Using In-Situ Methods to Characterize Phase Changes in Charged Lithium Nickel Cobalt Aluminum Oxide Cathode Materials

Stach, Eric A.; Hwang, Sooyeon; Karki, Khim; Kim, Seung Min; Chang, Wonyoung; Chung, Kyung-Yoon; Zhuo, Guangwen; Yang, Qiao-Xing; Whittingham, M. Stanley

doi:10.1017/s1431927619010882

Cited by 2 publications

(1 citation statement)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is higher for the reduced sample (the ratio is 1.55) and slightly lower when oxidized (the ratio is 1.42). This is consistent with previous publications, as metallic Co should exhibit a higher L 3 /L 2 ratio than oxidized Co. − Additionally, oxidized Co has a deeper trough between L 3 and L 2 than metallic Co, which is also evident in the spectra of Figure b. Thus, the EELS data indicate effective reduction of Co upon exposure to H 2 at 500 °C, as expected, and it is consistent with the XANES results discussed above.…”

Section: Resultssupporting

confidence: 92%

Structural and Valence State Modification of Cobalt in CoPt Nanocatalysts in Redox Conditions

et al. 2021

View full text Add to dashboard Cite

Platinum is the primary catalyst for many chemical reactions in the field of heterogeneous catalysis. However, platinum is both expensive and rare. Therefore, it is advantageous to combine Pt with another metal to reduce cost while also enhancing stability. To that end, Pt is often combined with Co to form Co–Pt nanocrystals. However, dynamical restructuring effects that occur during reaction in Co–Pt ensembles can impact catalytic properties. In this study, model Co2Pt3 nanoparticles supported on carbon were characterized during a redox cycle with two in situ approaches, namely, X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM) using a multimodal microreactor. The sample was exposed to temperatures up to 500 °C under H2, and then to O2 at 300 °C. Irreversible segregation of Co in the Co2Pt3 particles was seen during redox cycling, and substantial changes of the oxidation state of Co were observed. After H2 treatment, a fraction of Co could not be fully reduced and incorporated into a mixed Co–Pt phase. Reoxidation of the sample increased Co segregation, and the segregated material had a different valence state than in the fresh, oxidized sample. This in situ study describes dynamical restructuring effects in CoPt nanocatalysts at the atomic scale that are crucial to understand in order to improve the design of catalysts used in major chemical processes.

show abstract

Section: Resultssupporting

confidence: 92%