Controlled synthesis of high-performance silver/silver orthophosphate (Ag/Ag₃PO₄) interfaced photoanode with porous tetrahedrons layer for photoelectrochemical water splitting

In this study, a novel interfaced photoanode of silver/silver orthophosphate (Ag/Ag₃PO₄) was synthesised via the controlled oxidation of Ag foil which resulted in a top porous layer of {111} facets-bounded Ag₃PO₄ tetrahedrons layer. This was achieved through a systematic understanding and optimisation of the critical synthesis parameters, including: concentration ratio of polyvinylpyrrolidone (PVP) used as the capping agent to precursor (C/P), volume ratio of hydrogen peroxide (H₂O₂) to deionised water (H₂O) (H₂O₂:H₂O) and reaction time. It was revealed that the best-performing Ag/Ag₃PO₄ interfaced photoanode can be synthesised at the C/P ratio of 4, H₂O₂:H₂O ratio of 3:5 and reaction time of 20 h. This is owing to the synergistic reaction of Ag foil, NaH₂PO₄ and H₂O₂ under the assistance of PVP, which leads to the formation of the porous layer of highly reactive {111} facets-bounded Ag₃PO₄ tetrahedron structures. The optimised Ag/Ag₃PO₄ interfaced photoanode achieved an unprecedentedly high photocurrent density of 4.19 mA/cm² at 1 V vs Ag/AgCl with an accompanying measured H₂ evolution rate of 49.08 µmol/h cm². Additionally, the applied bias photon-to-current efficiency (ABPE) and incident photon-to-current efficiency (IPCE) for the Ag/Ag₃PO₄ interfaced photoanode were recorded at 0.55% (0.84 V vs Ag/AgCl) and 56.5% (1 V vs Ag/AgCl, 410 nm), respectively.