Transition Metal Ion Doping on ZIF-8 Enhances the Electrochemical CO₂ Reduction Reaction

The electrochemical reduction of CO₂  to diverse value-added chemicals is a unique, environmentally friendly approach for curbing greenhouse gas emissions while addressing sluggish catalytic activity and low Faradaic efficiency (FE) of electrocatalysts. Here, zeolite-imidazolate-frameworks-8 (ZIF-8) containing various transition metal ions-Ni, Fe, and Cu-at varying concentrations upon doping are fabricated for the electrocatalytic CO₂ reduction reaction (CO₂ RR) to carbon monoxide (CO) without further processing. Atom coordination environments and theoretical electrocatalytic performance are scrutinized via X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations. Upon optimized Cu doping on ZIF-8, Cu_0.5 Zn_0.5 /ZIF-8 achieves a high partial current density of 11.57 mA cm^-2 and maximum FE for CO of 88.5% at -1.0 V (versus RHE) with a stable catalytic activity over 6 h. Furthermore, the electron-rich sp² C atom facilitates COOH* promotion after Cu doping of ZIF-8, leading to a local effect between the zinc-nitrogen (Zn-N₄ ) and copper-nitrogen (Cu-N₄ ) moieties. Additionally, the advanced CO₂ RR pathway is illustrated from various perspectives, including the pre-H-covered state under the CO₂ RR. The findings expand the pool of efficient metal-organic framework (MOF)-based CO₂ RR catalysts, deeming them viable alternatives to conventional catalysts.