Theoretical insight on reactivity trends in CO2 electroreduction across transition metals

Abstract

Density Functional Theory (DFT) based models have been widely applied towards investigating and correlating the reaction mechanism of CO₂ electroreduction (ER) to the activity and selectivity of potential electrocatalysts. Herein, we examine the implications of the theoretical choices used in DFT models that impact the stability of the reaction intermediates and the limiting potential (U_L) of the activity/selectivity determining steps in CO₂ ER across transition metals. Three theoretical choices are considered: (i) the type of exchange-correlation (XC) functional, (ii) the surface facet of the metal electrocatalyst, and (iii) the effect of solvation. The impact of the theoretical choices is also studied in the context of deriving scaling relationships for electrocatalyst screening. The analyses reveal that the choice of XC functional (PBE versus RPBE) can alter binding energies of CO₂ ER intermediates by 0.30 eV, but have little impact on surface reaction energetics. Surface termination has greater impact, as OH*-terminated adsorbates bind weaker on average by 0.26 eV on stepped facets. Including explicit local solvation stabilizes the OH*-terminated adsorbates, preferentially decreasing the U_L for CO* → COH* reduction. Trends in CO₂ ER selectivity across metals predicted using scaling correlations differ signficantly from explicitly calculated values due to deviations from the linear binding energy correlations. The difference is most pronounced when the effect of explicit solvation is considered.