Revisiting the Electrochemical Reduction of CO₂ on Au₂₅(SR)^-₁₈Nanocluster

Previous experimental breakthrough reveals the potential to create novel heterogeneous catalysts for electroreduction of CO₂ to a high-value product CO using ligand protected Au-based nanoclusters. Since the chemical composition and geometric structures are precisely defined, it is possible to adopt robust design guidelines for the development of practical catalysts and to fundamentally elucidate the underlying reaction mechanism. In this work, the mechanistic aspect of CO₂ reduction reaction (CO₂RR) and hydrogen evolution reaction (HER) on the ligand protected nanocluster was revisited using DFT. Previous theoretical efforts are mainly based on thermodynamic viewpoint. Here, I report the first study that included activation barrier of each elementary step. The potential-dependent reaction and activation free energies were determined by combining Chan-Nørskov capacitor model and the computational hydrogen electrode (CHE) model. The study was able to furnish a much more nuanced view into the multi-step electrocatalytic reactions. From the reassessment of the ability of the nanocluster to release a -SR and -R ligand, it was found that while dealkylation is more thermodynamically feasible, the high calculated barrier indicates that the exposure of S active site is kinetically hindered. In contrast, dethiolation is predicted to be nearly barrierless, suggesting that Au site generation is more favorable in agreement with the experimental observation. From the calculated free energy barriers, CO₂RR on the Au site is predicted to be more active and selective than on the S site, supporting the experimentally observed performance of the dethiolated nanocluster.