A Cobalt Biphenanthroline Complex/Carbon Nanotubes Hybrid as Robust and Efficient Electrocatalyst for Nitrite Reduction to Ammonia

Electrocatalytic nitrite reduction (NO₂RR) based on transition metal complexes is a promising approach for the production of ammonia under mild conditions. Herein, we report a NO₂RR hybrid catalytic system based on a cationic cobalt complex with a planar 2,2′-bi-1,10-phenanthroline ligand (biphen), [Cobiphen]²⁺, that is immobilized on multiwalled COOH-functionalized carbon nanotubes (Cobiphen/CNT). This hybrid is a highly robust and efficient electrocatalyst for NO₂RR, with fast NH₃ production rate, high current density, and Faradaic efficiency approaching 100%. Such performance is attributed to strong binding and electronic communication of Cobiphen with CNT via π-π interactions between the extended aromatic rings of biphen with CNT, which is reinforced by the coordination of the COOH of CNT to the cationic cobalt center. DFT calculations were performed to provide insights into the mechanism.