Abstract
In a green energy economy, electrocatalysis is essential for chemical energy conversion and to produce value added chemicals from regenerative resources. To be widely applicable, an electrocatalyst should comprise the Earth's crust's most abundant elements. The most abundant 3d metal, iron, with its multiple accessible redox states has been manifold applied in chemocatalytic processes. However, due to the low conductivity of FeIII Ox Hy phases, its applicability for targeted electrocatalytic oxidation reactions such as water oxidation is still limited. Herein, it is shown that iron incorporated in conductive intermetallic iron silicide (FeSi) can be employed to meet this challenge. In contrast to silicon-poor iron-silicon alloys, intermetallic FeSi possesses an ordered structure with a peculiar bonding situation including covalent and ionic contributions together with conducting electrons. Using in situ X-ray absorption and Raman spectroscopy, it could be demonstrated that, under the applied corrosive alkaline conditions, the FeSi partly forms a unique, oxidic iron(III) phase consisting of edge and corner sharing [FeO6 ] octahedra together with oxidized silicon species. This phase is capable of driving the oxyge evolution reaction (OER) at high efficiency under ambient and industrially relevant conditions (500mAcm-2 at 1.50±0.025VRHE and 65°C) and to selectively oxygenate 5-hydroxymethylfurfural (HMF).
Highlights
Electrocatalysts are of fundamental relevance as with their help electricity can in situ X-ray absorption and Raman spectroscopy, it could be demonstrated that, under the applied corrosive alkaline conditions, the FeSi partly forms a unique, oxidic iron(III) phase consisting of edge and corner sharing [FeO6] octahedra together with oxidized silicon species
As a phase-pure sample, FeSi can be synthesized from stoichiometric amounts (1:1) of elemental iron and silicon by arc-melting
The phase purity of the obtained material was analyzed by various methods: powder X-ray diffraction with Rietveld refinement (PXRD, Figure S2, Supporting Information), inductively coupled plasma atomic emission spectroscopy (Table S1, Supporting Information), scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) mapping (Figure 1c–e and Figures S3–S5, Supporting Information), transmission electron microscopy (TEM) with selected-area electron diffraction (SAED, Figure 1b and Figures S6 and S7, Supporting Information), X-ray photoelectron spectroscopy (XPS, Figure 1f,g), Raman (Figure 2a), and X-ray absorption spectroscopy, including X-ray absorption near edge structure (XANES, Figure 2b) and extended X-ray absorption fine structure (EXAFS, Figure 2c) analyses
Summary
As a starting point of our investigation, we observed that, under corrosive alkaline conditions, intermetallic FeSi partly transforms to a unique, oxidic iron(III) phase consisting of edge and corner sharing [FeO6] octahedra together with oxidized silicon species.
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