Easing water apart
Traditional setups for splitting water into hydrogen and oxygen operate either in acid or in base. A bipolar membrane can potentially enhance efficiency by bridging acidic hydrogen evolution to basic oxygen evolution. Oener et al. undertook a systematic study of how catalysts paired with such a membrane might accelerate the preliminary step of water dissociation into protons and hydroxide ions. Using insights from this study for optimal catalyst integration, they were able to substantially lower the overpotential of a bipolar membrane electrolyzer.
Science, this issue p. 1099
Catalyzing water dissociation (WD) into protons and hydroxide ions is important both for fabricating bipolar membranes (BPMs) that can couple different pH environments into a single electrochemical device and for accelerating electrocatalytic reactions that consume protons in neutral to alkaline media. We designed a BPM electrolyzer to quantitatively measure WD kinetics and show that, for metal nanoparticles, WD activity correlates with alkaline hydrogen evolution reaction activity. By combining metal-oxide WD catalysts that are efficient near the acidic proton-exchange layer with those efficient near the alkaline hydroxide-exchange layer, we demonstrate a BPM driving WD with overpotentials of <10 mV at 20 mA·cm−2 and pure water BPM electrolyzers that operate with an alkaline anode and acidic cathode at 500 mA·cm−2 with a total electrolysis voltage of ~2.2 V.