From waste carbonated beverages to high performance electrochromic devices: a green and low-cost synthetic method for self-doped metal oxides.

Metal oxides with reversible optical modulation capability are in the spotlight for smart windows and other emerging optoelectronic devices. Improving the electrochromic performance at a low cost is the only way to popularize their applications. Herein, we demonstrate a facile and versatile strategy to synthesize high-performance electrochromic metal oxides, in which waste carbonated beverages are used as the raw materials for the first time. It can not only reduce the production cost of electrochromic materials, but also alleviate the environmental pollution caused by such liquid waste. With an ingenious carbonization pre-step, both nanoscale pores and oxygen vacancies are created in an annealed tungsten oxide thin film. Multiscale structure optimization endows the self-doped WO 3- x films with excellent electrochromic properties such as large transmittance modulation (81.2%), high coloration efficiency (98.7 cm 2 C -1 ) and good cycling stability. DFT calculations show that oxygen vacancies reduce the Li + ion insertion energy barrier, which is conducive to the interfacial reaction in coloring and bleaching processes. Moreover, this approach is universal to other oxides such as vanadium pentoxide, molybdenum oxide and nickel oxide. The waste-to-value concept paves the way for cost-effective electrochromic materials and sheds light on the multiscale optimization of superior metal oxides.