Photolysis of water for H 2 production with the use of biological and artificial catalysts

An aqueous mixture of chloroplasts, hydrogenase and an electron transfer catalyst on illumination liberates H 2 , the source of the H atoms being water. The rate and duration of H 2 production from such a system depends on the stability of chloroplast and hydrogenase activities in light and oxygen. Both chloroplasts and hydrogenases can be stabilized to a certain degree by immobilization in gels or by incubation in bovine serum albumin. Natural electron carriers of hydrogenases are ferredoxin, cytochrome c 3 and NAD. Viologen dyes and synthetic iron-sulphur particles (Jeevanu) can substitute for the biological carriers. Methyl viologen, photoreduced in the presence of chloroplasts, can liberate H 2 in combination with Pt (Adam’s catalyst). An aqueous solution of proflavine can be photoreduced in the presence of organic electron donors such as EDTA, cysteine, dithiothreitol, etc.; the reduced proflavine can subsequently liberate H 2 with MV-Pt, MV-hydrogenase, ferredoxin-hydrogenase or cytochrome-hydrogenase systems.