| Fuel cells are deemed to be the best way to solve the dilemma of energy sources and environment requirement in 21th century. Due to the high specific energy, the facile storage and refilling characteristics of methanol fuel, direct methanol fuel cells (DMFCs) have been attracting significant interest and research efforts for its great potential to be commercialized as the major power source for portable electric devices. Platinum-based catalysts are widely used in the field of DMFCs. However, be limited by the shortage of stock, maldistribution and high price of platinum, it is always necessary to improve the activity, stability and utilization efficiency of Pt-based catalysts in this field. High overpotential of methanol oxidization, surface poisoning and agglomeration of nanoparticles should be faced by Pt-based catalysts applied in the anodes of DMFCs. Commercial PtRu catalysts show the highest activity and ability of anti-poisoning in nowadays. However, Ru is quite unstable in electrochemical systems, and it always dissolves from the catalysts in operation, leading to the deterioration of catalytic activity. This article aims to improve the activity, ability of anti-poisoning and stability of PtRu catalysts. By different strategies of alloying, structure control, the synergistic effect between Pt-shell and Ru-core, and protection of Pt-shell, we designed ordered core-shell Ru@Pt catalyst with enhanced activity and stability. And main research contents and results were listed below.We synthesize Ru nanoparticles applying ethanol as reductant and microwave heating. Heat-treatment is used to improve the crystallinity and to reduce the surface defect of Ru NPs. XRD profiles and TEM images indicate that ordered Ru NPs with close-packed hexagonal (h.c.p) structure are obtained. Then ordered core-shell Ru@Pt NPs are fabricated after Pt coating. TEM images indicate that NPs posses uniform particle size and distribute homogeneously on carbon support. Only Pt (111) lattice fringes are observed in HRTEM images, which indicate that Ru cores are coverd by Pt atoms. HAADF-STEM and EDS analysis of single NP shows that well-defined and ordered core-shell Ru@Pt particles are obtained. According to the characterization of XPS, the bonding energy of Pt 4f shifts positively, illustrating the synergistic effect between Pt-shell and Ru-core. Ru@Pt catalysts show great ability of anti-poisoning because of the low onset potential (0.36 V) in CO-stripping test. And Ru@Pt shows high utilization of Pt for its ESA (150 m2/g). By methanol oxidization (MOR) test, Ru@Pt show excellent mass activity (1313 A/g) and low onset potential (0.34 V) towards the electro-oxidization of methanol which is the highest mass activity of Pt in literatures and higher than commercial PtRu catalysts. Ru@Pt catalyst shows superior stability in accelerated CV test. The onset potential only shifts by 30 mV and peak current (over 1100 A/g) decreases by 16% after 1000 cycles CV test. And core-shell structure is still observed by HAADF characterization. Ru@Pt catalyst reveals wonderful performance in single DMFC test. The highest power densities of Ru@Pt fuel cell are 185 mW/cm2 (by air) and 290 mW/cm2 (by O2), which is 1.5 times higher than commercial PtRu catalyst. Enhanced stability in single fuel cell is revealed by its high power density (180 mW/cm2) after life test. The relationship between catalytic activity, stability and core-shell structure is studied by comparison of core-shell catalysts with different shell thickness. The catalytic activity is proved to be negatively related to shell thickness and the stability is positively related to shell thickness. |
PDF Full Text Request