Photoanodic and cathodic role of anodized tubular titania in light-sensitized enzymatic hydrogen production

An anodized tubular titania (TiO 2) electrode (ATTE) is prepared and utilized as both a photoanode and a cathode in a photoelectrochemical system designed to split water into hydrogen (for use in fuel cells) with the assistance of a hydrogenase enzyme and an external bias of 1.5 V. In particular, the cathodic ATTE acts as a substrate for the immobilization of the enzyme due to its large surface area that results from the tubular oxides. The optimum molar concentration of KOH in anode and cathode compartments is 1.0 M and the optimum amount of enzyme for the cathode is ca. 3.66 units per geometrical unit area (1 cm × 1 cm) of the cathodic ATTE. After exposure to air for three weeks, the enzyme shows a hydrogen evolution rate that is 85.8% of that of an argon-purged enzyme. The rate of hydrogen evolution is increased from ca. 65 (in a slurry system) to more than 140 μmol cm −2 h −1, even after eliminating the electron relay (methyl viologen) and costly platinum counter electrode.