High-performance electrochromic supercapacitors enabled by self-assembled transition metal oxide/MXene heterostructure

The integration of electrochromic and energy storage functionalities into a single device offers a promising pathway toward smart energy management, yet the practical application of electrochromic supercapacitors (ECSCs) is hindered by the poor electrical conductivity, sluggish ion diffusion, and inadequate cycling stability of transition metal oxide electrodes, such as WO 3 . Although various nanostructuring and hybrid strategies have been explored, achieving a simultaneous enhancement in optical modulation, switching speed, and long-term durability remains challenging. To address these issues, we herein report a facile self-assembly strategy to construct conductive MXene-based heterostructures with WO 3 ·2H 2 O nanoparticles, yielding WO 3 ·2H 2 O/MXene (WM) composite thin-film electrodes. The optimal heterostructure (WM-7.5) exhibits enhanced conductivity and enriched electroactive sites, facilitating rapid ion/electron transport. This results in significantly improved optical modulation ( ΔT  = 62% at 700 nm) and accelerated switching kinetics (coloration/bleaching times of 4.5/4.0 s). Moreover, MXene serves as a conductive scaffold that buffers volume changes and suppresses active material aggregation, endowing the electrode with exceptional cycling durability (82% capacitance retention after 10,000 cycles). Furthermore, a complementary ECSC device assembled using WM-7.5 and Prussian Blue achieves a high optical modulation ( ΔT  = 61%), and fast switching (1.6/2.4 s). This work provides a general and effective route for designing high-performance, multifunctional ECSCs through rational heterostructure engineering.