An MOF-derived copper@nitrogen-doped carbon composite: the synergistic effects of N-types and copper on selective CO2 electroreduction

Abstract

The development of Cu-based complex electrocatalysts can lead to the facile realization of high activity and selectivity for reducing CO₂ to multi-carbon hydrocarbons; exploring the synergistic effect between Cu and other materials may help in designing highly efficient catalysts. This paper reports an impact factor for synergistic effects between Cu and nitrogen-doped carbon (NC) supports by comparing CO₂ reduction reaction (CO₂RR) performances on MOF-derived copper@nitrogen-doped carbon (Cu–NC) catalysts obtained by the calcination of N-containing benzimidazole-modified Cu-BTC (1,3,5-benzenetricarboxylic acid) MOFs (BEN-Cu-BTC) at different temperatures. Different types of Cu–NC samples show the N species- and content-dependent catalysis for the highly selective electroreduction of CO₂ to C₂ products. The characterization and experimental results indicate that the high contents of pyrrolic-N and Cu–N species formed at the annealing temperature of 400 °C can facilitate the C₂-product generation on a Cu surface, with the reaction rates and Faradaic efficiencies (FEs) for ethylene and ethanol being r_ethylene = 5.38 μmol m⁻² s⁻¹ (FE = 11.2%) and r_ethanol = 8.83 μmol m⁻² s⁻¹ (FE = 18.4%) at −1.01 V (vs. reversible hydrogen electrode (RHE)), respectively. However, excess graphitic-N and oxidized-N on the Cu surface result in considerable H₂ evolution and a rapid decrease in the CO₂RR activity. These may occur due to the differences in the adsorption and valence state affecting the Cu–NC interactions. These results indicate that the catalytic activity on MOF-derived Cu–NC catalysts can be controlled by the N-type species that dominates at the corresponding annealing temperature, offering a new tack for designing highly selective complex catalysts since the electrocatalytic performance of the Cu–NC catalysts remains stable over 8 h.