In situ efficient growth of Rubik nanocube WO₃0.33H₂O array films for high-performance electrochromic energy storage devices

Tungsten trioxide (WO3)-based electrochromic devices have attracted considerable attention due to their promising applications in smart windows, energy-efficient displays, and sunglasses. However, it is still challenging to fabricate high-performance WO3 electrochromic films using an efficient and facile wet method. Here, we report a one-step strategy for the in situ growth of WO30.33H(2)O Rubik nanocube films on fluorine-doped tin oxide (FTO) conducting substrates in hydrogen peroxide (H2O2) and an ethylene glycol (EG)-containing hydrothermal system that is seed layer-free. The complexing effect of H2O2 results in the highly efficient formation of WO30.33H(2)O films with good interface stability and a porous structure formed by the stacked Rubik nanocubes. Benefiting from the porous structure, the obtained WO30.33H(2)O film delivers outstanding electrochromic and electrochemical energy storage performance, such as large optical modulation over the wide-band visible-near-infrared (Vis-NIR) range (up to 80% at 633 nm and 90% at 1000 nm), high coloration efficiency (65.6 cm2 C-1), high rate capability as well as good cycling stability (with 80% transmittance retention over 1000 cycles). Furthermore, as a demonstration, a complementary electrochromic device was assembled based on the WO30.33H(2)O film, which offers a high coloration efficiency (92.6 cm2 C-1), optical modulation in the visible range (up to 70% at 633 nm), and large energy storage of 27.4 mA h m(-2) at 0.07 mA cm(-2). We believe that this efficient and facile wet method for preparing electrochromic films will provide a fresh approach to investigating high-performance electrochromic systems.