Properties Of Nickel-based Energy Materials And Their Synchrontron-based Characterizations

With the rapid development of the economy all over the world,both the industrial production activities and daily life needs have imposed much higher requirements on energy supply.However,the usage of traditional fossils not only releases a big amount of carbon dioxide and other gases which could aggravate the greenhouse effect,but also brings a series of environment problems such as fog and haze.Therefore,to meet the demand of sustainable energy development,we must optimize and adjust the existing energy supply structure which is dominated by fossil fuels.In order to realize this goal,developing energy technology including energy storage technology and energy conversion technology is an important method.Nevertheless,current energy materials show some disadvantages such as high cost,low energy storage density,insufficient energy efficiency,lack of stability and poor security,which greatly limit their usage in practical applications.In consequence,in order to further develop new materials for energy storage and energy conversion,we must thoroughly study the internal composition,crystal structure as well as electronic structure of these energy materials.Only with a clear insight understanding of the material structure,can we further study the structure-activity relationship between the material structures and their energy storage or conversion performance for application,which could be used to guide the design and synthesis of new energy materials,thus optimizing the existing energy supply structure.Recently,with the establishment of a lot of advanced synchrotron radiation sources around the world,the applications of synchrotron radiation characterization technology in energy field have become more and more extensive.Taking the advantages of high intensity,good collimation and wide spectrum distribution of synchrotron radiation,synchrotron radiation based characterization such as XANES and EXAFS could selectively obtain information such precise electronic structure and coordination structure of the specific atoms.As a results,these synchrotron radiation based technology is of great importance in studding the structure-activity relationship of energy materials.In this dissertation,we select the design and controllable synthesis of nickel-based energy materials as the entry point of our research.Synthetic strategy adjustment,element doping,carrier combination and a series of means were used in the synthesis of new energy materials.On this basis,a big variety of advanced synchrotron radiation based characterization techniques have been employed to study the coordination structure,electronic structure information,interaction between atoms and active material-carrier interface interactions.Combing the characterization of the electrochemical performance in energy storage and energy conversion,we further revealed the relationships between the microstructure and the macroscopic properties of some materials.The specific research details of this dissertation is showed as follows:1.There are many factors that affect charge/discharge performance of lithium battery cathode materials.In traditional research,scientists mostly pay attention to the crystal structure,particle morphology and so on,which is not enough.In this dissertation,the traditional material LiMn2O4 synthesized using simple high-temperature sintering method was served as the model material and then Ni element doping was employed.We explained the change of charge/discharge performance from the perspective of orbital hybridization and electronic structure.Briefly,the precise short-range order structure was firstly studied using the Ni/Mn K-edge EXAFS.The following experiment and simulation of Ni/Mn L2,3 edge XANES reveals the high ionic Ni-O bonds and the high covalent Mn-O bonds in the materials.Further DFT calculations as well as the O K-edge XANES results revealed the O-involved charge rebalance initiated by Ni doping,which cause the change of the electronic structure of the whole material system,and thereby triggering the electrochemical performance.This work will provide clues for design and preparation of next-generation lithium-ion battery materials.2.To further verify the influence of electronic structure engineering on the energy conversion material,a two-step synthesis process was used to uniformly dope the V atom into the model catalyst NiS2 by employing LDH as the precursor.And we successfully prepared V-Doped NiS2.The XRD patterns and Ni/V K-edge EXAFS clearly reveal the displacement doping of V atoms.The results of XPS and XANES demonstrate that the doping of V atoms modulates the whole electronic structure and thus the electron concentration on Ni sites increases.Moreover,combing theoretical DFT calculations and temperature-dependent resistivity test,we provide the successful demonstration of electronic structure reconfiguration of NiS2 from semiconductive characteristics to metallic V-doped NiS2 via V atom doping,and thereby high overall water splitting performance was delivered.This work reveals that electronic structure engineering might be an effective method to improve the energy conversion efficiency of energy materials.3.To further detailedly study catalyst-support interactions on catalytic performance.We fabricated a flexible self-standing electrode by combing NiFe-LDH with single-walled carbon nanotubes(SWNT)film using a facile one-pot hydrothermal method.The SEM and TEM results reveals the uniform growth of NiFe-LDH nanosheets on the SWNT bundles.Further X-ray photoelectron spectroscopy(XPS)and X-ray near-edge absorption spectroscopy(XANES)characterizations confirms the electron coupling and interaction between the NiFe-LDH and the carrier SWNT film via the M-O-C bond(M=Ni/Fe).Strong electron coupling not only improves the intrinsic catalytic activity of the NiFe-LDH but also accelerate the electron transport between the catalyst and the carrier,and thereby a dramatic improvement in OER catalytic activity is delivered.This work provides a platform for preparing high performance flexible self-standing electrodes via enhancing the electron coupling between catalysts and carriers.