The presence of oxygen vacancies and hydroxyl groups are both favorable for the methanol electro-oxidation on Pt-based catalysts.Understanding and differentiating the enhancing mechanism between oxygen vacancies and hydroxyl groups for high activity of Pt catalysts in methanol oxidation reaction(MOR) is essential but still challenging.Herein,we developed two kinds of co-catalyst for Pt/CNTs,Pr6O11 is rich in oxygen vacancies but contains substantially no hydroxyl groups,while Pr(OH)3 possesses abundant hydroxyl groups without oxygen vacancies.After a sequence of designed experiments,it can be found that both oxygen vacancies and hydroxyl groups can improve the performance of Pt/CNTs elec-trocatalysts,but the enhancing mechanism and improving degree of oxygen vacancies and hydroxyl groups for the MOR are different.Since the oxygen vacancies are more conducive to increasing the intrinsic activity of the Pt catalyst,and the hydroxyl groups play a decisive role in dehydrogenation and deprotonation of methanol,the co-catalysts with both oxygen vacancies and hydroxyl groups mixed with Pt/CNTs have higher catalytic performance.Therefore,hydroxyl-rich Pr6O11 ·xH2O was prepared and used as MOR electrocatalyst after mixed with Pt/CNTs.Benefiting from the synergistic effect of oxygen va-cancies and hydroxyl groups,the Pr6O11 ·xH2O/Pt/CNTs shows a high peak current density of 741 mA/mg,which is three times higher than that of Pt/CNTs.These new discoveries serve as a promising strategy for the rational design of MOR catalysts with low cost and high activity.