Unraveling the Role of Water on the Electrochromic and Electrochemical Properties of Nickel Oxide Electrodes in Electrochromic Pseudocapacitors

Although nickel oxide (NiO) is currently the most promising for industrialization as a counter electrode, it has proven challenging to achieve long-term-stable electrochromic devices. One of the crucial components is the mechanism of action of water on the active interface of the NiO counter electrode in the Li+-based electrolyte, which gives a basis of determinants for improving long-term cycling stability in devices. Herein, we investigate the role of water on the electrochemical and electrochromic properties of nickel oxide (NiO) electrodes. The finding of improved pseudocapacitive characteristics and reaction kinetics of NiO electrodes after introducing H2O into the Li+-based electrolyte can be originated from the increase of the number of ions and reduction of the electrolyte resistance and the interfacial charge-transfer resistance. On the one hand, the mechanisms for improved electrochemical and electrochromic properties such as a high coloration efficiency of 157.58 cm(2) C-1 under the potential window of +/- 1.4 V, an excellent rate capability and a superior long-term cycling stability of over 10,000 cycles in the ESCs based on WO3 and NiO electrodes are elaborated. On the other hand, electrical water splitting can give rises to a degradation of optically cyclic stability of the NiO-based ESCs under the potential of > +1.23 V. These results provide a significant contribution to the reversibility and stability of the active interfaces for high performance electrochromic devices.