Surface orientation dependent electrochemical stability of RuO2 and IrO2 under acidic oxygen evolution reaction

Ru- and Ir-oxides have considerable attentions as acidic oxygen evolution electrocatalysts for polymer electrolyte membrane water electrolysis. However, there have been no reports of comparative study of electrochemical stability depending on the surface orientations. Here, we prepared the ( hkl )-oriented ( hkl = 110, 001, 100) RuO 2 and IrO 2 thin films on rutile-TiO 2 single crystal substrates by arc-plasma deposition and investigated the surface orientation dependence of oxygen evolution reaction (OER) stability in 0.1 M HClO 4 electrolyte. At the initial state, RuO 2 showed a lower OER overpotential and smaller Tafel slope compared to IrO 2 for all the surface orientations. However, the overpotential of RuO 2 steeply increased during chronopotentiometry (CP) measurements, while the overpotential increase for IrO 2 was significantly suppressed. After the CP measurement, the overpotential of IrO 2 became smaller than that of RuO 2 for all the surface orientation. RuO 2 shows orientation dependence on the stability number, i.e. ratio of total charges used for CP and dissolution amount of Ru or Ir, while the IrO 2 didn't show a clear trend. The results demonstrated that the surface orientation of both RuO 2 and IrO 2 affects not only the activity, but also the stability, and elemental dissolution and the influence is more significant for RuO 2 . • Surface orientation dependences on electrochemical stability of RuO 2 and IrO 2 in acidic electrolyte are investigated. • Overpotential increase of (100) surface during CP was significantly suppressed compared to (110) and (001). • Elemental dissolution is sensitive to surface orientation for RuO 2 , but not for IrO 2 .