Tailoring Coordination Microenvironment of Cu(I) in Metal–Organic Frameworks for Enhancing Electroreduction of CO₂to CH₄

Abstract

The coordination microenvironment of metal active sites in metal–organic frameworks (MOFs) plays a crucial role in its performance for electrochemical CO2 reduction reaction (CO2RR). However, it remains a challenge to clarify the structure–performance relationship for CO2RR catalyzed by MOFs. Herein, a series of MOFs with different coordination microenvironments of Cu(I) sites (CuCl, CuBr, and CuI) to evaluate their performances for CO2RR is synthesized. With the increasing radius of halogen atom, the CO2 adsorption capacity increases and d‐band center of Cu positively shifts to the Fermi level, leading to enhance the selectivity of CO2 to CH4 conversion. CuI gives the highest total Faradaic efficiency (FE) of 83.2%, with a FE of CH4 up to 57.2% and CH4 partial current density of 60.7 mA cm−2 at −1.08 V versus reversible hydrogen electrode. Theoretical calculations reveal that the shifted d‐band center of Cu site contributes to reduced formation energies of *CH2O and *CH3O intermediates, which is the potential‐determining step of CO2RR and thus facilitates the electrocatalytic CO2 reduction to CH4. This study opens a new avenue for studying the relationship between the coordination microenvironment of active site and electroreduction reaction performance of MOFs.

Rational Design of Metal–Organic Frameworks for Electroreduction of CO2 to Hydrocarbons and Carbon Oxygenates

“…Therefore, the CO species can bind tightly on the CuO 5 site to form a more stable *CO intermediate (binding energy of −73.4 kJ mol –1 for the CuO 5 site versus that of −48.6 kJ mol –1 for the CuO 4 site in Cu-DBC ) (Figure a), as being verified by PDFT calculations, which promotes further hydrogenation of *CO to yield CH 4 . Similarly, Sun et al designed a series of MOFs with Cu 4 X (X = Cl, Br, or I) clusters (denoted as Cu–Cl , Cu–Br , and Cu–I , respectively) (Figure b) and elaborated the effect of halogen ligand on the electron structure of Cu site for ECR . According to the DFT results, with the increasing radius of the halogen atom from Cl to I, the d- band center of the Cu site positively shifts to the Fermi level, and the formation energies of the key intermediates *CH 2 O and *CH 3 O were successively reduced, leading to an enhanced Faradaic efficiency of CH 4 .…”

“…(a) Optimization of coordination geometry, (b) Decreasing the electronegativity of a coordinated atom, (c) enhancement of cuprophilic interaction, and (d) intensification of an electron-donating effect. Adapted with permission from refs , , and . Copyright 2021 and 2022 American Chemical Society, and from ref .…”

“… 57 Similarly, Sun et al designed a series of MOFs with Cu 4 X (X = Cl, Br, or I) clusters (denoted as Cu–Cl , Cu–Br , and Cu–I , respectively) ( Figure 5 b) and elaborated the effect of halogen ligand on the electron structure of Cu site for ECR. 59 According to the DFT results, with the increasing radius of the halogen atom from Cl to I, the d- band center of the Cu site positively shifts to the Fermi level, and the formation energies of the key intermediates *CH 2 O and *CH 3 O were successively reduced, leading to an enhanced Faradaic efficiency of CH 4 . Apart from the design of ligands, metal–metal interactions also have an impact on the electron structure of the metal ions.…”

“…59 According to the DFT results, with the increasing radius of the halogen atom from Cl to I, the d-band center of the Cu site positively shifts to the Fermi level, and the formation energies of the key intermediates *CH 2 O and *CH 3 O were successively reduced, leading to an enhanced Faradaic efficiency of CH 4 . Apart from the design of ligands, metal−metal interactions also have an impact on the electron structure of the metal ions.…”

Nitrogen-Adsorbed Hydrogen Species Promote CO2 Methanation on Cu Single-Atom Electrocatalyst

“…Previous studies have suggested that the CO 2 -to-CH 4 conversion undergoes multiple proton-coupled electron transfer steps, 28 while the *H adsorption sites for CO 2 protonation are still not clear. We first conducted hydrogen evolution reaction (HER) measurements to investigate water electrolysis for nitrogen-doped (N−C) and undoped carbon (C) materials.…”