Designing Catalytic Systems Using Binary Solvent Mixtures: Impact of Mole Fraction of Water on Hydride Transfer

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 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.

Recent developments in first-row transition metal complex-catalyzed CO2 hydrogenation

Our modern civilization is currently standing at a crossroads due to excessive emission of anthropogenic CO₂ leading to adverse climate change effects. Hence, a proper CO₂ management strategy, including appropriate CO₂ capture, utilization, and storage (CCUS), has become a prime concern globally. On the other hand, C₁ chemicals such as methanol (CH₃OH) and formic acid (HCOOH) have emerged as leading materials for a wide range of applications in various industries, including chemical, biochemical, pharmaceutical, agrochemical, and even energy sectors. Hence, there is a concerted effort to bridge the gap between CO₂ management and methanol/formic acid production by employing CO₂ as a C₁-synthon. CO₂ hydrogenation to methanol and formic acid has emerged as one of the primary routes for directly converting CO₂ to a copious amount of methanol and formate, which is typically catalyzed by transition metal complexes. In this frontier article, we have primarily discussed the abundant first-row transition metal-driven hydrogenation reaction that has exhibited a significant surge in activity over the past few years. We have also highlighted the potential future direction of the research while incorporating a comparative analysis for the competitive second and third-row transition metal-based hydrogenation.