Nitrogen-doped Porous Carbon As A Support Of Platinum Nanoparticles Catalyst For Enhanced Oxygen Reduction Reaction

The combustion,depletion and exhaustion of fossil fuels bring two worldwide challenges including environmental pollution and energy shortage.Therefore,it is urgent to develop new energy technologies with high efficiency and clean fuel friendly to the environment.As a kind of environmentally efficient energy conversion device,proton exchange membrane fuel cell(PEMFC)has attracted the attention of researchers all over the world because of its high energy density,low temperature operation and environmental friendliness,and been widely used in transportation.However,slow and complicated oxygen reduction reaction(ORR)at cathode has severely hampered the commercialization of fuel cells,since the precious metal platinum is still the only choice in practical application,despite the development of a large number of non-precious metal catalysts with less satisfied activity and durability.In this manner,lowering the content of Pt or improving the mass activity and stability in the catalysts become substantially crucial for a wide-ranging application of fuel cells.With the concern to tackle the above-mentioned problems,this thesis has carried out the following related studies:Firstly,the preparation of nitrogen-doped porous carbon(NPC)derived from zeolitic imidazolate framework 8(ZIF-8),which is a kind of widely studied metal organic frameworks(MOFs)material,and its application as a new kind of support for noble metal platinum nanoparticles to improve the catalytic performance of metal platinum for ORR.ZIF-8 was prepared by solvothermal method followed by the calcination at different temperatures and time to product porous carbon materials with adjustable concentration of nitrogen doping and bonding properties.The platinum precursor was impregnated by a simple double solvent impregnation method.After that,the metal ions were reduced by chemical reduction method.The catalytic system of platinum nanoparticles loaded on nitrogen-doped porous carbon was obtained.Cyclic voltammetry and linear scanning voltammetry were carried out by CHI 760e to characterize the catalytic activity of each catalyst in order to obtain the optimized home-made catalyst.Then,the stability of the optimized home-made catalyst was verified by accelerated durability tests(ADTs)and amperometric i-t test.The performance of the catalyst was improved due to the selected carrier,so it is considered that the carrier used for the best catalyst is the optimized carrier.Further,the relationship between the change of catalyst performance and the properties of the support was investigated.The results showed that both pyridinic-N and graphitic-N sites in the carbon materials can contribute to the catalytic activity for oxygen reduction.Additionally,graphitic-N,pyridine-N-oxide and carbonyl functional groups work as anchor of metal nanoparticles would influence the preferred orientation of crystal surface growth and thus help to improve the catalytic activity and stability for ORR.Secondly,on the basis of the optimized carrier,the the platinum metal is alloyed to adjust the d-band center of to further improve the catalytic activity of the composite.The double solvent impregnation method was used to introduce the platinum copper bimetallic precursor on the optimized support,by adjust the mass ratio of platinum copper precursor to form the structure of the alloy nanoparticles with different platinum-copper mass ratio on the surface of the support.To expose more catalytical active sites of metal platinum,0.1M perchloric acid was used to remove the copper on the surface of the platinum copper nanoparticles to form open-surface metal nanoparticles.After morphology characterized and catalytic activity tests,the catalyst with the best amount of copper was selected.The amperometric i-t test of the catalyst shows the composite material still shows better stability than commercial platinum carbon after 40000 s.Summarily,by changing the calcination temperature and duration of ZIF-8,the concentration of nitrogen doping and bonding properties in the porous carbon can be well regulated,which is helpful to manipulate the crystal orientation of Pt nanoparticles and their dispersion and loading on the NPCs.On this basis,adjustable amount of metal copper was further introduced,and finally the composite catalyst exhibits better catalytic activity and stability than commercial Pt/C.This work provides a detailed reference for the treatment of MOFs,especially MOFs formed by zinc ions and organic linkers,with the purpose of producing NPCs with adjustable types and contents of N to loading metal NPs and improves their ORR catalytic performance.