Insights into Metal–Organic Framework-Derived Copper Clusters for CO₂ Electroreduction

Abstract

The unique material properties of metal–organic frameworks (MOFs) (e.g., high porosity, facile modularity, and isolated sites) have highlighted their potential as a next-generation electrocatalyst candidate. However, utilizing MOFs as electrocatalysts necessitates investigations into the changes to the MOF structure under electrochemical bias and subsequent identification and benchmarking of structure–function relationships. Herein, we demonstrate the synthesis of a Cu-based MOF (HKUST-1) film from an in situ nucleation and film growth procedure and the morphological and structural transformation of the said film under electrochemical bias. Additionally, we benchmark the resulting MOF-derived (MOF-d) Cu-based material for electrochemical CO2 reduction (CO2R) applications. Both ex situ and in situ characterization methods highlight substantial morphological and structural changes to the HKUST-1 film during electrochemical CO2R in CO2-saturated 0.1 M KHCO3 aqueous supporting electrolytes. We found that a MOF-d film containing Cu clusters was formed during the electrolysis under a cathodic bias. Potential-dependent CO2R electrolysis experiments show that the normalized current density for CO2R production of the MOF-d Cu film when normalized by the electrochemically active surface area (ECSA) converges to the ECSA-normalized current densities for previously reported nanostructured metallic Cu materials, which indicates that the MOF-d Cu films function as a high surface area, nanostructured Cu electrode for CO2R. These results demonstrate the utility of in situ spectroscopic techniques to examine the morphological and structural changes to the HKUST-1 film under electrochemical bias and provide insights into the electrochemical CO2R activity of the MOF-d Cu film by critically benchmarking its intrinsic reactivity against known materials using established activity descriptors.