Polyoxotungstate-based nanocomposite films with multi-color change and high volumetric capacitance toward electrochromic energy-storage applications

• Published in: New journal of chemistry Vol. 45; no. 42; pp. 19977 - 19985
• Main Authors: Chu, Dongxue, Qu, Xiaoshu, Zhang, Shangfei, Zhang, Jianrong, Yang, Yanyan, An, Wenjia
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.11.2021
• Subjects: Capacitance; Color; Coordination compounds; Electrochemical analysis; Electrochromism; Electrode materials; Energy storage; Ion diffusion; Iron; Nanocomposites; Nanowires; Optical properties; Polyoxometallates; Self-assembly; Substrates; Titanium dioxide; Transition metal compounds
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d1nj03939c

Electrochromic energy storage devices (EESDs) can directly reflect the level of energy storage via color changes, and the exploration of high-performance electrode materials is an important means to develop these devices. In this study, we report a nanocomposite film, NW/P 2 W 17 /Fe(phen) 3 , based on Dawson-type monolacunary polyoxotungstate K 10 P 2 W 17 O 61 (abbreviated as P 2 W 17 ) and a transition metal complex, [Fe II (phen) 3 ](ClO 4 ) 2 [abbreviated as Fe(phen) 3 ], formed on a TiO 2 nanowire (abbreviated as NW) array substrate combining a facile hydrothermal process and a layer-by-layer self-assembly method. The existence of TiO 2 nanowire substrates significantly increased the active area of the nanocomposite film and facilitated the diffusion of ions during the electrochemical process. As bi-functional electrodes, the NW/P 2 W 17 /Fe(phen) 3 films successfully achieved bridging electrochromic behavior with energy storage, realizing the multi-color transition from orange-red to light blue-violet and then to dark blue-violet during the charging and discharging process, with superior electrochemical properties of large optical modulation (34.3% at 600 nm), fast switching time ( t c = 2.8, t b = 6.2 s), high coloring efficiency (194.5 cm 2 C −1 at 600 nm) and volumetric capacitance (135.8 F·cm −3 at 0.2 mA cm −2 ). The charged EESD constructed based on NW/P 2 W 17 /Fe(phen) 3 can light up an LED, indicating the feasibility of practical application of polyoxometalates for electrochromic and energy storage. A facile fabrication strategy is proposed to construct a POMs-based nanocomposite film. It realizes multi-color transition during charging and discharging process, thereby links electrochromic behavior with energy storage performance.