Redox Chemistry of Molybdenum Trioxide for Ultrafast Hydrogen-Ion Storage.

Hydrogen ions are ideal charge carriers for rechargeable batteries due to their small ionic radius and wide availability. However, little attention has been paid to hydrogen-ion storage devices because they generally deliver relatively low Coulombic efficiency as a result of the hydrogen evolution reaction that occurs in an aqueous electrolyte. Herein, we successfully demonstrate that hydrogen ions can be electrochemically stored in an inorganic molybdenum trioxide (MoO3 ) electrode with high Coulombic efficiency and stability. The as-obtained electrode exhibits ultrafast hydrogen-ion storage properties with a specific capacity of 88 mA hg-1 at an ultrahigh rate of 100 C. The redox reaction mechanism of the MoO3 electrode in the hydrogen-ion cell was investigated in detail. The results reveal a conversion reaction of the MoO3 electrode into H0.88 MoO3 during the first hydrogen-ion insertion process and reversible intercalation/deintercalation of hydrogen ions between H0.88 MoO3 and H0.12 MoO3 during the following cycles. This study reveals new opportunities for the development of high-power energy storage devices with lightweight elements.