High performance acidic water electrooxidation catalysed by manganese–antimony oxides promoted by secondary metals

Abstract

Herein, we demonstrate that introduction of secondary metals into the promising manganese–antimony oxide acidic water oxidation catalysts endows the resulting materials with superior activity and stability in operation. Using a simple solution-based method, we synthesised multi-metallic manganese antimonates [MnM + Sb]O_x with M = Ru, Co, Pb and Cr. All of the secondary metals examined notably increase the initial activity of the mixed oxides towards the oxygen evolution reaction (OER) in 0.5 M H₂SO₄ at ambient temperature, though [MnCr + Sb]O_x and [MnRu + Sb]O_x were found to be less stable. In contrast, [MnCo + Sb]O_x, [MnPb + Sb]O_x and [MnCoPb + Sb]O_x maintained high stability and improved the overpotential required to achieve the water oxidation rate of 10 mA cm⁻² by 0.040 ± 0.014, 0.08 ± 0.03 and 0.050 ± 0.014 V with respect to the parent [Mn + Sb]O_x catalyst, respectively. Similar improvements in performance were found after tests at elevated temperature of 60 ± 1 °C. The [MnPb + Sb]O_x system exhibits one of the highest activities for the OER at low pH reported for the noble-metal free catalysts so far, viz. 10 mA cm⁻² OER at 0.60 ± 0.03 V overpotential at 24 ± 2 °C with a flat electrode. We ascribe this improved performance to the stabilising effect of lead oxides on the catalytically active manganese sites, which is demonstrated herein by in situ spectroelectrochemical X-ray absorption analysis.