Abstract:

Nickel molybdate (NiMoO₄) is a material with excellent performance in the field of energy storage and catalysis, but lacking of further explorations in the field of electrochromism. In this work, porous NiMoO₄ films were grown on transparent conductive glasses by hydrothermal method without using seed layer. Crystalline phase and micromorphology of NiMoO₄ nanosheet films were characterized by grazing incidence X-ray diffractometer (GIXRD) and field-emission scanning electron microscope (FESEM), and the electrochromic and electrochemical properties were also investigated by using a UV-Vis-NIR spectrophotometer and an electrochemical workstation. The results show that the NiMoO₄ electrochromic films have a porous structure, which can provide sufficient channels for ion migration and reactive sites for the dynamic process of ion intercalation/deintercalation into NiMoO₄ film. Therefore, the NiMoO₄ films exhibit excellent electrochromic performance, including large optical modulation of 79.6% at 480 nm and high coloring efficiency of 86.2 cm²·C^-1. Meanwhile, the coloration and bleaching response time of the NiMoO₄ films are 9.5 and 12.7 s, respectively. Interestingly, there is a two-step process in the bleached process of NiMoO₄ electrochromic films, including a fast process and a slow process. And the optical modulation can still be maintained at 99.7% of the maximum optical modulation after 100 cycles. In addition, the NiMoO₄ films exhibit a large area specific capacitance of 49.59 mF·cm^-2 at 0.3 mA·cm^-2. These excellent properties support NiMoO₄ nanosheet films with promising application in high-performance electrochromic devices. And the next step is to focus on finding the suitable electrolyte and matched counter electrodes in the device assembly.

Key words: NiMoO₄, electrochromic, nanosheet, hydrothermal method