Decoupled Water Electrolysis with an Air-Stable Zwitterionic Azo Mediator

This is the authors' abstract. We don't add key points for this paper.

Decoupled water electrolysis (DWE) separates H2 and O2 evolution, improving safety and flexibility under intermittent renewable electricity, but requires durable, oxygen-tolerant redox mediators. Here we evaluate 4,4′-azo-bis(1-pyridinium-3-propane-sulfonate) (ABPS), a zwitterionic azo molecule, as an electron-coupled proton buffer for acidic DWE. Its azo/hydrazo core supports reversible two-electron/two-proton chemistry at 0.81 V vs RHE, while zwitterionic substituents provide high aqueous solubility and suppress crossover through low-cost sulfonated poly(ether ether ketone) membranes. Reduced H2ABPS shows no detectable oxidation after 90 days in air or during >5 h of continuous pure-O2 bubbling. Symmetric flow-cell cycling over 1000 h yields a capacity-fade rate below 1% year–1. With commercial catalysts at room temperature, decoupled flow cells reach 1.2 A cm–2 and operate for >200 h at 500 mA cm–2 with near-quantitative Faradaic efficiencies while producing high-purity H2 and O2. These results establish zwitterionic azo chemistry as an oxygen-tolerant, durable platform for high-rate decoupled hydrogen production.