Plasmonic-Enhancement of the Electro-Oxidation of Ethanol in Alkaline Media with Au-Fe 2 O 3 Thin Film, Embedded, Sandwi
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Plasmonic-Enhancement of the Electro-Oxidation of Ethanol in Alkaline Media with AuFe2O3 Thin Film, Embedded, Sandwich and Surface Configurations Joshua P. McClure*, Kyle N. Grew, Naresh C. Das, Deryn Chu, David Baker, Nicholas Strnad, Eric Gobrogge U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, Adelphi, MD, 2800 Powder Mill Road, Adelphi, MD 20783, U.S.A. ABSTRACT This paper highlights experimental and theoretical efforts dedicated to developing plasmonic-enhanced electrodes for the photo-electrochemical ethanol oxidation reaction (EOR) at room temperature in alkaline media. However, decoupling the electrocatalytic dark response from the plasmon-enhanced improvement presents a difficult challenge. To understand the plasmonic-enhancement of the photo-electrochemical EOR, multiple Au-Fe2O3 were fabricated and evaluated in parallel with discrete dipole approximation (DDA) modeling. Different AuFe2O3 were synthesized with Au nanoparticles located at variable positions within and/or on the Fe2O3 layer(s). The configurations investigated include thin film, embedded, surface and sandwich layered electrodes to facilitate optimal electrode design considerations for plasmonicenhancement. The design strategies and configurations were guided by DDA simulations to assess absorption, scattering, and near-field enhancements within or near the semiconductor band edge, as well as the solution/electrode interface. For the different Fe2O3 loadings and Au nanoparticle sizes/distributions considered, it is determined that the Au-Fe2O3 surface configurations significantly enhanced the EOR in terms of a large positive current density enhancement, an increased photo-voltage and a lower onset potential relative to the other electrode designs. INTRODUCTION Carbon-carbon (C-C) bonds are difficult to break at low temperatures (i.e. < 80°C); therefore, state-of-the-art electrochemical power sources typically (i) use simpler fuels which don’t contain C-C bonds (e.g. CH3OH, H2, etc.) or (ii) perform high temperature catalytic reformation steps which require additional reformation components.[1] For example, the electro-oxidation of ethanol (EOR) to CO2 is difficult to efficiently achieve at room temperature.[1] Therefore, several strategies have been devised to facilitate C-C bond cleavage.[2-3] Recently, plasmon-enhanced catalysis has demonstrated dramatic enhancement factors for chemical processes including water splitting (i.e.>10x)[4], carbon monoxide oxidation (i.e.>100x)[5] and hot-electron driven dissociation of H2[6]. T he incorporation of plasmonic nanoparticles (NPs)/arrays in semiconductor-metal composites is believed to allow for direct-electron transfer and/or plasmon-induced resonance energy transfer processes at the band-edge of the adjacent semiconductor.[7] The plasmonic-enhanced catalytic activity is attributed to a combination of processes such as (i) traditional electrochemical oxidation, (ii) localized electric-field enhancement, (iii) localized surface plasmon resonance (LSPR), (iv) localized heati
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