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 CO 2 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 CO 2 reduction reaction (CO 2 RR) 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−CO 2 ] 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 %.