Journal
JOURNAL OF MATERIALS CHEMISTRY A
Volume 3, Issue 38, Pages 19556-19562Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c5ta06315a
Keywords
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Funding
- VENI project of the Netherlands Organisation for Scientific Research (NWO)
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Different pH requirements for a cathode and an anode result in a non-optimal performance for practical solar fuel systems. We present for the first time a photo-assisted water splitting device using a bipolar membrane, which allows a cathode to operate in an acidic electrolyte while the photoanode is in alkaline conditions. The bipolar membrane dissociates water into H+ and OH-, which is consumed for hydrogen evolution at the cathode and oxygen evolution at the anode, respectively. The introduction of such a bipolar membrane for solar fuel systems provides ultimate freedom for combining different (photo) cathodes and -anodes. This paper shows that photo-assisted water splitting at both extreme pH gradients (0-14) as well as mild pH gradients (0-7) yields current densities of 2-2.5 mA cm(-2) using a BiVO4 photoanode and a bipolar membrane. The membrane potentials are within 30 mV of the theoretical electrochemical potential for low current densities. The pH gradient is maintained for 4 days of continuous operation and electrolyte analysis shows that salt cross-over is minimal. The stable operation of the bipolar membrane in extreme and mild pH gradients, at negligible loss, contributes to a sustainable and practically feasible solar fuel device with existing photoactive electrodes operating at different pH.
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