Study On Preparation And Oxygen Reduction Reaction Performance Of Transitional Metal Single-Atom Electrocatalysts Derived From MOFs

The rapid growth of modern society consumes large storage of energy.It’s a necessary way to achieve a low-carbon economy and reduce environmental pollution to looking for alternatives to fossil fuels.Recently,renewable energy sources containing wind energy have been widely developed.However,due to the constraints of weather,environment,cost and other factors,a safe,reliable and efficient method of storing renewable energy and sustainable energy is urgently needed.Both fuel cells and metal-air batteries are becoming the most promising energy storage devices due to high performance and high power density.However,sluggish oxygen reduction reaction kinetics is one of the most important key to limit the large-scale development of batteries.In order to increase the rate of the oxygen reduction reaction,it is necessary to develop an oxygen reduction catalyst with sophisicated design and long-life cycle stability.Platinum-based catalysts have outstanding catalytic performance for oxygen reduction reactions,which are limited by cost,stability,durability and other factors.Therefore,the development of high-performance non-precious metal catalysts is urgent.As a new type of catalyst,single-atom catalysts have broad development prospects in catalyzing oxygen reduction reactions.Based on the study of single-atom catalysts for oxygen reduction reactions,this work selects transition metal elements such as iron,nickel,cobalt,etc.,exploring new processes,and synthesizes method for preparation of single-atom catalysts with elaborated coordination.Researching and developing new catalytic mechanism through ORR,zinc-air battery and DFT.Understanding relationship of the catalyst from structure to activity.The main content of this work includes three parts:1.Construction of a Ni-N-C catalyst with precisely coordinated Ni-C₄-C₁₀ active sites.In this work,a liquid phase reaction method is used to encapsulate the nickel source in the ZIF-8 cavity,and Ni-N₄-C₁₀ active sites are constructed on the nitrogen-doped porous carbon through high-temperature pyrolysis and applied to oxygen reduction reactions and zinc-air batteries.Compared with Pt/C,the half-wave potential of Ni-N-C catalyst is positively shifted by 76 mV,and the kinetic current density（J_k@0.9 V vs.RHE）is 10.8 times that of Pt/C.The power density of the Ni-N-C catalyst-based zinc-air battery is 1.47 times that of the Pt/C catalyst-based zinc-air battery,and it has excellent battery performance.2.Preparation of high performance SA-Fe-NC iron single atom catalyst containing Fe-N_x.In this work,iron phthalocyanine was transported via gas diffusion strategy into the nitrogen-doped porous carbon,and converted into iron single-atom sites at high temperatures.The research results show that the SA-Fe-NC catalyst has excellent electrochemical catalytic activity and electrochemical stability,and its half-wave potential is better than the half-wave potential of Pt/C of 38 m V,and it has excellent electrochemical stability.The kinetic current density（J_k@0.9 V vs.RHE）is2.76 times that of Pt/C,and the catalytic reaction of SA-Fe-NC is a four-electron transfer during reaction process.Power density of 172 mW·cm^-2 and energy density of833 mA hg_Zn^-1 was exerted by SA-Fe-NC catalyst-based zinc-air battery at current density of 5 mA·cm^-1,which are higher than that of commercial Pt/C.3.Preparation of Co,Fe-N/C carbon-based catalysts containing Fe-N_x and Co-N_xactive sites.In this work,using MOF-5 as a sacrificial template,Fe-N_x sites were obtained by pyrolysis and liquid phase reaction method,and Co-N_x sites were prepared by adding Co element through gas diffusion method.Compared with the single Fe-N_xsite catalyst,the introduction of Co not only increases the content of carbon defects but also increases the specific surface area of porous carbon,and assists in improving the performance of the oxygen reduction reaction.The research results show that the half-wave potential(E_1/2)of Co,Fe-N/C catalyst is 36 mV higher than that of Pt/C,and the kinetic current density（J_k@0.9 V vs.RHE）is 1.18 times that of Pt/C.Co,Fe-N/C catalyst-based Zn-Air battery has high power density and long-term constant open circuit voltage stability.It has a certain practical value of Zn-Air battery cathode catalyst.