Fast-Response, Long-Cycle Life and Multi-Color Electrochromic Devices of Transition Metal-Doped Potassium Vanadate Films

Abstract

Most multi-color electrochromic devices based on vanadate have attracted significant attention due to their low energy consumption, broad color range and visual friendliness. However, challenges such as poor cyclic stability and slow response times hinder their widespread use. In this study, we propose a novel approach to enhance the response time and cyclic stability of vanadate-based electrochromic materials by incorporating transition metal ions (Fe³⁺, Co²⁺, Ce³⁺) into potassium vanadate film (KVO film). Experimental results demonstrate that the introduction of transition metal ions stabilizes the lattice structure, enhances electrochemical processes, and facilitates the rapid ion diffusion through KVO layers in ion insertion and extraction. Additionally, a Zn²⁺/Li⁺ propylene carbonate (PC) hybrid electrolyte was prepared, which effectively prevents the dissolution of potassium vanadate film which significantly improving its electrochemical performance and cyclic stability. The electrodes in the hybrid electrolyte demonstrated three orders of magnitude accelerated zinc ion diffusion coefficients ($D_{Z{n}^{2+}}$$D_{Z{n}^{2+}}$) and faster electrochromic response times: Fe-KVO (t_b/t_c = 6.1/6.6 s), Co-KVO (t_b/t_c = 8.4/4.8 s) and Ce-KVO (t_b/t_c = 6.3/7.6 s) compared with H-KVO (t_b/t_c = 21.9/7.2 s), and lower net round-trip energy consumption (both below 90 mWh m⁻²). All vanadate film electrodes sustain their performance over 1000 cycles. The device's color variations under different applied potentials, such as green, olive green, yellow, light brown, amber, and orange-red. These findings highlight the potential of transition metal ion doping to enhance properties of vanadate films, paving the way for their broader application in multi-color electrochromic devices.