Controllable Controllable Preparation And Oxygen Reduction Of Carbon Monatomic Catalyst And Oxygen Reduction Of Carbon Monatomic Catalyst

Due to the rapid development of science and technology and the rapid growth of population,the demand for energy has increased greatly.Even though the efficiency of fossil energy utilization has been significantly improved,we are still faced with severe challenges such as energy crisis and ecological and environmental damage,so energy reform is the general trend.The large-scale use of renewable energy（such as solar,wind,hydropower,etc.）is limited by its inherent intermittency and volatility;Hydrogen is a clean secondary energy carrier,which can be easily converted into electricity and heat,with high conversion efficiency and wide sources.It can provide fuel for proton exchange membrane fuel cells,so that it is possible to achieve a smooth transition from fossil energy to renewable energy sustainable cycle,the birth of sustainable hydrogen economy.A metal-air battery with metal as a negative electrode and oxygen as a positive electrode is also a solution.Zinc-air battery has the advantages of high power density and high stability.However,the oxidation-reduction reaction（ORR）process is slow in both batteries.Therefore,efficient catalysts are needed to speed up the ORR reaction process.At present,the most commonly used catalysts are Pt-based precious metals,but this kind of catalyst has the disadvantages of high cost and poor durability.Therefore,we need to find low-cost and high stability catalyst as an alternative.Among them,the metal single-atomic site（SAC）catalyst with carbon material as the support has the advantages of single active site and high atomic utilization rate,which has become the most potential ORR catalyst.Moreover,the emerging Covalent organic framework（COF）,which has the advantages of high specific surface area and high stability,can become the more popular carbon matrix materials.However,monatomic catalysts also have disadvantages such as instability,inability to take advantage of collective effects of adjacent sites,and symmetrical electron distribution.Therefore,in this paper,the structure of Co F-metals was scientifically designed through the synergistic components such as defects,monatom/cluster,etc.,a series of monatomic catalysts of COF metals were prepared,and their active sites,components and catalytic activities were thoroughly studied.The main contents of this paper are as follows:（1）Aiming at the disadvantages of the traditional SAC catalyst with low density of active sites and poor activity,a simple KOH etching strategy was adopted in this paper to prepare cobalt-oxygen reduction catalyst with defects and synergic enhancement of metal clusters(Co _AC-SAs/N-C@CNT).Firstly,COF is synthesized as the carrier,and then KOH is introduced to etch and activate it,and carbon carrier with abundant defects is obtained.OH^-will also compete with N for Co coordination.After high temperature annealing,Co ion with OH^-coordination will form Co clusters,while Co ion with N coordination will form Co single atom.Finally,the structure of Co single atom and Co cluster coexist.The introduction of defects will expose more active sites,and the introduction of Co clusters will change the coordination environment and surrounding electron distribution of Co monatoms,promoting charge transfer and speeding up the reaction rate.Co _AC-SAs/N-C@CNT showed better ORR performance in alkaline electrolytes than conventional monatomic catalysts(Co _SAs/N-C@CNT).The zinc-air battery was prepared by using it as the cathode,and the high power density and stability are obtained,which proves that the Co _AC-SAs/N-C@CNT has great potential for practical application.It is also confirmed that Co _AC-SAs/N-C@CNT has better structure by DFT calculation.（2）In order to change the coordination environment and electron distribution of a single atom,in order to accelerate the charge transfer rate and improve the catalytic activity,this work studied the addition of two different metal atoms（Fe,Co）and a single metal atom（Fe/Co）on the performance of the change.After the performance test in alkaline electrolyte,the bimetallic catalyst has a higher half-wave potential,which confirms that adding another metal atom can also change the coordination environment and electron distribution to optimize the performance of the metal monatomic catalyst.（3）Although commercial platinum carbon has excellent ORR catalytic activity,it is now the most commonly used catalyst.However,Pt has high cost and few resources,so we are now focusing on reducing the use of platinum to reduce the cost while maintaining the excellent performance of platinum.The preparation of platinum single-atom catalysts is one solution,but the disadvantages of traditional single-atom catalysts still exist.Therefore,the research results of Work 2 were used to optimize the COF-supported precious metal（Pt）single atoms.By adding Fe,Co ions（Pt,Fe,Co/N-C）,the coordination environment and electron distribution of traditional Pt-N-C were changed to improve the catalytic efficiency.Pt,Fe,Co/N-C exhibited higher half-wave potential in alkaline electrolyte than Pt/N-C and Pt/N-C single-atom,and showed excellent cyclic stability and much better tolerance to methanol than PT/N-C,which proved that Pt,Fe,Co/N-C had excellent ORR catalytic performance.（4）According to the results of the previous two chapters,although the COF-based polymetallic single-atom catalysts have excellent ORR catalytic performance,fuel cells and zinc-air batteries also involve oxygen evolution reaction（OER）in addition to ORR reaction.Therefore,in addition to further increasing the types of transition metals,Ru was also added in this work to catalyze OER reaction,and five kinds of metal bifunctional catalysts（Pt,Fe,Co,Ni,Ru/N-C）based on COF were prepared.Performance tests show that Pt,Fe,Co,Ni,Ru/N-C has much better ORR catalytic activity than commercial platinum carbon in alkaline electrolyte.At the same time,the OER catalytic performance test was carried out,corresponding to the current density of10 m A/cm²,Pt,Fe,Co,Ni,Ru/N-C has lower overpotential than the commonly used OER catalyst（Ru O2）on the market,proving that it also has excellent OER catalytic performance,so Pt,Fe,Co,Ni,Ru/N-C is an excellent bifunctional catalyst.