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 CO₂ reduction without loss of selectivity (i.e., H₂ evolution). Fast pre-equilibrium metal-hydride formation, at 10⁸ M^-1 s^-1, boosts the CO₂ 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.

We have developed an electrical-biological hybrid system wherein an engineered microorganism consumes electrocatalytically produced formate from CO₂ to supplement the bioproduction of isobutanol, a valuable fuel chemical. Biological CO₂ sequestration is notoriously slow compared to electrochemical CO₂ reduction, while electrochemical methods struggle to generate carbon-carbon bonds which readily form in biological systems. A hybrid system provides a promising method for combining the benefits of both biology and electrochemistry. Previously, Escherichia coli was engineered to assimilate formate and CO₂ in central metabolism using the reductive glycine pathway. In this work, we have shown that chemical production in E. coli can benefit from single carbon substrates when equipped with the RGP. By installing the RGP and the isobutanol biosynthetic pathway into E. coli and by further genetic modifications, we have generated a strain of E. coli that can consume formate and produce isobutanol at a yield of >100% of theoretical maximum from glucose. Our results demonstrate that carbon produced from electrocatalytically reduced CO₂ can bolster chemical production in E. coli. This study shows that E. coli can be engineered towards carbon efficient methods of chemical production.