S-Scheme Heterojunction Photocatalyst

The significance of photocatalysts is unquestionable, and scientists are devoted to improving their photocatalytic efficiency. To solve the high recombination rates of photogenerated electron-hole pairs and their low reduction and oxidation abilities in a single photocatalyst, heterojunction manipulation is urgently required. Two mainstream heterojunctions—type-II and Z-scheme heterojunctions—have been widely acknowledged. However, we soberly reflect the charge-transfer mechanism from many perspectives and are finally aware of the fundamental challenges they face. To ensure a correct understanding, it is necessary to share our analysis with others. Moreover, step-scheme (S-scheme) heterojunctions, consisting of a reduction photocatalyst and an oxidation photocatalyst with staggered band structure, are introduced to avoid misinterpretation. The differences in the charge-transfer mechanism between S-scheme, type-II, and Z-scheme heterojunctions are highlighted. Finally, limitations and the future research direction of S-scheme photocatalysts are discussed.