An Advanced Technique to Evaluate the Electrochromic Performances of NiO Films by Multi-Cycle Double-Step Potential Chronocoulometry

Abstract

NiO films with amorphous and crystalline structure are prepared via sol-gel method. The electrochromic performances are evaluated in a KOH electrolyte by cyclic voltammetry (CV), which demonstrates that the crystalline NiO thin film has excellent stability and durability compared with the amorphous film. Meanwhile, the unique method of multi-cycle double-step potential chronocoulometry (MDPC) is firstly employed to analyze the electrochromic performance of the NiO films. It shows that the cyclic tendency obtained from MDPC is consistent with the CV evolutions. The relationship between charge densities and cycles can be directly obtained by MDPC, consequently, the reversibility of films can be directly evaluated by the ratio of the extracted/inserted charges. As a primary advantage, the response charges obtained by MDPC technique can be divided into three parts including Faradic charges (Q f ) associated with redox activity leading to chromic change, the capacitive charges (Q dl ) corresponding to charging and discharging of electrodeelectrolyte double-layer capacitor, and parasitic charges (Q ads ) consumed by electrolysis of adsorbed species. The electrochromic mechanism of NiO films are further explored by analyzing the cycle dependence of Q f and Q ads evolutions. It adequately supports that MDPC has significant advantage to analyze the electrochromic performance and mechanism of electrochromic materials.

Understand the Degradation Mechanism of Electrochromic WO3 Films by Double‐step Chronoamperometry and Chronocoulometry Techniques Combined with in situ Spectroelectrochemical Study

“…The applied potentials were set to À1 V to 1 V, À1.5 V to 1.5 V and À2 V to 2 V at a scan rate of 50 mV/s. In addition, the area of the CV curves increases as the potential window increases, which is proportional to the number of exchanged Li + ions as shown in the following equation [18]: where I is the instantaneous current density, V is the instantaneous potential, v is the scan rate of the CV curves, which is a constant and known value during the experiment, and t is the sampling time in seconds. As shown in Figure 2(a), it presents classical characteristics of amorphous tungsten oxide.…”

“…According to equation (1), large quantities of WO 3 can participate in the reaction, and eventually, the reaction arrives at a balanced state in the coloration process. When the quantity of Li x WO 3 is completely consumed, the anodic current returns to zero [18]. The quantity of Li x WO 3 is limited when the coloration time is limited.…”

“…At present the main method for characterizing the durability of electrochromic materials is cyclic voltammetry (CV) [14][15][16][17]. More importantly, according to the structure of working electrode in electrolyte, the response charges should not be completely considered as the charges involving in the chromic process of the film [18]. However, the electrochemical process taking place on the interface between film and electrode, and the diffusion of electroactive species on electrode are shielded.…”

“…However, the electrochemical process taking place on the interface between film and electrode, and the diffusion of electroactive species on electrode are shielded. In our previous study, these techniques have been applied to a multi-cycle system to investigate the electrochromic mechanism of the NiO films, and the extraordinary role of multi-cycle double-step potential chronocoulometry (MDPC) for characterizing the electrochromic performance and exploring the electrochromic mechanism has been demonstrated [18]. More importantly, according to the structure of working electrode in electrolyte, the response charges should not be completely considered as the charges involving in the chromic process of the film [18].…”

Improved Electrochemical Cycling Durability in a Nickel Oxide Double‐Layered Film

“…However, the compact structure makes it harder for ions to be inserted into/extracted from the films, which results in a slow switching speed and limited optical modulation range . Owing to the high specific surface area, amorphous NiO x films exhibit a short response time and a large optical modulation range, but the cycling durability and stability are poor . Therefore, the idea of our work was to combine the advantages of both crystalline and amorphous films.…”