The role of coverage effects on the structure-sensitivity of formic acid electrooxidation on Pd surfaces

Direct formic acid (FA) fuel cells (DFAFCs) with Pd anode catalysts are promising for small portable appli-cations. During the electrooxidation of formic acid (FAO), CO accumulates on the Pd electrocatalyst, thereby decreasing its performance. In this work, we use density functional theory (DFT; RPBE) to eluci-date the significance of coverage effects on the structure-sensitivity of FAO over four low-index Pd sur-faces: Pd(1 1 1), Pd(1 0 0), Pd(1 1 0), and Pd(2 1 1). We construct coverage-dependent Gibbs free energy diagrams and in agreement with experiment, predict that Pd(1 0 0) and Pd(2 1 1) are the most active sur-faces. Additionally, we find that the presence of CO spectator species can alter the preferred electrooxi-dation pathway under different applied potentials. Such pathway transitions appear to be critical for rationalizing experimental trends regarding electrocatalytic activity and are only captured when cover -age effects are accounted for. Insights derived from this work may facilitate the design of improved FAO electrocatalysts. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

In this study, the significance of coverage effects on the structure-sensitivity of formic acid electrooxidation (FAO) over Pd surfaces in direct formic acid fuel cells (DFAFCs) with Pd anode catalysts was investigated using density functional theory (DFT). The results showed that Pd(100) and Pd(211) surfaces are the most active surfaces, and the presence of CO spectator species can alter the preferred electrooxidation pathway under different applied potentials. These findings provide insights for the design of improved FAO electrocatalysts.