Unraveling the evolution of exsolved Fe–Ni alloy nanoparticles in Ni-doped La 0.3 Ca 0.7 Fe 0.7 Cr 0.3 O 3− δ and their role in enhancing CO 2 –CO electrocatalysis

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 10; no. 5; pp. 2280 - 2294
• Main Authors: Ansari, Haris Masood, Bass, Adam Stuart, Ahmad, Nabeel, Birss, Viola I.
• Format: Journal Article
• Language: English
• Published: 01.02.2022
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/D1TA07552G

The growth and phase evolution characteristics of exsolved metal nanoparticles (NPs) in a Ni-doped La 0.3 Ca 0.70 Fe 0.7 Cr 0.3 O 3− δ (LCFCrN) perovskite is investigated in H 2 –N 2 and CO–CO 2 environments. Exsolution kinetics are rapid in H 2 –N 2 while those in CO–CO 2 atmospheres are sluggish, possibly due to a combination of p O 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 CO 2 –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 : CO 2 at 800 °C, indicating that the NPs are resistant to coarsening and stable for use in highly reducing CO–CO 2 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 CO 2 reduction reaction (CO 2 -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.