High-performance electrochromo-supercapacitors based on the synergetic effect between aqueous Al3+ and ordered hexagonal tungsten oxide nanorod arrays

Abstract

Recently, electrochromic and energy storage devices based on the intercalation of Al³⁺ ions have attracted much attention due to their low-cost, safe and environmentally friendly characteristics. However, Al³⁺ ions usually suffer from strong electrostatic interaction. Here we propose an adaptive material, hexagonal tungsten oxide nanorod arrays (h-WNRAs) with an ordered channel structure, which showed a good match with trivalent Al³⁺ ions. Due to the synergetic effect between aqueous Al³⁺ and h-WNRAs, the material displayed excellent electrochromic performance such as high optical modulation (81.5%), low response time (9 and 14 s at 660 nm), high coloration efficiency (149.9 cm² C⁻¹ at 800 nm), good reversibility (97.9%, 96.7% and 89.3% coulombic efficiency at 50, 20 and 2 mV s⁻¹, respectively) and good cycling stability (90.6% and 80.0% charge retention after 1000 cycles at 50 and 20 mV s⁻¹, respectively). Meanwhile, good capacitive performance including good specific capacitance (235.4 F g⁻¹ at 1 A g⁻¹ in a narrow potential window of −0.7–0 V), good rate capability (58.2% retention of specific capacitance and 79.4% retention of optical modulation at 10 A g⁻¹ compared with their initial values at 1 A g⁻¹) and long-term stability during charging/discharging processes (86.2% retention of specific capacitance after a galvanostatic test at 5 A g⁻¹ for 4000 cycles) was also achieved. This kind of system, using safe and environmentally friendly aqueous solution as electrolyte solvent, cheap and resourceful Al³⁺ as the electrolyte ion, and ordered h-WNRAs as the electrochromic and capacitive material (ECM), provided a new thinking for the development of dual-functional electrochromo-supercapacitors for the future.