Cobalt porphyrin immobilized on the TiO_(2) nanotube electrode for CO2 electroreduction in aqueous solution

Herein we report CO_(2) electrochemical reduction reaction(CO_(2) ERR)on the cobalt tetraphenylporphyrin(Co TPP)modified TiO_(2) nanotube(TNT)electrode.It was found the axial coordination of drop-casting solvent to Co TPP and the porphyrin structure are the major factors that have significant effects on the catalytic performance of the electrode.As confirmed by spectrophotometric titration,pyridine has a stronger coordination bond to Co TPP than DMF and THF thus leading to the highest efficiency among the dropcasting solvents tested in the study.Based on the spectrophotometric analysis,possible coordination mechanism between drop-casting solvents and Co TPP is put forward.On the other hand,introduction of-COOMe substituents in phenyl rings of Co TPP weakens the coordination bond between pyridine and Co TPP as clearly evidenced by deuterium NMR spectra,resulting in a detrimental effect on CO_(2) ERR.Therefore,the manipulation of the coordination environment around the metal center of immobilized catalyst is crucial in designing an efficient electrocatalytic system.