Limits of steering selectively gas evolving reaction on Ru rich oxide phases in Ru-Mn-O system were investigated by combined theoretical and experimental approach. Ru_1-xMn_xO₂ materials of single phase nature conforming to the rutile structure were prepared by the spray freeze - freeze drying approach and tested for activity in oxygen and chlorine evolution reactions. The overall electrocatalytic activity of the prepared materials increases with increasing Mn content. In this manner also increases the selectivity towards oxygen evolution in acidic chloride containing solutions. Closer analysis shows that the amount of evolved oxygen (for a given electrode material) is practically independent of the chloride concentration. This is illustrated by the order of the oxygen evolution reaction with respect to chloride concentration being close to 0 in the whole range of the prepared Ru-Mn-O phases. The high selectivity towards oxygen evolution reaction coincides with low tendency of Ru-Mn-O phases to evolve oxygen via lattice oxygen activation (LOER). The experimental behavior is further confirmed by DFT analysis of the reactivity of the Ru-Mn-O surfaces.