Exploiting Interfacial Cl<sup>–</sup>/Cl<sup>0</sup> Redox for a 1.8-V Voltage Plateau Aqueous Electrochemical Capacitor
Xiaoli Zhao, Yuanyuan Wang, Yayun Shi, Xiaojun Yan, Yinbing Tian, Zhijun Zuo, Xiaowei Yang
Abstract
The ideal way to boost the energy storage of an aqueous-electrolyte electrochemical capacitor (EC) is to increase its capacity at high voltage. However, oxygen evolution of aqueous electrolytes and poor reversibility exclude high-potential redox reactions, resulting in an unsatisfying plateau voltage and a limited energy density. To address this issue, this study arms aqueous ECs with regulated anionic hydration structure and intensified interfacial affinity for realizing the high-potential Cl–/Cl0 redox reaction, which has rarely been utilized before. Experiments and simulations show that the hetero-ion invaded solvation structure can put chlorine redox potential below oxygen evolution potential, and negatively charged functional groups on the wall of two-dimensional nanochannels increase the energy barrier of the Heyrovsky step and decrease the tendency for Cl2 desorption. Furthermore, we demonstrate the advantage of chlorine redox in the bi-redox activity of a chloride ion-containing electrolyte, methyl viologen dichloride, which delivers a sustained discharging voltage plateau of 1.8 V and a high energy density.