Stabilizing RuO2 against over-oxidation: how Ni dopants kinetically inhibit Ru dissolution via mild oxidation state modulation.

Ruthenium dioxide (RuO2) is a highly active electrocatalyst for the oxygen evolution reaction (OER) in acidic media, but its practical application is hindered by instability caused by surface reconstruction and over-oxidation to soluble RuO4 species. Using constant-potential density functional theory (CP-DFT), we systematically investigate how Ni doping enhances the stability of RuO2 under OER conditions. Our calculations reveal that subsurface Ni doping significantly elevates the energy barrier for Ru surface reconstruction, thereby preserving the active surface structure. Furthermore, the dissolution of surface Ni atoms creates vacancies that further inhibit reconstruction. Electronic structure analysis demonstrates that both processes are accompanied by an increase in the oxidation state of surface Ru sites, reducing their thermodynamic propensity for further oxidation to RuO4. These theoretical insights rationalize the improved stability against Ru reconstruction-driven dissolution observed in experimental Ni-doped RuO2 systems. This conclusion provides general atomic-scale insights into how dopants mitigate degradation via mild oxidation of Ru.