Pd-Ni Based Nano-Micro Materials: Morphology Control And Catalysis For Alcohol Electro-oxidation

As a clean energy conversion device,fuel cell could solve the problems of resource shortage and environmental pollution caused by traditional fossil fuels.Fuel cell has a high volume of energy density and is easy to store and transport.The characteristics of simple structure,small size,and light weight can meet the requirements of people for portable electrical appliances.Nowadays,there are still two main problems in the anode oxidation for direct alcohol fuel cells:1)Slow oxidation kinetics,strong adsorption of carbon monoxide on noble metal atoms,resulting in catalyst poisoning and rapid deactivation;2)Most of the catalysts currently used are expensive Pt-rich materials,which are not conducive to industrialization.Compared with Pt,Pd-based catalysts have advantages in price and anti-CO poisoning property.Morphology regulation is an effective way to optimize catalytic performance.The hollow/porous nanomaterials exhibit excellent physicochemical properties including excellent electrical conductivity,high specific surface area,and catalytic stability.However,in the absence of a template,the preparation of hollow/porous structures based on Ostwald ripening of self-polymerized nanoparticles has rarely been reported.In addition,the bimetallic phosphide has a"synergistic effect"between the metals,morphological controllability,thermal stability,and excellent catalytic properties.In this thesis,Pd-Ni submicron cage?MCs?and Pd-Ni-P yolk-shell particles?YS Pd-Ni-P?were prepared by heat-treating self-polymerized nanoparticles to achieve improved catalytic activity and stability in alcohol electro-oxidation reaction.Pd-Ni MCs were synthesized by a bottom-up method as a self-supporting catalyst for methanol oxidation reaction?MOR?,showing excellent activity and durability.The key is to use phosphine oxide as a weak capping agent to allow the aggregation of Pd-Ni NPs.The subsequent thermal ripening of the assembled NPs lead to the formation of the Pd-Ni MCs.Due to the high porosity,electrical conductivity,and atomically stepped surfaces,these MCs afford a current density of3.2 mA/cm²_Pd in MOR in an alkaline medium,which is superior to those of Pd-Ni NPs and Pd NPs.Thanks to the well-defined bicontinuous self-supported structure,more than 91.4%of the current remained after 2000 cyclic voltammetry cycles.The excellent catalytic durability makes the MCs superior to the carbon-supported NP catalysts.This work provides a facile and environmentally benign approach to fabricate porous precious metallic nanomaterials as a highly active and durable electro-catalyst with enhanced utilization of the precious metals.YS Pd-Ni-P was prepared based on thermal ripening of the aggregated NPs.The material has abundant nanopores in both the core and the shell parts.Size distribution analysis based on density functional theory shows the width of the nanopores is around 15 nm.Based on the electro-chemical active area of palladium,the supported yolk-shell Pd-Ni-P catalyst affords a high electro-catalytic activity(1.9 mA/cm_Pd^-2)in methanol oxidation reaction which is 1.5,3.1,3.8,or 5.5 times higher than those of face-centered cubic Pd-Ni-P,amorphous Pd-Ni-P,Pd-Ni,or Pd NPs,respectively.Impressively,87%of the current density remains after 2000 cycles'cyclic voltammetry with yolk-shell catalyst as the anode,which is much superior to those values with other related Pd-based NPs.Ultra-small amorphous Pd-Ni-P NPs?around 4 nm in diameter?were synthesized by a solvothermal synthesis method.Aiming at the catalytic application of ethylene glycol and glycerol,the effects of Pd-Ni-P on C2 and C3 alcohols fuel cells were investigated.On the one hand,it is easy to form weak coordination bonds between Pd with-OH due to the existence of positively charged Pd in the form of Pd-P;on the other hand,the synergistic effect between Pd and Ni metals can also improve the electrooxidation performance.The electrochemical test results showed that Pd-Ni-P/C as an anodic catalyst exhibited excellent catalytic activity in the oxidation of ethylene glycol and glycerol,which was 2.8 and 2 times as much as commercial Pd/C,respectively.The effect of alkali concentration on the electro-oxidation performance of two alcohols was further investigated,and the mass transfer characteristics of the reaction and the electro-catalytic behavior of Pd-Ni-P/C were revealed.