Surface/Interface Modulation,Catalytic Performance And Synchrotron Radiation Studies Of Carbon-Based Catalysts

With the continuous consumption of global petroleum and other fossil sources,energy and environment issues have become the big problem faced by whole body of mankind.Human society also has a higher requirement for the life quality due to the rapid development of economy.Overuse of fossil energy and lack of attention to the clean energy use have caused much problems,such as the greenhouse effect and haze,which have attracted much concerns over the world.In order to realize the green and sustainable development of human civilization and better cope with the energy and environmental crisis,it is exigent to exploit efficient and sustainable energy facilities.Catalytic reactions are central for various clean energy generation systems.As for electrochemical water splitting,fuel cells and other fields,high-efficient catalysts can effectively improve the conversion efficiency of electrochemical devices.As for hydrogen energy field,the development of suitable hydrogen storage materials and the efficient dehydrogen from hydrogen storage materials are also the research hot point.To data,the catalysts with highest efficiency are mainly made up of noble metals?Pt,Ru,Ir,et al.?.However,the scarcity and high-costs still hinder their large-scale applications.Therefore,it is important to developing high-efficient noble metal free catalysts.Carbon-based materials have been regarded as one of the most competitive candidates among noble metal free catalysts due to their unique physical and chemical properties.Generally,when carbon compounds with other metal compounds,a larger specific surface area for more exposed active sites could be obtained.In addition,it can also promots the reaction kinetics due to the excellent electrical conductivity.In this thesis,we have prepared various carbon-based interfacial materials under rational design and controllable synthesis.The electronic structure,geometric configuration and interfacial electronic behavior have been deeply studied and revealed.Aiming to figure out the reconstruction process of the carbon based interfacial catalysts,we also pre-studied the reconstruction by choosing single component as an example.The detailed research content and the innovation of the thesis have been listed in the following points:?1?The unique Ni/NiO@C ternary interfacial structure was obtained through annealing treatment towards the simple metal coordination compounds.The"pomegranate" like ternary interfacial structure consist of ultrafine Ni nanoparticles,ultrathin NiO clusters on the Ni surface and defective ultrathin carbon layers.Thus,the ternary interfacial structure was successfully obtained by these three components with strong interfacial coupling.The precise structural informations of the ternary interfacial structure were obtained through atomic-level characterizations?especially soft and hard XAFS analysis?.The HER performance of the ternary interfacial structure was further evaluated through systematic electrochemical tests.In addition,theoretical calculations probed that the Ni/NiO interfacial structure had a significant modulation effect on the energy barrier of the rate-determining step of HER,which accelerates the water activation.?2?In order to further reveal the activation effect of water molecules from multiple interface structures,we then fabricated a new type of carbon-supported Ni/Ni₂P nanoparticles?C-Ni/Ni₂P?via controllabe phosphation reaction.Several synchrotron radiation-based technologies were further used to reveal the interfacial structure and electronical states of the heterostructure.The catalytic performance of the C-Ni/Ni₂P hybrids was systematically evaluated in the ammonia borane hydrolysis reaction.The catalytic results show that the adjustable reaction rate during the ammonia borane hydrolysis could be achieved by adjusting the ratio of Ni and Ni₂P in C-Ni/Ni₂P.Density functional theory?DFT?calculations further confirmed that the hetero-structure exhibits higher adsorption energies of water molecules and amino ia borane molecules,which can efficaciously accelerate the subsequent catalytic process.More importantly,the heterogeneous structure showed a lower rate-determining step energy barrier?activation of water molecules?,which promotes the attack of water molecules on ammonia borane molecules.?3?To further reveal the asymmetric distribution phenomenon of interfacial charge among carbon-based catalysts and the effect of this charge redistribution towards the catalytic process.We developed a new type of CoP and defective carbon?CoP-DC?composite.The interfacial charge transfer process of CoP-DC composites was further confirmed through synchrotron-based X-ray absorption spectroscopy?XAS?,ultraviolet photoelectron spectroscopy?UPS?,and X-ray photoelectron spectroscopy?XPS?combining with density functional theory?DFT?calculations.The redistribution of interfacial charges was directly observed between CoP and DC as the interfacial electrons gathered towards the DC surface while the positively charged holes formed on the CoP surface.The negatively-charged DC and positively-charged CoP serve as the catalytic active centers of ORR and OER,which showed ideal performance and stability towards ORR/OER bifunctional process.?4?In order to further reveal the structural reconstruction of carbon-based interfacial catalysts and excavate its influence on dynamical process.The self-reconstruction behavior of the catalyst in the electrochemical process was studied to further probe the surface evolution of electrocatalysts,which may quiet important for the carbon-based interfacial catalysts.Sulfur atomically doped Bi nanobelt?S-Bi?catalyst was constructed based on the self-reconstruction process towards electrochemical process.Several characterizations further revealed the existence of S atoms in the Bi lattice.Both theoretical and experimental methods confirmed that the S-Bi nanobelt electrocatalyst exhibited higher catalytic performance in the electrocatalytic nitrogen fixation reaction.