Potential Co-catalyst application of novel M 3 P 2 (M=Zn, Cd) in photocatalytic hydrogen evolution reaction from water splitting

New noble-metal-free co-catalysts based on transition metal phosphides, Zn 3 P 2 and Cd 3 P 2, were fabricated and loaded on hetero-structure of BiFeO 3 –CdWO 4 with the aim of promoting hydrogen evolution from water splitting without using sacrificial agent. The opto-electrochemical properties of the photocatalysts were investigated by various characterization techniques and it was observed that the co-catalyst loaded BiFeO 3 –CdWO 4 exhibited better light harvestability, charge separation efficiency and charge mobility. The photocatalytic hydrogen productivity reached up to 572.81 μmol h −1.g cat −1 h by loading 12 wt% Zn 3 P 2 and 488.25 μmol h −1.g cat −1 by loading 9 wt% Cd 3 P 2 over BiFeO 3 –CdWO 4. Zn 3 P 2 and Cd 3 P 2 have shown light absorption in visible to near IR region, thus they may also have the additional role of a photocatalyst other than being active sites for the photocatalytic reduction half-reaction. Loading the co-catalysts also resulted in multiplication of specific surface area which means an increase in the number of surface active sites. We observed a higher hydrogen productivity with lower photocatalytic rate by loaded Zn 3 P 2 in compared with Cd 3 P 2. This is attributed to the different photoresponsivity and band edge energy of the co-catalysts. The details of charge transfer mechanism between the host hetero-structure photocatalyst and loaded co-catalysts has been discussed.