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 H 2 SO 4 electrolyte (0.01 M) achieves stable cycle performance of MoO 3 anode materials. The surface functionalization, specifically hydroxyl and carboxyl groups grafted on the interface of MoO 3 electrodes, facilitates successive adsorption and insertion of H + and/or H 3 O + even in proton-deficient electrolytes. The usage of mildly acidic electrolytes obviates the corrosion challenge, achieving promising stable cycle performance of MoO 3 that otherwise rapidly loses capacity in strong acids. The MoO 3 //0.01 M H 2 SO 4 //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.