Incorporation of Fe into NiO nanocubes tracked during electrochemical cycling

How can Fe incorporation into catalysts help increase catalytic activity?

Fengli Yang, See Wee Chee, and their colleagues at the Fritz-Haber-Institut der Max-Planck-Gesellschaft published recent work demonstrating the powerful capability of the Hummingbird Scientific Gen V in-situ bulk liquid-electrochemistry TEM sample holder to perform operando scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) on octahedral NiO catalyst particles during repeated electrochemical cycling in a liquid cell infused with Fe-containing electrolyte.

Cyclic voltammogram collected in a borate buffer without Fe to compared to those obtained at 60 and 120 cycles after Fe(NO₃)₃ was added into the electrolyte. b-d) In-situ STEM images, combined Ni/Fe chemical EDS maps and STEM/Fe EDS maps of NiO octahedra: b) at open circuit potential; c) after 60 cycles of CV, and d) after 120 cycles of CV from 0.7 to 1.9 VRHE. e) Ex situ EDX maps of as-prepared NiO octahedron. f,g) Ex situ EDX maps of NiO catalysts obtained from in situ experiments f) after 60 cycles and g) after 120 cycles. Copyright © 2023 Microscopy Society of America

In-situ and ex-situ STEM and chemical maps were acquired for the particles prior to injection of Fe(NO₃)₃, after 60 cyclic voltammetry cycles and after 120 cycles. By 60 cycles, a NiFe layered double hydroxide (LDH) formed on the surface of the nanoparticles. By 120 cycles, Fe aggregate formation was observed. The impact of Fe incorporation on catalytic properties is demonstrated by the elevated current during LDH formation but slightly decreased current during aggregate formation. The team used the Hummingbird Scientific liquid cell with bulk reference and counter electrodes to track these two stages of Fe incorporation at real-world levels of electrochemical cycling in situ, which is otherwise not possible because of artefacts that arise from having all electrodes on-chip.

Reference:

Fengli Yang, Mauricio Lopez Luna, Felix T Haase, Daniel Escalera-Lpez, Aram Yoon, Ali Kosari, Mauro Porcu, Arno Bergmann, Beatriz Roldan Cuenya, See Wee Chee, Microscopy and Microanalysis 29 Issue Supplement1_1 (2023) DOI: 10.1093/micmic/ozad067.666

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