Investigation On The Ti-Based Nitride And Titanium Nitride Based Low Platinum Catalysts Towards Oxygen Reduction

With the rapid development of economy,the global are suffering several challenges such as the exhaustion of fossil fuel and the worsening of environmental pollution.Therefore,it is urgent to develop efficient and clean energy resources and technologies.Fuel cell,an electrochemical device that can directly convert the chemical energy of fuel into electric energy,presents low emission,low noise,and high energy conversion efficiency.This makes it become one of the important ways to address the global challenges of environmental pollution and energy exhaustion problems.Due to its simple structure,low operation temperature,high power density and fast startup,proton exchange membrane fuel cell?PEMFC?has been recognized as promising application on the vehicle,portable electronics and cogeneration system.The insufficient activity of the electrocatalyst for oxygen reduction reaction?ORR?at cathode is one of the several barriers that hinder the popularization of PEMFC.To date,the platinum?Pt?-based catalysts are considered as the benchmark for ORR.The large-scale use of the noble metal Pt can result in high cost of the catalysts.Besides,the corrosion of conventional carbon support of the catalyst under the operated potential will lead to the deterioration of the cell performance.These limit the industrialization of cathode catalyst for PEMFC.Compared with the traditional Pt/C catalyst,Pt-based core-shell catalyst not only reduces the use of precious Pt and the cost of catalyst but also improves the electrocatalytic activity and stability,which makes it a promising ORR catalyst for commercialization.The pulse electrodeposition is a novel method reported by our group,for the preparation of core-shell catalyst with low-Pt content,high activity and stability.A Ti_0.9Cu_0.1N@Pt/N-CNT core-shell catalyst with 6.9 time of the ORR mass activity compared to commercial Pt/C was developed by this method,where a low-cost transition-metal nitride?TMN?with high conductivity was used as the core material.Furthermore,TMN supported on different carbon supports have yielded distinct effect on the state of the deposited Pt.In this thesis,Ti_0.9Cu_0.1N was supported on nitrogen-doped carbon nanotube?N-CNT?and nitrogen-doped reduced graphene oxide?N-rGO?,respectively.Then the obtained supported Ti_0.9Cu_0.1N materials went through a pulse electrodeposition of Pt to investigate different support on the state and effect of the deposited Pt.It was found that Pt preferred to deposit on Ti_0.9Cu_0.1N supported by N-CNT to form a core-shell structure,achieving a high mass activity of 1.03 A?mg of Pt?^-1.As for Ti_0.9Cu_0.1N/N-rGO,the Pt trend to aggregate on N-rGO support rather than deposit on Ti_0.9Cu_0.1N,performing an undesirable mass activity of 0.16 A?mg of Pt?^-1.The derived Ti_0.9Cu_0.1N@Pt/N-CNT exhibits higher stability than that of Pt-Ti_0.9Cu_0.1N/N-rGO.Transition electron microscopy?TEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,and Raman analysis indicated that the tendency of Pt depositing on different surface under pulse electric field can be ranged as below:N-rGO>Ti_0.9Cu_0.1N>N-CNT.Moreover,the core support distributed with high density of defects is detrimental for the deposition of Pt on the core.The thesis has investigated the support condition of the core materials for preparation of Pt-based core-shell catalysts by pulse electrodeposition.This is significant on guiding the popularization of pulse electrodeposition for preparing Pt-based core-shell catalysts.Additionally,porous carbon materials are most widely used as the support for electrocatalyst for their low cost,excellent conductivity and high surface area.Nevertheless,the corrosion under the work potential of the carbon material would decrease the durability of the catalyst,which perplex the researcher in the recent years.Given this,a Ti_0.95Ni_0.05N nanotube(Ti_0.95Ni_0.05N NT)support combining multi-structure morphology of one dimension,hollow and layer has been synthesized by a facile tow-step method in this thesis as well.The Pt loaded Ti_0.95Ni_0.05N catalyst Pt/Ti_0.95Ni_0.05N NT outperformed the carbon supported Pt?Pt/C?catalyst with 50 mV of the half-wave potential surpassing.More importantly,the half-wave potential of Pt/Ti_0.95Ni_0.05N NT decreased only 12 mV after 10000 cycles in the durable test;while the Pt/C lost almost 29 mV of that merely after 2000 cycles.This indicates that the Ti_0.95Ni_0.05N NT support exhibits much higher durability than the conventional carbon support.The Ti_0.95Ni_0.05N NT support developed in this thesis exhibits porous structure,which is beneficial for the dispersion of catalyst particle and the mass transfer for the reactant.Furthermore,the excellent electrochemical corrosion resistance of Ti_0.95Ni_0.05N NT support has greatly enhanced the stability of the catalyst,which offers a new strategy for promoting the durability of the cathode catalyst for fuel cell.