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Kinetics of Hydride Transfer from Metal-Free Hydride Donors to CO2
preprintsubmitted on 27.11.2020, 15:35 and posted on 30.11.2020, 08:52 by Ravindra Weerasooriya, Jonathan L. Gesiorski, Abdulaziz Alherz, Stefan Ilic, George Hargenrader, Charles B. Musgrave, Ksenija Glusac
Selective reduction of CO2 to formate represents an ongoing challenge in photoelectrocatalysis. To provide mechanistic insights, we investigate the kinetics of hydride transfer (HT) from a series of metal-free hydride donors to CO2. The observed dependence of experimental and calculated HT barriers on the thermodynamic driving force was modeled using the Marcus hydride transfer formalism to obtain the insights into the effect of reorganization energies on the reaction kinetics. Our results indicate that, even if the most ideal hydride donor were discovered, the HT to CO2 would exhibit sluggish kinetics (less than 100 turnovers at 0.1 eV driving force), indicating that the conventional HT may not be an appropriate mechanism for Solar conversion of CO2 to formate. We propose that the conventional HT mechanism should not be considered for CO2 reduction catalysis and argue that the orthogonal HT mechanism, previously proposed to address thermodynamic limitations of this reaction, may also lead to lower kinetic barriers for CO2 reduction to formate.