Selective CO₂ Reduction in Tap-Water Electrolyte Catalyzed by Impurity-Resistant Mn-Complex Supported on Carbon

Electrocatalysts have been developed for reducing CO2 to value-added chemicals. Although numerous metal catalysts have been reported, trace amounts of impurities such as Fe in the electrolytes deactivate the metal catalysts by deposition of metallic impurities onto their surface, generating the active sites for hydrogen evolution. To address this issue, numerous researchers have developed strategies to sustain catalytic performance. The present work demonstrates that a Mn-complex supported on multiwalled carbon nanotubes can selectively reduce CO2 in the presence of impurities when a tap water-based electrolyte is used. Even when ionic metals and 15 vol % O2 are present, our catalyst can selectively reduce CO2 to CO with a Faraday efficiency of 87% for 12 h. Whereas a Ag electrode was deactivated by metallic impurities in the electrolyte, the Mn-complex exhibited stable performance, presumably because its selective coordination with CO2 prevented interference from metal ionic impurities. Operando surface enhanced Raman spectroscopy revealed the importance of the coordination properties of a metal complex for selective CO2 reduction in the presence of ionic impurities.