Fabrication of a Dual P-N Heterojunction Consisted of NiCo2O4/NiO/Al-doped SrTiO3 for Boosted Photocatalytic Overall Water Splitting

In this study, NiCo2O4/NiO/Al: SrTiO3 (labeled as NCO/NO/ASTO) with dual p-n heterojunction structure was devised and in-situ fabricated for the first time, in which metal-organic framework (MOF)-derived NiCo2O4/NiO (NCO/NO) was utilized as the O2-producing co-catalyst. This dual p-n heterojunction with the matching built-in electric field made it possible to separate and transfer charge carriers in a manner that was substantially more effective than the use of a single p-n heterojunction. The NCO/NO/ASTO-1 exhibits an excellent overall water splitting performance of 1.74 (H-2)/0.85 (O-2) mmol g(-1)h(-1) when exposed to UV radiation, which is 1.3 and 2.6 times that of NiCo2O4/Al: SrTiO3 (NCO/ASTO) and NiO/Al: SrTiO3 (NO/ASTO) with single p-n heterojunction structure, respectively. The electrostatic adsorption force and matching built-in electric field between ASTO and NCO/NO have been demonstrated, ensuring the presence as well as the stability of the dual p-n junction and accelerating the migration of photogenerated carriers. Moreover, density functional theory (DFT) was used to offer theoretical evidence of the driving force for the interfacial charge transfer in the NCO/NO/ASTO dual p-n heterojunction, which could be attributed to the difference in the work functions (Phi) of the components of NO, NCO, and ASTO.