Decoupled Redox Catalytic Hydrogen Production with a Robust Electrolyte-Borne Electron and Proton Carrier

Electrolytic water splitting is an effective approach for H₂ mass production. A conventional water electrolyzer concurrently generates H₂ and O₂ in neighboring electrode compartments separated by a membrane, which brings about compromised purity, energy efficiency, and system durability. On the basis of distinct redox electrochemistry, here, we report a system that enables the decoupling of both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) from the electrodes to two spatially separated catalyst bed reactors in alkaline solutions. Through a pair of close-loop electrochemical-chemical cycles, the system operates upon 7,8-dihydroxy-2-phenazinesulfonic acid (DHPS) and ferricyanide-mediated HER and OER, respectively, on Pt/Ni(OH)₂ and NiFe(OH)₂ catalysts. Near unity faradaic efficiency and sustained production of hydrogen has been demonstrated at a current density up to 100 mA/cm². The superior reaction kinetics, particularly the HER reaction mechanism of DHPS as a robust electrolyte-borne electron and proton carriers, were scrutinized both computationally and experimentally. We anticipate the system demonstrated here would provide an intriguing alternative to the conventional water electrolytic hydrogen production.