Mitigating Oxygen Evolution Reaction by Surface Engineering on Graphite to Suppress Self-Discharge in Aqueous Dual-Ion Batteries

Oxygen evolution reaction (OER) occurs on the graphitic cathode that triggers a series of side reactions, resulting in significant self-discharge. In this study, a surface engineering strategy is applied for increasing the overpotential of water decomposition to mitigate the OER, thereby suppressing self-discharge in aqueous dual-ion batteries. Al2O3, SiO2, Nb2O5 and TiO2 are studied as coating materials to graphitic carbon (KS6), revealing that significant improvement in self-discharge preventing is achieved by Al2O3 coating layer on surface of KS6 graphite. After 50 h, a terminal potential of 1.07 V is sustained, which is significantly higher than the 0 V terminal potential observed for the cell utilizing a pristine KS6 graphite cathode. More importantly, this study revealed Al2O3 coating layer effectively mitigate OER on the cathode due to the inherently higher OER overpotential of Al2O3 phase. Additionally, the OER mitigation results in a reduced potential dropping of the cathode and anode, leading to a slower side reaction. Besides, the Al2O3 coating layer effectively preserves the crystallinity of KS6 graphite throughout charge–discharge cycles and floating conditions, thereby enhancing the reversibility of the battery. Through suppressing surface oxidation on the KS6 cathode with Al2O3 coating, aqueous dual-ion batteries become highly attractive as energy storage devices with low cost and high energy density.