Anion Influenced Hydride Formation on Cu(111) during Electrocatalysis

Abstract

In aqueous systems several environmentally relevant proton-coupled electron transfer reactions such as the reduction of O2, NO3, CO or CO2 are known to proceed on Cu surfaces in combination with proton and/or water reduction. Among these, the electrochemical reduction of CO2 receives the most attention because of Cu’s unique ability to produce varying degrees of hydrogenated multicarbon products. Despite intense experimental and theoretical studies, understanding of Cu’s facet specific selectivity is still limited especially regarding the role of H in hydrogenation steps. Using operando electrochemical mass spectrometry (ECMS) and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) this work identifies the existence of surface hydride on Cu(111) (Figure 1a) under conditions relevant for the aforementioned reduction reactions. The identified surface hydride is significantly impacted to changes in electrolyte composition, such as the cation, anion or dissolved gas species and likely has significant impact over electrocatalytic performance. ECMS plots (Figure 1b) of hydride formation and decomposition show that the stronger the binding affinity of the anion to the Cu(111) surface the larger the overpotential required for hydride formation (e.g. Cl- vs ClO4 -). Likewise, decomposition occurs at more negative potentials. Peak areas of respective vibrational modes (Figure 1 c-d) corroborate the ECMS data, also demonstrating that in the presence of Cl- (vs SO4 2-) both hydride formation and decomposition shifts negatively by nearly 100 mV. These dynamics among other more quantitative analysis of hydride coverage and kinetics will be presented within this talk. Figure 1