Correlation of electrical and physical properties of photoanode with hydrogen evolution in enzymatic photo-electrochemical cell

In this study, the electrical and physical properties, including the current density, open-circuit voltage, morphology and crystalline structure, of an anodized TiO2 electrode on a titanium foil are correlated with the hydrogen production rate in an enzymatic photo-electrochemical system. The effect of light intensity at ca. 74 and ca. 146 mW cm(-2) on the properties is also examined. Anodizing (20 V; bath temperature 5 degrees C; anodizing time 45 min) and subsequent annealing (350-850 degrees C for 5 h) of the Ti foils in an O-2 atmosphere led to the formation of a tube-shaped, or a compact layered, TiO2 film on the Ti substrate depending on the annealing temperature. The annealing temperature has a similar effect on the properties of the sample and the hydrogen evolution rate. The generated electrical value, the chronoamperometry (CA), is +13 to -229 and +13 to -247 mu A for light intensities of ca. 74 and ca. 146 mW cm(-2), while the corresponding open-circuit voltage (OCV) is in the range of -41 to -687 and -144 to 738 mV, respectively. In the absence of light (dark), the CA is 13-29 mu A and the OCV is +258 to -126 mW cm(-2). The trend in the electrical properties for the different samples is well matched with the rate of hydrogen evolution. The samples with higher activities (450, 550, and 650 degrees C) have similar X-ray diffraction (XRD) patterns, which clearly indicates that the samples showing the highest evolution rate are composed of both anatase and rutile, while those showing a lower evolution rate are made of either anatase or rutile. Increasing the intensity of the irradiated light causes a remarkable enhancement in the rate of hydrogen production from 71 to 15 3 mu mol h(-1) cm(-2) (c) 2008 Elsevier B.V. All rights reserved.