The Synthesis Of Surface Clean Fuel Cell Noble Metal Nanocatalyst And Their Performance

Surfactant plays a pivotal role in nanosynthesis,which enhances the electrocatalytic performance of nanomaterials by increasing their the specific surface area.However,surfactant blocks the access of reactant molecules to the surface atoms,and disturbs the charge transfer,restraining the electrocatalytic performance of catalyst.Therefore,searching the alternative for surfactant is an effective solution for the contradiction of surfactant during the synthesis and catalysis process.In this paper,cations and bacteria were utilized to replace the surfactant in the synthesis process,resulting a series of surface clean nanomaterials with excellent electrocatalytic performance.(1)Clean Synthesis of an Economical 3D Nanochain Network of PdCu Alloy with Enhanced Electrocatalytic Performance towards Ethanol OxidationA 3D nanochain network(NNC)of PdCu alloy catalyst is fast synthesized by a one-pot method without any surfactant.The composition of the as-prepared PdCu alloy catalysts can be precisely tuned by changing the precursor ratio of Pd to Cu.First,the Cu content changes the electronic structure of Pd in the 3D NNC of PdCu alloy.Second,the 3D network structure offers large open pores,high surface areas,and self-supported properties.Third,the surfactant-free strategy results in a relatively clean surface.These factors all contribute to better electrocatalytic performance towards ethanol oxidation.Moreover,the use of copper in the alloy lowers the price of the catalyst by replacing the noble metal palladium with non-noble metal copper.The composition-optimized Pdg0Cu20 alloy in the 3D NNC catalyst shows an increased electrochemically active surface area(80.95 m2 g-1)and a 3.62-fold enhancement of mass activity(6.16 A mg-1)over a commercial Pd/C.(2)Microbial synthesis of highly disperse PdAu alloy for enhanced electrocatalysis.Bio-synthesis based on the reducing capacity of the electrochemically active bacteria is frequently used in the reduction of metal ions into nanoparticles as an eco-friendly way.However,those bio-nanoparticles can not be used directly as electrocatalysts due to the poor conductivity of cells substrates.In the thrid chapter,this problem was solved by a hydrothermal reaction,which also contributes to the heteroatom doping and alloying between Pd and Au.With the protection of graphene,the aggregation of nanoparticles was successfully avoided and the porous structure was maintained,resulting in better electrocatalytic activity and durability than commercial Pd/C in both alkaline(CH3CH2OH,6.15-fold of mass activity)and acidic(HCOOH,6.68-fold of mass activity)conditions.The strategy developed in this work opens up a horizon into designing electrocatalysts through making fully utilizing of the abundant resources in nature.(3)Microbial synthesis of porous Pt nanosphere as highly active and stable oxygen reduction catalysts.Porous Pt based nanostructures show enhanced performance in the cathodic oxygen reduction reaction(ORR)in the fuel cells,due to the porous frameworks can not only increase the active area and provide efficient mass transfer for reactant molecules,but also improve electron mobility in the solid ligaments.In order to keep the stability of porous nanostructures,surfactants are unavoidable to be used to reduce their ultrahigh surface energy during the synthesis process.However,added surfactants have negative effects on the properties of these materials and surfactant-removing processes are always difficult or required to be performed under harsh conditions,which largely impede the practical application of porous nanomaterials.In the fourth chapter,it is the first time to develop a surfactant-free method to synthesize porous Pt nanospheres via utilizing microbe.Firstly,a layer of Pd nanoparticles was in-situ synthesized on the surface of Shewanella oneidensis MR-1.Then,K2PtCl4 was reduced on the surface of Pd nanoparticles by ascorbic acid,giving botryoidal porous nanosphere.Lastly,the non-conducting bacterium cell was remove by HC1 solution,giving Bio-porous Pt nanosphere(BPPS).The as-prepared BPPS was used to test their ORR performance.Their half-wave potential showed 34 mV positive shift than that of commercial Pt/C,and the mass activity and area activity of BPPS was 3.8-fold and 4.19-fold than that of commercial Pt/C.In addition,the stability of BPPS was much better than commercial Pt/C.After the accelerated durability test,the half-wave potential only showed 3 mV negative shift in BPPS,while negative shifted 21 mV in commercial Pt/C.