Redox non-innocent ligand-controlled selective CO₂ reduction to HCOOH by a Co(II) catalyst

The electrochemical reduction of carbon dioxide (CO₂) to value-added chemicals presents a promising pathway for sustainable carbon management. Herein, we report a homogeneous cobalt-based molecular electrocatalyst [Co(N3Q3)(H₂O)Cl]Cl [Co1] {where N3Q3 = N,N-bis(quinolin-8-ylmethyl)quinolin-8-amine} that selectively converts CO₂ to HCOOH with high selectivity by utilizing H₂O as a proton source. The catalyst exhibits a high selectivity of 91% toward HCOOH formation at an applied potential of -2.0 V vs. Fc^+/0, demonstrating strong product selectivity and minimal competitive hydrogen evolution. Kinetic analysis reveals a turnover frequency TOF_max of 1780 s^-1, highlighting the rapid catalytic turnover enabled by the cobalt center and its tailored ligand environment. The study confirms that electrocatalyst [Co1] was highly effective in converting CO₂ to HCOOH via a 2H⁺/2e^- reduction process with an overpotential of 500 mV. Structural and electrochemical investigations suggest that the catalysis proceeds through the formation of a Co-H intermediate, which undergoes a CO₂ insertion reaction to generate HCOOH as the end product. DFT calculations lend support to the experimental findings and indicate that the formation of HCOOH is more feasible than CO.