Investigation of hetero-phases grown via in-situ exsolution on a Ni-doped (La,Sr)FeO3 cathode and the resultant activity enhancement in CO2 reduction

[Display omitted] •Reducing environment above 400 °C caused exsolution of B-site metal (Fe, Ni) ions.•Ruddlesden-Popper phase formed along the evolution of B-site metal nanoparticles.•Nanoparticles were anchored in a perovskite socket, giving them thermal stability.•Exsolution improved the LSNF perovskite cathode’s activity for CO2 reduction.•Nanoparticles and oxygen vacancies had greater impact on activity than RP phase. Exsolution of metal nanoparticles from a perovskite oxide combined with concomitant oxygen vacancy creation can enhance the catalytic activity of the parent perovskite. In this study, a Ni-doped (La,Sr)FeO3 perovskite was subjected to a controlled reduction environment for populating its surface with B-site metal nanoparticles and oxygen vacancies, which also led to the evolution of a Ruddlesden-Popper (RP) oxide phase. Environmental TEM and in-situ XRD showed that the metal nanoparticles started forming at temperatures as low as 400 °C and were firmly pinned to their position inside a perovskite socket, giving them high thermal stability and allowing the usage of such active materials as cathodes for high-temperature CO2 reduction in solid oxide electrolysis cells. Electrocatalytic activity of the cathode for CO2 reduction was improved following exsolution, wherein the enhancement brought about by the nanoparticles and oxygen vacancies was much greater than that caused by the evolved RP phase.