Near-infrared (NIR) electrochromism is of academic and technological interest for a variety of applications in advanced solar heat regulation, photodynamic therapy, optical telecommunications, and military camouflage. However, inorganic materials with outstanding NIR modulation capability are quite few. Herein, we propose a promising strategy for achieving strong NIR electrochromism in tungsten oxide that is closely related to its electrochemical transformation from battery-type behavior to pseudocapacitance, induced by introducing an interlayer space with water molecules within tungsten oxide. Further evidence demonstrates that the interlayer water molecules significantly reduced the energy barrier to ion diffusion and increased the ion flux in tungsten oxide. As a result, compared with anhydrous WO3, the as-synthesized WO3·2H2O nanoplates exhibited remarkably improved NIR electrochromic properties, including a large transmittance modulation (90.4%), high coloration efficiency (322.6 cm2 C-1), and high cyclic stability (maintaining 93.7% after 500 cycles), which were comparable to those of the best reported NIR electrochromic materials. Moreover, the application of the WO3·2H2O nanoplate-based electrochromic device resulted in a temperature difference of 11.9 °C, indicating good solar thermal regulation ability.
Keywords: capacitive charging; electrochromism; free electron concentration; interlayer water; near-infrared.