Pt(II)-Terpyridyl-Based Photocatalysts for Efficient Hydrogen Evolution Reaction

Abstract

The persistent global energy crisis can be addressed by focusing on the advancement of cleaner energy sources. As a clean, efficient, and renewable option, hydrogen has long been regarded as a promising alternative to fossil fuels. Light-driven hydrogen evolution reaction (HER) offers a viable substitute for nonrenewable energy sources, since hydrogen is an energy-dense (143 MJ·kg–1) carbon-free fuel. In this respect, a handful of Pt(II) square-planar complexes, such as [Pt(II)(tpy)Cl]+ (where tpy = 2,2′:6′,2′′-terpyridine) have been reported in the literature for proton reduction, albeit with low turnover numbers (TONs) and a tendency to decompose to Pt nanoparticles. With these facts in mind, two Pt(II) terpyridyl complexes with varying electron densities were synthesized, structurally characterized, and successfully used for photocatalytic hydrogen production under different conditions (Pt catalyst + Ru photosensitizer, Co catalyst + Pt photosensitizer, and Pt photosensitizer + Pt catalyst) under varying light illumination. These complexes were found to be active for hydrogen production without the formation of nanoparticles, and a maximum turnover number of 1340 and a turnover frequency above 10000 for the combination of a Pt-complex as a catalyst and [Ru(bpy)3]2+ as a photosensitizer was achieved. Mechanistic studies revealed a reduced hydride dimer active for photocatalytic HER.