First-principles description of electrocatalytic characteristics of graphene-like materials

Graphene-like materials (GLMs) have received much attention as a potential alternative to precious metal-based electrocatalysts. However, the description of their electrocatalytic characteristics may still need to be improved, especially under constant chemical potential. Unlike the case of conventional metal electrodes, the potential drop across the electrical double layer (phi (D)) at the electrode-electrolyte interface can deviate substantially from the applied voltage (phi (app)) due to a shift of the Dirac point (e phi (G)) with charging. This may in turn significantly alter the interfacial capacitance (C-T) and the relationship between phi (app) and free-energy change (Delta F). Hence, accurate evaluation of the electrode contribution is necessary to better understand and optimize the electrocatalytic properties of GLMs. In this work, we revisit and compare first-principles methods available to describe the phi (app)-F relation. Grand-canonical density functional theory is used to determine Delta F as a function of phi (app) or electrode potential (phi (q)), from which the relative contribution of e phi (G) is estimated. In parallel, e phi (G) is directly extracted from a density functional theory analysis of the electronic structure of uncharged GLMs. The results of both methods are found to be in close agreement for pristine graphene, but their predictions deviate noticeably in the presence of adsorbates; the origin of the discrepancy is analyzed and explained. We then evaluate the application of the first-principle methods to prediction of the electrocatalytic processes, taking the reduction (hydrogenation) and oxidation (hydroxylation) reactions on pristine graphene as examples. Our work highlights the vital role of the modification of the electrode electronic structure in determining the electrocatalytic performance of GLMs.