Highly Selective Electrocatalytic CO<sub>2</sub> Reduction by [Pt(dmpe)<sub>2</sub>]<sup>2+</sup> through Kinetic and Thermodynamic Control
Bianca M. Ceballos, Jenny Y. Yang
Abstract
CO2 reduction pathways for sustainable fuel generation are often limited by product selectivity for carbon-based products or a competitive hydrogen evolution reaction (HER). The thermodynamic and kinetic factors that direct the mechanism of [Pt(dmpe)2]2+ (dmpe = 1,2-bis(dimethylphosphino)ethane), a catalyst that reduces CO2 to formate with high Faradaic efficiency and low overpotential, is explored. Quantitative measurements of electron transfer rates, protonation, and CO2 binding at proposed intermediates are used to construct an energy landscape with intermediate energies and relative kinetic barriers. Our findings indicate that rapid protonation at the reduced metal is critical for selective metal hydride formation. Additionally, the rate-limiting step is C–H bond formation by CO2 insertion into the metal hydride or formate (product) release. Ultimately both kinetic and thermodynamic control lead to high selectivity for HCO2– by favoring a protonation-first pathway, followed by the exergonic reaction of the hydride with CO2. This quantitative mechanistic study outlines key factors that control competitive reactivity in order to achieve high product selectivity.