Anti-Ferromagnetic RuO2: A Stable and Robust OER Catalyst over a Large Range of Surface Terminations

Rutile RuO2 is a prime catalyst for the oxygen evolution reaction (OER) in water splitting. Whereas RuO2 is typically considered to be non-magnetic (NM), it has recently been established as being anti-ferromagnetic (AFM) at room temperature. The presence of magnetic moments on the Ru atoms signals an electronic configuration that is markedly different from what is commonly assumed, the effect of which on the OER is unknown. We use density functional theory (DFT) calculations within the DFT+U approach to model the OER process on NM and AFM RuO2(110) surfaces. In addition, we model the thermodynamic stability of possible O versus OH terminations of the RuO2(110) surface and their effect on the free energies of the OER steps. We find that the AFM RuO2(110) surface gives a consistently low overpotential in the range 0.4-0.5 V, irrespective of the O versus OH coverage, with the exception of a 100% OH-covered surface, which is, however, unlikely to be present under typical OER conditions. In contrast, the NM RuO2(110) surface gives a significantly higher overpotential of ∼0.7 V for mixed O/OH terminations. We conclude that the magnetic moment of RuO2 supplies an important contribution to obtaining a low overpotential and to its insensitivity to the exact O versus OH coverage of the (110) surface.