Moreno Fernández, Harol ; Gallenberger, Julia ; Mempin, Crizaldo ; Khalek, Isobel ; Neumann, Marie ; Lotfi, Soroush ; Kim, Sun Myung ; Li, Mohan ; Tian, Chuanmu ; Hofmann, Jan P. (2024)
Phase transitions in NiO during the oxygen evolution reaction assessed via electrochromic phenomena through operando UV–Vis spectroscopy.
In: Electrochimica Acta, 498
doi: 10.1016/j.electacta.2024.144626
Artikel, Bibliographie

Kurzbeschreibung (Abstract)

Due to its high activity and stability, nickel oxide (NiO) has shown significant promise as an electrocatalyst for the alkaline oxygen evolution reaction (OER). In parallel, NiO exhibits a well-known electrochromic phenomenon, changing its optical properties in response to an applied electric potential. This study investigates the relationship between NiO phase changes that occur during the OER and the connected optical modulation using operando UV–visible reflectance spectroscopy. The correlation between the OER activity and the electrochromic behavior of NiO is explored, providing insights into the underlying physicochemical mechanisms governing both phenomena. Strong reduction of the reflected light at higher applied potentials cannot be attributed solely to the change in optical bandgap due to the phase change or the change in the material's refractive index when different phases form. Therefore, in-gap states responsible for increasing the absorption at higher applied potentials were experimentally characterized by ultraviolet photoelectron spectroscopy (UPS) and X-ray absorption spectroscopy (XAS). The results show that phase changes in NiO during OER influence its optical absorption characteristics, which in turn give access to following active phase changes of the electrocatalyst material through a non-invasive, optical, operando probe in real time allowing for kinetic studies of the involved solid-state conversion reactions.

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