[EN] Widening the use of renewable sources requires more efficient energy storage systems to overcome the inherent intermittence of solar energy. In this respect, thermal energy storage coupled to concentrated solar power represents an inexpensive technology to achieve that goal. In particular, the use of reversible thermochemical reactions is promising due to a higher energy storage density if compared with commercial sensible heat storage on molten salts. However, some of these systems that rely on gas-solid reactions can suffer a cycle-to-cycle loss of activity due to slow kinetics and materials degradation, which is detrimental for its potential future commercialization. In this work, we have assessed the incorporation of Cr cations in the redox couple Mn2O3/Mn3O4, as a way to stabilize the multi-cyclic activity over prolonged operation at high temperatures (650-1000 degrees C). Reduction has been studied with in situ XRD and kinetic analyses, which confirm that Cr incorporation shifts the reaction towards high temperatures. Long term redox cycling tests confirm that 5% Cr incorporation helps to stabilize the redox activity of Mn2O3/Mn3O4. AJC would like to thank the support of Juan de la Cierva Formaci ' on research fellowship by the Spanish Ministry of Science, grant number FJCI-2017-33967. Financial support from project ACES2030 from "Comunidad de Madrid" and European Structural Funds to (P2018/EMT-4319) is fully acknowledged.