Photo-induced redox catalysis for proton reduction to hydrogen with homogeneous molecular systems using rhodium-based catalysts

Abstract

Solar driven water-splitting into hydrogen (H2) and oxygen (O2) has emerged as a very attractive sustainable approach to produce the fuel H2, which can be considered as promising clean and renewable energy carrier for the future. The development of homogeneous multi-component photocatalytic systems for the reduction of protons to H2 based on molecular compounds has experienced considerable growth since the end of the seventies. Such systems are generally composed of a light-harvesting antenna (photosensitizer), a hydrogen-evolving catalyst and a sacrificial electron donor coupled in some cases with an electron mediator. This review will survey the literature on homogeneous molecular multi-component photocatalytic systems for hydrogen production using rhodium complexes as catalysts with a special highlight on those operating in fully aqueous solution. In all of these studies, ruthenium-tris(bipyridine) or heteroleptic cyclometalated iridium complexes have been used as photosensitizers. Rhodium(III) complexes with poly(bipyridyl) ligands have been employed as catalysts in most of the studies. These multi-components photocatalytic systems are based on two different approaches: (i) multi-molecular systems, and (ii) systems involving an assembled structure (photocatalyst) that chemically couples in the same molecule the photosensitizer and the catalyst.