Microenvironment Matters: Copper–Carbon Composites Enable a Highly Efficient Carbon Dioxide Reduction Reaction to C2 Products

Copper is the catalyst widely used to produce multicarbon products for the carbon dioxide reduction reaction (CO₂RR). The surrounding microenvironment of copper plays a crucial role in determining its catalytic activity and selectivity. In this study, we compare three copper electrocatalysts with different microenvironments: pure metallic copper, a copper metal-organic framework (MOF), and a MOF-derived copper-carbon composite. Operando X-ray absorption spectroscopy, transmission electron microscopy, and Raman spectroscopy reveal that copper in the copper-carbon composite remains in a metallic state, encapsulated by a carbon matrix. The composite catalyst achieves a Faradaic efficiency of 75.6% for C₂ products, including ethylene and ethanol, at a current density of 500 mA cm^-2, with a C₂ current density of 377.9 mA cm^-2. This performance suppresses pure metallic copper, which reaches an optimal Faradaic efficiency of 64.5% for C₂ products at a current density of 300 mA cm^-2, with a C₂ current density of 193.5 mA cm^-2. The copper-carbon composite also significantly overperforms the copper-MOF catalyst, which shows an optimal Faradaic efficiency of 52.0% for C₂ products at a current density of 400 mA cm^-2, with a C₂ current density of 208.0 mA cm^-2. These findings highlight the importance of the microenvironment near active copper sites in determining CO₂RR efficiency. We hope that our results provide valuable insights for advancing catalyst design in carbon dioxide reduction, contributing to reduced carbon emissions and improved environmental sustainability.