Preparation Of ZIF-67 Derived Materials And Study On Their Electrocatalytic Oxygen Evolution Reaction Performance

With the continuous development of society,the request for energy continues to increase.The use of energy sources such as fossils and coal has caused pollution to the environment,and reserves are decreasing.Developing green and renewable energy can availably solve the above problems.Hydrogen energy is a green energy and can replace traditional fossil energy.At present,large-scale hydrogen production often adopts the method of electrocatalytic water decomposition.The method is simple to operate and pollution-free,resultinh a promising hydrogen production technology.However,due to the complex four-electron oxidation process of the anodic oxygen evolution reaction(OER),the kinetics of OER is slow and requires a high potential to promote the reaction.Therefore,it is necessary to find a stable and efficient catalyst to promote the reaction.At present,noble metal oxides such as RuO2 have good electrocatalytic oxygen evolution reaction performance.However,due to its high price and scarce resources,its large-scale application and development have been limited.Metal-organic framework compound(MOFs),consisting of metal ions and organic ligands interconnected by self-assembly.MOFs,which generally have a large surface area,and the size and morphology can be changed by changing the synthesis conditions,MOFs are gradually used to prepare electrode materials and electrochemical catalysts because of their superior properties.ZIF-67 is a zeolite imidazole framework(ZIFs),a kind of MOFs,which has better stability than general MOFs.In addition,the metal element of ZIF-67 is Co,which has better electrocatalytic hydrolysis performance.However,because the coordination of the metal and skeleton in ZIF-67 is almost saturated,the conductivity is poor,which makes its catalytic activity worse.In this thesis,we calcined ZIF-67,encapsulated nanoparticles within ZIF-67,and coated ?-conjugated molecules on the surface to improve its electrocatalytic activity.The specific research content is as follows:1.We put cobalt nitrate hexahydrate and 2-methylimidazole in methanol solvent to synthesize ZIF-67.ZIF-67 was then calcined at low temperature under N2 atmosphere to dissociate its partial distributor from the metal and form coordination unsaturated bonds.The obtained material is called quasi-ZIF-67 and has a large Brunauer-Emmett-Teller surface area of 2038.2 m2·g-1.The material has better electrocatalytic activity than ZIF-67.At a current density of 10 mA cm-2,the overpotential is 286 mV and the Tafel slope is 84 mV dec-1.Therefore,in the case of maintaining the basic skeleton of the compound,low-temperature calcination can expose more metal active sites to accelerate electron transfer to improve electrochemical catalytic activity.2.We put cobalt nitrate hexahydrate,2-methylimidazole,and gold nanoparticles in a beaker at the same time via one-step method,and left it for 24 h.The size of gold nanoparticles is about 13 nm.The smaller the particles,the better the catalytic activity.The prepared product was Au@ZIF-67,and then calcined at different temperatures under a protective atmosphere.Samples calcined at 500? has good electrocatalytic oxygen evolution performance.The overpotential is 367 mV(j=10 mA cm-2),which is better than overpotential of ZIF-67.The Tafel slope of Au@ZIF-67-500 is 233 mV dec-1.3.We put Co(NO3)2·6H2O,2-methylimidazole,and 2,3,6,7,10,11-hexahydroxytriphenyl(HHTP)in the reactor,and added methanol and DMF as solvent via a simple one-step solvothermal method.It was then sonicated for 5 minutes,and finally placed in an oven at 60? for 2 hours.Since HHTP is a ?-conjugated molecule with high efficient charge transfer rate,recombination with ZIF-67 could enhance the electron transport of ZIF-67,thus improving its electrical conductivity,improving its electrochemical activity and improving the electrochemical catalytic efficiency of MOF materials.The results of electrochemical tests show that the material has an overpotential of 23 8 mV(j=10 mA cm-2)and a Tafel slope of 104 mV dec-1.