Oxygen Sensing of Pt/PEO-TiO(2) in Humid Atmospheres at Moderate Temperatures

Here, we show that the presence of adsorbed water improves the oxygen-sensing properties of Pt/TiO [Formula: see text] at moderate temperatures. The studied interface is based on porous plasma electrolytic oxidized titanium (PEO-TiO [Formula: see text]) covered with platinum clusters. The electrical resistance across Pt/PEO-TiO [Formula: see text] is explained by an electronic depletion layer. Oxygen adsorbates further increase the depletion by inducing extrinsic interface states, which are occupied by TiO [Formula: see text] conduction band electrons. The high oxygen partial pressure in ambient air substantially limits the electron transport across the interface. Our DC measurements at defined levels of humidity at 30 [Formula: see text] C show that adsorbed water counteracts this shortcoming, allowing oxygen sensing at room conditions. In addition, response and recovery times from temporal oxygen exposure decrease with humidity. We attribute the effects to competing adsorption processes and reactions of water with adsorbed oxygen species and/or lattice oxygen, which involve electron re-injection to the TiO [Formula: see text] conduction band. Elevated temperatures up to 170 [Formula: see text] attenuate the effects, presumably due to the lower binding strength to the surface of molecular water compared with oxygen adsorbates.