(704a) Tuning Activity and Selectivity between Chlorine and Oxygen Evolution over Graphene Supported Single Atom Electrocatalysts

The production of Cl₂ and NaOH from chlor-alkali processes is responsible for about half of all turnovers in the chemical industry. The desired reaction to facilitate their production is the chlorine evolution reaction (CER) which directly competes with the oxygen evolution reaction (OER). Likewise, OER is the rate limiting process in seawater electrolysis to produce H₂, but its implementation is stifled by its competition with CER. It has been speculated that the two reactions are correlated on bulk materials, but single atom catalysts with unique electronic properties that deviate from its 3D counterpart due to quantum confinement may be highly selective for either OER or CER.

Graphene-supported single transition atom catalysts (TMN_X@G) have garnered significant popularity for a variety of electrocatalytic reactions owed to their easily tunable structural and electronic properties. In this study, we evaluated the tunability of TMN_X@G catalysts towards the selectivity of Cl₂ and O₂ through a computational study of OER/CER anodes with isolated active sites comprised of a single transition metal atom and N_X ligands (X=1, 2, 3, 4) on graphene supports. We use density functional theory to compute the electrochemical reaction diagrams of both OER and CER for 40 transition metals coordinated with N_X ligands (X=1, 2, 3, 4) for a total of 160 graphene supported catalysts. We also estimated the selectivity between OER and CER based on the reaction energies of the potential determining step. Lastly, we elucidate the effects of N-ligand coordination on the reaction energies and overpotential of each graphene supported transition metal. By understanding the synergistic roles between ligands and dopants we can provide fundamental insights into the tunability of SACs and support efforts to tailor low dimensional materials as high-performance electrocatalysts.