A similar type of behavior was also reported for oxides intended as anode materials for water electrolysis in acidic media, i.e. RuO 2 and IrO 2 based catalysts. In this case the literature data show a certain controversy regarding the extent of the lattice oxygen activation to the overall evolution reaction. While the original data on sputtered ruthenium dioxide electrodes indicate a significant contribution of lattice oxygen evolution reaction (LOER) to the overall oxygen evolution , more recent data presented on well characterized or even oriented nanocrystalline RuO 2 electrodes reflect low to negligible contribution of LOER for RuO 2 based materials . Differential electrochemical mass spectroscopy (DEMS) studies of RuO 2 substitutionally doped with transition metal cations find that LOER tendency is generally increased in such systems compared to the pure system . Additionally, the extent of the lattice oxygen activation increases with electrode potential .