Tailoring Chemical Composition To Achieve Enhanced Methanol Oxidation Reaction and Methanol-Tolerant Oxygen Reduction Reaction Performance in Palladium-Based Nanowire Systems

摘要

In this article, we address two key challenges in the development of electrocatalysts for direct methanol fuel cells by rationally tailoring the morphology and chemical composition of Pd-based nanowires (NWs) for enhanced performance. First, we have examined the morphology and composition-dependent performance of Pt_(1-x)Pd_x NWs toward the methanol oxidation reaction (MOR). Elemental Pt NWs were found to possess a significant morphology-dependent enhancement of nearly 3-fold in terms of peak MOR-specific activity over that of commercial Pt NP/C. In addition, tailoring the chemical composition in Pt_(1-x)Pd_x NWs can lead to measurable increases in MOR kinetics, which can be attributed to improved oxidation of formic acid and, potentially, increased selectivity for a direct, CO-free pathway. Second, we have explored the stability of ORR performance in the presence of measurable concentrations of methanol as a function of chemical composition in Pt_(1-x)Pd_x NWs and Pt-free Pd9Au NWs. In the context of the Pt_(1-x)Pd_x NWs, a distinctive volcano-type dependence has been noted with respect to chemical composition, and on the basis of the MOR activities and methanol tolerant ORR behavior, Pt7Pd3 NWs have been highlighted as an optimal catalyst architecture. We have also analyzed the methanol tolerance in Pd9Au NWs, which represents a highly active, durable Ptfree alternative to traditional Pt-based nanostructured catalysts. Herein, we have demonstrated that Pd9Au NWs (0.42 mA/cm~2) with no effective Pt content can outperform Pt-based nanostructures, such as Pt NWs (0.32 mA/cm~2) and nanoparticulate Pt NP/C (0.24 mA/cm~2) in the presence of 4 mM methanol/0.1 M HClO4.