Electro-Catalysis for H $$_2$$ 2 O Oxidation and Chlorine Evolution

Electrocalaysts facilitate the transformation of renewable electrical energy into chemical feedstocks and fuels. However, our limited understanding of electrocatalysis limits our ability to design the catalysts needed to enable a renewable energy economy. Chlorine production through the chlorine evolution reaction (CER) is one of the few industrially relevant electrocatalytic reactions. Modern analytic methods struggle to probe the electrified solid/liquid interface, which has constrained our ability to develop mechanistic understanding. Ab initio computations do not suffer the same difficulty and can be employed to study the electrocatalytic chemistry occurring at electrified solid/liquid interfaces. A major hurdle with the application of ab initio methods is, however, the large computational cost associated with such simulations. Unlike gas-phase catalysis, accurate treatment of the electrolyte/solid interface requires 100s to 1000s of atoms for minimal simulations, and finite temperature effects must be included to prevent electrolyte freezing. Thus, realistic study of even the simplest electrocatalytic system requires long ab initio quality molecular dynamics simulations. In the first phase of the ECHO project we demonstrated such simulations are feasible using efficient density functional theory (DFT) codes on modern supercomputers and went on to uncover the unexpected role of surface oxidation state in the oxygen evolution reaction (OER) over iridium oxide. In this extension of the ECHO project, we have extend this approach to study the CER over iridium oxides. This system is especially pertinent owing to the scale of chlorine production. It also offers a relative simple system with which to study electrocatalytic selectivity, which proves to be more complex than selectivity in thermal catalysis. These results are highlighted, and, as they were only possible due to the efficient scaling of our approach on Hawk, a discussion about parallelization strategies is also included.