Tailoring a Pt-Ru catalyst for enhanced methanol electro-oxidation

Abstract

A carbon-supported (1:1) Pt-Ru (Pt-Ru/C) alloy catalyst has been prepared in-house by the sulfito-complex route, and has been tailored to achieve enhanced activity towards methanol electro-oxidation by annealing it at varying temperatures in air. The catalyst samples annealed between 250 and 300 °C in air for 30 min exhibit superior catalytic activity towards methanol electro-oxidation in a solid-polymer-electrolyte direct methanol fuel cell (SPE-DMFCs) operating at 90 °C. Both the as-prepared and annealed Pt-Ru/C catalysts have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and cyclic voltammetry. It is conjectured that while annealing the Pt-Ru/C catalysts, both Pt-Pt and Pt-Ru bonds increase whereas the PtO bond shrinks. This is accompanied with a positive variation in Ru/Pt metal ratio suggesting the diffusion of Ru metal from the bulk catalyst to surface with an increase in oxidic ruthenium content. Such a treatment appears seminal for enhancing the electrochemical activity of Pt-Ru catalysts towards methanol oxidation.