Galvanic-cell Synthesis And Electrocatalytic Property Of Carbon-supported Core-shell Nanoparticles

Direct liquid（such as methanol,formic acid,and ethanol）fuel cells are deemed as one of the most promising energy-conversion devices due to the advantages of clean and high conversion rate.However,the disadvantages of direct liquid fuel cells such as slow kinetics and high toxicity in anodic reactions impede its practical applications.The kernel in commercializing direct liquid fuel cells is to develop efficient anodic catalysts.Anodic catalysts in direct liquid fuel cells are nano-structured Pt-and Pd-based materials.Core-shell（N_cM_s）structure can realize the control of catalytic property by the mismatch of core and shell atoms,and thus arouse great attention in past decade.However,the practical application of N_cM_s/C in direct liquid fuel cells needs the facile synthetic methods.In this thesis,we report a galvanic-cell method to prepare N_cM_s/C.Without precise control,auxiliary reagents or expensive instruments,this method can spontaneously synthesize uniform-structure high-performance N_cM_s/C.The whole research contains three sections as below:1.Synthesis of Au/C and discovery of galvanic-cell method.Firstly,Au/C with a20%loading and 3.8 nm size is successfully obtained by mono-dispersion method.In this synthesis,we find that carbon black in the solution can reduce Au³⁺.By experimental investigation and theoretical analysis,we reveal that the oxygenated groups on carbon black reaction and Au nanoparticles can form a galvanic cell(（-）C|oxygenated groups（OG）||Au³⁺（C）|Au（s）（+）),and thus drive the reduction of gold salt.2.The use of galvanic-cell method in the synthesis of core-shell catalyst.Based on the above principle,we propose to constitute galvanic cell(（-）C|OG||Nⁿ⁺（C）|M（s）（+）)for preparing M_cN_s/C.Exemplified by Au_cPd_s/C:1.The growth mechanism of its core-shell structure is clarified by monitoring the synthesis process.2.As-prepared Au_cPd_s/C has been demonstrated to possess the uniform and stable core-shell structure.3.Compared with Pd/C,the electrocatalytic ethanol oxidation performance of as-prepared Au_cPd_s/C is enhanced by about 4 times.Moreover,a variety of core-shell structure catalysts,such as Au_cPt_s/C,Au_cAg_s/C,Au_cRu_s/C,Pt_cAg_s/C,Pd_cRu_s/C and Au_cPt-Ru_s/C,have been synthesized using such galvanic cells.3.The use of improved galvanic-cell method in the synthesis of core-shell catalyst.We further propose the improved galvanic-cell method to synthesis core-shell catalysts.In this method,the core-shell catalyst can be obtained by stirring the salt solution of two metals with carbon black.Based on the difference of redox potential between two metals with the carbon functional groups,two kinds of galvanic cells were formed in the solution system,which promoted the competitive reduction deposition of two metal ions and finally formed core-shell structure.The feasibility of this method is demonstrated by Au_cPd_s/C and Au_cPt_s/C.A variety of characterizations are employed to analyze the obtained materials and elucidate the synthetic mechanism.And,as-prepared Au_cPt_s/C also shows a considerably efficient electrocatalytic performance of methanol oxidation.