Unveiling the Outstanding Oxygen Mass Transport Properties of Mn-Rich Perovskites in Grain Boundary-Dominated La_0.8Sr_0.2(Mn_1–xCo_x)_0.85O_3±δ Nanostructures

Abstract

Ion transport in solid-state devices is of great interest for current and future energy and information technologies. A superior enhancement of several orders of magnitude of the oxygen diffusivity has been recently reported for grain boundaries in lanthanum–strontium manganites. However, the significance and extent of this unique phenomenon are not yet established. Here, we fabricate a thin film continuous composition map of the La0.8Sr0.2(Mn1–xCox)0.85O3±δ family revealing a substantial enhancement of the grain boundary oxygen mass transport properties for the entire range of compositions. Through isotope-exchange depth profiling coupled with secondary ion mass spectroscopy, we show that this excellent performance is not directly linked to the bulk of the material but to the intrinsic nature of the grain boundary. In particular, the great increase of the oxygen diffusion in Mn-rich compositions unveils an unprecedented catalytic performance in the field of mixed ionic–electronic conductors. These results present grain boundaries engineering as a novel strategy for designing highly performing materials for solid-state ionics-based devices.

Engineering Transport in Manganites by Tuning Local Nonstoichiometry in Grain Boundaries

“…Regarding the surface exchange (Figure e), an analogous trend to the oxygen diffusion is observed in the Mn deficient GBs. The strong coupling of the two oxygen parameters, along with the observed oxygen depletion in the GBs, corroborate the hypothesis that the accumulation of oxygen vacancies is at the origin of the large improvement of the oxygen reduction reactions reported for manganite thin films by different authors . This conclusion is also supported by theoretical works from Choi et al and Mastrikov et al, where the scarce concentration of oxygen vacancies was found as the limiting factor for oxygen incorporation in bulk LSM.…”

“…It was recently discovered that GBs in La 0.8 Sr 0.2 MnO 3± δ (LSM) thin films are responsible for a substantial enhancement of oxygen diffusion and oxygen reduction reactions (ORR), contrary to what is determined in many oxides where the GBs are known to hinder the oxygen mobility . The improvement of oxygen mass transport properties is able to completely change the nature of the material converting the mainly electronic LSM into a good mixed ionic–electronic conductor (MIEC).…”

Rare earth elements based oxide ion conductors

“…Therefore, solid electrolytes need to have high ionic conductivity with negligible electronic conductivity. [17][18][19] Although SOFCs have so many advantages and broad application prospects, they have not been widely commercialized due to their high operating temperatures (>750°C), which is mainly determined by the oxide ion conductivity of the electrolytes. Such high operating temperatures lead to a series of issues, such as expensive fuel-cell components, higher plant cost, slow start up and shut down, poor cycling capability, and poor durability arising from thermal and chemical compatibility between the components.…”

Engineering mass transport properties in oxide ionic and mixed ionic-electronic thin film ceramic conductors for energy applications

“…Special attention has been put on the enhanced mixed ionic-electronic properties of strontium-doped lanthanum manganites (LSM). [27,[86][87][88] Two independent studies by Saranya et al [27,88] and Navickas et al [86] reported fast oxygen conduction properties through grain boundaries of LSM. In both works, it was shown how grain boundaries improve the mixed ionic electronic character of a mainly electronic conductor such as LSM, thus opening up the possibility for LSM to be employed as an electrode for solid oxide fuel cell (SOFC) systems.…”