Catalytic activity of metal-based nanoparticles for photocatalytic water oxidation and reduction

Precious-metal catalysts, predominantly platinum (Pt), have been used to minimize the overpotentials for both the oxidation and reduction of water. This article focuses on the catalytic activity of non-Pt metal nanoparticles for the photocatalytic oxidation and reduction of water. Efficient photocatalytic hydrogen evolution was made possible by using ruthenium nanoparticles (RuNPs) instead of platinum nanoparticles (PtNPs) under basic conditions (pH 10) with 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh⁺-NA) as an organic photocatalyst and dihydronicotinamide adenine dinucleotide (NADH) as an electron source. Nickel nanoparticles (NiNPs) can also be used as a non-precious metal catalyst in the photocatalytic hydrogen evolution with QuPh⁺-NA and NADH maintaining 40% of the catalytic activity of PtNPs. On the other hand, some metal-based nanoparticles can also act as catalysts for photocatalytic water oxidation. Iridium hydroxide nanoparticles (Ir(OH)_xNPs) formed during the thermal oxidation of water by (NH₄)₂[Ce ^IV(NO₃)₆] as an oxidant and cobalt hydroxide nanoparticles (Co(OH)_xNPs) were produced during the photocatalytic oxidation of water with Ru(bpy)₃²⁺ as a photocatalyst and persulphate as a sacrificial oxidant using Ir and Co complexes with organic ligands as precatalysts. The catalytic activity and stability of Ir(OH) _xNPs and Co(OH)_xNPs were improved significantly as compared with Ir and Co precatalysts.