Highly defective CeO2 as a promoter for efficient and stable water oxidation

Water oxidation is a critical step in water splitting to make hydrogen fuel. RuO2 is one of the most active anode oxides for the oxygen evolution reaction (OER). However, RuO2 is very expensive and unstable under alkaline water electrolysis conditions. Here, we report a CeO2 supported RuO2 as a highly efficient electrocatalyst for the OER in alkaline media. We fabricated nano-sized CeO2 particles by an "explosion" reaction using Ag@CeO2 core-shell nanospheres as the precursor. High resolution transmission electron microscopy and Raman spectroscopy reveal that the obtained CeO2 particles possess a large number of oxygen defects. We decorated the defective CeO2 with nano-sized RuO2 (3-5 nm) through wet impregnation. The OER activity of RuO2 is improved by similar to 150% on the defective CeO2 as compared to the pristine RuO2 electrocatalyst. Moreover, the RuO2 supported on defective CeO2 shows better stability in 0.1 M KOH electrolyte. The improved activity and stability likely originate from the highly oxidative oxygen species O-2(2-)/O- formed in the defective CeO2, which can easily migrate from CeO2 and "spillover" to the surface of RuO2 during the OER process.