The genesis and importance of oxide–metal interface controlled heterogeneous catalysis; the catalytic nanodiode

摘要

Much of the research by Konrad Hayek’s group is focused on the influence of oxide–metal interfaces in heterogeneous catalysis. In this paper, we show that electronic excitations at the metal surface induced by exothermic catalytic reactions lead to the generation of energetic (hot) electron flows. We detected the flow of hot electrons during oxidation of carbon monoxide using Pt/TiO2 Schottky diodes. The thickness of the Pt film used as the catalyst was 5 nm, less than the electron mean free path, resulting in the ballistic transport of hot electrons through the metal. The electron flow was detected as a chemicurrent if the excess electron kinetic energy generated by the exothermic reaction was larger than the effective Schottky barrier formed at the metal-semiconductor interface. We found that heat generated by the reaction caused a negligible increase of temperature in our experimental range, suggesting that this thermal effect is not responsible for the generation of hot electron flow. We tested the stability and reversibility of chemicurrent generated during CO oxidation at 413~573 K. The activation energy calculated from the measurement of chemicurrent is quite close to that of the turnover rate of chemical reaction, which indicates that the generation mechanism of hot electrons is closely correlated with the chemical reaction. This correlation suggests that hot electron flow could be a new tool to probe the role of oxide–metal interfaces in heterogeneous catalysis.