not-yet-known not-yet-known not-yet-known unknown 4.1 Preparation of 1T/2H mixed phase MoSe2 powder. Na2MoO4∙2H2O (0.007 mol, 1.645 g), Se powder (0.02 mol, 1.5492 g), and NaBH4 (0.007 mol, 0.2595 g) were introduced into the solvent composed of 25 mL DI water and 25 mL ethanol and then magnetically stirred at 250 rpm for 30 min at 25 °C. The resultant solution was subsequently transferred to a 100 mL stainless-steel autoclave and heated at 200 °C for various times (1, 6, 12, 24, 36, and 48 h). The solution was rapidly cooled to 25 °C within 15 min to introduce the formation of a mixed phase of MoSe2 powder. The cooled solution was centrifugated at 8000 rpm for 5 min to collect the MoSe2 powder. The MoSe2 powder was washed three times with DI water and subsequently with ethanol. Then the MoSe2 powder was dried at 80 °C for 12 h under N2 atmosphere. The quantified yield of MoSe2 was approximately 1g. The MoSe2 with different synthesis times denoted MoSe2-P-X (X=1, 6, 12, 24, 36, and 48 h). P and X indicate powder and synthesis time, respectively. The loading amount onto the carbon paper of MoSe2-P samples was about ~5 mg.