Materials capable of simultaneously modulating light transmission and storing electrochemical energy would be invaluable as “green” smart window platforms and/or displays for homes and businesses. While electrochromic materials—those that can change in color or opacity by applying voltage—are often considered for these applications, attaining useful energy storage requires the injection of large charge densities that correspondingly degrade their coloration efficiency, limiting device performance.
Professor Abdulhakem Elezzabi and his research group at the University of Alberta (Edmonton, AB, Canada) have overcome this limitation by developing a hybrid nanocomposite material consisting of colloidal nanocrystalline molybdenum oxide (MoO3) dispersed within a tungsten-molybdenum-oxide (W0.71Mo0.29O3) nanowire matrix, simultaneously yielding 100% enhanced energy capacity and 50% optical contrast modulation. Essentially, the team turned a smart window into a high-capacity rechargeable battery. Using an inexpensive and scalable process of applying the hybrid MoO3-W0.71Mo0.29O3 films with a spray-coating technique, electrical energy can be stored in the window while colored, and recovered on demand to power electrical devices. An 8 × 8 cm prototype of the window exhibited fully reversible contrast switching and can power a light-emitting diode (LED) for around 10 min. after inducing coloration with a -2.5 V signal for 1 min. The window has a Coulombic efficiency of 66% and a capacity of 2.33 mAh/m2, which is a factor of 1.5 and 1.6 better, respectively, than the best switchable windows composed of inkjet-printed CeO2/TiO2 and WO3/poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) ﬁlms fabricated to date. Reference: H. Li et al., Nano Energy, 47, 130–139 (2018).