Effect of Water Vapor on Pt/TiO2/Ti Electromotive Force Cells

We study the humidity dependence of the generated current of Pt/TiO2/Ti electromotive force (emf) cells by means of microcalorimetry, current–voltage (I–V) characteristics, and electrochemical impedance spectroscopy. We prepare TiO2 with a high-voltage electrochemical anodization and the Pt electrode via a paste process. We find that short-circuit current densities (J sc) significantly vary by adding water vapor to the 2.1 vol % hydrogen-in-air mixture used to generate the emf, while the open-circuit voltage (V oc) always increases with increasing relative humidity (RH). J sc increases from 8.2 mA/cm2 (RH = 0%) to a maximum value of 9.4 mA/cm2 (RH = 10%). At RH > 10%, J sc decreases slightly. The increase in J sc is interpreted as enhanced electron transport as a consequence of the interaction of water with TiO2, while the decrease in J sc seems to be related to a large amount of water negatively affecting the rate-determining step for emf.