Unraveling the evolution of exsolved Fe-Ni alloy nanoparticles in Ni-doped La0.3Ca0.7Fe0.7Cr0.3O3-δ and their role in enhancing CO2-CO electrocatalysis

The growth and phase evolution characteristics of exsolved metal nanoparticles (NPs) in a Ni-doped La0.3Ca0.70Fe0.7Cr0.3O3-delta (LCFCrN) perovskite is investigated in H-2-N-2 and CO-CO2 environments. Exsolution kinetics are rapid in H-2-N-2 while those in CO-CO2 atmospheres are sluggish, possibly due to a combination of pO(2) difference in excess of three orders of magnitude as compared to that in H-2-N-2, and a different reaction pathway in the two atmospheres. NPs grown in H-2-N-2 exhibit a compositional and structural progression from an initially Ni-rich phase to an Fe-rich phase at short and long heat treatment durations, respectively. Once the subsurface Ni depletes, the NPs seem to coarsen via a combination of addition of Fe from the parent perovskite and Ostwald ripening. For longer heat treatment durations, CaO particles are observed to be appended to the Fe-Ni NPs. Exsolution also occurred in CO2-CO atmospheres exhibiting similar trends, although the composition of the NPs was Ni-rich even after a 25 h reduction treatment in 70 : 30 CO : CO2 at 800 degrees C, indicating that the NPs are resistant to coarsening and stable for use in highly reducing CO-CO2 environments. In reversible solid oxide cells (RSOC) applications, the CO oxidation kinetics are typically sluggish on single phase perovskite electrodes. However, for Fe-Ni alloy NP-decorated LCFCrN (Fe-Ni@LCFCrN), the NPs are shown to enhance the CO oxidation kinetics (by ca. 75%) and the CO2 reduction reaction (CO2-RR) kinetics (by ca. 15%) as compared to the parent material, LCFCr. This makes the Fe-Ni@LCFCrN catalyst equally active for both reactions, hence significantly enhancing its potential for use in reversible solid oxide cell applications.