Insights into the Effect of Pb on Formic Acid Electro-Oxidation on Pt

Abstract

Formic acid is a promising energy carrier and electrochemical formic acid oxidation can serve as an important reaction within fuel cells. Although Pt remains the best-known catalyst, but the major currents contributing pathways is indirect oxidation pathways, which leads to poor activities at low potentials. The surface adatoms like Pb have been known to promote the direct oxidation pathways significantly. We have carried out theoretical calculations, and experiments to probe the reason for this enhancement. Theoretical results show an upshift of Pt energy levels above the Fermi energy upon adsorption of Pb on the Pt surface, which influences the binding energy of the adsorbates. Reaction free energy calculations of typical intermediates from water (H2O) and formic acid (HCOOH) molecule indicate that Pb adsorption suppresses the adsorption of Hydrogen atoms at potentials typical of underpotential deposition on Pt electrode. This results in larger number of vacant sites on the Pt surface which is now able to carry out formic acid oxidation to CO2. The calculations were supported by electrochemical experiments of underpotentially deposited hydrogen and potential dependent apparent activation energies. Figure 1