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 rela-tionship (LFER) for electrocatalysis, leading to rate enhancement five orders of magnitude and lowering of overpotential by 100 mV to almost thermoneutral at 10 mV. This approach is applied to pre-equilibrium formation of a metal-hydride interme-diate to achieve fast formate formation rates from CO2 reduction without loss of selectivity (ie. H2 evolution). Fast pre-equilibrium metal-hydride formation, at 108 M-1s-1, boosts the CO2 electroreduction to formate rate up to 5.26 × 102 s-1 at an overpotential of just ~10 mV. Compared with molecular catalysts that have similar overpotential, this rate is enhanced by five orders of magnitude. As an alternative comparison, overpotential is lowered by 100 mV compared to catalysts with similar rate. The principles elucidated here to obtain pre-equilibrium reaction kinetics via catalyst design are general. Design and devel-opment that builds on these principles should be possible in both molecular homogeneous and heterogeneous electrocatalysis.