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Decoupling hydrogen and oxygen evolution during electrolytic water splitting using an electron-coupled-proton buffer

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Abstract

Hydrogen is essential to several key industrial processes and could play a major role as an energy carrier in a future ‘hydrogen economy’. Although the majority of the world's hydrogen supply currently comes from the reformation of fossil fuels, its generation from water using renewables-generated power could provide a hydrogen source without increasing atmospheric CO2 levels. Conventional water electrolysis produces H2 and O2 simultaneously, such that these gases must be generated in separate spaces to prevent their mixing. Herein, using the polyoxometalate H3PMo12O40, we introduce the concept of the electron-coupled-proton buffer (ECPB), whereby O2 and H2 can be produced at separate times during water electrolysis. This could have advantages in preventing gas mixing in the headspaces of high-pressure electrolysis cells, with implications for safety and electrolyser degradation. Furthermore, we demonstrate that temporally separated O2 and H2 production allows greater flexibility regarding the membranes and electrodes that can be used in water-splitting cells.

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Figure 1: Schematic of the ECPB-based approach to water splitting.
Figure 2: Cyclic voltammograms showing the reversible redox waves of phosphomolybdic acid.
Figure 3: Current–voltage curves obtained when stirring with and without an ECPB.
Figure 4: Comparison of current densities for H2 and O2 evolution with and without the use of 0.5 M 50:50 (H3O+)[H2PMo12O40]:(H3O+) [H4PMo12O40].
Figure 5: Current densities and gas chromatography for H2 evolution using an ECPB.

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Acknowledgements

This work was supported by the Engineering and Physical Sciences Research Council (UK) and Glasgow Solar Fuels. L.C. thanks the Royal Society/Wolfson Foundation for a Merit Award. M.D.S. thanks the University of Glasgow for a Lord Kelvin Adam Smith Research Fellowship. We are grateful to J. McIver (University of Glasgow) for assistance with the GC headspace analyses, H. N. Miras (University of Glasgow) for mass spectrometry and J. Liddell (University of Glasgow) for manufacturing numerous bespoke electrolysis cells.

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M.D.S. and L.C. conceived the idea, planned experiments and co-wrote the paper, and M.D.S. performed the experiments and analysed the data.

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Correspondence to Leroy Cronin.

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Symes, M., Cronin, L. Decoupling hydrogen and oxygen evolution during electrolytic water splitting using an electron-coupled-proton buffer. Nature Chem 5, 403–409 (2013). https://doi.org/10.1038/nchem.1621

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