The Synthesis And Application Of PtRu Based Nanoparticle Electrocatalysts For DMFC

The direct methanol fuel cell(DMFC)has been a subject of intense studies because of numerous advantages such as simple configuration,low operating temperatures and high energy density.However,the commercial viability of the DMFC is greatly hindered by several problems,such as high Pt usage and high overpotentiai on the anode.Meanwhile,the lifetime of a DMFC is quite limited due to the possible particle aggregations and to the component loss during the long-term operation.So far,the PtRu/C catalysts are considered as effective anode catalyst for the DMFCs.To further improve the activity and stability of the catalysts,in this dissertation,the effects of atomic composition,structure and particle size on the performance of the catalysts have been investigated systematically,and the preparation technique is optimized, which will be beneficial for the development of practical catalysts for the DMFCs.In this dissertation,the PtRu/C,PtRuNi/C and PtRuSi/C nanosized anode electrocatalysts have been synthesized via a carbonyl complex route.The relationship between structure and performance of the catalysts has been studied and compared with that of commercially available PtRu/C(Johnson Matthey,J-M)catalyst.The obtained results are shown as follows:1.The PtRu/C,PtRuNi/C and PtRuSi/C catalysts of different atomic compositions have been synthesized.These catalysts have very small mean particle sizes and a narrow particle size distribution.The mean particle size can be controlled in the range of 1～3 nm.Especially,the addition of Si is very effective to reduce the particle size.The X-ray diffraction(XRD)results indicate that all the catalysts are principally single-phase disordered structures.Thus,under these conditions,comparing electrocatalytic activity for methanol oxidation would be justified.2.Research results show the activity and stability of the catalysts for methanol oxidation are closely related with their composition and structure.The highest activity is found for the PtRu/C catalysts with a Pt:Ru atomic ratio of 2:1 and heat-treated at 175℃,which is about 22% higher than that of PtRu/C(1:1,J-M).For the PtRuNi/C catalysts,the highest activity was found for a Pt:Ru:Ni atomic ratio of 60:30:10 and heat-treated at 175℃.Such a ternary catalyst presents a higher catalytic activity than the Pt₂Ru₁/C catalyst prepared with the similar procedure.The enhanced catalytic activity can be ascribed to the high dispersion of the catalysts and to the role of Ni as a promotion agent.3.The stability of the catalysts is improved for the PtRu/C and PtRuNi/C catalysts heattreated at elevated temperatures.The high catalytic activity of the PtRu/C and PtRuNi/C catalysts heat-treated at 175℃can be ascribed to the highest content of RuO_xH_y within the catalysts,while the improved stability for the catalysts heat-treated at higher temperatures could be due to a higher alloying degree.Obviously,the RuO_xH_y species is an effective component for the activity improvement of the catalysts and the degree of alloying is a crucial factor in determining good stability of the Pt-Ru based catalysts.This conclusion helps in answering the apparent conflicting dependency of the activity and stability on the temperature for methanol oxidation using Pt-Ru electrocatalysts.4.The PtRu/C catalyst with a high metal loading of 50wt.%has been prepared and used as an anode catalyst for the membrane electrode assembly(MEA)of the DMFC.The MEA with the home-made PtRu/C presents higher power density than that with J-M PtRu/C catalyst with a high metal loading,again accessing that the home-made PtRu/C catalyst exhibits better catalytic activity than the commercial catalyst.5.The addition of Si into the Pt-Ru based catalysts effectively reduces the particle size and improves the stability of the catalysts,while their catalytic activity remains almost the same value.Clearly,the PtRu based catalysts can be easily prepared via a carbonyl complex route. The home-made PtRu/C,PtRuNi/C and PtRuSi/C catalysts present enhanced catalytic activity and good stability for methanol oxidation as compared to the commercial PtRu/C(J-M) catalyst.Importantly,research results answer the apparent conflicting dependency of the activity and stability on the temperature for methanol oxidation using Pt-Ru electrocatalysts.