Hierarchically structured VxO2x+1 films: dual-function electrochromic capacitors with multi-state color switching and high cycling stability

This study synthesizes mixed-phase vanadium oxide (V x O 2x+1 ) thin films with dual electrochromic and capacitive functionalities through a synergistic combination of sol–gel processing, electrochemical deposition, and thermal annealing. The VO-350 film, annealed at 350 °C, exhibits a hierarchically ordered “dense-layer/porous-interior” architecture, achieving exceptional areal capacitance and superior optical modulation. This single-material system exhibits an unparalleled four-state multicolor switching capability (yellow, green, blue and brown) with rapid kinetics (<20 s) and ultrahigh cycling stability, retaining 51.29% of its initial capacitance and exhibiting zero optical modulation decay after 2,000 cycles. When integrated into VO-350/WO 3 electrochromic devices, the system delivers dual-band high modulation (58.39% @750 nm and 59.11% @1000 nm after 3000 cycles) alongside enhanced switching dynamics. This work pioneers a methodology that precisely orchestrates reduction potentials and thermal annealing strategies to directionally regulate vanadium oxidation states, crystallographic phases, and morphological features, this establishes a standardized paradigm for designing dual-functional electrochromic capacitors.