Realizing a Mildly Acidic Proton Battery via Surface Functionalization

Aqueous proton batteries (H-ion batteries) hold the potential to fill the gap between batteries and capacitors but suffer from severe electrode material corrosion caused by caustic acid electrolytes. Here, we report a mildly acidic proton battery in which an interfacial functionalization technique together with an ultradiluted H2SO4 electrolyte (0.01 M) achieves stable cycle performance of MoO3 anode materials. The surface functionalization, specifically hydroxyl and carboxyl groups grafted on the interface of MoO3 electrodes, facilitates successive adsorption and insertion of H+ and/or H3O+ even in proton-deficient electrolytes. The usage of mildly acidic electrolytes obviates the corrosion challenge, achieving promising stable cycle performance of MoO3 that otherwise rapidly loses capacity in strong acids. The MoO3//0.01 M H2SO4//CuFe-TBA mildly acidic full battery delivers 109.1 mAh g–1 capacity after long cycling with 91.18% capacity retention. This work opens an avenue for the rational design of low-corrosion and long-life aqueous proton batteries.