The biocatalytic effect of Halobacterium halobium on photoelectrochemical hydrogen production

Hydrogen gas can be produced electrochemically by leading a current through two electrodes immersed in a NaCl solution. Bacteriorhodopsin (BR) a prote in found in the purple membrane of Halobacterium halobium, is known to pump protons across the membrane upon illumination. In this study, the effect o f BR on photoelectrochemical hydrogen production was investigated. A batch type bio-photoelectrochemical reactor was designed and constructed. The pho toelectrochemical hydrogen production experiments were performed with free H. halobium packed cells or immobilised H. halobium cells. The cells were e ither immobilised in polyacrylamide gel (PAG) or on cellulose acetate membr ane (CAM). Experiments were also performed with purple membrane fragments o f H. halobium immobilised on cellulose acetate membrane. It was found that the presence of bacteriorhodopsin (BR) in the reactor enhances the hydrogen production rate upon illumination. Immobilisation increased the amount of hydrogen produced per mole of BR. Compared to control experiments without B R, the power requirement of the photoelectrochemical reactor per amount of hydrogen produced decreased fourfold when purple membrane fragments immobil ised on CAM were used. The presence of BR regulates the pH of the system, i ncreases the hydrogen production rate and causes light-induced proton disso ciation, which lowers the electrical power requirement for the electrochemi cal conversion. (C) 1999 Elsevier Science B.V. All rights reserved.