Herein we report CO2 electrochemical reduction reaction(CO2ERR)on the cobalt tetraphenylporphyrin(CoTPP)modified TiO2 nanotube(TNT)electrode.It was found the axial coordination of drop-casting sol-vent to CoTPP and the porphyrin structure are the major factors that have significant effects on the cat-alytic performance of the electrode.As confirmed by spectrophotometric titration,pyridine has a stronger coordination bond to CoTPP than DMF and THF thus leading to the highest efficiency among the drop-casting solvents tested in the study.Based on the spectrophotometric analysis,possible coordination mechanism between drop-casting solvents and CoTPP is put forward.On the other hand,introduction of-COOMe substituents in phenyl rings of CoTPP weakens the coordination bond between pyridine and CoTPP as clearly evidenced by deuterium NMR spectra,resulting in a detrimental effect on CO2ERR.Therefore,the manipulation of the coordination environment around the metal center of immo-bilized catalyst is crucial in designing an efficient electrocatalytic system.