Low-Energy Electrocatalytic CO₂ Reduction in Water over Mn-Complex Catalyst Electrode Aided by a Nanocarbon Support and K⁺ Cations

Electrocatalytic CO 2 reduction over a Mn-complex catalyst in an aqueous solution was achieved at very low energy with a combination of multiwalled carbon nanotubes (MWCNTs) and K + cations. Although the bare Mn-complex did not function as a catalyst in an aqueous solution, the combined Mn-complex/MWCNT cathode promoted electrocatalytic CO 2 reduction at an overpotential of 100 mV where neither the bare MWCNTs nor bare Mn-complex were catalytically active. The Mn-complex/MWCNT produced CO at a constant rate for 48 h with a current density of greater than 2.0 mA cm –2 at −0.39 V (vs RHE). The MWCNTs with electron accumulation properties, together with surface adsorbed K + ions, provided an environment to stabilize CO 2 adjacent to the Mn-complex and significantly lowered the overpotential for CO 2 reduction in an aqueous solution, and these results were consistent with density functional theory (DFT) calculations. Experiments clarified that the synergetic effect of the MWCNTs and K + ions was also applicable to Co and Re complexes that were almost inert with regard to CO 2 reduction in an aqueous solution.