Two-dimensional WO3 nanosheets for high-performance electrochromic supercapacitors

Abstract

In the present study, two-dimensional (2D) WO₃ nanosheet arrays with (101) preferential orientation facets (WO₃ NSHs) were successfully assembled on a fluorine-doped tin oxide (FTO) electrode through a simple solvothermal method. Physicochemical properties analysis affirmed the prepared WO₃ was a single-crystal-like monoclinic nanosheet with an anomalous intense [101] dominant orientation. As an electrochromic supercapacitor (ESC) cathode electrode, the WO₃ NSHs/FTO electrode delivered a high areal capacity of 59.55 mF cm⁻² and corresponding transmittance modulation (ΔT) of 85.05% (at 1000 nm) at 5 mV s⁻¹, and remarkable optical-electrochemical cycling stability in AlCl₃ electrolyte. The superior optical-electrochemical bifunctional performance could be attributed to the synergistic effect of the WO₃ nanosheet arrays structure and highly preferential (101) crystal facets. Furthermore, the internal mechanism affecting the optical-electrochemical performance, namely the synergistic reaction between the single-phase reaction for Al³⁺ ions insertion/extraction into monoclinic WO₃ tunnels and the surface pseudocapacitance-controlled reaction, was confirmed by utilizing in situ X-ray diffraction. Similarly, the ESC device based on the WO₃ NSHs/FTO electrode also displayed excellent optical-electrochemical performance in AlCl₃ electrolyte, such as 26.11 mF cm⁻² areal capacitance, 42.39% ΔT (at 650 nm), and 94.87% capacitance retention after 5000 cycles. In addition, we could judge the capacity for the ESC device by the color changes.