Effects of dead volume and inert sweep gas flow on photocatalytic hydrogen evolution over Pt/TiO2

Abstract

In this study, the effects of dead volume and sweep gas flow rate on photocatalytic hydrogen production over Pt/TiO2 were examined to determine their possible impact on hydrogen production rates. Five different dead volumes (15, 45, 75, 190, 425 ml) under constant reaction solution and interfacial area experimented by using custom made reactors. It was found that higher dead volumes in the gas phase inversely affect the measured hydrogen production. The difference between highest and lowest H2 production rates (at steady state) among five dead volumes is found as 30 μmol/h gcat which is 24% of the highest rate. On the other hand, the difference due to sweep gas flow rates (15, 30, 45 ml/min Ar) was not as significant. It was concluded from these results that measured hydrogen production rate in photocatalytic systems depend strongly on the reactor size through gas phase dead volume and operational factors like sweep gas flowrate. The difference between highest and lowest hydrogen production rates for different dead volumes or sweep gas flow rates is too great to ignore when the average photocatalytic hydrogen production levels (∼500 μmol/h gcat) in the literature are considered. Uncertainties associated with these factors together with well-known difficulties in measurement (or reporting) of the amount of energy and the characteristics of light absorbed by the reaction solution make the comparison of results from different studies impossible. The results of this study confirm the need for standard protocols of measurement and testing in the photocatalysis field in general, and photocatalytic hydrogen production particularly.