Synthesis of h-MoO3

h-MoO₃ was prepared by a simple hydrothermal method^25,94. Typically, 1 g Mo powders were added into 30 mL hydrogen peroxide (30 wt%) solution with rapid stirring in an ice-water bath. After continuous stirring for 1 hour, 35 mL water and 0.56 g NH₄NO₃ were added to the solution. The mixture was transferred to a 100 mL Teflon-lined autoclave (Anhui Kemi Machinery Technology Co., Ltd) and heated at 150 °C for 12 hours. After cooling to room temperature, the samples were centrifuged and washed with water and ethanol several times, and then dried in a vacuum drying at 60 °C overnight. Nanostructured h-MoO₃ were prepared by mechanical ball milling using a planetary ball mill at 450 rpm for 20 h in an argon atmosphere. For the preparation of α-MoO₃, all experimental procedures and parameters were the same except that 0.56 g NH₄NO₃ was replaced by 0.5 mL HNO₃ (65 wt%).