Unravel the mechanism of d-orbital modulation and oxygen vacancy in cerium-doped RuO2 catalysts for acidic oxygen evolution reaction

Ruthenium (Ru) and its compounds with abundant d-orbital electrons are considered as potential candidates to replace commercial iridium-based catalysts for proton exchange membrane water electrolysis. However, the low corrosion resistance of ruthenium oxide in acidic conditions seriously hinders their large-scale application. Heteroatom doping can modulate the local bonding environment and electronic structure, and becomes a practical means to promote RuO2 in acid oxygen evolution reaction (OER). Here, we report Ce dopants in high-performance and durable Ce-RuO2 catalysts during acidic OER. Significantly, the Ce-RuO2 had high OER activity with a small overpotential of 191 mV (10 mA·cm−2), which was better compared with RuO2 (229 mV) and commercial RuO2 (351 mV). Theoretical analysis showed Ce in Ce-RuO2 had a lower peak at the Fermi level, indicating the adsorption capacity of oxygen-containing species is weaker than that of Ru. The introduction of Ce significantly impacts the d orbital, causing a positive shift in the d band of Ru, and raises the peak of Ru to the Fermi level, which promotes electron transfer. Furthermore, the rate-determining step for OER on the RuO2 (1 1 0) surface is the conversion of O to OOH, and the lower reaction energy of Ce-RuO2 than that of RuO2 (0.31 vs. 0.77 eV) demonstrates the thermodynamic advantage of Ce-doped RuO2 over pristine RuO2.