The Catalytic Effect Of Metal And Metal Oxide Promoters On The Catalytic Oxidation Of Methanol By Pt

The most effective catalyst material for the anodic methanol oxidation reaction?MOR?of direct methanol fuel cells?DMFCs?is Pt.However,Pt is very expensive and it is easily poisoned by the CO-like intermediates during the process of MOR,which would depress the catalytic activity and stability of Pt.To enhance the catalytic properties and anti-poisoning ability of Pt catalyst,we rationally design the nanostructures of the Pt-based catalysts.In this work,the second component/promoter is introduced into Pt to form bi-component Pt-based catalysts.The promoters include Au,MnO₂ and CeO₂.Owing to the electronic effects or synergistic effects between the promoters and Pt,the surface electronic structure of Pt can be rationally tuned.The CO resistance ability and catalytic performance?activity and stability?of Pt can thus be significantly improved.The main contents of this work are as follows:1.A series of graphene-supported nonalloyed PtmAu bimetallic catalysts?m refers to the atomic Pt/Au ratio,m = 0.5 2.0?are synthesized through the co-reduction method in liquid phase.The relationship between the nanostructure and the catalytic performance of the catalysts toward methanol oxidation reaction?MOR?in alkaline medium is investigated.The catalysts are comprehensively characterized by SEM,TEM,XRD,XPS and electrochemical techniques including cyclic voltammetry?CV?and chronoamperometry?CA?.Results show that the promoter Au can significantly improve the catalytic performances and anti-poisoning of Pt in alkaline medium and the improvement is related to the atomic Pt/Au ratios.CO stripping voltammograms and CV curves suggest that the improved electrocatalytic properties of the PtmAu/RGO catalysts are especially attributed to the decreased CO formation rather than the facile CO removal on the surface of Pt.In this work,the catalyst with m = 1.0 exhibits the most negative initial potential and the highest peak current,showing the highest catalytic activity and electrochemical stability.The initial potential of Pt1.0Au/RGO catalyst?-0.78 V?is about 140 mV more negative than that of Pt/RGO?-0.64 V?.The peak current of Pt1.0Au/RGO catalyst?0.81 A mg-1Pt+Au?is about 2.70,1.62,1.15 and 1.97 times higher than that of Pt/RGO?0.30 A mg-1Pt+Au?,Pt0.5Au/RGO?0.50 A mg-1Pt+Au?,Pt0.8Au/RGO?0.70 A mg-1Pt+Au?and Pt2.0Au/RGO?0.41 A mg-1Pt+Au?,respectively.2.MnO₂ nanoplates,corallines and nanorods are synthesized through the simple chemical precipitation method and used as the promoter and support for Pt catalysts.The as-prepared catalysts are denoted as Pt/MnO₂-P?Pt/MnO₂-C and Pt/MnO₂-R,respectively.The catalysts are comprehensively characterized by SEM,TEM,XRD,XPS and electrochemical techniques.The promoting effects of the oxides with different morphologies to Pt catalysts toward methanol oxidation reaction?MOR?in acidic medium are investigated.Results show that the promoting effects are closely related to the morphologies of the promoters.Pt/MnO₂-R exhibits the most negative initial potential?0.34 V?during the CO stripping process,which is ca.70 and 100 mV more negative as compared with Pt/MnO₂-C and Pt/MnO₂-P catalysts,respectively.The intrinsic activity?IA?of Pt in Pt/MnO₂-R catalyst is 30.46 A m-2Pt,which is ca.2.31 and 3.53 times higher than that of Pt/MnO₂-C catalyst?16.21 A m-2?and Pt/MnO₂-P catalyst?10.60 A m-2?,respectively,showing the highest catalytic properties among the MnO₂ promoted catalysts.Our findings suggest that the morphologies of the metal oxides promoters have important effect on the Pt catalytic performance and the change in the structure of Pt is responsible for this phenomenon.Bifunctional mechanism or synergistic effects contribute to the improvement of the catalytic properties.3.CeO₂ nanooctahedron,nanosphere and nanocube are sucucssfully prepared through the hydrothermal method and used as the promoter/support for the Pt catalyst.The as-prepared catalysts are denoted as Pt-CeO₂/C-O,Pt-CeO₂/C-S and Pt-CeO₂/C-C,respectively.The promoting effects to Pt catalyst toward methanol oxidation reaction in alkaline electrolyte are investigated by electrochemical techniques including cyclic voltammetry and chronoamperometry.Results show that the CeO₂ promoters with different morphologies exhibit different catalytic features and the promoting effects are closely related to the calcinated temperatue of Ce O₂.Among the Pt-CeO₂/C catalysts,Pt-CeO₂/C-S400 catalyst shows the highest catalytic performance for the oxidation of methanol owing to the relatively low particles size and rough surface of CeO₂ nanospheres.The rough surface can not only increase the exposed surface area of CeO₂ and strengthen the interaction between Pt nanoparticles and CeO₂,but also increase the number of suface low-coordinated atoms,which would increase the active sites of surface Pt atoms and thus enhance the catalytic properties of Pt.This change in the geometric structure of Pt may contribute to the improvement of the catalytic properties.