On the promotional effect of Cu on Pt for hydrazine electrooxidation in alkaline medium

Abstract

Pt/C and PtCu/C electrocatalysts with nominal Pt:Cu atomic ratios of 75:25, 50:50, and 25:75 were prepared using N2H4 as reducing agent and carbon black Vulcan XC-72R as support. The obtained materials were physically characterized by X-ray diffraction, Energy-Dispersive X-ray analysis, Transmission Electron Microscopy images, X-ray Photoelectron Spectroscopy (XPS), and Temperature-Programmed Reduction analysis. Cyclic voltammetry, linear sweep voltammetry, and chronoamperometry (TPR) measurements were carried out in a three-electrode glass cell to evaluate the electrochemical activity towards hydrazine electrooxidation in alkaline medium along with single-cell direct hydrazine fuel cell (DHFC) tests. The actual composition of the electrocatalysts evidenced a slightly lower Cu fraction compared to the nominal one. The X-ray diffractograms of the electrocatalysts showed the typical face-centered cubic structure of Pt alloys, with the highest fraction of Cu alloyed to Pt being achieved with the almost equiatomic catalyst. An important fraction of the remaining non-alloyed Cu is in the form of a copper oxide, as evidenced by XPS and TPR measurements. The electrochemical tests evidenced that the coexistence of part of the Cu alloyed with Pt and copper oxide achieved in the PtCu/C electrocatalysts enhances the performance compared to Pt/C. In particular, the optimum formulation is attained by the Pt53Cu47/C electrocatalyst, allowing maximization of the electrocatalytic activity towards hydrazine electrooxidation and the single-cell performance at 60 and 80 °C.