X-ray Absorption Fine Structure And Modulating Differential Approach Applied In Electrocatalysis

High-efficiency energy conversion and utilization based on electrochemistry is expected to alleviate the energy and environmental pressures brought by traditional fossil fuels.The precise research and rational development of electrocatalysts urgently needs to clarify the internal structure-activity relationship of different materials and grasp the performance evolution law under working conditions.As one of the most important modern scientific installations,synchrotron radiation has gradually become a comprehensive research platform for exploring frontier scientific issues in electrocatalysis.In particular,the development of synchrotron radiation spectroscopy has brought important opportunities for clarifying the structure-activity relationship of electrocatalytic materials and further guiding their precise preparation.Among a variety of synchrotron radiation characterization techniques,synchrotron radiation X-ray absorption spectroscopy has element selectivity and can detect the local coordination environment and electronic structure of the sample,which is a powerful tool for characterizing catalytic materials and understanding the catalytic mechanism.The traditional hard X-ray absorption spectrum signal comes from the average of all atoms of the element to be detected in the sample,which is a means of bulk phase detection.By taking the difference of the two spectra to obtain the difference spectrum,the constant part of the system can be deducted,and the local or surface changes of the sample can be highlighted.To obtain high-quality differential spectra,modulated differential methods have been developed and applied in many fields of research,but electrochemical-based modulated differential methods remain to be developed.In this dissertation,we developed a measurement system for electrochemical modulated X-ray absorption differential spectroscopy and wrote the corresponding data processing program.Subsequently,several electrocatalytic systems were intensively studied using the developed X-ray absorption spectroscopy and its modulation differential method,revealing the intrinsic relationship between the catalyst microstructure and catalytic performance,and proposing the evolution regularity of the catalyst in the catalytic reaction.The main research contents and results are as follows:(1)Electrochemical modulated differential X-ray absorption fine structure measurement systems are built based on three ideas:direct differential,electronic filtering and digital filtering.We tested the influence of experimental parameters on the differential spectrum and gave an optimized experimental scheme,and wrote a data processing program based on digital filtering.From the results,the direct differential and digital filtering methods are more successful,and a high-quality differential spectrum is obtained.This study has successfully developed an electrochemically modulated X-ray absorption spectroscopy method and an on-line test system,which is expected to provide more precise experimental evidence for electrocatalysis research.(2)The structural self-optimization phenomenon of carbon substrates in OER catalysts was investigated by X-ray absorption spectroscopy and its differential spectrum.We synthesized Fe2O3-CNT catalyst,which exhibited excellent OER performance.In the subsequent characterization,it was found that the carbon nanotube substrate collapsed after the reaction.X-ray absorption spectroscopy and differential spectrum indicated that this structural collapse enhanced the interaction of Fe2O3 nanoparticles with the carbon substrate,thereby enhancing the electrocatalytic performance.This study is expected to draw researchers’ attention to the self-optimizing behavior of substrates.(3)The structure-potential response behavior of model catalyst IrOx was investigated by electrochemically modulated differential X-ray absorption spectrum.The results show that the accumulation of charges on the catalyst surface will not only lead to the change of the oxidation state of the catalyst,but also cause the shrinkage of the crystal lattice.Quantitative results show that the degree of bond length shortening is proportional to the amount of charge accumulated on the surface.Similar phenomenon was also found in K-RuO2 catalysts.This study provides new experimental evidence for understanding the surface adsorption behavior of electrocatalysts and also suggests that the modulation differential method can be a powerful tool for in situ studies of electrocatalysis.