Beyond Steady-state Kinetics: Improving Catalytic Activity through Potential Oscillation

Reactions that proceed via dissociative mechanisms have competing requirements, namely empty sites for the dissociation step and high coverage of species for the subsequent product formation. This competition reduces activity and selectivity under steady-state conditions and allows for improved catalytic activity by potential oscillation. We analyze steady-state and potential oscillation kinetics at three levels of complexity, first with a simple model based on surface coverages, then with a DFT-informed microkinetic model for electrochemical ammonia formation on the Ru(111) surface, and finally by using the microkinetic model for Co, Fe and high-entropy alloy (111) surface sites. We use the potential oscillation to alternate the coverages of intermediate species on catalyst surfaces. In the case of the ammonia synthesis, we alternate between low H* coverage for N₂ dissociation and high H* coverage for NH3 formation. We find that potential oscillation, in general, moves catalysts closer to the apex of the Sabatier volcano, which allows for higher time-averaged NH₃ formation rates and substantial improvements in faradaic efficiencies. We believe that the emergence of proton-conducting membranes make it experimentally realizable to oscillate the electric potential, alternate the availability of reactant hydrogen, and possibly obtain the predicted catalytic activity improvement for e.g. electrochemical ammonia production.