Dynamic Electrocatalysis: Examining Resonant Catalytic Rate Enhancement Under Oscillating Electrochemical Potential

It has been shown through recent simulations that heterogeneous catalysts with dynamic properties – for example, the ability to vary adsorbate binding energy with time – could, in principle, reach higher turnover frequencies (TOFs) than an optimized catalyst operating at steady state (i.e. the “volcano curve” maximum, assuming typical scaling relations between elementary steps of the reaction). The enhancements are maximized near resonant frequencies in line with the time scales of the elementary steps. In this work, we perform a microkinetic analysis on a generalized electrochemical mechanism in order to evaluate the extent to which electrochemical potential can be used as a lever to achieve resonant catalytic rate enhancement. We illustrate that, because changing the electrochemical potential changes the free energy of reaction, the approach is conceptually distinct from oscillating binding energies of catalytic intermediates in isolation. However, benchmarks for rate and efficiency gains relative to potentiostatic operation can still be defined. We show that for faradaic reactions in series, no enhancements relative to the maximum steady-state TOF (within the potential range spanned by oscillation) can be achieved, even in cases where the dynamic potential limits favor adsorption and desorption, respectively. Enhancements relative to the average steady-state TOF (weighted by time at each potential), can be achieved at specific frequency/amplitude/duty cycle combinations, but only if the elementary reactions show disparate symmetry factors. In contrast, if a faradaically-driven parallel reaction controls the coverage of a strongly-adsorbed blocking species on a surface, significant dynamic rate enhancements over the maximum steady-state TOFs can be achieved, albeit at a significant cost of thermodynamic efficiency. We discuss how these simulations elucidate the possible sources of rate enhancements observed experimentally for dynamic electrocatalytic systems.