Electrolyzer Design for Flexible Decoupled Water Splitting and Organic Upgrading with Electron Reservoirs

Conventional water-splitting electrolysis drives the H-2 and O-2 evolution reactions (HER and OER, respectively) simultaneously with large voltage inputs. Herein, two inexpensive iron complexes as proton-independent electron reservoirs (ERs) are described for decoupled water electrolysis. (Ferrocenylmethyl) trimethylammonium chloride and Na-4[Fe(CN)(6)], which have proper redox potentials in aqueous media, are able to couple their oxidation with HER. The subsequent reduction of the oxidized ER+ is then paired with OER. Both steps require much smaller voltage than that of direct water splitting. Nearly 100% Faradic efficiency and remarkable cycling stability were obtained for both ERs. Such decoupled water splitting could also be driven by photovoltaic cells with small photovoltages under sunlight irradiation. Furthermore, a two-step electrolysis of HER and the oxidation of 5-hydroxymethylfurfural mediated by Na-4[Fe(CN)(6)] was demonstrated under alkaline conditions, producing H-2 and 2,5-furandicarboxylic acid. This work presents a decoupled water electrolyzer design with great flexibility and safety advantages.