Unlocking the Critical Role of Anion and Oxygen Vacancies in MoO_3–x Nanobelts for High-Performance Proton Storage

Protons are regarded as ideal current carriers in making green batteries with high power density and long life. Molybdenum trioxide (MoO 3 ) is suitable for proton storage because of its unique layered structure, but its low conductivity and moderate charge storage kinetics limit its energy storage applications. In this study, a stable electrode was developed for the use of aqueous proton batteries (APBs). This electrode is based on sulfur-doped MoO 3– x (S-MoO 3– x -200 °C) nanobelts with abundant oxygen vacancies introduced via a simple annealing reaction. Benefiting from the synergistic effect of improved charge mobility and accelerated ion diffusion, the optimized S-MoO 3– x -200 °C electrode has a high specific capacity (237.8 mAh g –1 ) and satisfactory rate capability with a capacity retention of 73.1% even up to 20.0 A g –1 . Furthermore, the mechanism of proton intercalation and deintercalation in the S-MoO 3– x -200 °C electrode during the charge and discharge is revealed. The APB assembled with an anode composed of optimized S-MoO 3– x -200 °C nanobelts and an N-doped active carbon cathode has a maximum energy density of 106.3 Wh kg –1 at a power density of 797.5 W kg –1, demonstrating its immense potential for high energy storage.