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

Abstract 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. RuO 2 shows relatively low cost but poor stability. Here, the critical role of sulfate anion doping in promoting OER activity and stability of RuO 2 is reported. Coupled with the Fe cation doping, the sulfate‐functionalized RuFeO x (S‐RuFeO x ) 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‐RuFeO x 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 RuO 2 is a promising candidate for highly efficient OER electrocatalysts.