Fluorine-Decoration Induced Deep Reconstruction of Iron Cobalt Oxide for High-Efficiency Oxygen Evolution Reaction

Abstract

OER reaction is a key process in water electrolysis systems, while it’s extremely challenging to develop the cheap and highly active OER electrocatalysts with earth-abundant material through facile methods. Here, FeCo oxides and its fluorides were prepared using one-step synthesis at room temperature and fluorination with fluorine gas. The OER performance of Fe, Co, and FeCo oxides was compared, and investigated the effect of fluorine doping on their physical properties and OER performance. The results showed that the overpotential of FeCo-O bimetallic oxide was 370 mV in alkaline electrolyte at a current density of 10 mA/cm2, which was much better than that of monometallic Fe-O (1 V) and Co-O (467 mV) OER performance. The fluorine modification of the three materials significantly improved their OER performance of (Fe-OF (570 mV), Co-OF (330 mV) and FeCo-OF (285 mV)), in which, FeCo-OF, in a continuous OER test for 12 h, showed a stable lower overpotential value than that of commercial RuO2 (289 mV). Electrochemical analysis and spectral characterization indicated that with the help of fluorine ion electronic regulation, the spent catalyst FeCo-OF can provide efficient electrocatalytic active sites after in situ self-reconstruction, and thus showed stable and excellent OER performance. DFT calculations showed that the modification of bimetallic oxides by fluorine could reduce the O⁎ Gibbs free energy from 4.86 to 2.44 eV, and thus promote the OER reaction kinetics.

Keywords: oxygen evolution reaction, electrocatalyst, fluorine modification, iron, cobalt.