Luo Zhihui, Liu Lei, Yang Xiaoyong, Luo Xuan, Bi Peng, Fu Zhenjin, Pang Aimin, Li Wei, Yi Yong
State Key Laboratory for Environment-Friendly Energy Materials, Southwest University of Science and Technology, Mianyang 621010, China.
School of Physics, Beihang University, Beijing 100191, China.
ACS Appl Mater Interfaces. 2020 Sep 2;12(35):39098-39107. doi: 10.1021/acsami.0c09606. Epub 2020 Aug 18.
Nickel oxide (NiO) is considered one of the most promising positive anode materials for electrochromic supercapacitors. Nevertheless, a detailed mechanism of the electrochromic and energy storage process has yet to be unraveled. In this research, the charge storage mechanism of a NiO electrochromic electrode was investigated by combining the in-depth experimental and theoretical analyses. Experimentally, a kinetic analysis of the Li-ion behavior based on the cyclic voltammetry curves reveals the major contribution of surface capacitance versus total capacity, providing fast reaction kinetics and a highly reversible electrochromic performance. Theoretically, our model uncovers that Li ions prefer to adsorb at fcc sites on the NiO(1 1 1) surface, then diffuse horizontally over the plane, and finally migrate in the bulk. More significantly, the calculated theoretical surface capacity (106 mA h g) accounts for about 77.4% of the total experimental capacity (137 mA h g), indicating that the surface storage process dominates the whole charge storage, which is in accordance with the experimental results. This work provides a fundamental understanding of transition-metal oxides for application in electrochromic supercapacitors and can also promote the exploration of novel electrode materials for high-performance electrochromic supercapacitors.
氧化镍（NiO）被认为是用于电致变色超级电容器最具前景的正极材料之一。然而，电致变色和能量存储过程的详细机制尚未阐明。在本研究中，通过结合深入的实验和理论分析，对NiO电致变色电极的电荷存储机制进行了研究。实验上，基于循环伏安曲线对锂离子行为进行的动力学分析揭示了表面电容对总电容的主要贡献，提供了快速的反应动力学和高度可逆的电致变色性能。理论上，我们的模型揭示锂离子倾向于吸附在NiO(1 1 1)表面的面心立方（fcc）位点，然后在平面上水平扩散，最后在体相中迁移。更重要的是，计算得到的理论表面容量（106 mA h g）约占总实验容量（137 mA h g）的77.4%，表明表面存储过程主导了整个电荷存储，这与实验结果一致。这项工作为过渡金属氧化物在电致变色超级电容器中的应用提供了基本认识，也有助于推动高性能电致变色超级电容器新型电极材料的探索。
