Optimal selection of RuO2 for durable oxygen evolution reactions in acidic media by continuous regulation of Ru–O covalency†

Precisely regulating the electron transfer capacity and Ru–O covalency of RuO₂-based catalysts is crucial and challenging for resolving the problem of the inadequate performance of RuO₂-based acidic oxygen evolution reaction (OER) catalysts in proton exchange membrane water electrolyzers (PEMWEs). Here, we propose to select Cr, an element with an atomic radius similar to that of Ru, for continuous doping of RuO₂ and to achieve continuous regulation of the electron transfer capacity and Ru–O covalency of RuO₂-based catalysts via adjusting the Cr content, thus optimizing the activity and stability of RuO₂-based catalysts. According to the experimental results, it was found that the acidic OER stability of Cr-doped RuO₂ catalysts (Cr_xRu_1−xO₂) tended to increase and then decrease with the gradual increase of the Cr doping level, and the tendency was almost consistent with the variation of the Ru–O covalency predicted by theoretical calculations. The RuO₂-based catalyst (Cr_0.31Ru_0.69O₂) showed optimal stability at a Cr/Ru ratio of 0.31/0.69 (Cr content similar to theoretical prediction), and was operated stably for over 1400 hours at a 10 mA cm⁻² current density with almost no degradation. Moreover, as the catalyst also has the best electron transfer ability, its activity is also the highest, requiring an overpotential of only 176 mV to deliver a 10 mA cm⁻² current density. Most importantly, the catalyst can be operated for at least 2300 hours at a 300 mA cm⁻² current density when applied to a PEMWE's anode, which strongly demonstrates its great potential for practical applications.