Enhancing reversible proton storage and low-temperature performance of MoO3 enabled by cosolvent electrolyte

Protons emerge as superior charge carriers due to the lowest mass-to-charge ratio, ultra-high natural abundance, and the smallest ionic radius. Herein, 2.0 M H2SO4 dissolved in EG (ethylene glycol)/H2O cosolvent is investigated as an aqueous proton battery electrolyte, which not only enhances the cycling performance of MoO3 nanorod anode but also improves its low-temperature electrochemical performance. Specifically, the EG tightly adsorbs onto the surface of MoO3 nanorods, thereby inhibiting the corrosion from H2O molecules in the electrolyte and suppressing the dissolution of MoO3. In addition, EG molecule disturbs the hydrogen-bond network between H2O molecules, which greatly decreases the freezing point of the electrolyte, endowing the MoO3 nanorods with excellent low-temperature electrochemical performance. Therefore, the MoO3 nanorods exhibit a capacity retention of 96.9 % after 2000 cycles at a current density of 10 A g−1 in a three-electrode system. After assembling with CuHCF cathode, under −40 °C, the full battery displays negligible capacity decay for over 2500 cycles at 1 A g−1. These results indicate that the cosolvent strategy has the promising potential in enhancing the performance of aqueous proton batteries.