Studies On Preparation And Performance Of Pt-based Catalysts For Direct Methanol Fuel Cell

A fundamental challenge for practical applications of direct methanol fuel cells（DMFC）is to develop high-performance electrocatalysts with high activity and durability for two and a half reactions,namely,methanol oxidation reaction（MOR）at the anode and oxygen reduction reaction（ORR）at the cathode.Currently,Pt group metal based catalysts are still the best choice for the bipolar reaction of DMFC in practical applications,but their high prices have seriously hindered the commercialization of DMFC.In addition to high cost,Pt-based catalysts also have problems such as easy migration and aggregation,CO poisoning,and long-term instability.Due to the problem of methanol membrane penetration,cathode ORR catalysts also need good resistance to methanol poisoning to avoid generating large mixing potential and causing significant energy loss.Therefore,one strategy is to develop highly selective anode/cathode electrocatalysts to maximize electrochemical energy conversion at high concentrations of methanol.In addition,alloy catalysts with special morphology can be constructed to improve the utilization rate of Pt,thereby reducing material costs.This article aims to synthesize efficient and low-cost catalyst materials,and conducts a series of research on DMFC electrode reaction catalysts.Several catalyst materials with high specific surface area and low Pt loading have been developed,and their performance improvement mechanisms have been explored and analyzed.Firstly,multi skeleton Pt Pd Ni nanodendrites（Pt Pd Ni NDs）were successfully formed through a simple one pot method and structural directing agents.The modification of Pt electronic structure and its interaction due to compression strain were studied by using basic characterization techniques.This shows that Pt Pd Ni NDs have a Pt rich surface,which confirms that the catalytic activity of oxygen reduction reaction in acidic media is higher.Pt Pd Ni NDs have higher electrochemical surface area(63 m² g^-1)and earlier initial potential（1.01 V）than Pt Pd NDs,Pt Ni NDs,and commercial Pt/C catalysts,indicating excellent ORR performance.High mass activity and specific activity,as well as excellent durability after accelerated degradation test（ADT）,highlight the significant electrocatalytic performance of Pt Pd Ni NDs over other materials.Therefore,improving Pt utilization by forming Pt Pd Ni NDs may be a reliable strategy for improving the application of ORR electrocatalysis in DMFC.Secondly,we successfully prepared a ternary Pt Pd Co mesoporous nanospheres（MNs）,developed by a soft template-assisted method,as an efficient electrocatalyst for methanol oxidation reaction（MOR）.The physicochemical characterizations demonstrate that Pt Pd Co MNs possess abundant mesoporous channels,nanospheres assembly of tiny nanoparticles,and strong interatomic interaction and synergistic effect.Electrochemical test shows that this unique metal alloy brings superior MOR catalytic performance.The mass activity（MA）and specific activity（SA）of Pt Pd Co MNs are 2.05 A mg _Pt^-1 and 3.31 m A cm^-2 respectively,which are 3.87/3.8 times of commercial Pt Ru/C,4.27/4.47 times of commercial Pt/C.In addition,the measurements of i-t（3600 s）and ADT（2000 cycles）further revealed the superior durability of the Pt Pd Co MNs.These results indicate Pt Pd Co MNs outperform to reported benchmark catalysts and this study represents a novel approach to reducing Pt costs while achieving high MOR performance.Thirdly,we report Pt Pd nanocubes（NCs）grown in situ on commercial carbon powder（Vulcan XC-72R）using a facile one-pot method.The as-prepared Pt Pd NCs/C（～20 wt.%metal）possess Pt-enriched surfaces,enabling the mass activity（MA）of methanol oxidation reaction（MOR）up to 1.77 A mg _Pt^-1,which is 3.34/3.69 times that of commercial Pt Ru/C and Pt/C,respectively.With an average size of 8–10 nm,the Pt Pd NCs/C exhibit high stability,retaining over 80%initial MA against MOR in an accelerated durability test.For practical direct-methanol fuel cell（DMFC）operation,the Pt Pd NCs/C as an anode catalyst delivered a maximum power density of 0.232 W cm^-2 with high-concentration methanol（10M）flow,which is 1.6 times higher than that for commercial Pt Ru/C under the same conditions.Moreover,the Pt Pd NCs/C demonstrated excellent durability for DMFC operation with much lower voltage decay than commercial Pt Ru/C,indicating its excellent potential for practical DMFC applications.