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Solar water splitting by photovoltaic (PV) electrolysis is a promising route for sustainable hydrogen production. However, multiple PV cells connected in series are generally required to fulfil the practical electrolytic voltages, which inevitably increases the system complexity and resistance. Decoupled water electrolysis for separate hydrogen and oxygen evolution needs smaller voltage to drive each half-reaction, which provides a feasibility to achieve the single PV cell driven water electrolysis. Herein, by introducing sodium nickelhexacyanoferrate (Na-NiHCF) as the redox mediator, decoupled acid water electrolyzer and amphoteric water electrolyzer were respectively constructed. The required voltages for the hydrogen or oxygen evolution steps matched with the output voltages of the perovskite solar cell (PSC). Impressively, by combining one 1 cm 2 FAPbI 3 -based PSC (efficiency: 18.77 %) with the decoupled amphoteric water electrolyzer, a solar-to-hydrogen (STH) efficiency of 14.4 % was achieved, which outperformed previously reported PSC-driven water electrolysis cells.

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Accelerating electrocatalytic water splitting via hydrogen spillover has received increasing attention. However, the underlying mechanism of hydrogen spillover on hydrogen evolution is still ambiguous. Herein, a simulation study was carried out to determine the role of hydrogen spillover in pH- and potential-dependent hydrogen evolution over the NiCu bimetal catalyst. It was found that the current density was most prominently improved by hydrogen spillover in the neutral condition at −0.35 to −0.2 V vs reversible hydrogen electrode. By the parameter study, it was indicated that the potential and pH could improve the effect of hydrogen spillover on the current density by altering the surface reaction rates which include the hydrogen adsorption and desorption rates on the Ni and Cu particles. The pH would also affect the current density enhancement from the hydrogen spillover by the mass transfer limitation. To effectively utilize the hydrogen spillover for improved electrocatalytic hydrogen production, managing the surface reaction rate was important. Typically, the key principle was increasing the hydrogen adsorption rate of hydrogen donors and hydrogen desorption rate of hydrogen acceptors in the presence of hydrogen spillover. This fundamental understanding of hydrogen spillover contributes to the development of advanced electrocatalytic systems for hydrogen production.