Development Of Pt-based Catalysts And Studies On Their Performances For Methanol Oxidation Reaction

Direct methanol fuel cell（DMFC）is identified as the ideal choice for portable power sources in the future due to high energy density,easy fuel storage and transportation,and simple system design.Nevertheless,the slow methanol oxidation reaction（MOR）on the anode side of the DMFC severely limits the performance of the cell.Until now,the platinum（Pt）group noble metals are still broadly regarded as the most promising electrocatalysts for facilitating the activity of MOR owing to the relatively high catalytic activity and durability.However,the exorbitant price and relatively low storage capacity of Pt severely hinder its practical application.In addition,the intermediate species(like CO_ads)produced in the MOR process are easily adsorbed on the surface of Pt and cause catalyst poisoning,further resulting in a significant decrease in the activity and durability of the Pt catalyst.Therefore,exploring and developing high-performance and low-cost Pt-based MOR electrocatalysts is of great significance for the commercial development of the DMFC.In this essay,the perspective of reducing costs and increasing the utilization rate of Pt are selected to attempt to prepare Pt-based catalysts through the methods of the low-cost support development,metal alloying,the regulation of the morphology and structure,and surface doping engineering.Moreover,the corresponding electrochemical properties of the Pt-based catalysts have also been characterized in detail.The research content is as follows:Firstly,the porous derivative carbon material（SC）containing Fe and N co-doped from organic sludge is prepared and then utilized as the carrier of Pt nanoparticles for electrocatalytic oxidation of methanol.The results demonstrate that the low-cost SC carbon material support possesses great application potential in the field of MOR.The as-prepared Pt/SC catalyst is characterized in detail by TEM,SEM,XRD,XPS,CV and CA tests.The results show that the Pt/SC catalyst exhibits a slightly larger particle size compared with the Pt/C catalyst.However,for the test of electrocatalytic oxidation of methanol,the mass activity of Pt/SC catalyst is much higher than that of Pt/C.In addition,the synthesized Pt/SC also shows better stability to MOR.The improvement of performance for the Pt/SC catalyst may be due to the high specific surface area and the synergy of many heteroatoms（especially the N and Fe contained in the SC support and their oxides）.This research also provides a potential way for the utilization of SC resources.Secondly,it is reported that the uniform morphology and size Pt Pd Cr/C ternary alloy nanoparticles catalyst with low platinum loading（～5 wt.%）is successfully synthesized via a simple two-step co-reduction method and then applied to the electrocatalytic oxidation of methanol.The average particle size of the as-prepared catalyst is about 4.5nm from the characterization of TEM and XRD.The electrochemical performance for methanol oxidation of the Pt Pd Cr/C is found to be higher with the catalytic activity of969 m A·mg^-1 compared to Pt Ru/C(725 m A·mg^-1)and Pt/C(581 m A·mg^-1),which is attributed to the synergistic and electronic effects of Cr and Pd as co-catalysts with Pt,further improving the overall stability of the catalyst while reducing the content of Pt and increasing the utilization rate of Pt,and proving that the Pt-based catalyst with ternary alloy is a promising strategy for MOR.Thirdly,it is reported that the Pt₃Mn alloy catalyst with nanowire network structure（NWNs）is successfully obtained by a facile soft template method.The soft template（CTAB）used therein plays a key role in the formation of NWNs,which can form micelles in the two-phase system and provide flexibility for the growth of Pt₃Mn alloy nano-network structure.The morphology and elemental composition and electrochemical behavior for Pt₃Mn NWNs catalyst towards MOR are elaborative investigated by physical and electrochemical representation.The results demonstrate that the Pt₃Mn NWNs possess excellent activity and stability towards MOR compared with Pt NWNs and commercial Pt/C.The mass and specific activities of Pt₃Mn NWNs are 0.843 m A·mg^-1and 1.8 m A·cm^-2 respectively,which is about twice as much as commercial Pt/C.Moreover,the result of the CA test proves that Pt₃Mn NWNs catalyst also shows better stability than Pt NWNs and commercial Pt/C catalysts.This work proves the importance of the adjustment of the alloy morphology to the improvement of MOR performance.Finally,a facile trace Ir-doping strategy is proposed to fabricate Ir-Pt Zn and Ir-Pt Cu alloy nanodendrites（NDs）catalysts in aqueous medium under room temperature.It can be observed that the as-synthesized Ir-Pt Zn/Cu NDs catalysts exhibit the obvious nanodendritic-like structure with an average diameter of about 4.1 nm by TEM and HRTEM,and the atom utilization and catalytic performance of Pt toward methanol oxidation activity are further improving by the Ir doping engineering strategy.The electrochemical characterizations reveal that the as-obtained Ir-Pt Zn/Cu NDs show increased mass activities of nearly 1.23 and 1.28-times higher than those of undoped Pt Zn and Pt Cu,and approximately 2.35 and 2.67-fold higher than that of Pt/C respectively.More importantly,the as-prepared Ir-Pt Zn and Ir-Pt Cu NDs still preserve about 88.9%and 91.6%of the initial mass activities after ADT test,which further highlights the key role of the Ir doping in the catalytic performance.These results simultaneously suggest that trace Ir-doping engineering may be a promising way to develop advanced electrocatalysts for MOR.