| Electrochemical reactions such as oxygen reduction,oxygen evolution reaction and hydrogen evolution reaction are the core electrode processes of metal-air battery and overall water splitting.However,the kinetic speed of these reactions is slow,and efficient electrocatalysts need to be designed to promote the reaction.Among them,because of high catalytic activity,Pt-based catalysts have attracted much attention.However,its high cost,poor toxicity resistance and stability limit the development and application of metal-air battery and overall water splitting.Therefore,the preparation of low cost,good stability and high activity of non-Pt or low Pt catalysts to replace the Pt-based catalysts has become the focus of the field of electrocatalysis.Therefore,this dissertation,the basis on of ZIF with large specific surface area,high porosity,good structural stability and rich nitrogen content,is focused on metal/nonmetal doping by CVD and low temperature phosphating methods to prepare ZIF derived low platinum catalyst and non-platinum catalysts with different morphology and structure,and applied to the Zn-air batteries and over water spliting.In this paper,ZIF with large specific surface area,high porosity,good structural stability and rich nitrogen content were used as precursors.Metal/non-metal doping of ZIF materials was carried out by means of vapor deposition and low temperature phosphating to prepare low platinum and non-platinum catalysts derived from ZIF with different morphology and structure.It is also used as electrode catalyst in zinc-air battery and total water solution device.The morphology,structure,composition and electrochemical performance are researched in detail.A series of innovative research results haved obtained.Details are as follows:（1）Design and prepare of PtZn alloy-Nitrogen doped porous carbon composites with ultra-low platinum loading.PtZn alloy supported on nitrogen-doped porous carbon composite（PtZn@NC）was obtained by pyrolysis,ZIF-8 as precursor and coated with tannic acid,and platinum was deposited on the surface.The weak acid of tannic acid could break the ZIF coordination bond to obtain a hollow structure.The characterization results show that the nitrogen-doped porous carbon exhibits the structure of cross-linked pore cavities in which the PtZn alloy is highly dispersed,the specific surface is 1170.151 m2 g-1,the particle size is about 50 nm,and the contents of Pt and Zn are 6.7 wt%and 2.07 wt%,respectively.The material was used as an electrochemical catalyst for oxygen reduction.Catalysts exhibits remarkable oxygen reduction activity and cycling stability in both acidic and alkaline solutions,with electrochemical surface area（ECSA）of 10.85 m F cm-2,twice that of commercial Pt/C(3.6 m F cm-2).In the Zn-air batteries test,the open circuit voltage is 1.45 V,the maximum power density is 126 W cm-2,and the specific capacity at 5 m A cm-2 also reaches 997.8 m Ah g-1.（2）Design and prepare of trimetallic single atoms（Fe,Co,Ni）supported on ZIF porous carbon for rechargeable Zn-air batteries.Taking advantage of the property of ferrocene that is easily sublimated to flowing vapor and deposited on the surface of Co Ni-ZIF-8,chemical vapor deposition（CVD）synthesis was performed.With the increase of the pyrolysis temperature,the iron deposited on the surface can be captured and reduced by nitrogen-doped carbon,and a high-porosity nitrogen-doped porous carbon electrocatalyst Fe Co Ni-Nx is obtained,which is loaded with trimetallic active center（Fe,Co,Ni）.The characterization results show that Fe Co Ni-Nx’s specific surface area is 946.75 m2 g-1,compared with other bimetallic catalysts,Fe Co Ni-Nx has a co-existing structure of mesopores and micropores.Mesopore is beneficial to accelerate material transfer and micropore is beneficial to expose catalytic active sites.It presents a uniform distribution of atomic states,maximizes the catalytic perpormance,has bifunctional catalytic activity.The material was used as an electrochemical catalyst for oxygen reduction.The results show that the initial potential and half-wave potential in alkaline medium are 1 V and 0.89 V,respectively,which are better than the initial potential（0.9 V）and half-wave potential（0.815 V）of Pt/C.In acidic medium,the initial potential and half-wave potential are 0.85 V and0.737 V,respectively,which are better than the initial potential（0.84 V）and half-wave potential（0.714 V）of Pt/C.The material was used as an electrochemical catalyst for oxygen evolution reaction.The current density of 10 m A cm-2 can be achieved only at328 m V overpotential in alkaline medium,which is lower than that of Ru O2（330 m V）.As the cathode of the rechargeable Zn-air batteries,the results show that it has high open circuit potential（1.5 V）,energy density(135 m W cm-2),battery capacity(846.795m Ah g-1),excellent cycle stability（88 h）and prospects in the field of electronic equipment.（3）Design and fabricate of CoP-NiCoP heterojunction nanosheets and investigate its overall water splitting properties.Cobalt-Nickel bimetallic nanosheets were prepared by a one-pot solvothermal method,ZIF-67 as a precursor,adding nickel nitrate,and then CoP/NiCoP bimetallic heterojunction nanosheet was obtained by low-temperature phosphating method.The results show that the introduction of nickel can help to form a large number of heterogeneous interfacial active sites on the surface of nanosheets.In the HER/OER test,the introduction of Ni can speed up the electrochemical reaction rate and reduce the charge transfer resistance.At a current density of 10 m A cm-2,the HER and OER overpotentials are 217 m V and 319 m V,respectively,and can be used for overall water splitting with excellent cycling stability.The hydrogen evolution reaction overpotential of Pt/C was 86 m V,and that oxygen evolution reaction of Ru O2 was 296 m V. |
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