Chemical Sensing and Surface Energy Transfer on Mesoporous Metal-Semiconductor Nanostructures

This research investigated the role that interfaces play in the generation of chemical reaction-induced current on mesoporous Pt/TiO2 and Pt/ZrO2 nanocomposites, both of which operate as chemical-to-electrical transducers through their ability to produce a steady-state current under exposure to gas mixtures of oxygen and hydrogen. This stationary current can only be explained by the involvement of both Pt and the oxide substrate, highlighting the importance of interfaces during this steady-state process. Synthesis parameters implemented during plasma electrolytic oxidation of ZrO2 were altered, allowing for tunable manipulation of the substrate morphology, with both the pore density and diameter controlled. Investigation into these modified interfaces reveals a correlation between the Pt/ZrO2 interfacial length and the magnitude of current that is produced during hydrogen oxidation. In a well reproducible manner, the overall steady-state current derived from porous samples yielded a larger output than from their less porous counterparts. To confirm the source of electromotive force driving the steady-state current, similarly synthesized Pt/TiO2/Ti nanocomposites were exposed to hydrogen and oxygen. The water turnover frequency (TOF) asymptotically approaches an upper limit attributed to the saturation of the Pt/TiO2 interface. The existence of a rate-determining step in the TOF, in addition to an observed current polarity reversal simultaneously with an increase in water concentration, provides direct evidence that the production of water is the dominant force behind the generated electromotive force under steady-state room temperature conditions. This work was a pioneering effort to better understand the crucial role interfaces play in both adiabatic and non-adiabatic processes within catalytic nanocomposite systems. The results presented unveil the auspicious potential for electrolyte-free nanodiode systems, vaulting them into candidacy for low energy/power applications. Optimizing the Pt/semiconducting interfaces for an increased rate of water desorption will further enhance the extraordinary properties of these chemical−electrical transducers. The experimental methodologies detailed here can be extended into the field of analytical chemistry to broaden the capabilities of both the detection of, as well as the monitoring of, catalytic chemical reactions.