Preparation And Investigation Of Carbon-based Molybdenum Composite Supports On Electrocatalytic Performance Of Pt Catalysts

With the advent of energy crisis,environmental deterioration and other increased serious problems increasingly serious,the development and application of green energy sources gradually come into the public view.The direct methanol fuel cell?DMFC?,for potential applications in electric vehicles and portable electronic devices,has attracted extensive attention due to its high energy density,convenient manipulation and fast start-up.The needs of good battery performance,long cycle life and low cost are required to enable commercialization.Since Pt-based catalyst is the core for DMFC anode,the performance of DMFC is directly influenced by the activity and stability of catalyst.To solve these problems,this thesis is focused on the synthesis of low cost,high efficiency and stable carbon-based molybdenum composite supports in order to obtain high activity and stability of Pt-based catalyst for methanol electrooxidation.A new method to synthesize NCQDs-MWCNT and NCQDs-GN composite support was proposed based on one simple hydrothermal treatment to improve the activity of Pt-based catalysts.The performance of Pt-based catalysts was analysed as well.The results showed that NCQDs were tethered with MWCNT after hydrothermal treatment.The oxygen-containing groups on NCQDs have been proposed to provide more deposition sites for Pt nanoparticles.At the same time,Pt nanoparticles were uniformly distributed over the whole surface,and many Pt nanoparticles resided closely to NCQDs on bare MWCNT.The methanol eletrocatalytic activity of Pt/NCQDs-MWCNT and Pt/NCQDs-GN was found higher than that of Pt/MWCNT and Pt/GN catalyst,respectively.The effect of different precursor contents on the performance of Pt/NCQDs-MWCNT catalysts for methanol electrooxidation was investigated.With an increase of the precursor content,more aggregated NCQDs were anchored on bare MWCNT.The aggregation of NCQDs will lead to less oxygen functional groups that have been utilized by the Pt nanoparticles,thus decreasing the performance of catalyst.Taking into account both activity and stability of catalyst,the optimum content of precursor was determined for Pt/NCQDs-MWCNT catalyst.To further improve the activity and stability of catalyst,molybdenum oxides?including Mo O₂ and Mo O₃?and carbon were used as supports of Pt-based catalyst.The effects of sintering temperature on the structure and the performance of catalyst were investigated.The hierarchical carbon coated Mo O₂?Mo O₂@C?nanotubes was synthesized by template self-assembly method,and Mo O₂ was combined well with carbon.These results implied that the Pt/Mo O₂@C catalyst exhibited the best activity and durability for methanol electrooxidation when the sintering temperature is 800 oC.If the sintering temperature is too low,the surface of support is not completely carbonized which is not conducive to the deposition of Pt nanoparticles.If the sintering temperature is too high,the crystal phase was changed,resulting in the disordering of carbon layer and the instability of support structure.The novel Pt/Mo O₃-C catalyst was prepared by sintering treatment,which possesses higher activity and durability for methanol oxidation compared with Pt/Mo O 2@C catalyst.The reason of significant enhancement for catalyst performance is that the oxygen-containing groups on Mo O₃ surface could provide more active sites for Pt nanoparticles deposition.Mo O₃ is helpful for the conversion of CO intermediates into CO₂,which could enhance the corrosion resistance of support.When the sintering temperature is 800 oC,the activity of Pt/Mo O₃-C is 1.95 times higher than that of commercial Pt/C catalyst and exhibits a durability of 2.36 times better compared with commercial Pt/C.In order to further improve the stability and durability of catalys t and reduce the cost under the condition of ensuring the activity.Mo S 2 and carbon materials as composite supports were designed.Effects of MoS₂ with different additive contents on the performance of Pt-based catalysts have been systematically studied.The hierarchical MoS₂-GN nanosheets were constructed by hydrothermal treatment.The layered MoS₂-GN composite support could provide more transport channels,which promotes the charge transfer effectively.MoS₂ has good corrosion resistance and its hierarchical support structure is conducive to fasten Pt nanoparticles,which could greatly improve the stability of catalyst.The experimental results show ed that the Pt/MoS₂-GN catalyst possessed the best electrocatalytic activity and stability when the additive content was 15 %.Compared with the Pt/GN catalyst for methanol electrooxidation,the activity of Pt/MoS₂-GN was determined to be 1.92 times and the durability was increased by 26.7 %.Pt/MoS₂-MWCNT showed a higher stability compared with Pt/MoS₂-GN catalyst.The results presented that the performance of Pt/MoS₂-MWCNT catalyst was the best when the additive content was 37.5 %.Compared to Pt/MWCNT,the activity on Pt/MoS₂-MWCNT catalyst was 2.0 times and the stability increased by 33.2 % for methanol electrooxidation.Such outstanding electrocatalytic performance of Pt/MoS₂-MWCNT catalyst for methanol electrooxidation is attributed to the construction of 3D-network architectures,which has high porosity and efficient transport channel.MoS₂ could inhibit the aggregation of MWCNT and provide more active sites for the deposition of Pt nanoparticles.Moreover,strong corrosion resistance of MoS 2 combined with good conductivity of MWCNT,which could enhance the electrochemical performance of Pt/MoS₂-MWCNT catalyst.The possibility of molybdenum phosphide?Mo P?and carbon composite as the catalyst support for DMFC was investigated.Pt-based catalysts were synthesized by microwave-assisted polyol process.The experimental results showed that the methanol oxidation current density of Pt/Mo P-GN catalyst was 1.54 times and the durability was increased by 17.5 %.The explanations of dramatic improvement for catalyst performance are summarized as follows:?1?The electronic effect between Mo P and Pt.?2?Mo P provides functional groups on the surface of graphene,improving the dispersion of Pt nanoparticles.?3?The strong interaction between Mo P and GN,enhancing the corrosion resistance of catalyst support.