Defect-Rich MoO3 Nanobelt Cathode for a High-Performance Hybrid Alkali/Acid Zn-MoO3 Rechargeable Battery

Protons (H+) and hydroxide ions (OH–) are regarded as ideal charge carriers for rechargeable batteries thanks to their small size, high ion mobility, low cost, and wide flexibility compared to the metal ions. However, the implementation of storage of both H+ and OH– in one electrochemical energy device faces grand challenges due to incompatibility between H+ and OH–. Herein, we report an alkali-acid Zn-MoO3 hybrid battery that employs H+ and OH– as charge carriers of the cathode and anode, respectively, in which the insertion/deinsertion of H+ take place on the defect-rich MoO3 porous nanobelt (d-MoO3 PNB) cathode in acid while OH– are involved in the alkaline conversion of Zn anode, which offers a promising route to better address the incompatible issues of H+ and OH– in one system. The d-MoO3 PNB with abundant oxygen vacancies holds more favorable properties for H+ storage than the MoO3 NB, as verified by the fact that the former can deliver significantly enhanced capacity and robust stability relative to the latter. The density functional theory (DFT) calculations demonstrate that the d-MoO3 can lower the barrier for H+ storage with improved conductivity, which is beneficial for improving the electrochemical performance. As a result, the alkali-acid Zn-MoO3 hybrid battery can deliver a high open-circuit voltage of 1.85 V, a high rate capability of 158 mAh g–1 at a current density of 5 A g–1, and excellent capacity retention of above 90% over 200 cycles. This work sheds light on the development of aqueous energy devices with high voltage and energy density through materials engineering and device optimization.