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 ∼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 O₂^2-/O^- formed in the defective CeO₂, which can easily migrate from CeO₂ and "spillover" to the surface of RuO₂ during the OER process.