Preparation And Electrocatalytic Application Of Palladium Modified MOF Carbon-based Composites

Energy plays a pivotal role in the rapid development of global science and technology and economy,as well as in the process of rapid population growth.Because of the limited reserves and rapid deleption of traditional fossil fuels,it is urgent to develop clean,efficient and sustainable new energy technologies.Among them,zinc-air batteries?ZABs?have the advantages of high theoretical energy density,safety,environmental friendliness and so on.ZABs have been considered to be a new type of energy storage and conversion equipment/technology with great marketing potential.However,there are still some problems in the commercialization of ZABs,and the key to solve these problems lies in the development of efficient and stable electrocatalysts and advanced electrochemical technologies.Therefore,the development of efficient,durable and low-cost electrocatalysts for the oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?for ZABs'air-cathode is critical for its large-scale commercial applications.In this thesis,using metal-organic framework?MOF?as sacrificial templates,a series of carbon-based nano-Pd composite catalysts with cost-effectiveness,excellent activity and robust long-term stability were prepared by green,facile and efficient strategies.The relationship between the structure,element composition,Pd content,interfacial electronic interaction and electrocatalytic activity of the samples was analyzed by a variety of characterization methods.The performance and stability of the catalyst in practical application were studied by ZABs test.The main contents of this thesis are as follows:?1?Firstly,Mo-MOF was used as sacrificial template to obtain nanotube?-Mo₂C through a facile carbonization process,and then Pd nanoparticles were in-situ fabricated on?-Mo₂C by a wet chemical method.The carbon-based nano-Pd composite catalyst Mo₂C-Pd_y?y denotes the initial Pd mass loading percentage?was employed to catalyze ORR and electrocatalytic hydrogen evolution reaction?HER?.Through electrochemical tests,it was found that with the increase of Pd content,the ORR and HER activities of the catalysts increased at first and then decreased,among which Mo₂C-Pd-9%showed the best performance.In ORR and HER tests,Mo₂C-Pd-9%also exhibited better electrocatalytic performance and long-term stability than commercial Pd/C catalyst.?2?Secondly,a series of rod-like mesoporous FeNi₃C_x-Pd_y?x represents the indeterminate amount of carbon?carbon matrix composites were successfully prepared by carbonization and surface modification using bimetallic MOF?FeNi₃-MOF?as precursor.Among them,FeNi₃C_x-Pd-7%showed the best performance as bifunctional oxygen electrocatalyst.In OER test,the overpotential at the current density of 50 mA cm^-2 was only288 mV,which is superior to that of the state-of-the-art RuO₂ electrocatalyst,and its catalytic performance for ORR was also close to that of Pt/C catalyst.Furthermore,it also showed good durability for both OER and ORR.?3?Finally,Mo₂C-Pd_y and FeNi₃C_x-Pd-7%prepared in the above two parts were employed as air cathode catalysts for self-assembled ZABs.By testing the performance and stability of ZABs:?i?Through the Mo₂C-Pd-9%-based ZAB in the actual battery operation,Mo₂C-Pd-9%-based ZAB showed the best battery performance in the Mo₂C-Pd_y series.The constant current discharge voltage,specific capacity and corresponding energy density all exceed the discharge capacity of Pt/C-based ZAB.?ii?The power density,energy density and specific capacity of FeNi₃C_x-Pd-7%-based ZAB are 234 mW cm^-2,967 Wh kg^-1 and 772 mAh g^-1,respectively,which are better than those of Pt/C+RuO₂-based ZAB.In addition,it also showed an efficient long cycle life?900 charge-discharge cycles?,and the total overpotential at 10 mA cm^-2 was only 0.72 V,demonstrating great commercial application potentials.