Stable Tetrasubstituted Quinone Redox Reservoir for Enhancing Decoupled Hydrogen and Oxygen Evolution

Redox reservoirs (RRs) may be used to decouple the two half-reactions of water electrolysis, enabling the spatial and temporal separation of hydrogen and oxygen evolution. Organic RRs are appealing candidates for this application; however, their instability limits their utility. Here we show that a tetrathioether-substituted quinone, tetramercaptopropanesulfonate quinone (TMQ), exhibits significantly enhanced stability relative to anthraquinone-2,7-disulfonate, the most effective organic RR reported previously. The enhanced stability, confirmed by symmetric flow-battery experiments under relevant conditions, enables the stable electrochemical production of H-2 and O-2 in a continuous-flow electrolysis cell. The reduced RR, tetramercaptopropanesulfonate hydroquinone, is not susceptible to decomposition, whereas the oxidized state, TMQ, undergoes slow decomposition, evident only after sustained operation (>60 h). The analysis of the byproducts provides the basis for a decomposition mechanism, establishing a foundation for the design of new organic RRs with even better performance.

Automated summary

The organic Redox reservoir Tetramercaptopropanesulfonate quinone (TMQ) shows enhanced stability compared to previous candidates, enabling stable electrochemical production of H-2 and O-2 in a continuous-flow electrolysis cell. The analysis of byproducts provides insights for the design of new organic RRs with even better performance.