Designing Electrolyte Structure to Suppress Hydrogen Evolution Reaction in Aqueous Batteries

Aqueous batteries (ABs) have attracted increasing attention because of their inherent safety and low cost. Nevertheless, hydrogen evolution reaction (HER) at the anode presents severe challenges for stable and safe operation of ABs. Instead of passivating the anode surface to hinder HER kinetics, a design strategy is proposed here to suppress the HER via alternating its thermodynamics pathway. Addition of a hydrogen bond acceptor, dimethyl sulfoxide (DMSO) can delay the onset potential of HER by as much as 1.0 V (on titanium mesh). Spectral characterization and molecular dynamics simulation confirm that the formation of hydrogen bonds between DMSO and water molecules can reduce the water activity, thereby suppressing the HER. This strategy has proven to be universal in expanding the electrochemical window of aqueous electrolytes. For instance, unconventional V2+ ↔ V3+ redox processes in Na3V2(PO4)3 (−1.2 V versus Ag/AgCl) can be realized in ABs.