Dresden 2020 – wissenschaftliches Programm
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CPP 55: Materials for Energy Storage and Conversion - Battery and Fuel Cell Materials (joint session MM/CPP)
CPP 55.6: Vortrag
Dienstag, 17. März 2020, 15:30–15:45, IFW D
Analysis of LixMn2O4 for catalysis of the oxygen-evolution-reaction (OER) using STEM-EELS — •Florian Schönewald1, Max Baumung1, Marcel Risch1,2, and Cynthia Volkert1 — 1Institut für Materialphysik, Universität Göttingen — 2Helmholtz-Zentrum Berlin für Materialien und Energie
Controlling the OER is an important step for achieving a sustainable renewable energy future. The process of generating molecular oxygen from water by chemical means is severely kinetically limited. Here LixMn2O4 is studied as a model electrocatalyst. To understand the role of manganese valence and covalency for the OER these are manipulated by electrochemical de-/lithiation. Characterisation of the particles is performed before and after OER, for different lithiation states. Specific attention is given to Mn at the surface since it is directly involved in electron transfer.
With EELS of the O K- and Mn L-edge a surface layer with strongly reduced Mn has been discovered and attributed to changes in Mn/O ratio. This state is also preserved under delithiation. In previous studies, this effect has been explained by tetragonal Mn3O4 forming at the surfaces . However, no second phase matching Mn3O4 or related structures was identified by X-ray powder diffraction. According to the estimated surface volume share of about 10 %, Mn3O4 formation can be excluded. Instead, a combination of oxygen vacancies and additional manganese on tetrahedral sites as antisite defects is taken into account to explain the apparent Mn valence change at surfaces.
 Daichun Tang et al, Chem. Mater. 2014, 26, 11, 3535-3543