Gallium phosphide photoanodes coated with nickel oxyhydroxide cocatalyst for stable photoelectrochemical water splitting reactions

Abstract

Gallium phosphide (GaP) is a promising material for photoelectrochemical (PEC) water splitting due to its appropriate bandgap and straddling band alignment with the water redox level. However, it suffers from poor charge transport and sluggish reaction kinetics. To mitigate these limitations and improve the PEC water splitting efficiency, simple and facile photodeposition followed by electrodeposition of nickel oxyhydroxide (NiOOH) as a cocatalyst on GaP was carried out. As a result, NiOOH-deposited GaP photoanodes exhibit much-improved PEC water splitting performance compared to bare GaP photoanode. The optimally deposited NiOOH cocatalyst on GaP enhanced the PEC activity of the photoanode with a photocurrent density of 1.15 mA/cm2, giving rise to a 10-fold enhancement compared to bare GaP (0.114 mA/cm2) and shifting the onset potential towards water reduction potentials (−553 mV vs Ag/AgCl). The best photoanode showed a 1.38% photoconversion efficiency at 0 V vs Ag/AgCl, which was 10 times higher than the bare GaP photoanodes (0.142%). Furthermore, all the NiOOH-deposited GaP photoanodes manifested long-term stability over 40000 s under illumination. The enhancement is attributed to the reduced onset potential, enhanced reaction kinetics by efficiently transporting the photogenerated holes and preventing the corrosion of GaP surface upon deposition of NiOOH cocatalyst.