Resolving reaction pathways under constant potential from first-principles calculations is important for understanding electrocatalysis phenomena. Here we report a charge-induced structure relaxation effect that has been mostly overlooked in previous constant-potential simulations. This effect increases the effective capacitance of certain transition states in the high voltage range, resulting in a steeper slope in the reaction barrier versus applied voltage plot. We have developed two computational methods to include this effect: one is a direct saddle point search algorithm under constant voltage with both atomic positions and number of electrons as free variables; the other is a correction scheme based on the full Hessian matrix calculated at zero-charge. Accurate voltage dependent barriers from these methods can help to better understand the rate-limiting step and selectivity in electrocatalysis. Applying these methods to the O-O bond formation reaction on RuO2 (110), we find the proton coupled electron transfer (PCET) mechanism has a lower barrier compared to the water dissociation pathway under voltages of interest. And the saddle point of PCET has a strong charge-structure coupling effect. Moreover, different from the common belief that OOH must be visited as an intermediate, we show that OOH is actually not along the minimum energy path at 1.6 V vs. SHE. We believe that our results provide new insights into the highest oxygen evolution activity of RuO2 and will be useful in new catalyst design.

Simulation of potential-dependent activation energies in electrocatalysis: Mechanism of O−O bond formation on RuO2

ACS Fall 2021

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