Abstract
Reaction induced currents in planar metal/semiconductor nanostructures can provide a direct insight into underlying charge transfer processes involved in chemical energy dissipation at solid surfaces. This letter provides clear evidence of the nonthermal nature of chemicurrent induced by H2 adsorption on a Pt/SiC nanostructure at room temperature in 760Torr N2/O2 mixtures with various oxygen fractions. The thermal effect of the reaction is reproduced also with admission of N2 molecules to the sample. Only the process with H2 leads to a detectable chemicurrent proving participation of nonthermal electrons in the charge transfer induced by hydrogen evolution on the nanostructure surface.
Highlights
Understanding of the basic charge transfer processes at solid interfaces with reactive gas mixtures is a pathway toward advanced sensing, novel catalysts and energy conversion applications
Currents induced in surface reactions on catalytic nanofilms forming a Schottky or metal-oxide-semiconductor (MOS) type contact with a semiconductor substrate have received considerable attention during the last decade [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]
Chemicurrents generated in the course of continuous catalytic oxidation of molecular hydrogen [4,5,15] are interesting in the context of novel energy conversion applications; demonstration of their nonthermal nature is challenging at higher pressures in the gas phase [15]
Summary
Understanding of the basic charge transfer processes at solid interfaces with reactive gas mixtures is a pathway toward advanced sensing, novel catalysts and energy conversion applications. The surface released chemical energy is transferred directly to the electron subsystem of the solid catalyst to produce a population of mobile hot electrons in the metal nanofilm or e-h pairs in a semiconductor layer able to travel over the internal potential barrier, which performs a charge separation function, Figure 1. Such currents, could directly represent basic mechanisms of charge transfer in chemical transformations on solid surfaces, and their nonadiabatic origin in adsorption related process at cryogenic temperatures and vacuum conditions [7,8,9,10,11,12] is well recognized. A reverse argument for the case of H2 oxidation could be placed forward by recalling that 76% of total energy of the H2(g) + 1/2O2(g) → H2O(g) process on Pt is released during the initial adsorption stages [19], and by observing a nonthermal effect of H2 adsorption alone in a high pressure environment rather than in vacuum [7,8,9,10,11,12]
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