Electrochromic and pseudocapacitive behavior of hydrothermally grown WO3 nanostructures

We report the direct synthesis of various WO3 nanostructures (nanoplates, nanobricks, and stacked nanosheets) on fluorine-doped tin oxide conducting substrates for electrochromic and pseudocapacitive energy storage applications. These nanostructures were formed by varying the pH of the hydrothermal solution, which led to monoclinic and triclinic crystal structures. Among these structures, vertically aligned WO3 nanoplates showed good electrochromic properties, with rapid and reversible response of the colored and bleached states in 0.5 M H2SO4 electrolyte. Moreover, the vertically aligned WO3 nanoplates exhibited promising energy storage behavior as a negative electrode material with a higher areal capacitance of 72.6 mF cm(-2) in 0.5 M Na2SO4 electrolyte and better electrochemical performance than the nanobricks and stacked nanosheets. The two-dimensional WO3 nanoplates exhibit strong potential for use in smart windows and negative-electrode pseudocapacitors.