Electrode Surface-Modified Strategy for Improving the Voltage of Aqueous Supercapacitors

Endowing aqueous supercapacitors (SCs) with high voltage is of great practical significance, but it is restricted by the water decomposition reaction occurring in the electrodes. Here, a novel surface treatment strategy is proposed to inhibit the hydrogen evolution reaction/oxygen evolution reaction at the cathode and anode by forming a passivation layer at the whole electrode surface, which widens the electrochemical stability window of the electrode and working voltage of the aqueous SCs. In addition, the cathode overpotential is increased from -1.3 to -1.48 V, and the anode is expanded from 1.42 to 1.59 V. Importantly, the aqueous SCs can work stably at 3 V operating voltage, enabling the coulombic efficiency and capacitance retention of the optimized SCs is 97% and 96% after 5000 cycles, respectively. This strategy of surface modification provides effective guidance to achieve high-voltage aqueous energy storage devices. A key to achieving the high voltage of aqueous supercapacitors is the character of the electrode/electrolyte interface. The kinetic process of water decomposition can be classified into the physical adsorption and charge transfer processes. Therefore, introducing the passivation layer to impede the adsorption or restrain the charge transfer process is an effective strategy to broaden voltage.image