Decoupled electrolysis using a silicotungstic acid electron-coupled-proton buffer in a proton exchange membrane cell

The storage of renewably-generated energy as hydrogen via the electrolysis of water is a fundamental cornerstone of a sustainable hydrogen economy. Conventional electrolysers usually require stable power inputs in order to operate effectively and safely and so may be unsuited to harnessing renewable power, which is often intermittent and diffuse. Electrolysis mediated by Electron-Coupled-Proton Buffers has the potential to overcome some of the challenges surrounding electrolysis using low and/or sporadic power inputs (especially those related to gas crossover) as the use of Electron-Coupled-Proton Buffers allows the oxygen and hydrogen evolution reactions to be completely decoupled from one another. Herein, we show that silicotungstic acid can be used as an Electron-Coupled-Proton Buffer in a proton exchange membrane cell, decoupling the hydrogen and oxygen evolution reactions at steady state current densities as high as 500 mA cm⁻². O₂ and H₂ can be produced continuously by this system by cycling a fixed volume of the Electron-Coupled-Proton Buffer solution. Even at current densities as low as 25 mA cm⁻², the level of hydrogen in the oxygen stream is <0.4%, whereas a conventional proton exchange membrane electrolyser operating at this current density produces oxygen containing nearly 2% hydrogen (unacceptable for most applications). Furthermore, using silicotungstic acid as an Electron-Coupled-Proton Buffer also confers greater tolerance to non-deionised water inputs and reduces fluoride release from the perfluorosulfonated membrane (a marker for membrane degradation) relative to a conventional proton exchange membrane electrolyser. Together, these results highlight the promise and potential advantages of Electron-Coupled-Proton Buffers (and silicotungstic acid in particular) for the electrolytic production of hydrogen and oxygen over a wide range of current densities, such as might be delivered by renewable power inputs.