Accurate design of spatially separated double active site in Bi4NbO8Cl single crystal to promote Z - Scheme photocatalytic overall water splitting

Abstract

The efficiency of photocatalytic overall water splitting was mainly limited by the slow reaction kinetics of water oxidation. How to design effective surface active site to overcome the slow water oxidation reaction was a major challenge. Here, we propose a strategy to accelerate surface water oxidation through the fabrication spatially separated double active sites. FeCoPi/Bi4NbO8Cl-OVs photocatalyst with spatially separated double active site was prepared by hydrogen reduction photoanode deposition method. Due to the high matching of the spatial loading positions of FeCoPi and OVs with the photogenerated charge distribution of Bi4NbO8Cl and corresponding reaction mechanisms of substrate, the FeCoPi and OVs on the (001) and (010) crystal planes of Bi4NbO8Cl photocatalyst provided surface active site for water oxidation reaction and electron shuttle reaction (Fe3+/Fe2+), respectively. Under visible light irradiation, the evolution O2 rate of FeCoPi/Bi4NbO8Cl OVs was 16.8 μmol h−1, as 32.9 times as Bi4NbO8Cl. Furthermore, a hydrogen evolution co-catalyst PtRu@Cr2O3 was prepared by sequential photodeposition method. Due to the introduction of Ru, the Schottky barrier between PbTiO3 and Pt was effectively reduced, which promoted the transfer of photogenerated electrons to PtRu@Cr2O3 thermodynamically, the evolution H2 rate on PtRu@Cr2O3/PbTiO3 increased to 664.8 times. On based of the synchronous enhancement of the water oxidation performance on FeCoPi/Bi4NbO8Cl-OVs and water reduction performance on PtRu@Cr2O3/PbTiO3, a novel Z - Scheme photocatalytic overall water splitting system (FeCoPi/Bi4NbO8Cl-OVs) mediated by Fe3+/Fe2+ had successfully constructed. Under visible light irradiation, the evolution rates of H2 and O2 were 2.5 and 1.3 μmol h−1, respectively. This work can provide some reference for the design of active site and the controllable synthesis of OVs spatial position. On the other hand, the hydrogen evolution co catalyst (PtRu@Cr2O3) and the co catalyst FeCoPi for oxygen evolution contributed to the construction of an overall water splitting system.