Aqueous intelligent bi-functional electrochromic-energy storage device on heterostructured nanoarrays:In-situ repairability and Al3+ ion effect

In this paper, well oriented TiO2@WO3 nanorod arrays were synthesized and applied in AlCl3 aqueous (AlCl3-H2O) electrolyte for enhancing dual-function of single material. Benefiting from large specific surface area and stable structure of TiO2@WO3, as well as small ionic radius and trivalent characteristics of Al3+, the composite showed excellent electrochromic-capacitive properties and super stability, including large optical modulation (83.5% at 800 nm), excellent stability (the optical modulation only decreased by 2.3% after 3000 cycles; the specific capacitance value remained 92% after 1000 cycles at 5 A/g) and good energy storage level (248.3 F/g at 1A/g). Notably, the “ion trap” model was firstly applied to the Al3+ aqueous electrolyte to clarify the degradation and repair mechanisms of electrode. Different from Li + based organic electrolyte, only “eliminable trap” that eroded the colored state was generated after long cycles. The “non-eliminable trap” that reduced the transmittance of the bleached state was hardly produced, which was attributed to the limited voltage range of the aqueous solution and the characteristics of Al3+. In addition, the slightly reduced electrochromic and capacitive properties were both recovered in-situ through applying a constant voltage for de-trapping treatment, suggesting the novel construction of “TiO2@WO3 composite nanoarrays/AlCl3-H2O electrolyte” was the key for durable and repairable electrochromic-supercapacitor (ECSC). More importantly, real devices of TiO2@WO3-based ECSC were constructed and exhibited excellent bifunctional performance. Three devices with 3 × 4 cm2 in series could lit the LED light up, and its color changed with the power supply time, bringing a bright prospect in visual monitoring field. •“TiO2@WO3/AlCl3-H2O” showed excellent bifunctional performances and repairability.•The “ion trap” model firstly clarified the degradation mechanism in AlCl3-H2O.•The reduced electrochromic and capacitive properties were recovered by de-trapping.•Intelligent ECSC was applied to visually monitor changes in energy storage levels.•ECSCs could light up a LED, and the color changed with the energy storage level.