Pre-Equilibrium Reaction Mechanism as a Strategy to Enhance Rate and Lower Overpotential in Electrocatalysis.

Pre-equilibrium reaction kinetics enable the overall rate of a catalytic reaction to be orders of magnitude faster than the rate-determining step. Herein, we demonstrate how pre-equilibrium kinetics can be applied to breaking the linear free-energy relationship (LFER) for electrocatalysis, leading to rate enhancement 5 orders of magnitude and lowering of overpotential to approximately thermoneutral. This approach is applied to pre-equilibrium formation of a metal-hydride intermediate to achieve fast formate formation rates from CO 2 reduction without loss of selectivity (i.e., H 2 evolution). Fast pre-equilibrium metal-hydride formation, at 10 8 M -1 s -1 , boosts the CO 2 electroreduction to formate rate up to 296 s -1 . Compared with molecular catalysts that have similar overpotential, this rate is enhanced by 5 orders of magnitude. As an alternative comparison, overpotential is lowered by ∼50 mV compared to catalysts with a similar rate. The principles elucidated here to obtain pre-equilibrium reaction kinetics via catalyst design are general. Design and development that builds on these principles should be possible in both molecular homogeneous and heterogeneous electrocatalysis.