Interface-engineered silicon photocathodes with a NiCoP catalyst-modified TiO2 nanorod array outlayer for photoelectrochemical hydrogen production in alkaline solution

Abstract

To assemble efficient photoelectrochemical (PEC) cells for total water splitting, the inexpensive photocathodes that are active and stable in alkaline solutions are strongly desired, as the known earth abundant catalyst-decorated photoanodes display high activity and good stability for water oxidation mostly in basic media. Herein, we report a Si-based composite photocathode with its front surface coated orderly by an N-doped graphene nanolayer (CN) and a TiO2 nanorod array (TiO2(ALD/NR)), which is loaded with Ni/Co phosphide catalyst (NiCoP) nanoparticles. The optimized Si/CN/TiO2(ALD/NR)/NiCoP electrode exhibits a photocurrent density of −19.87 mA cm−2 at 0 V, an onset potential at 0.42 V vs RHE, and an applied bias photon-to-current efficiency of 1.28% for H2 production in 1.0 M KOH under simulated 1 sun illumination. The impacts of TiO2 NR array outlayer and surface-loaded NiCoP catalyst on interfacial energetics, charge transfer kinetics, and PEC performance of photocathodes are comparatively studied by using a series of reference electrodes. The results indicate that the TiO2 NR array makes a major contribution to the evidently improved PEC activity of Si/CN/TiO2(ALD/NR), and that the NiCoP loaded on the surface of TiO2 NR array greatly enhances the charge transfer efficiency and boosts HER kinetics of the photocathode.