Formate Binding Strength as Strong Descriptor of Formic Acid Oxidation Selectivity over Charged Electrocatalytic Surfaces

Abstract

Formic acid oxidation (FAO) over platinum electrocatalysts has been widely studied as an anodic reaction for fuel cell technologies, but the lack of experimental data accounting for the binding strength of formate intermediates under relevant electrochemical conditions hampers optimization of catalyst–electrolyte interfaces. In this work, we use two-dimensional correlation surface enhanced infrared adsorption spectroscopy (2D COS SEIRAS) to probe the adsorption of formic acid between 25 and 65 °C, and to determine the adsorption enthalpy of formate on platinum (−46 ± 3 kJ mol–1 at −0.2 V vs RHE). Adsorption isotherms collected at different potentials reveal that positively charged platinum surfaces facilitate higher formate coverages despite weaker binding strength. Comparison of adsorption enthalpies and electro oxidation selectivities over platinum and copper catalysts suggests that binding strength to a metal surface is an important descriptor of FAO catalysis. This works provides a method to reliably determine adsorption enthalpies of reaction intermediates under different electrochemical conditions, which will be key to better engineer catalyst systems that promote oxidative conversion of organics.