| Direct hydrazine fuel cell（DHFC）and zinc-air cell（ZAB）have attracted extensive attention because of their advantages such as high specific energy and convenient operation.However,the catalytic material is an important part of those kind of battery.It is well known that precious metal based catalytic materials（such as platinum and palladium）are considered as ideal electrocatalytic materials,but their sky-high price and scarcity limit their large-scale commercial application.To reduce the cost of catalytic materials,improve the activity of catalytic materials,the exploration of non-expensive catalytic materials system is imminent.Transition metal carbide（TMC）have attracted much attention because of their advantages of low cost,high electrical conductivity,corrosion resistance and good chemical stability.Moreover,their d-band electron density is close to that of precious metals,which they can exhibit Pt-like behavior in the electrocatalytic process.In addition,heteroatom doped materials,including N,B,S,and P doped materials,also exhibit remarkable electrocatalytic properties.Therefore,the composite of metal carbides and heteroatom doped materials can not only improve the electrical conductivity of the catalytic materials,but also induce a good synergistic effect between them,so as to get an advanced electrocatalytic performance.Therefore,it is of great significance to study the fabrication of carbides-based composite materials and apply them to the corresponding devices.This thesis is arm to prepare low-cost and high-activity catalytic materials for batteries.Taking reducing the cost of catalytic materials as the starting point,three kinds of carbide-based composite non-expensive catalytic materials have been obtained and used in the devices.Firstly,molybdenum carbide-nitrogen-doped carbon composite material was prepared for DHFC;then the multi-carbide based iron molybdenum carbide-nitrogen-doped carbon composite material were obtained to be used in ZAB;Finally,a multi-carbide based iron cobalt carbide-nitrogen-doped carbon composite material was obtained for the study of ZAB.In these three parts,physical characterizations,such as transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman,and selected electron diffraction（SAED）were used to characterize the structure of the prepared catalytic materials.Meanwhile,at the same time,their electrocatalytic performance and the performance of the assembled device were also tested.Part Ⅰ:Preparation of MoCx-NC composite carbon material applied in DHFCIn this part,a series of MoCx-NC electrocatalytic materials were prepared by high temperature carbonization.It is proved that the MoCx-NC is a composite carbon material of carbides and nitrogen-doped carbon by TEM,XPS and Raman characterization.Because of the strong interaction and synergistic effect between MoCx-NC and NC,the optimum MoCx-NC（900℃,5%）shows better hydrazine oxidation（Hz OR）performance,the current density is 3.56 mA cm-2,and the stability of 500 cycles reaches to 86.1%.When the catalyst was further assembled into a DHFC,it was found that the device had a high open-circuit potential of 0.96 V,a peak power density of 158.26 mW cm-2with good stability.This catalytic material would be a noble metal-free electrocatalytic material with great application potential in DHFC in the future.Part Ⅱ:Preparation of Mo FeCx-NC composite carbon material applied in ZABUsing the same method as above experiment,molybdenum iron carbide-based composite carbon material was prepared.By regulating the metal element ratio of catalyst and carbonization temperature,it was found that when the material mass ratio of molybdenum and iron was 1:3 and carbonization temperature is 950℃,Mo FeCx-NC electrocatalyst shows good catalytic performance of oxygen reduction(E1/2=0.839 V)and good stability（current retention 89.1%）.Furthermore,when Mo FeCx-NC was used as an oxygen electrode material,the assembled ZAB showes a high power density(79.1 mW cm-2),high specific capacity(548mAh gZn-1 at 10 mA cm-2;623 mAh g-1Znat 5 mA cm-2),and an open circuit voltage of 1.40 V.Part III:Fabrication of FeCoCx-NC composite carbon materials applied in ZABFeCoCx-NC electrocatalytic material was prepared by high temperature carbonization method.By adjusting the ratio of processing temperature and metal in the preparation process,it was found that,when the mass ratio of Fe-Co was 1:3,and the temperature was 900℃,the catalyst has excellent oxygen reduction performance with initial potential of 0.923 V and half-wave potential of 0.848 V with has good cycling stability.When used as catalytic material for oxygen electrode of ZAB,the obtained battery has a high open circuit potential（1.42 V）and peak power density(106.8 mW cm-2).In addition,XPS,XRD and EDS tests show that the prepared electrocatalytic material is composed of FeCo carbide and nitrogen-doped carbon,which contain Fe,Co,Mo,C and N elements. |
