Synthesis And Catalytic Properties Of Palladium/metal Carbonate Hydroxide Nanocomposite Catalysts Towards Ethanol Oxidation Reaction

The development and utilization of clean new energy is the promising way for human society to fundamentally solve global problems such as energy shortage,environmental pollution and destruction.Fuel cells,as a new device that directly converts chemical energy into electrical energy,possess technical advantages such as highly efficient energy conversion,environmental friendliness,high reliability,and wide range of application and are thus expected to play an indispensable role in the future energy economic system.Among the variety of fuels of choice,ethanol has attracted much attention thanks to non-toxicity,easy of storage and transportation,and mature technology for large-scale production.In addition,direct ethanol fuel cell?DEFC?also has high theoretical operating voltage?1.15 V vs.SHE?and high theoretical energy density(8.01 Wh?g^-1),therefore it has always been a research hotspot in the field of energy technology.Researches have shown that Pd and Pt possess high catalytic activity towards ethanol oxidation reaction?EOR?,but suffering from serious problems of poor durability,which seriously hinder the practical application of DEFC.At present,due to the lack of in-depth understanding of the complex mechanism of EOR,it is still the dominant research strategy to improve the stability of precious metal catalysts by the incorporation of synergistic-modified phases.Driven by the perspective of exploring a new synergistic-modified phase,our study focuses on the synthesis of low-loading with high-dispersion Pd-based nanocomposite catalysts,the modified effect and mechanism of metal carbonate hydroxide.The main research progress and conclusions of this work are as follows:?1?Nanostructured cobalt carbonate hydroxide?CCH?nanowires on carbon fiber cloth?CFC?were synthesized via a hydrothermal reaction,then Pd O nanoparticles were introduced on the surface of CCH through the interface reaction between Pd precursor and CCH.Finally,Pd/CCH/CFC was prepared by hydrogen reduction under low temperature.The use of this simple method not only ensures the uniform distribution of tiny Pd nanoparticles on the surface of nanostructured CCH nanowires,but also enhances the strong interactions between these two component phases,both of which can facilitate the exposure of abundant accessible active sites while reducing the amount of precious metals.The results of electrochemical performance tests show that the Pd/CCH/CFC catalyst exhibits significantly improved mass-specific activity and durability towards the alkaline EOR,which were over two-fold higher than those of Pd/C.Based on the phase structure and microstructure of the catalyst together with results of design experiments,it is inferred that the modified effect of the CCH composite phase may be derived from the adsorbed OH,which is beneficial to the oxidative removal of CO adsorbed on the nearby Pd sites.?2?A combination of synergistic catalysis and nanostructures was used to design and synthesize the Pd/Ni Co-carbonate hydroxide/CFC catalyst that can effectively catalyze alkaline EOR.First,a large number of nanowire-structured Ni Co-carbonate hydroxide?Ni Co-CH?was grown on the carbon cloth by hydrothermal method and then the metal Pd was introduced by hydrolysis process and reductive annealing.Compared with commercial Pd/C catalyst,Pd/Ni Co-CH/CFC catalyst has better mass-specific activity and stability towards alkaline EOR.The improvement in catalytic performance could be attributed to that the Ni Co-CH composite phase can adsorb OH species,which is beneficial to oxidative removal of the adsorbed carbonaceous intermediates and/or products on Pd.The above work designed and synthesized two palladium-based nanocomposite catalysts for EOR via simple experimental methods and modification strategies,and the experimental results proved the application potential of transition metal carbonate hydroxides as a synergistic-modified phase to improve the catalytic performance of noble metal catalyst towards the alkaline EOR,which provided an experimental basis for reducing catalyst cost and improving catalyst performance.