One of the methods to improve the catalytic activity of anode candidates for Solid Oxide Fuel Cells is to exsolve metallic nanoparticles from their host oxide lattice. The exsolution process occurs under reducing conditions and offers an even distribution of particles, as well as very well attachment to the host material. When bimetallic or even ternary alloys are formed, the properties of the materials can be even further improved. As compared to the monometallic Ni nanoparticles, the Fe-Ni alloy nanoparticles exhibit higher site activities, greatly improved durability over long-term testing and increased tolerance towards sulfur-based atmospheres [1]. Simultaneously, these bimetallic alloys demonstrate outstanding microstructural stability and high tolerance towards coking, similar to that presented by monometallic Ni nanoparticles [2].
Among the methods to form bimetallic alloys one can find a so-called topotactic ion-exchange exsolution. In this concept a host perovskite oxide yields x moles of exsolved metal by the ion exchange with x moles of the guest cation (deposited e.g. in a form of additional layer) and finally form an alloy on the surface [2]. The aim of this work was to verify the possibility of forming Ni-Fe and Co-Fe alloys via the topotactic ion-exchange exsolution in the Fe-infiltrated (La,Sr,Ce)(Ni,Ti)O₃ or (La,Sr,Ce)(Co,Ti)O₃ ceramics.
For this purpose the La_0.27Sr_0.54Ce_0.09Ni_0.1Ti_0.9O_3-δ and La_0.27Sr_0.54Ce_0.09Co_0.1Ti_0.9O_3-δ single-phase compounds were synthesized by the Pechini method. Then the porous pellets were formed and further they were infiltrated by a H₂O/EtOH (90/10 vol.%) solution of iron nitrate with a β-cyclodextrin additive. After each infiltration step the nitrate solution was decomposed at 500°C in air for 30 min. The infiltration procedure was repeated several times to achieve the 5, 10 and 15% gain of total sample’s weight. Finally the infiltrated samples were reduced at 1200°C in dry H₂ to perform the topotactic ion-exchange exsolution. Such a high temperature of reduction was chosen to force the increase of forming particles in order to allow their characterization via the XRD and EDS methods. Based on the performed experiment, it was found that the suggested procedure utilizing the topotactic ion-exchange exsolution is an effective method of producing uniformly distributed particles of bimetallic alloys on the surface perovskite-based compounds.
 
References
[1] S. Joo, O. Kwon, K. Kim, S. Kim, H. Kim, J. Shin, H.Y. Jeong, S. Sengodan, J.W. Han, G. Kim,  Nat. Commun. 10 (2019) 1–9.
[2] J.H. Kim, J.K. Kim, J. Liu, A. Curcio, J.S. Jang, I.D. Kim, F. Ciucci, W.C. Jung, ACS Nano. 15 (2021) 81–110.
 
Acknowledgements
The research project was supported by the National Science Center under grant No. NCN 2021/42/E/ST5/00450.