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期刊论文 2

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2017 2

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Design of efficient Pt-based electrocatalysts through characterization by X-ray absorption spectroscopy

Nebojsa S. MARINKOVIC, Kotaro SASAKI, Radoslav R. ADZIC

《能源前沿（英文）》 2017年第11卷第3期页码 236-244 doi: 10.1007/s11708-017-0487-1

摘要： A method is described to determine the internal structure of electrocatalyst nanoparticles by X-ray absorption spectroscopy (XAS). The nondestructive spectroscopic technique typically utilizing synchrotron radiation as the source measures changes in the X-ray absorption coefficient as a function of energy. The bulk technique has found its use for materials characterization in all scientific areas, including nanomaterials. The analysis of the internal structure of nanoparticles reveals interatomic distances and coordination numbers for each element, and their values and mutual relations indicate whether the elements form a homogeneous or heterogeneous mixture. The core-shell heterogeneous structure in which certain elements are predominantly located in the core, and others form the encapsulating shell is of particular importance in catalysis and electrocatalysis because it may reduce the amount of precious metals in nanoparticles by replacing the atoms in the core of nanoparticles with more abundant and cheaper alternatives. The examples of nanoparticle structures designed in the laboratory and the approach to model efficient catalysts through systematic analysis of XAS data in electrochemical systems consisting of two and three metals are also demonstrated.

关键词： X-ray absorption spectroscopy EXAFS XANES nanocatalysts core shell

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β-Nickel hydroxide cathode material for nano-suspension redox flow batteries

Yue LI, Cheng HE, Elena V. TIMOFEEVA, Yujia DING, Javier PARRONDO, Carlo SEGRE, Vijay RAMANI

《能源前沿（英文）》 2017年第11卷第3期页码 401-409 doi: 10.1007/s11708-017-0496-0

摘要： As part of an effort to build a prototype flow battery system using a nano-suspension containing β-Ni(OH) nanoparticles as the cathode material, nano-sized β-Ni(OH) particles with well-controlled particle size and morphology were synthesized via the one-step precipitation of a NiCl precursor. The composition and morphology of the nanoparticles were characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The XRD patterns confirmed that β-Ni(OH) was successfully synthesized, while SEM results showed that the particle sizes range from 70 to 150 nm. To ensure that Ni(OH) could be employed in the nano-suspension flow battery, the electrochemical performance of the synthesized β-Ni(OH) was initially tested in pouch cells through charge/discharge cycling. The phase transformations occurring during charge/discharge were investigated using X-ray absorption spectroscopy to obtain the shift in the oxidation state of Ni (X-ray adsorption near edge structure, XANES) and the distances between Ni and surrounding atoms in charged and discharged states (extended X-ray absorption fine structure, EXAFS). XANES results indicated that the electrode in the discharged state was a mixture of phases because the edge position did not shift back completely. XAFS results further proved that the discharge capacity was provided by β-NiOOH and the ratio between β-Ni(OH) and g-NiOOH in the electrode in the discharged state was 71:29. Preliminary nano-suspension tests in a lab-scale cell were conducted to understand the behavior of the nano-suspension during charge/discharge cycling and to optimize the operating conditions.

关键词： nano-suspension flow battery β-Ni(OH)₂ scanning electronic microscopy (SEM) X-ray diffraction (XRD) X-ray adsorption near edge structure (XANES) extended X-ray absorption fine structure (EXAFS)