The photocatalytic reaction process involves three steps: (i) light absorption related to the band gap/defect level; (ii) charge transfer and separation related to the charge mobility, conductivity, defect level/conduction/valence position; and (iii) surface catalytic reaction related to the adsorption/desorption energy, active site number, and reaction activation energy [
11
,
12
]. The band gap of photocatalysts should meet the thermodynamic reaction potentials. The conduction/valence position of photocatalysts should align the potential of the adsorbate to facilitate the redox reaction process. Particularly, in the photocatalytic reduction process, most of the electrons and protons will combine to generate H
2
, rather than the CRR and NRR. The intense competition of HER on the photocatalyst’s surface results in unsatisfactory photocatalytic CRR and NRR activity. Promoting the OER reaction can provide additional electrons and protons for the CRR and NRR process. In these reactions, the absorption range of light and charge transfer are crucial factors for enhancing photocatalytic activity. Therefore, developing highly efficient photocatalysts is imperative [
12
,
13
].
