| Fuel cell is a device for converting chemicalenergy into electricity directly,which related to chemical thermodynamics,electrochemistry,catalysis,materials science,electric power system and automatic control.Because of its high efficiency,non-pollution,non-limitation of charging time,high efficiency,and widely application,fuel cell is expected to be one of the most potential devices to solve the problem of global energy.Among all the components,the electro-catalyst is the key of fuel cell.Now the most widely used electro-catalyst is Pt and Pt-based precious metal nanomaterials.In order to promoting the commercialization and improving the utilization of precious metal Pt,design and synthesis of Pt and Pt-based catalysts with low content and high catalytic activity have been an important approach for the widely application of fuel cell.In order to improve the utilization of precious metals,The present research showed much methods.(?)The design of carrier-based metal composite nanomaterials was one of the effective ways to improve the utilization of precious metal catalyst.High conductive nanomaterials,such as carbon nanotubes and graphene,have drawn much attention due to its fast electron transfer rate during electro-catalytic process.(?)The way of non-noble metal doping also can reduce the content of precious metals effectively.By electronic effect and synergy effect between two different components,the utilization precious metals can be improved.Transition metals,such as Fe,Co,Ni,were often used to form alloy with precious metals.(?)Design and synthesis precious metal nanomaterials with controlled morphology and size have been an efficient pathway.Among various structures,precious metal nanocrystals with hollow porous structure showed excellent eletro-catalytic performance and thus attracted due to its high specific surface area,low density,and abundant catalytic active site.Based on the above,the controllable synthesis of hollow nanostructure and corresponding electro-catalytic performance were studied for enhancing the utilization ratio of the precious metals in this paper.By increasing the specific surface area,corresponding more active sites,alloying to adjust electronic nanostructure,introducing carrier nanomaterials,the electro-catalytic activity and stability can be further improved.The main results can be summarized as follows:1.Large scale synthesis of noble metal nanoparticles with hollow porous structure have attracted much attention owning to their high surface area,abundant active sites and relatively efficient catalytic activity.Herein,we reported a general method to synthesize hollow porous Pd nanospheres(Pd HPNSs)and hollow porous Pt-Pd alloy nanospheres(Pt-Pd HPNSs)by templating sacrificial SiO2 nanoparticles through layer-by-layer self-assembly approach.The growth mechanism was studied based on the analysis of diverse experimental observations and physicochemical characterization of Pd HPNSs and Pt-Pd HPNSs were integrallty characterized by various physical techniques,such as Transmission electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy.The as-prepared Pd HPNSs and Pt-Pd HPNSs exhibited clearly enhanced electrocatalytic activity and durability for the formic oxidation reaction(FAOR)and methanol oxidation reaction(MOR),respectively.2.To further enhance the catalytic activity of nobel metal catalysts,graphene was introduced as a support to enhance dispersity,stability,and conductivity of hollow electrocatalysts owning to its large theoretical surface area(?2630 m2 g-1),high conductivity,thermal stability,and robust mechanical properties.In this work,a 3D graphene hollow sphere was designed to minimize wrinkles,maximize specific surface area,and realize the regular clipping of 2D graphene.The 3D graphene hollow sphere served as skeleton to support Pd nanoparticles for the formation of 3D RGO@Pd HPNSs,not only acted as inner conducting shell to promote electron and ion kinetics but also be crucial for enhance the permeate of small organic molecule in fuel cells.As inspired by this,the 3D RGO@Pd HPNSs exhibited clearly enhanced electrocatalytic activity and durability for the formic oxidation reaction(FAOR)in acid medium compared with both 2D RGO-Pd nanosheet and commercial Pd/C catalyst.3.Hererin,for promoting electron and ion kinetics and enhancing the permeation of small organic molecule electrolyte in fuel cells,a 3D graphene hollow sphere was designed to serve as inner skeleton based on chapter three.Then transition metals,such as Fe,Co,Ni,were introduced to increase utilization of noble metals.According to this,a universal sacrificial template-based synthesis strategy was reported to prepare three dimensional(3D)graphene supported PtM(M=Fe,Co,Ni)hollow nanospheres.The 3D PtM(M=Fe,Co,Ni)/RGO HNSs exhibited clearly enhanced electrocatalytic activity and durability for methanol reaction(MOR)in acid medium compared with commercial Pt/C catalyst.This study provided a versatile approach to realize controlled synthesis of 3D graphene-metal hybrid nanostructures irrespective of the components of the metal domains.4.Herein,for further promoting the mass transferthe,a D holey graphene hollow sphere was designed to open up the mesoporous channels,which enabled large surface area,uniform particle size distribution,facilitated ion and electron transport,and superior permeation of micromolecule.Sparse Pt nanoparticles were deposited onto the inner surface while a uniform layer with innumerable pony-size Pt nanoparticles were deposited onto the external surface of 3D holey hollow nanospheres for realizing fully-open form of Pt atoms and maximum utilization of graphene.As inspired by its 3D wrinkle-free base,mesoporous mass transfer channels,and fully-open active sites of Pt atoms,the as-prepared 3D Pt/holey G/Pt HNSs exhibited observably enhanced electrocatalytic activity and durability for oxygen reduction reaction(ORR)and methanol oxidation reaction compared with commercial Pt/C catalyst.5.Based on the above,a two-dimensional(2D)noble metal nanomaterial was designed as an superior eleltro-catdyst,which could be located on the 3D graphene hollow spheres.As we know,noble metal atoms have a strong preference for three-dimensional(3D)close-packed structures,leading to a challenge for studying simple and efficient strategy of two-dimensional(2D)noble metal nanostructure.Herein we reported a one-pot hydrothermal synthesis of ultrathin porous Pd nanosheets with pH-dependent self-assembly mechanism.The obtained 2D porous Pd nanosheets with length of 1.2±0.2 ?m,width of 0.8 ±0.1 ?m,and thickness of?20 nm are flat knitted-like with interlaced nanowires.Impressively,the as-prepared Pd nanosheets exhibit excellent electrocatalytic activity and durability for the formic oxidation reaction in acid medium compared to commercial Pd black electrocatalyst.Hopefully,this 2D porous Pd nanosheets can be located on 3D graphene hollow spheres for further enhancing eletro-catalytic performance. |
PDF Full Text Request