First-Principles Study on Exsolution of Ni and Ni–M (M = Fe, Co, Cr, Cu) Alloy Nanoparticles in the SrTiO₃ Model as the Perovskite Cathode of Solid Oxide Electrolysis Cells

Abstract

Ni-YSZ (yttria-stabilized zirconia) stands out among the cathode side materials of a solid oxide electrolysis cell (SOEC) due to its low cost and excellent catalytic performance. The agglomeration and coarsening of Ni greatly limit their performance during the long-term operation of SOEC. In this regard, the exsolution of metal nanoparticles in perovskite cathodes has attracted lots of attention. Meanwhile, the optimal mechanisms of the exsolution of metals or alloys are still unclear. With the SrTiO 3 material system as an example of SOEC cathode, several metal dopants (M = Fe, Co, Cr, Cu) and two different models: bulk codoping (i.e., Ni and M are doped in bulk crystal) or surface doping are introduced. The separation energy, electronic structure, and electronic interaction force are analyzed. Ni−M (M = Cr, Cu) in the model of bulk codoping and M (M = Fe, Co, Cr, Cu) in the mode of surface doping promote the exsolution of Ni or Ni−M alloy nanoparticles, respectively. The analysis of energy and electronic behaviors reveals that there is an electronic interaction force between the doped atoms, the oxygen atoms, and the B-site element of the material itself. The electronic interaction force contributes to the difference in separation energy. The promotion of Ni exsolutions is attributed to the reduction of Ni−O bond energy and the weakening of the electronic interaction force of the Ni-B site element, which is beneficial for the exsolution of Ni elements.