The electro-oxidation of formic acid on Pt–Pd single crystal bimetallic surfaces

Abstract

The interrelationship between the macroscopic kinetic rate of HCOOH oxidation in 0.1 M HClO₄ solution and the morphology/composition of the electrode is studied on Pt(111) modified by Pd (denoted hereafter as the Pt(111)–Pd_xML system, 0 < x < 1) and on Pt–Pd bulk single crystal alloy surfaces (denoted hereafter as the PtPd_xat%(111) system, x = 6 and x = 25). The Pd surface composition of the Pt(111)–Pd_xML and PtPd_xat%(111) electrodes was established previously ex-situ by low energy ion scattering (LEIS) measurements. The nature of adsorbed intermediates (CO_ad) and the electrocatalytic properties (the onset of CO₂ formation) at the Pt(111)–Pd_xML and the PtPd_xat%(111) interface were studied by FTIR spectroscopy. The results show that Pd atoms either on the surface or in the surface have an unique catalytic activity for HCOOH oxidation, with Pd atoms being three (bulk alloys) or five times (Pd films) more active than Pt atoms at 0.4 V. FTIR spectra reveal that on Pt atoms adsorbed CO is produced from dehydration of HCOOH, whereas no CO adsorbed on Pd can be detected although a high production rate of CO₂ is observed at low potentials, indicating that the reaction can proceed on Pd at low potentials without the Pt typical “poison” formation.