Rational Strategy for Tuning Electrocatalytic Oxygen Evolution Activity of Perovskite Oxides via Low-Temperature Fluorination

The electrochemical oxygen evolution reaction (OER) is an important anode reaction for electrochemical water splitting to generate hydrogen using renewable energy sources. Perovskite oxides (PV) have attracted attention as highly active OER catalysts in alkaline solutions, even without the use of precious metal elements. Here, we achieve precise tuning of the valence state of transition metal cations in BaFe 1– x Co x O 3– d ( x = 0, 0.1, 0.2) and enhancement of the OER activity by broad-range fluorine substitution using a low-temperature fluorination approach. Fluorine was homogeneously distributed across the PV particles, and the valence states of Fe and Co changed as the amount of fluorine increased. The OER activities of Co-containing PVs were successfully enhanced through fluorination; the OER current was increased about four-fold for fluorinated BaFe 0.8 Co 0.2 O 3– d with F/Ba = 1.0. This work may provide a new strategy for tuning the electronic state of transition metal cations in PVs and the catalytic properties of these compounds.