Unlocking the Critical Role of Anion and Oxygen Vacancies in MoO3–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 (MoO3) 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 MoO3–x (S-MoO3–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-MoO3–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-MoO3–x-200 °C electrode during the charge and discharge is revealed. The APB assembled with an anode composed of optimized S-MoO3–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.