Evolving Highly Active Oxidic Iron(III) Phase from Corrosion of Intermetallic Iron Silicide to Master Efficient Electrocatalytic Water Oxidation and Selective Oxygenation of 5-Hydroxymethylfurfural

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 (FeOxHy)-O-III 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 (500 mA cm(-2) at 1.50 +/- 0.025 V-RHE and 65 degrees C) and to selectively oxygenate 5-hydroxymethylfurfural (HMF).

Automated summary

In a green energy economy, the essential role of electrocatalysis for chemical energy conversion and producing value-added chemicals from renewable resources is highlighted. The study showed that incorporating iron into conductive intermetallic iron silicide can efficiently drive the oxygen evolution reaction (OER) and selectively oxygenate 5-hydroxymethylfurfural (HMF), demonstrating great potential for targeted electrocatalytic oxidation reactions.