Nonadiabatic Chemical-to-Electrical Energy Conversion in Catalytic Schottky Junction Nanostructures
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Nonadiabatic Chemical-to-Electrical Energy Conversion in Catalytic Schottky Junction Nanostructures Eduard G. Karpov and Jyotsna Mohan Civil & Materials Engineering, University of Illinois, Chicago, IL 60607, U.S.A.
ABSTRACT Nonadiabatic energy dissipation by electron subsystem of nanostructured solids unveil interesting opportunities for the solid-state energy conversion and sensor applications. We found that planar Pd/n-SiC, Pt/n-GaP and Pd/n-GaP Schottky structures with nanometer thickness metallization demonstrates a nonadiabatic channel for the conversion into electricity the energy of a catalytic hydrogen-to-water oxidation process on the metal layer surface. The observed abovethermal current greatly complements the usual thermionic emission current, and its magnitude is linearly proportional to the rate of formation and desorption of product water molecules from the nanostructure surface. The possibilities and advantages of utilizing the nonadiabatic functionality in a novel class of chemical-to-electrical energy conversion devices are discussed. The technology has a potential for a very high volumetric energy density due to the intrinsically planar device architecture. INTRODUCTION Hydrogen fuel cells are expected to comprise an integral segment of the hydrogen economy cycle, burning hydrogen, the cleanest chemical fuel, and generating electric power without any moving parts for transportation vehicles, and portable electronic devices. Largescale cells could be used for stationary applications, and serve as a key element of the future photocatalysis energy plants, utilizing solar power for the catalytic dissociation of water into the gaseous hydrogen and oxygen components. Some of the most notable drawbacks limiting the desired functionality of the current fuel cells are low power-to-weight ration, high temperature operation, and short lifetimes. It is important to note the fuel cell is essentially an electrochemical device employing the flow of electrons participating in a chemical redox process for the chemical-to-electrical energy conversion. A similar approach though with the oxidant and reagent being stored in the device volume has been used in the usual electrochemical cells and batteries since the eighteenth century. The goal of this work is to investigate the possibility and practical feasibility of an entirely distinct type of chemically driven solid-state electric generators. These generators will incorporate the nonadiabatic energy conversion processes similar to those in solar cells, but utilize catalytic oxidation of hydrogen to water on the device surface as the energy source. The nonadiabatic functionality refers to the above-thermal regime of chemically induced excitation of hot electrons in a class of nanostructured materials, where the electrons are not allowed to achieve thermal equilibrium with surrounding atoms, and thus lose their useful energy. This possibility exists due to the fact that many chemical processes on metal surfaces flow highly exothermally providing energies in the orde
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