“…Among these Co oxides, Co 3 O 4 is a P-type semiconductor with great potential for application in electrode materials, magnetic materials, catalysts, gas sensors, supercapacitors, etc. [34][35][36][37][38][39] Specifically, the band gap energy of Co 3 O 4 is 2.1 eV, so electrons and holes can be produced under light irradiation to improve the catalytic activity for the HER. 40 Subsequently, Co 3 O 4 is considered to be one of the most promising photocatalysts for the HER.…”