Preparation Of Boron-and Nitrogen-doped Carbon Materials And Their Performance For Electrocatalytic Oxidation Of Alcohols

The alkaline direct alcohol fuel cells(ADAFC),one type of energy conversion device,has attracted wide attention owing to its inexpensive alcohol fuel,superior theoretical power density,non-toxic to the environment.The high cost and relatively low catalytic performance of catalysis on the anode still retard the commercial development of AD AFC.Carbon supported palladium is the most potential anode catalyst in ADAFC.However,the relatively low activity and stability of electrocatalytic oxide alcohols and the toxicity of intermediate carbon monoxide(CO)analogues to palladium(Pd)are still the main obstacles to their further application.The catalysis performance could be enhanced by the optimization of metal components and support materials.Recent research had shown that the support materials are essential for immobilizing the metal nanoparticles and improving the catalyst durability.The carbon materials doped with heteroatoms can provide abundant active sites,large specific surface area and good electrical conductivity,which are considered to be as one of the ideal carbon support materials.Compared with other carbon carriers,carbon carriers doped with boron(B)and nitrogen(N)have the following advantages:B and N atoms have similar atomic radius as carbon atom,and which are easy to be doped into the carbon lattice.B atom coubld provide abundant active sites for the fixation and dispersion of Pd nanoparticles(NPs).B and N atoms can improve the synergistic effect between carbon carrier and Pd NPs.The porous structure of carbon could provide more electrochemical reaction space,which is beneficial for mass transport and charge transfer in electrocatalytic oxide process.The above advantages can effectively improve the performance of electrocatalytic oxidation of alcohols on B,N doped carbon supported Pd catalysts.It is a very effective method of high temperature pyrolysis of precursors containing boron and nitrogen heteroatoms to prepare B and N doped porous carbon materials.This thesis focuses on the design of precursor materials from the perspective of carbon catalyst optimization.We have supported Pd-based catalysts on different conmponents,morphologies,and structures of carbon materials with B doped,and B and N co-doped.Meanwhile,the performance of electrocatalytic oxidation of ethanol and methanol for Pd-based catalysts has been investigated.The major content of this thesis encompasses the following three topics:(1)Palladium nanoparticles supported on B-doped porous carbon as electrocatalyst toward ethanol oxidation reactionThe phenylborate-cobalt compounds containing cobalt and boric acid ligands were prepared by the coordination of cobalt ion(Co2+)and 3,5-dicarboxylic phenylboric acid.The B-doped carbon materials were synthesized via high temperature pyrolysis of the phenylborate-cobalt compounds and acid washing process,and served as support for Pd catalysts.The effect of reaction temperature on the morphology and structure of BC materials has been investigated.The porous carbon carrier(BC-2)with high boron content(3.38%)and ideal morphology was prepared at 900℃,which was beneficial of uniformly supporting Pd composite catalysts(Pd/BC-2)and adjusting of the electron structure of Pd nanoparticles.The performance of electrocatalytic ethanol oxidation reaction(EOR)over catalysts was systematically investigated.The EOR electrocatalytic activity of Pd/BC-2(3614.11 mA)is 4.5 times that of commercial palladium carbon(Pd/C),showing the best electrocatalytic activity among the four catalysts.Meanwhile,the Tafel slope of Pd/BC-2(184.2 mV s-1)is 10.8 mV s-1 lower than that of Pd/C,indicating a faster reaction kinetics of Pd/BC-2 than that of Pd/C.(2)Palladium nanoparticles immobilized on B,N doped porous carbon as electrocatalyst for ethanol oxidation reactionThe mesoporous materials(Co/Zn-ZIF@BA)were prepared by ligand exchange been 5-bop and partial of 2-methylimidazole through the bimetal Co/Zn-ZIF as template.The B,N co-doped porous carbon containing cobalt NPs was prepared by pyrolysis procedures of Co/Zn-ZIF@BA,The Pd nanoparticles immobilized on B,N co-doped porous carbon(Pd/BNC-50)through replacing cobalt path at room temperature.The influence of the chemical composition of the support,the Co content,and reaction temperature on the morphology,structure and EOR performance of the catalysts has been analyzed in detail.And,compared with carbon doped with N atom,the carbon co-doped with B and N dural atoms could disperse Pd nanoparticles more effectively,thus improving EOR performance.The peak current density of Pd/BNC-50(2638.41 mA mgpd-1)is 1.37,3.77 fold that Pd immobilized on N doped porous carbon and Pd/C,which displays more excellent eclectrocatalytic activity.The 500th peak current density of Pd/BNC-50 is higher 9.60 fold than that of Pd/C,which means the higher durability of Pd/BNC-50.(3)Flower-like B,N co-doped carbon materials supported palladium applied in electrocatalytic oxidation ethanol and methanol reactionThe precursor of flower-like phenylborate-cobalt compounds(Co-BA)was produced by ZIF-67 as cobalt sources and 5-bop as ligands.The flower-like B,N codoped carbon containing cobalt NPs were prepared through the pyrolysis procedure of flower-like Co-BA,which can immobilize the Pd nanoparticles(Pd/BNCF)through the Co replacing path at room temperature.The open space of flower-like structure and the high concentration of boron doping are favorable for mass transport and uniform dispersion of Pd nanoparticles.We investigeted the impacts of pyrolysis temperature on the size of Pd NPs and performance of EOR and MOR.The results exhibited that the Pd nanoparticles on the Pd/BNCF-800 prepared at 800℃ have the smallest size distribution(10.1±1.9 nm)of those prepared at three pyrolysis temperatures.The higher catalytic activities of Pd/BNCF-800 compared with Pd/C were demonstrated in both EOR and MOR.The EOR and MOR peak current density of Pd/BNCF-800 is 1989.2 and 680.40 mA mgpd-1,which is 2.84 and 4.87 fold that of Pd/C,respectively.The oneset potential of CO oxide reaction for Pd/BNCF-800 have shifted 30 mV to the left compared to Pd/C,meaning the better resistance to CO toxicity.