Decoupled Electrochemical Water Splitting for Hydrogen Production

Decoupled electrochemical water splitting represents a transformative approach to clean hydrogen production by separating the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) into distinct processes. Traditional water electrolysis couples both half-reactions in a single cell, necessitating expensive membranes to prevent gas crossover and demanding continuous, high-purity operation. In contrast, decoupled systems employ redox mediators or auxiliary reactions to shuttle charge between spatially or temporally separated electrodes. This architecture allows hydrogen and oxygen to be generated in different cells or at different times, simplifies device design, reduces reliance on costly separators and enhances tolerance to intermittent renewable power. Recent advances have demonstrated membrane-free operation, high faradaic efficiency and compatibility with near-neutral electrolytes, opening pathways to modular, low-cost electrolysers. By enabling continuous or batch operation without cross-contamination, decoupled electrolysis holds promise for scaling green hydrogen production in sectors ranging from grid balancing to transport fuel and industrial feedstocks.

Research from Nature Portfolio

Recent studies have introduced a continuous, membraneless process operating in a near-neutral sodium bromide electrolyte. Here, bromide is electro-oxidised to bromate concurrent with hydrogen evolution in one cell, and bromate is chemically reduced back to bromide in a separate catalytic chamber that evolves oxygen. This cycle achieves both high faradaic and overall electrolytic efficiency at industrially relevant rates without membranes or thermal swings. Earlier work using nickel hydroxide as a solid redox mediator decoupled hydrogen and oxygen evolution in alkaline conditions by cycling between Ni(OH)₂ and NiOOH. During hydrogen production the mediator is oxidised, and a subsequent reduction step yields oxygen, effectively preventing gas mixing and enabling coupling to renewable power fluctuations. These foundational demonstrations set benchmarks for mediator-based architectures and have inspired a new class of membrane-free electrolyser designs.

Decoupled Electrochemical Water Splitting for Hydrogen Production publication trend

The graph below shows the total number of articles in decoupled electrochemical water splitting for hydrogen production across all publications each year (not limited to Nature Index journals).

Technical terms

Decoupled electrolysis: A process in which the oxygen and hydrogen evolution reactions occur separately in either time or space, preventing gas mixing and allowing for flexible operation with intermittent power inputs.

Redox mediator: A chemical species that alternately undergoes oxidation and reduction to carry electrons between electrode reactions, enabling the split of half-reactions into distinct steps or cells.

Faradaic efficiency: The fraction of the total electrical charge that contributes to the desired electrochemical reaction, expressed as a percentage of ideal conversion.

Electron-coupled proton buffer (ECPB): A solvated redox mediator that simultaneously transfers electrons and protons, facilitating the decoupled evolution of hydrogen and oxygen in separate processes.

References

1. Electrochemical and chemical cycle for high-efficiency decoupled water splitting in a near-neutral electrolyte. Nature Materials (2024).
2. Separating hydrogen and oxygen evolution in alkaline water electrolysis using nickel hydroxide. Nature Communications (2016).
3. Decoupled Electrochemical Water Splitting: From Fundamentals to Applications. Advanced Energy Materials (2020).
4. Membrane-less amphoteric decoupled water electrolysis using WO 3 and Ni(OH) 2 auxiliary electrodes. Energy & Environmental Science (2022).
5. Decoupled electrolysis using a silicotungstic acid electron-coupled-proton buffer in a proton exchange membrane cell. Electrochimica Acta (2020).