The photocatalytic hydrogen evolution and photoreduction CO2 selective enhancement of Co3O4/Ti3+-TiO2/NiO hollow core-shell dual pn junction

The potential and threshold would be the most important issues for photocatalysis, including hydrogen evolution reaction (HER) and CO 2 selective photoreduction. The Co 3 O 4 /Ti 3+ -TiO 2 /NiO hollow core-shell heterojunction is fabricated via a continuous chemical-hydrothermal-annealing-reduction method. As demonstrated, the as-prepared Co 3 O 4 /Ti 3+ -TiO 2 /NiO hollow core-shell heterojunction exhibits remarkable photocatalytic performance enhancement than single TiO 2 , including H 2 evolution (∼2134.63 μmol/g∙h, ∼80 folds) and CO 2 photoreduction (H 2 /CH 4 /CO: ∼34.85/132.25/12.65 μmol/g∙h, ∼30 folds), and achieves enhanced CO 2 photoreduction selectivity, which can be mainly ascribed to the synergism of Ti 3+ /O v and dual pn junction. There, the Ti 3+ /O v can not only increase the solar efficiency, but also decrease the threshold of H 2 O*→H* and *CO→*CHO to enhance HER and CH 4 selectivity, including promote H + diffusion and H 2 O/CO 2 /*CO absorption. All these can be supported by the density functional theory (DFT) calculation. Additionally, the formed Co 3 O 4 /Ti 3+ -TiO 2 /NiO dual pn junction can promote the photo-generated carrier separation/transport efficiently. Furthermore, the hollow core-shell structure obtained by Cobalt 2-methylimidazole (ZIF-67) self-template can increase solar efficiency, and the NiO nanosheets and Co 3 O 4 nanoparticles can increase active sites. • >Ti 3+ /O v decreases threshold of H 2 O*.→H* to enhance HER (−0.15 to 0.93 eV) • >Ti 3+ /O v decreases threshold of *CO.→*CHO to enhance CH 4 selectivity (0.72–0.47 eV) • >Dual pn junction can promote carrier efficiency via appropriate potential (2 folds). • >Hollow 3D structure can increase interface heterojunction (∼132.11 m 2 /g).