Crystalline Nanocarbon Supported Pt-like Co-catalysts And Their Synergic Catalytic Effect With Noble Metals

Transition metal carbides have the Pt-like catalytic activities. They have been utilized as active components by themselves, as support materials or co-catalyst component in the fuel cells. Two of the most actively studied system are tungsten carbide (WC) and molybdenum carbide (Mo2C). It has been confirmed that WC or Mo2C could play the synergic effect with noble metals that would improve the catalytic activity and stability. However, the current preparations are still limited in the conventional metallurgy, which often suffers from the large size and the aggregation of particles, not suitable for nanomaterial applications. Meanwhile, studies on the design, the controllable preparation and the prediction of carbides are still few. These factors restrict our further probe into the catalytic essence. It is critical, therefore, to develop a high efficient carbides materials from the standpoint of design, and to apply them in the fuel cells so that the cells’power density could be further imporved and their cost could be reduced.In this study, we fabricated the WC and Mo2C nanoparticles as co-catalysts on graphitic carbon based on the understanding of "structure-performance" relationship. Our final aim is to integrate the electrochemical functions of both carbides and graphtic carbon, where carbides would play the synergistic effect with noble metals, and the graphtic carbon is used to improve the electronic transportation in electrochemical reactions.Based on above design, we prepared the small-sized and high-dispersed carbides on the crystalline carbon via two kinds of design idea,. First, we presented an "in situ simultaneous synthesis" of Mo2C/graphitic carbon nanocomposite (Mo2C/GC) by using commercial ion-exchange resin as carbion resource. The final material consists of well-dispersed Mo2C particles (typically-10nm) on graphitic carbon. After loading the Pt, Pd catalysts, the resultant material exhibits excellent supporting effect on the electro-oxidation of methanol, ethanol and formyl acid. This method is very simple, practical, low-cost and makes a systematic design of new, predictable catalysts enable. Besides, we fabricated the small-sized (-5nm) and high-dispersed carbides on graphene. After loading Pt partilces, the new Pt-WC/graphene catalyst exhibited a high catalytic efficiency to methanol oxidation, with a mass activity of1.98and4.52times to those of commercial PtRu/C and Pt/C catalysts, respectively. It also showed the best stability and suggested a great potential in commercial application. Furthermore, we combined the experiments and density functional theory (DFT) calculations to study on the interaction among carbides, graphene and noble metal catalyst. The results showed that the strong covalent interaction between WC and graphene is necessary for small-sized and high-dispersed WC, moreover, Pt particles are preferential to grow on WC, forming the Pt-WC contacts beacause of the strong interaction between Pt and WC X-ray absorption fine structure spectroscopy (XAFS) approved the intimate contacts between Pt and WC, and firstly demonstrated the presence of WC can facilitate the crystallinity of Pt particles. These work enable us take a deep understanding on the relationship between material structure and catalytic performace, as well as the synergistic effect between co-catalyst and catalyst.