Attaining remarkable switching speed of nickel oxide-based electrode for electrochromic energy storage devices

Integrating the electrochromic (EC) with energy storage devices (EC-ESDs) can considerably drop the energy-storing cost. In this direction, Nickel oxide (NiO) is considered a potential electrode material for EC devices owing to its superior coloration efficiency (CE), wide dynamic range, excellent cycling capability, and cost-effectiveness. On the flip side, NiO-based EC-ESDs experience low CE, slow switching speed, and soft chromatic contracts. To this end, a highly porous NiO nano-sheets (NSs) of thickness < 20 nm are grown on the hydrophilic surface of the FTO glass using a hydrothermal process. With this, an extremely low series (1.68 Ω) and marginal charge transfer (85.96 Ω) resistances are obtained. Thus, the switching speeds for coloration and bleach are significantly reduced to 0.85 and 0.30 s, respectively. Furthermore, the achieved optical modulation is 66.9%; whereas, the CE is 48.51 cm²/C. The obtained areal capacitance is 129.32 mF/cm² at the scan rate of 5 mV/s. Admirable capacity retention (92.3% at 10 mV/s) is observed after 1000 cycles. The obtained outcomes suggest that NiO can be a potential candidate for EC-ESDs.