(66h) Electrochemical Reduction of CO2 on Metal Doped Graphene
Single atom transition metals embedded at single vacancies of graphene provide a unique paradigm for catalytic reactions.1,2 We present a density functional theory study of such systems for the electrochemical reduction of CO2. Using an explicit description of the solvent at the electrochemical interface, the activation energies for key proton-electron transfer steps were determined. On transition metals, the first proton transfer (*CO + H+ + e- -> *CHO) has been shown to be the critical rate determining step in C1 product formation. On these single atom sites, the corresponding barrier scales more favorably with the CO binding energy than for 211 and 111 transition metal surfaces, in the direction of improved activity.3 Hydrogen evolution intermediates, on the other hand, are found to less stable than those on transition metals, which suggests a lower hydrogen evolution activity. Using a simple microkinetic model based on the calculated electrochemical barriers, we present a rate volcano for the production of methane from CO. All the considered transition metal dopants (Cr, Mo, W, Mn, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, and Cu) form stable doped-graphene structures, and a subset of these dopants (Ru, Fe, Ni, Pd, Pt, Rh, Co, and Ni) are not expected to be poisoned by oxide species. The presence of nitrogen near the active site was found to affect intermediate and transition state energies, but variations in these energetics followed the same scaling determined for these materials without nitrogen. We identify promising candidates with high activity, stability, and selectivity for the reduction of CO2. This work highlights the potential of these systems as improved electrocatalysts over pure transition metals for CO2 reduction.
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