High-spin transition metal atoms drive acidic oxygen evolution reactions

Why this matters for clean energy

Turning water into hydrogen fuel using electricity could power factories, vehicles, and even cities without releasing carbon dioxide. But today’s most efficient devices for this task rely on rare and costly metals like iridium and ruthenium. This paper reports a new way to use abundant cobalt, tuned at the level of electron spin, to drive the crucial oxygen-forming half of water splitting in harsh acidic conditions, potentially making green hydrogen far cheaper and more scalable.

The challenge of making oxygen from water

In proton-exchange membrane water electrolyzers, electricity splits water into hydrogen and oxygen. The bottleneck is the oxygen evolution reaction at the anode, which involves a slow four-electron process. Existing industrial devices typically employ oxides of iridium or ruthenium, elements that are both scarce and expensive. Attempts to swap these for cheaper transition-metal oxides, such as cobalt oxide, have run into fundamental limits: reaction steps involving oxygen intermediates are “spin-forbidden,” meaning the electrons in these intermediates are misaligned with those in the final oxygen molecule and require extra energy to rearrange.

Using spin to unlock faster chemistry

The authors focus on cobalt in the +3 oxidation state, a promising and earth-abundant candidate for oxygen evolution. In ordinary cobalt oxide (Co3O4), most cobalt(III) ions sit in a low-spin configuration that does not optimally couple to oxygen intermediates. Theory suggests that if more cobalt ions could be pushed into a high-spin state, their outer d orbitals would hold unpaired electrons with spins aligned in a way that makes it easier for two oxygen atoms to pair up and form O2. This would shrink the energy barrier for the key bond-forming step and speed up the overall reaction, but high-spin cobalt(III) is usually unstable, especially in acidic environments.

A carbon scaffold that twists the lattice

To stabilize high-spin cobalt, the team grows cobalt oxide on a special carbon sheet called graphdiyne. This material has a porous network of carbon atoms with abundant, electron-rich sites that bond strongly to cobalt. Computer simulations show that when cobalt oxide is anchored to graphdiyne, the surrounding octahedral cages of oxygen atoms become slightly distorted. This distortion reduces the usual energy gap between different cobalt d orbitals and triggers the so-called Jahn–Teller effect, encouraging electrons to jump into higher orbitals and creating high-spin cobalt(III). Measurements of magnetism confirm that nearly 60% of the cobalt(III) ions in the new material, named HSS-CoOx/GDY, adopt this high-spin state, far more than in standard cobalt oxide.

From atomic spins to device performance

With this spin-engineered structure, the catalyst shows markedly better behavior in acidic solution. Compared to plain Co3O4, the new cobalt–graphdiyne system needs about 140 millivolts less extra voltage to reach a modest oxygen-producing current and remains stable for more than 400 hours of continuous operation. Detailed electrochemical tests reveal faster charge transfer at the catalyst surface and shorter lifetimes for stored charge, consistent with a reaction that proceeds quickly rather than piling up sluggish intermediates. Calculations of the reaction energy landscape show that the rate-limiting step for forming the O–O bond requires less energy on the high-spin catalyst, directly linking the altered spin states to improved kinetics.

Toward practical hydrogen from common metals

When integrated into a full proton-exchange membrane electrolyzer, the cobalt–graphdiyne anode delivers an industrially relevant current density of 1.0 ampere per square centimeter at a cell voltage of 1.80 volts, with low energy consumption and slow performance degradation. In contrast, a device using regular cobalt oxide fails rapidly. To a non-specialist, the key idea is that by using a clever carbon scaffold to twist cobalt’s atomic environment, the researchers reprogram the spins of its electrons so that oxygen can form more easily. This strategy shows that electronic spin, not just composition, can be engineered in common metals to rival the performance of precious ones, pointing toward more affordable and sustainable technologies for large-scale green hydrogen production.

Citation: Ping, X., Xue, Y., Chen, S. et al. High-spin transition metal atoms drive acidic oxygen evolution reactions. Nat Commun 17, 2904 (2026). https://doi.org/10.1038/s41467-026-69682-9

Keywords: green hydrogen, water electrolysis, cobalt catalyst, oxygen evolution, graphdiyne