Proton Tunneling Distances for Metal Hydrides Formation Manage the Selectivity of Electrochemical CO₂ Reduction Reaction

Abstract

A series of manganese polypyridine complexes were prepared as CO2 reduction electrocatalysts. Among these catalysts, the intramolecular proton tunneling distance for metal hydride formation (PTD‐MH) vary from 2.400 to 2.696 Å while the structural, energetic, and electronic factors remain essentially similar to each other. The experimental and theoretical results revealed that the selectivity of CO2 reduction reaction (CO2RR) is dominated by the intramolecular PTD‐MH within a difference of ca. 0.3 Å. Specifically, the catalyst functionalized with a pendent phenol group featuring a slightly longer PTD‐MH favors the binding of proton to the [Mn−CO2] adduct rather than the Mn center and results in ca. 100 % selectivity for CO product. In contrast, decreasing the PTD‐MH by attaching a dangling tertiary amine in the same catalyst skeleton facilitates the proton binding on the Mn center and switches the product from CO to HCOOH with a selectivity of 86 %.

Effect of Variable Amine Pendants in the Secondary Coordination Sphere of Manganese Bipyridine Complexes on the Electrochemical CO2 Reduction

“…Simultaneously, a novel intermediate characterized by stretches at 1984 and 1884 cm −1 becomes increasingly prominent (Figures 4a and S8), which is consistent with the formation of MnH . As noted, the hydride species is formed from Mn − that is reacting with the protons transferred from the acid through the pendant amine groups [9a,19,31] . Moreover, MnH is instrumental in the production of formate and hydrogen (Eqs.…”

Mechanistic insights of electrocatalytic CO2 reduction by Mn complexes: synergistic effects of the ligands

“…However, the catalytic mechanisms of pyrox based Mn complexes and the distinctions between pyrox-based and bpy-based catalysts have not been theoretically studied. As we are deeply interested in the mechanism of Mn electrocatalytic reduction of CO 2 , 62–66 an in-depth theoretical study of the mechanism of pyrox-based Mn complexes was carried out. In our study, the electrocatalytic mechanisms of CO 2 reduction by the Mn complexes Cat1–Cat3 were investigated at the outset.…”

Bio-inspired bimetallic models for electrochemical CO2 reduction

“…Our previous work had found that the proximity of the second coordination sphere to the catalytic center in fac-Mn(bpy-R)(CO) 3 Br (bpy-R = 6-(2-phenol)-2,2′bipyridine) complex is more feasible than the Fe porphyrin derivates, owing to the face-to-face rotation of the second coordination sphere and the Mn(CO) 3 cluster. 17 Previously, Kubiak had characterized the solid structure of a [fac-Re(bpy-t Bu)(CO) 3 ] − species stabilized by potassium 18-crown-6. 18 In this manuscript, we integrate the K N 18C6 into the framework of [fac-Re(bpy)(CO) 3 Cl] as the second coordination sphere by three pathways and obtained a family of heterobimetallic models for CO 2 -to-CO conversion (Chart 1).…”