In the process of electrochemical reduction of CO2 in aqueous solution, the cathode mainly undergoes the CO2 reduction reaction, and the anode undergoes the oxygen evolution reaction (OER). Developing an efficient OER catalyst is very important for improving the energy efficiency of electrochemical reduction of CO2; however, only few reports are concerned with this problem for now. Herein, N-doped multiwalled carbon nanotubes surface modified IrOx nanoparticles (IrOx /CNx NTs) as a highly active catalyst for OER at neutral pH was prepared by solvothermal method. The obtained lowest overpotentials for OER in a HCO3-/CO2 system at neutral pH are 171 and 472 mV at the current densities of 1 and 10 mA cm(-2) separately, which are better than the most catalysts those were reported for neutral media. No obvious current density decay was observed after 12-h electrolysis testing. The energy efficiency is a key factor which can reflect the real energy input for CO2 conversion. By using IrOx /CNx NTs as the anode catalyst, the energy efficiency for electrochemical reduction of CO2 to formate on Sn cathode can achieve 44.7%.