Construction And Electrocatalytic Performances Of MOF-Derived Carbon-Based Non-Noble Metal (Co,Fe) Catalysts

Energy is an important basis for the development of human society.With the continuing global demand for energy,the environmental pollution and climate change are increasingly serious,so the energy transformation and"carbon neutrality"have become urgent problems nowadays.Among these clean,renewable,and efficient energy conversion technologies,zinc-air batteries and water splitting hydrogen production devices have great development potentials in energy storage and energy conversion.However,these technologies suffer from large overpotentials during the electrochemical reactions,thereby the efficient,low-cost,and readily available electrocatalysts are required to facilitate the hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）,and oxygen reduction reaction（ORR）.Currently,the commercial catalysts are precious metals with high cost and scarce resources such as iridium,ruthenium and platinum,which is difficult to meet the needs of large-scale industrial applications.Accordingly,the development of non-precious metal-based electrocatalysts is particularly important and urgent.Non-noble-metal-based catalysts not only have the advantages of low cost and wide sources,but also show a great potential.The present thesis focuses on the design,syntheses,and electrocatalytic performances of carbon-based non-precious metal catalysts derived from metal-organic framework（MOF）.The specific research contents are as follows:1.Preparation and electrocatalytic oxygen evolution reaction performance of Co Fe@NC catalystsElectrocatalytic oxygen evolution reaction is one of the important reactions for rechargeable zinc-air batteries and water splitting devices.The development of high-performance OER catalysts is very important for energy storage and energy conversion,but it is also challenging.In this study,Co Fe alloyed nanoparticles are uniformly dispersed on the surface of nitrogen-doped carbon spheres by in-situ growth of MOF on polydopamine（PDA）spheres,followed by a high-temperature pyrolysis.The electrocatalyst shows an excellent OER activity and stability owing to the synergistic effect and structural advantages of active species.The results reveal that the formation of Co₇Fe₃alloy plays a key role in improving the catalytic performance.In addition,the support size has a significant effect on the catalytic activity.The optimal performance can be achieved by adjusting the geometrical and electronic structure of the catalyst.This study provides a new idea to explore the effects of composition and support on OER performance.2.Preparation,electrocatalytic oxygen reduction reaction,and zinc-air batteries performances of Fe-NC@NCNT catalystsOne-dimensional metal/nitrogen-doped carbon materials show a great potential as efficient ORR electrocatalysts.The Fe/N-doped carbon nanotubes（Fe-NC@NCNT）are prepared by the in situ reaction and calcination using polypyrrole（PPy）tubes and Fe/Zn-based zeolite imidazole frameworks as the precursors/templates.Due to the hierarchical pore structure,high electrical conductivity,and abundant Fe-N_xactive species,the electrocatalysts show a comparable catalytic activity to commercial Pt/C.It is found that the Fe-NC@NCNT possesses a four-electron transfer pathway in an alkaline electrolyte and shows a high half-wave potential（0.88 V vs.RHE）,excellent cyclic stability,and methanol resistance.When the electrocatalyst is used as the air electrode for rechargeable liquid and all-solid-state zinc-air batteries,the devices exhibit superior device performances than those of（Ru O₂+Pt/C）-based one.This study provides a guidance for the construction of Fe/N-doped one-dimensional tubular ORR electrocatalysts.3.Preparation,electrocatalytic,zinc-air batteries,and water splitting performances of Co-NCNT@NHC catalystsExploring the electrocatalysts with ORR,OER and HER trifunctionalities is very important for the development of rechargeable zinc-air batteries（ZABs）and water splitting devices.In this study,Zn O polyhedra derived from zeolite imidazole framework（ZIF）are employed as the support for a secondary growth of ZIF particles.After a pyrolysis treatment,a trifunctional electrocatalyt with a rambutan-like architecture is constructed.The Co nanoparticles in the structure are firmly encapsulated in N-doped hollow carbon polyhedra（NHC）grafted with in situ N-doped carbon nanotubes（NCNTS）,resulting in the formation of Co-NCNT@NHC.The results show that the strong coupling between N-doped carbon support and Co nanoparticles endows the catalyst with an excellent catalytic activity and stability.The ORR half-wave potential of the optimized Co_0.01-NCNT@NHC in an alkaline electrolyte is 0.88 V,together with an OER overpotential of 300 m V at 20 m A cm^-2and HER overpotential of 180 m V at 10 m A cm^-2.The Co-NCNT@NHC exhibits a good device performance when it is used as the electrode catalyst for water splitting and zinc-air batteries,meanwhile the self-driven water slitting hydrogen production system also shows a good performance.This study is helpful for constructing high-performance multifunctional electrocatalysts in the application of practical integrated energy systems.