Metal (oxide) modified (M = Pd, Ag, Au and Cu) H2SrTa2O7 for photocatalytic CO2 reduction with H2O: The effect of cocatalysts on promoting activity toward CO and H2 evolution

Ag, Pd, Au, Cu2O as cocatalysts were loaded on the layered H2SrTa2O7 (HST) for photocatalytic CO2 reduction with H2O. The characterization revealed that cocatalysts loaded on the surface of HST can effectively promote the separation of photogenerated electrons and holes due to the formation of Schottky barrier or p-n junction, thus enhancing photocatalytic activity. Of note, Ag, Pd, Au, Cu2O loading exhibited obviously different performance on promoting photocatalytic activity of HST toward CO evolution and H-2 evolution because of the different overpotentials of CO evolution and H-2 evolution on loaded photocatalysts. Cocatalysts with low overpotentials of CO or H-2 evolution act as active sites for CO or H-2 evolution, thus controlling the selectivity toward CO or H-2. The Au/HST exhibited high activity for only H-2 evolution (17.5 mu mol g(-1) h(-1)) due to relative low overpotential for H-2 evolution (0.67 V) while the Cu2O/HST exhibited high activity only for CO evolution (0.23 mu mol g(-1) h(-1)) due to relative low overpotential for CO evolution (0.40 V). The Pd/HST sample exhibits high photocatalytic activity for both CO and H-2 evolution rates due to the low overpotential for CO and H-2 evolution, reaching 4.0 and 4.7 times of bare HST, respectively. This work here gives an in-depth understanding of the effect of cocatalysts on promoting photocatalytic activity and selectivity and can also give guidance to design photocatalysts with high activity and selectivity for photocatalytic CO2 reduction with H2O. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.