CO2 Reduction at Low Overvoltage in Neutral Aqueous Solution by Ni-cyclam Attached Polyallylamine Polymer

(cyclam=1,4,8,11 tetraazacyclotetradecane) and its derivatives are known to be efficient in CO ‐ 2 to CO conversion and the macrocyclic ligand, cyclam is known to stabilize Ni(I) state. However, those compounds still have ca. 0.6 V of overvoltages and the use of mercury electrode is essential to suppress hydrogen evolution on the electrode at such a negative potential. We found that the incorporation of the Ni(cyclam) unit into polyallylamine (PALA) backbone by Schiff’s base condensation via axial coordination of 4 pyridine carboxaldehyde is effective in ‐ lowering overvoltage and it enables the catalyst to be used with carbon electrode material in neutral aqueous solution. The resulting redox polymer, Ni(cyclam) PALA converts CO ‐ 2 to CO near its thermodymic potential, 0.78 ‐ V vs. Ag/AgCl in pH 8, 50 mM tris buffer on glassy carbon electrode with current efficiency of over 90%. The axial coordination of 4 pyridine unit is mainly responsible for lowering the overpotential and the attached ‐ polyallylamine partly helps.