Preparation And Electrocatalytic Properties Of Carbon-based Metal-free Catalysts Based On Defects And Doping

Climate change and environmental pollution caused by CO2 emissions from burning fossil fuels make humans face a severe energy and environmental crisis.The development of emerging renewable energy systems,such as fuel cells and rechargeable metal-air batteries,has become an urgent priority for human development.Electrocatalysts play a crucial role in renewable energy technologies and other important industrial processes.Currently,precious metals and metal oxides are the most widely used electrocatalysts.However,metal-based catalysts often have various weaknesses including high cost,low selectivity,poor durability,impurity poisoning,fuel cross-over effects,and adverse effects on the environment.While carbon-based metal-free materials have the advantages of abundant resources,environmental friendliness,high electrical conductivity,large specific surface area,controllable atomic layer structure,and excellent stability under harsh conditions.In addition,it can effectively remove organic matter in air or water during advanced oxidation,thereby reducing air/water purification costs and avoiding cross-contamination by eliminating the release of heavy metals/metal ions.As a result,it can be used as a green catalyst and has become the most promising advanced energy conversion and storage electrode material for quasi-capacitors,fuel cells and metal-air batteries,receiving increasing attention.The development of low-cost,high-efficiency carbon-based metal-free catalysts(CMFC)for renewable energy technologies and other fields has become a common opportunity and challenge worldwide.In order to solve the key scientific problems in the field of electrocatalysis,a series of metal-free catalysts with excellent performance for oxygen reduction has been prepared through the control of the inherent defects and doping of carbon materials,offering new ideas for better understanding and rational design of CMFC.The main research results are as follows:1.Based on the highly oriented pyrolytic graphite(HOPG)with regular structure and almost no defects,a series of customized molybdenum meshes with periodically arranged holes are used as templates to prepare matrix arranged edge-type defects with controllable pore size and number on the HOPG surface by inductively coupled plasma technique.The effects of different plasma atmospheres(O2,Ar,NH3)treatment,treatment time and defect sizes and number on graphene-based carbon materials for oxygen reduction(ORR),oxygen evolution(OER)electrocatalysis were explored.This experiment has certain guiding significance for understanding the effect of defects on CMFC and reasonably designing electrocatalyst with excellent performance.2.The soluble polyvinyl imidazole was prepared by using vinyl imidazole as monomer.By coordinating with different masses of zinc chloride,the pyrolysis was carried out to prepare micropores?mesopores and large ones with different specific surface areas.A series of carbon-based non-metal catalysts with adjustable pores were used to explore the effect of pore size on the performance of carbon material electrocatalysts.Finally,the catalytic activity and stability in 0.1M KOH alkaline medium were better than those of commercial Pt/C catalysts.The method is simple and efficient and can be used for the preparation of large-scale non-metal oxygen reduction catalysts.3.A 3D layered porous N-doped carbon material(PNC)was fabricated by pyrolyzing the ZIF-8 precursor using 3D silica assembled from silica nanoparticles as a template.Thermal decomposition of nitrogen-rich ZIF-8 produces N-doped carbon with a microporous structure,while assembled silicas having different diameters can form mesoporous and macroporous structures after being etched.The three-dimensional layered porous structure of PNCs not only facilitates the exposure of more active sites,but also contributes to the promotion of electrolyte transport,resulting in efficient electrocatalytic performance.The obtained 3D porous N-doped carbon(PNC-30)showed an excellent catalytic activity for ORR in both alkaline and acidic media,and the half-wave potential in a 0.1 M HCIO4 acidic medium was 0.76 V(The half-wave potential of commercial 20%Pt/C is 0.83 V),and the half-wave potential in a 0.1 M KOH alkaline medium is 0.90 V(The half-wave potential of commercial 20%Pt/C is 0.85 V),which is the best CMFC so far reported in ORR in alkaline medium.Further using of this newly developed PNC-30 as a highly efficient metal-free electrocatalyst for renewable energy devices such as fuel cells and rechargeable zinc-air batteries exhibits good performance.Therefore,the preparation of the catalyst provides a new idea for the construction of high-efficiency electrocatalysts,opening up new avenues for the development of renewable energy conversion and storage equipment.