Nano-structural Manipulation Of Transition Metal-based Materials By Carbonized Polymer Dots For Electrochemical Water Splitting

Due to its high energy density and environmental friendliness,hydrogen energy is considered as a clean renewable energy that is expected to replace the traditional fossil energy and thus solve the energy and environmental crisis.Electrochemical water splitting,as an important approach with high efficiency,good selectivity and easy manipulation on the reaction process to obtain hydrogen energy,has attracted extensive research interest in recent years.In order to realize highly efficient and stable electrochemical water splitting to produce hydrogen,it is very important to develop effective electrocatalysts for hydrogen evolution and oxygen evolution to accelerate the reaction kinetics of water dissociation.In recent years,researchers have developed many excellent transition metal-based water-splitting electrocatalysts.However,these catalytic materials also encounter some problems such as poor electrical conductivity and stability,single catalytic function,and even high cost.Because of their unique structural and electronic properties,as well as excellent stability,carbonized polymer dots(CPDs)have great potential in regulating the nanostructure and catalytic activity of transition metal-based electrochemical water-splitting materials.Specifically,the abundant structural sites on the surface of CPDs can provide a high-density metal binding sites,providing interfacacial modification and support for transition metal-based materials,and thus optimize the reaction kinetics of intermediates in the catalytic process,and even reduce the amount of precious metals.The excellent electron donor-acceptor character of CPDs play an important role in regulating the composition of the catalyst,and can also promote the electron transfer kinetics of the catalyst.These structural and electrical characteristics make CPDs have great potential to enhance the activity and stability of transition metal-based electrocatalytic water-splitting materials.Based on the above backgrounds,this thesis aims to utilize CPDs with abundant structural sites and electron donor-acceptor character to construct interfacial electronic coupling with metal-based materials,regulating the electronic structure,composition and morphology of transition metal-based materials,so as to develop highly efficient and stable water-splitting electrocatalysts.Specifically,this thesis mainly includes the following three aspects:In the second chapter,we used the strong metal coordination ability and unique electron transfer property of CPDs with high nitrogen and oxygen content to construct in situ nitrogen-doped carbon coated cobalt nanoparticles(N-C@Co NPs)and CPDs-supported cobalt trioxide nanoparticles(CPDs@Co₃O₄)water-splitting electrocatalysts.This work revealed that CPDs can act as a nanotemplate for the formation and crystallization of cobalt-based nanoparticles,thus endowing the catalyst with unique morphology and bonding structure.The synergistic effect of CPDs and cobalt-based materials on catalyst activity enhancement was studied in detail.CPDs@Co₃O₄catalyst system further verified the versatility of CPDs in regulating the component,morphology,interfacial structure of transition metal-based materials as well as the catalytic activity.The obtained N-C@Co NPs exhibited good bi-functional electrocatalyst activity and stability for HER and OER,while the N-C@Co NPs catalysts showed highly efficient and stable OER activity.In the third chapter,taking advantage of the abundant metal binding sites of CPDs,which can not only inherit the Co doping in the precursor,can also coupled with foreign Ru atoms,we developed a effective,stable,p H-universal electrochemical overall water-splitting material(Ru Co@CPDs).The experiment and theory results showed that the alloying of Ru with Co atom,and interfacial modification by CPDs can reasonably regulate the bulk and interfacial electronic structures of Ru through strong electron coupling,i.e.,changing the chemical structure and valence state of Ru,thus optimizing the electron transfer kinetics and water dissociation kinetics of the catalyst.The developed electrocatalyst exhibited high efficiency and stable HER and OER activities over a wide p H range.This work firstly enables Ru Co to obtain the highly efficient,stable and and p H-universal overall water-splitting performance,and established the relationship between the chemical valence/electronic structure and catalytic activity at the atomic level.In the fourth chapter,we developed a CPDs-coupled Ru O₂-based water-splitting electrocatalyst by utilizing the abundant metal binding sites on the surface of metal ions doped CPDs as well as the unique electron acceptor(assisted oxidation)properties.The experimental results showed that the designed catalyst has abundant charge transfer channels and high crystallinity of Ru O₂,and the in-situ doped Mn makes the catalyst form more lattice oxygen sites and oxygen vacancy,which endow the catalyst with excellent oxygen evolution activity and stability.The doped Ru-Ru atomic arrangement in Ru O₂can not only synergistically enhance the oxygen evolution performance of Ru O₂,but also act as an active site for hydrogen evolution.The optimized catalyst exhibits highly efficient,stable and p H-universal OER performance,as well as excellent HER performance in alkaline media.In summary,we fully utilized the interfacial modification and supporting characteristics of CPDs through its structural design,to regulate the morphology,composition and electronic structure of transition metal-based materials,thus realizing the effective and stable electrocatalytic water-splitting process.In this thesis,a universal strategy was established for the preparation of efficient and stable CPDs/transition metal-based composite electrocatalysts,which pave a new pathway for broaden the application of CPDs in the field of catalysis.