Use of anodized tubular TiO₂ photoanodes in light-sensitized enzymatic hydrogen production

Abstract

In this study, an anodized tubular TiO₂ electrode (ATTE) on titanium foil was prepared and used both as a photoanode and a cathode in an enzymatic photoelectrochemical system to split water into oxygen and hydrogen. The effect of applied voltage when anodized, thickness of the foil, electrolytes, annealing temperature, and cathodes was investigated (optimum conditions: 20 V of applied voltage in 0.5 vol.% of hydrofluoric acid, 0.25-mm foil thickness, and 450–650°C annealing temperature). The samples with higher activities had similar X-ray diffraction (XRD) patterns, clearly indicating that the samples showing the highest evolution rate were composed of both anatase and rutile, while those showing a lower evolution rate were made of either anatase or rutile. The ATTE successfully replaced the Pt mesh cathode and the immobilization of the enzyme enhanced the H₂ evolution by 50% (from ca. 66 to 99 μmol/(h × cm²)). Moreover, the use of KOH instead of Tris–HCl buffer in a cathodic compartment further increased the H₂ evolution to 115 μmol/(h × cm²).