Oxygen-deficient bimetallic oxide M0.11W0.89O3−x for flexible energy storage and electrochromic applications

Abstract

The development of multifunctional materials that combine energy storage and electrochromic properties is crucial for next-generation flexible electronics. Herein, we introduce a novel dual-functional approach through a single-material solution for two distinct applications: a flexible supercapacitor and a large-area electrochromic smart window. We report a facile solvothermal synthesis of an oxygen-deficient molybdenum-tungsten bimetallic oxide (M_0.11W_0.89O_3−x) engineered with multiple oxidation states and enlarged interplanar spacing to facilitate ion transport and accommodation. As a supercapacitor electrode, the optimized material delivers a remarkable areal capacitance of 975 mF cm⁻² at 5 mV s⁻¹ and a specific capacitance of 234 F g⁻¹ at 5 A g⁻¹. A fabricated flexible symmetric supercapacitor demonstrates excellent cycling stability, retaining its performance over 10 000 cycles at 1 A g⁻¹, while retaining functionality under various mechanical bending and environmental conditions. Simultaneously, the material exhibits significant electrochromic behavior, with rapid optical switching times of 1.5 s for coloring and 3.5 s for bleaching. A large-area (5 × 5 cm²) electrochromic device constructed with this oxide achieves a high optical modulation of 43% at 700 nm and a superior coloration efficiency of 147 cm² C⁻¹. This work underscores the dual functionality of a solution-processed Mo–W bimetallic oxide, presenting it as a highly promising candidate for integrated flexible energy storage and smart electrochromic systems.