Sulfate‐Functionalized RuFeOx as Highly Efficient Oxygen Evolution Reaction Electrocatalyst in Acid

The design of highly active, stable, and low‐cost electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzer remains a challenge. RuO2 shows relatively low cost but poor stability. Here, the critical role of sulfate anion doping in promoting OER activity and stability of RuO2 is reported. Coupled with the Fe cation doping, the sulfate‐functionalized RuFeOx (S‐RuFeOx) displays a remarkable OER performance with a low overpotential of 187 mV at 10 mA cm−2 in acid, and much enhanced stability. The excellent OER activity of S‐RuFeOx is attributed to the dual positive effects that the sulfate dopants weaken the adsorption of the *OOH intermediate, and Fe dopants promote the deprotonation of chemisorbed water molecules to form *OOH. The enhanced stability is in part due to the sulfate dopants which stabilize the lattice oxygen. These results demonstrate that the anion and cation co‐doped RuO2 is a promising candidate for highly efficient OER electrocatalysts. Anion and cation co‐doped S‐RuFeOx shows remarkable oxygen evolution reaction activity and stability in acid. The sulfate anion and Fe cation dopants both contribute to the high activity by reducing the binding energy of the *OOH intermediate and promoting the deprotonation of chemisorbed H2O. The sulfate dopants stabilize the lattice oxygen to prevent the over‐oxidation of Ru.