Enhancing Alcohol Oxidation Activity Using Carbon-Modified Silicon Oxide Encapsulated Pt Electrodes

Abstract

The performance of direct alcohol fuel cells (DAFCs) is frequently constrained by the efficiencies of the electrocatalysts used for the necessary alcohol oxidation reactions (AORs), which require high overpotentials to remove poisoning CO intermediates from the catalyst surface. Silicon Oxide (SiOx) encapsulated Pt electrodes have previously been shown to reduce the potential required to remove CO, and greatly enhance the activity of Pt-based catalysts for alcohol oxidation. To better understand the mechanism of this enhancement, silicon oxide layers with varying concentrations of residual carbon were employed to probe the compositional effects of overlayer composition on AORs. Overall, it was found that carbon-free, SiOx encapsulated samples exhibited the largest reduction in CO oxidation potential, with carbon rich samples still demonstrating a slight decrease in required potential compared to unencapsulated, bare Pt. Surprisingly, samples that demonstrated the largest reductions in CO oxidation potentials did not show the highest activity enhancement for alcohol oxidation. Instead, samples that had the highest concentration of carbon showed the highest degree of current enhancement for formic acid, methanol, and ethanol oxidation. For larger alcohols like propanol and butanol, the measured activity for alcohol oxidation on encapsulated samples began to diminish, credited to the additional mass transport resistance that the overlayer introduces. These observations offer insights into how the composition and properties of SiOx overlayers can affect the reactivity and transport of species in an electrochemical system, and offer an additional level of design for the development of future electrocatalyst architectures.