Hydrogen production by molecular photocatalysis

Hydrogen can be produced by means of molecular photocatalysis from RH dehydrogenations. This is where the proton and electron equivalents for H2 production originate from C-H or O-H bonds. The most well-defined schemes for photocatalytic H2 production is alkane dehydrogenation, which happens by classical organometallic mechanisms involving alkane C-H bond activation. An alternative photocatalytic route is through mercury photosensitization of the dehydrodimerization of alkanes and was made viable for the formation of C-C bonds. Another is alcohol photo-dehydrogenation to ketones or aldehydes. They are not limited to late transition metal centers and can open a coordination site to support a two-electron oxidation state change to generate H2. A recent technique involves catalytically dehydrogenate NADH analogs in anaerobic acetonitrile solution under irradiation. H2 can also be produced from low-energy substrates directly such as acids. In order to enrich the hydrogen content in water gas after the steam reforming of methane, photochemical water-gas shift are widely used in industry. In a three-component system, the scheme is composed of one-electron photosensitizer, a redox mediator and the redox-storing catalyst. Another is through photobiological approaches to H2 production and is depended on th activity of photosynthetic organisms or the enzymatic activity of hydrogenase. It can be done through the activity of hydrogenase or isolated chloroplasts.