MnO2 nanoparticles advancing electrochemical performance of Ni(OH)2 films for application in electrochromic energy storage devices

In this study, we report a unique material design of interconnected MnO2 nanoparticles covered with a Ni(OH)2 layer as an electrochromic energy storage device. MnO2/Ni(OH)2 electrodes are prepared via sequential electrodeposition within a short duration. During the electrodeposition of Ni(OH)2, the electrodeposited interconnected MnO2 nanoparticles on the substrate provide additional nucleation sites, indicating the porous morphology of the Ni(OH)2 layer without any significant cracks. The synergistic effects generated by the hybrid structure combined with interconnected MnO2 nanoparticles and Ni(OH)2 layer improve the charge transfer kinetics by shortening the transport pathway, facilitating electrochromic performance with fast switching times (2.66 s for bleaching process and 2.72 s for coloring process) and significant transmittance retention. In addition, the energy storage performance of the MnO2/Ni(OH)2 electrode shows an excellent areal capacitance (26.0 mF cm−2 at an operating current density of 0.2 mA cm−2). The electrochromic energy storage device with a two-electrode system (MnO2/Ni(OH)2 as the positive electrode and TiO2 as the negative electrode) exhibits comparable switching times (1.79 s for bleaching time and 3.28 s for coloring time) and areal capacitance (1.21 mF cm−2 at an operating current density of 0.2 mA cm−2) over a wide potential range. [Display omitted] •The MnO2 covered with an Ni(OH)2 layer is prepared by electrodeposition method.•The MnO2/Ni(OH)2 exhibited high surface area and additional synergistic effect.•The MnO2/Ni(OH)2 showed high performance in electrochromic energy storage devices.