Rocking-chair proton battery based on a low-cost “water in salt” electrolyte

A novel "water in salt" electrolyte is reported for the design of a rocking-chair proton battery. In 20 M ZnCl₂ + 1 M HCl electrolyte, the electrochemical proton storage performance using MoO₃ is significantly improved. When coupled with a Ni-PBA cathode, the device exhibits a good cycling stability of 76.1% after 400 cycles. This work opens a new avenue for designing low-cost "water in salt" electrolytes for aqueous proton electrochemistry.