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

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 angstrom 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 angstrom. 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 %.

Automated summary

A series of manganese polypyridine complexes were investigated as CO2 reduction electrocatalysts. The intramolecular proton tunneling distance significantly affected the selectivity of the CO2 reduction reaction, with a difference of approximately 0.3 angstroms. Catalysts with longer intramolecular proton tunneling distances favored proton binding to the [Mn-CO2] adduct, resulting in 100% selectivity for CO production. In contrast, catalysts with shorter distances showed a switch in product from CO to HCOOH with a selectivity of 86%.