sulfur planes are stacked by weak van der Waals forces, allowing them to be peeled into atomically thin layers. It exists in three main polymorphs: the semiconducting 2H phase, thermodynamically stable and abundant in nature; the metallic 1T phase, which can be synthesized by chemical intercalation or growth tricks; and the rhombohedral 3R phase, whose broken inversion symmetry gives it distinctive optical behavior. Because bulk 2H-MoS2 has an indirect bandgap while a single layer has a direct one, researchers can tune its electronic and optical properties simply by controlling layer number and phase composition, a flexibility few catalysts offer.

Yet pristine MoS2 has a dirty secret that the review confronts head-on: it is largely inert. Catalysis happens almost exclusively at the edges of the sheets, where molybdenum atoms bind hydrogen with a Gibbs free energy of just 0.08 electron volts, nearly matching platinum’s ideal value of zero. The vast basal planes, meanwhile, do almost nothing. That mismatch between hype and reality is why the authors stress distinguishing genuine intrinsic activity from apparent gains produced by auxiliary components or interfacial effects, a critical eye they bring to every doping strategy they survey.

The physics of why doping works is rooted in the two half-reactions of water splitting. At the cathode, the hydrogen evolution reaction proceeds through a Volmer step, in which protons or water molecules are reduced to adsorbed hydrogen atoms, followed by either a Heyrovsky step, where those atoms react with another proton and electron to release H2, or a Tafel step, where two adsorbed atoms recombine. At the anode, the oxygen evolution reaction demands a punishing four-electron transfer through *OH, *O and *OOH intermediates, making it the kinetic bottleneck of the whole process. Splitting water thermodynamically requires a minimum cell voltage of 1.23 volts, but kinetic overpotentials and ohmic losses push real devices well beyond that. Dopants attack the problem on multiple fronts: they modify electronic structure, improve conductivity, create new active sites and optimize how strongly intermediates bind to the surface.

The review organizes dopants by their position in the periodic table, and the s-block delivers some of the most dramatic transformations. Lithium insertion drives a phase transition from semiconducting 2H to metallic 1T-prime MoS2, and Li0.14MoS2 delivers hydrogen evolution overpotentials of roughly 240 to 280 millivolts at 10 milliamperes per square centimeter with Tafel slopes of 65 to 85 millivolts per decade. Sodium-doped MoS2 nanotubes, grown as ultra-long one-dimensional structures with high surface area, boost charge transfer and have even served as counter electrodes with power conversion efficiencies up to 5.85 percent. On the theoretical side, first-principles calculations show that doping monolayer MoS2 with alkaline earth metals from beryllium to barium narrows the bandgap and shifts optical absorption toward longer wavelengths, with beryllium, magnesium and calcium variants offering the best band structures for photocatalytic water splitting.

P-block doping may be the star of the show. Phosphorus-doped MoS2, prepared by ball-milling with black phosphorus so that phosphorus atoms fill sulfur vacancies, achieves overpotentials as low as 93 millivolts for hydrogen evolution and 316 millivolts for oxygen evolution at 10 milliamperes per square centimeter in alkaline media, with a full water-splitting cell running at about 1.59 volts. Pairing phosphorus doping with a nickel sulfide heterostructure on nickel foam pushes overall splitting down to roughly 1.48 volts. Tin-doped MoS2 grown on nickel foam by microwave-assisted hydrothermal synthesis needs only 149 millivolts for hydrogen evolution and 259 millivolts for oxygen evolution, comfortably beating its undoped counterpart. Computational work on nickel and phosphorus co-doping of the metallic 1T phase predicts a near-ideal hydrogen adsorption free energy of 0.083 electron volts.

Transition-metal dopants from the d-block exploit the interplay between molybdenum’s 4d electrons and the 3d electrons of iron, cobalt, nickel, copper, vanadium, chromium and manganese. Chromium-doped MoS2 nanosheets reach a hydrogen evolution overpotential of 142 millivolts with a Tafel slope of 61 millivolts per decade, indicating a Volmer-Heyrovsky mechanism and faster kinetics than pristine material. A chromium-doped MoS2/WS2 catalyst acts as a robust bifunctional electrode, needing just 145 millivolts for hydrogen evolution and 181 millivolts for oxygen evolution while surviving 72 hours at a punishing 100 milliamperes per square centimeter. Co-doping compounds the gains: iron-cobalt co-doped MoS2 shows Tafel slopes of 50 to 79 millivolts per decade for oxygen evolution, and cobalt-vanadium co-doping yields a hydrogen evolution overpotential of just 86 millivolts, with cobalt activating basal-plane sulfur sites while vanadium tunes hydrogen binding toward thermoneutrality. Perhaps most audacious, a high-entropy alloy of iron, cobalt, nickel, manganese and chromium supported on MoS2 nanosheets delivers oxygen evolution at about 210 millivolts with a Tafel slope of 40.3 millivolts per decade.

Photocatalysis adds a solar dimension to the story. When light strikes a semiconductor, electrons jump to the conduction band and holes remain in the valence band, and if the photon energy exceeds the bandgap, those carriers can respectively reduce water to hydrogen and oxidize it to oxygen. Silver-modified MoS2 nanosheets produce about 1600 micromoles of hydrogen per gram per hour under visible light, a 4.5-fold improvement over pristine MoS2, because silver nanoparticles form Schottky barriers that trap electrons and suppress recombination, with catalytic efficiency reported up to 99 percent and over 90 percent activity retained after 20 hours. A computationally designed cobalt-phosphorus co-doped MoS2 establishes dual active sites, with phosphorus driving oxygen evolution and activated sulfur sites facilitating hydrogen evolution at a near-ideal 0.08 electron volt adsorption energy, while extending photogenerated carrier lifetime from 64 to 123 picoseconds. An 8 percent cobalt-doped 1T/2H mixed-phase catalyst achieves overpotentials of minus 127 millivolts for hydrogen evolution and 292 millivolts for oxygen evolution under sunlight in alkaline media.

Just as important as the performance numbers is the evidence that these catalysts survive real operating conditions. The review catalogues meticulous before-and-after characterization: X-ray photoelectron spectroscopy and extended X-ray absorption fine structure confirm lithium-induced phase transitions, with the molybdenum-molybdenum bond distance shrinking from 3.16 to 2.80 angstroms in the 1T-prime phase; solid-state lithium-7 NMR and in situ infrared spectroscopy with nitric oxide probe molecules track dopant environments and edge sites. Electron paramagnetic resonance verifies the sulfur vacancies that make phosphorus-doped MoS2 active, and post-electrolysis imaging shows lamellar morphology essentially unchanged after long-term testing. Vanadium-doped monolayers grown by chemical vapor deposition hold stable current for 9000 seconds with only a 13 millivolt shift after 500 cycles, while nickel-doped electrodes endure 10,000 seconds of chronoamperometry with negligible degradation.

The synthesis toolbox is equally mature, spanning hydrothermal autoclave reactions at 180 degrees Celsius, chemical vapor deposition for atomically precise doped monolayers, solid-state ion exchange, and microwave-assisted growth directly on conductive nickel foam, meaning these catalysts are not laboratory curiosities but materials with plausible routes to scale. The authors are careful not to oversell: pristine MoS2’s inert basal plane, the complexity of oxygen evolution mechanisms, which in some materials proceed through conventional adsorbate pathways and in others through lattice oxygen participation, and questions of long-term durability all remain open challenges. But the trajectory is unmistakable. By treating the periodic table as a tuning dial, chemists are converting a cheap layered semiconductor once dismissed as mostly inactive into a family of bifunctional electrodes that split water with efficiencies once reserved for platinum and iridium, bringing solar- and electricity-driven green hydrogen a significant step closer to economic reality.

Subject of Research: Doped molybdenum disulfide electrocatalysts and photocatalysts for hydrogen production via water splitting

Article Title: Recent advances in doped MoS2 electrocatalysts and photocatalysts for water splitting

Article References: Nath, A., Paul, S. R., & Patra, S. G. (2026). Recent advances in doped MoS2 electrocatalysts and photocatalysts for water splitting. Discover Electrochemistry, 3(1), Article 47. https://doi.org/10.1007/s44373-026-00133-2

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00133-2

Keywords: MoS2, water splitting, hydrogen evolution reaction, oxygen evolution reaction, electrocatalysis, photocatalysis, doping, transition metal dichalcogenides, green hydrogen, overpotential, phase engineering, renewable energy

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 central insight of the study concerns how adjacent RuO6 octahedra, the basic building blocks of ruthenium dioxide, are connected to one another. Conventional rutile-type RuO2, the workhorse acidic OER catalyst, arranges its octahedra in corner-sharing and edge-sharing motifs that do not provide the most favorable electronic geometry. In the newly synthesized 1T phase, the octahedra share edges in a configuration that aligns the ruthenium 4d orbitals in parallel across neighboring clusters. This parallel alignment opens a highway for intersite electron transport: electrons generated during the four-proton, four-electron OER sequence can hop efficiently from one ruthenium center to the next rather than becoming localized at a single active site. The result is a catalyst in which electronic communication, rather than isolated site chemistry, becomes the rate-enhancing factor.

The performance numbers reported by the team are striking by any benchmark in the field. In acidic electrolyte, the 1T-RuO2 single layer requires an overpotential of just 77 millivolts to drive a current density of 10 milliamperes per square centimeter, a figure that places it among the most active acidic OER catalysts described to date. At a potential of 1.50 volts versus the reversible hydrogen electrode, the material achieves a mass activity of 3,743.43 amperes per gram of ruthenium and a turnover frequency of 23.99 per second, both substantially exceeding the corresponding values for rutile-RuO2 measured under the same experimental framework. These metrics matter because ruthenium, while cheaper than the iridium that currently dominates commercial PEM anodes, is still a precious metal; extracting more catalytic turnover per gram directly reduces the loading, and therefore the cost, of the precious metal in each device.

Activity alone has never been the hard part of acidic water oxidation. The acidic OER environment is brutally corrosive: highly oxidizing potentials, a flood of protons and reactive oxygen intermediates combine to dissolve most transition-metal oxides within hours. Ruthenium dioxide is comparatively robust, yet even it tends to degrade through ruthenium dissolution and lattice-oxygen-mediated pathways that corrode the catalyst from within. The durability demonstrated by the 1T single layer is therefore arguably the most consequential result of the study. When integrated into a full proton-exchange membrane water electrolyser, the catalyst sustained a current density of approximately 2.9 amperes per square centimeter at a cell voltage of 1.70 volts for more than 1,100 hours of continuous operation. Industrial electrolysers typically operate at current densities in the range of one to a few amperes per square centimeter, so the demonstration sits squarely in the regime that matters for real-world deployment.

Reaching that level of performance required first solving a synthesis problem that has long frustrated materials chemists. The 1T phase of RuO2 is metastable, meaning it is not the thermodynamically favored arrangement of ruthenium and oxygen atoms; left to its own devices, the material prefers to settle into the rutile structure. Metastable phases in two-dimensional materials, from the 1T polymorphs of molybdenum disulfide to exotic iridium oxide phases, often carry enhanced catalytic properties precisely because their unusual geometries reshape the electronic structure, but stabilizing them at scale is notoriously difficult. The Soochow-led team designed and fabricated a mechanothermal reactor, developed by co-author Mingwang Shao, to drive the formation of the single-layer 1T phase, and confirmed the resulting structure through a battery of characterization techniques including synchrotron-based X-ray absorption spectroscopy performed at facilities in Taiwan and Hefei.

The spectroscopic evidence was central to establishing why the edge-sharing geometry works. Using in situ ruthenium L3-edge X-ray absorption spectroscopy, together with total-electron-yield measurements at other absorption edges, the researchers probed the electronic and geometric state of the catalyst while it was actively evolving oxygen. Complementary density functional theory calculations, carried out by Zhiwei Hu, Jing Zhou, Chang-Yang Kuo and colleagues, rationalized the observations: the edge-sharing motif aligns the ruthenium 4d orbitals across adjacent octahedra, lowering the barriers for electron delocalization and stabilizing the reaction intermediates along the OER pathway. Attenuated-total-reflectance infrared measurements tracked the surface intermediates during operation, allowing the team to connect the macroscopic electrochemical performance to specific molecular events at the active sites.

The broader significance of the work lies in its reframing of catalyst design for acidic water oxidation. Much of the recent effort in the field has focused on compositional strategies: doping ruthenium oxide with rhenium, rhodium or tantalum, creating high-entropy oxides, or stabilizing iridium in perovskite-derived frameworks. Those approaches tune the electronic structure of essentially rutile-like lattices. The new study demonstrates that the connectivity of the octahedral network itself, an architectural variable rather than a compositional one, can be the decisive lever. By choosing a phase in which edge-sharing octahedra create parallel orbital alignment, the researchers achieved both the activity and the stability that compositional tuning has struggled to deliver simultaneously. This suggests a rich design space of metastable oxide phases, particularly in two-dimensional form, that the community has only begun to explore.

There are, of course, caveats and next steps. The 1T phase is metastable, and while the electrolyser test exceeded 1,100 hours, commercial PEM systems are expected to operate for tens of thousands of hours; long-term phase stability under thermal and potential cycling remains to be proven. Scaling the mechanothermal synthesis from laboratory batches to the kilogram quantities needed for stack manufacturing will require engineering development. And the precise balance between adsorbate-evolution and lattice-oxygen mechanisms on the 1T surface, a question the operando spectroscopy begins to answer, will continue to be refined as more theoretical and experimental data accumulate. Nevertheless, the combination of a 77-millivolt overpotential, a turnover frequency approaching 24 per second and sustained industrial-scale current density in a working electrolyser represents a level of integrated performance that few acidic OER catalysts have approached.

If the durability and manufacturability hurdles can be cleared, the implications for the hydrogen economy are substantial. PEM electrolysers are prized for their fast response and high output pressure, making them natural partners for intermittent renewable electricity, but their reliance on iridium, one of the scarcest elements on Earth, has been viewed as a hard ceiling on global deployment. A ruthenium-based anode catalyst that is both more active and more stable than rutile RuO2, and that has already demonstrated more than a thousand hours of operation at 2.9 amperes per square centimeter, offers a credible path toward easing that constraint. The edge-sharing single layer of ruthenium dioxide may thus be remembered less as a single catalyst and more as a proof of principle: that in the search for efficient acidic water splitting, the way atoms are wired together can matter as much as which atoms are chosen.

Subject of Research: Edge-sharing single-layer 1T-RuO2 electrocatalysts for acidic oxygen evolution in proton-exchange membrane water electrolysis

Article Title: Edge-sharing RuO2 single layer for stable and low overpotential acidic water electrolysis

Article References: Zhu, W., Zhou, J., Ma, M., Liu, H., Liao, F., Huang, H., Kuo, C.-Y., Lin, Y., Pao, C.-W., Chang, Y.-C., Haw, S.-C., Hsu, S.-Y., Chen, J.-M., Ni, M., Liu, Y., Shao, M., Hu, Z., Kang, Z., Huang, X., & Shao, Q. (2026). Edge-sharing RuO2 single layer for stable and low overpotential acidic water electrolysis. Nature Nanotechnology. https://doi.org/10.1038/s41565-026-02255-5

Image Credits: AI Generated

DOI: 10.1038/s41565-026-02255-5

Keywords: ruthenium dioxide, water electrolysis, oxygen evolution reaction, green hydrogen, proton-exchange membrane, electrocatalysis, two-dimensional materials, metastable phase, overpotential, PEM electrolyser, single-layer catalyst, acidic water oxidation