| Carbon supported metal nanocluster catalysts have attracted much attention because of their excellent activity and selectivity for a wide range of important reactions,such as the electrocatalytic oxygen reduction reaction,small molecules oxidation reaction,and various hydrogenation/dehydrogenation reactions.Yet the carbon supported catalysts suffer from metal sintering and consequent deactivation owing to the weak interaction between metals and inert carbon surface.According to the soft-hard-acid-base principle,sulfur-containing species as soft bases has a strong trend to form covalent bonds with noble metals as soft acids.Therefore,one efficient solution for overcoming the metal sintering is to chemically functionalize the inert carbon surface by doping sulfur atom for strengthening the metal-carbon interaction.Unfortunately,so far the porous S-doped carbon(S-C)used for catalyst supports were generally prepared with the hard template methods or the chemical activation method.The additional cost of the templates or the chemical activators and the tedious preparation processes restrict the large-scale production of these S-C supports for practical applications.In this thesis,a template-free synthesis strategy is reported to prepare high-surface-area S-C supports by carbonization of microporous conjugated polythiophene,which is synthesized by polymerization of 3,3'-bithiophene at mild conditions.The conjugated polythiophene-derived S-C exhibit strong capability for loading Pt nanoclusters with average size of less than 2 nanometer owing to the strong interaction between Pt and doped sulfur atoms.Importantly,the S-C supported Pt nanocluster(Pt/S-C)catalysts show outstanding sintering-resistant properties under high temperature up to 700? or harsh hydrothermal conditions.Moreover,the Pt/S-C catalysts display much enhanced catalytic performance for formic oxidation reaction(FAOR)compared to the commercial Pt/C catalyst,demonstrating the application prospect of microporous conjugated polythiophene-derived S-C as supports for metal catalysts.The main results can be summarized as follows:1.A template-free synthesis is developed to prepare highly porous S-C materials with high surface area.The S-C materials with high sulfur content(up to?27 wt%)and large specific surface areas(700?1000 m2 g-1)is prepared by carbonization of microporous conjugated polythiophene,which is synthesized through the polymerization of 3,3'-bithiophene with FeCl3 as initiator in CHCl3 at room temperature.The sulfur contents and porosity of the S-C materials can be controlled by changing the carbonization temperature.2.A sintering-resistant metal catalyst is prepared based on the strong interaction between metal and the doped sulfur atoms.A high dispersion of Pt clusters(?1.0 nm)even with a large Pt loading of 20 wt%is achieved on the S-C supports by the conventional wet-impregnation method.More importantly,the Pt/S-C catalysts can tolerate high-temperature treatments up to 700? and harsh hydrothermal conditions(alkaline water,2 Mbar H2,200? for 12 h).The strong capability of the S-C supports for loading metals and the outstanding sintering-resistant properties of the Pt/S-C catalysts are associated to the strong chemical Pt-sulfur interaction,which is definitely verified by the X-ray photoelectron spectroscopy(XPS),Energy-dispersive X-ray spectroscopy(EDS),and X-ray absorption near edge structure(XANES)analyses.3.The Pt/S-C catalysts show much enhanced electrocatalytic performance for FAOR.FAOR is a size-sensitive reaction and reducing metal particle size can greatly enhance the reactivity.The Pt/S-C catalysts exhibit much lower onset potential(0.18 V versus reversible hydrogen electrode)and a high FAOR mass activity of 3.15 A mgPt-1,which is 7 times higher than that of the commercial Pt/C catalysts.The enhanced FAOR activity of the Pt/S-C catalysts can be ascribed to the improved intrinsic activity and high Pt atom utilization,which are induced by the small-size effects. |
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