Oxygen Vacancy Engineering in Cu-Doped Ruddlesden–Popper Oxides for Reversible Solid Oxide Cells

The Ruddlesden–Popper (R–P) structured oxides, PrSrFeO₄ (PSF), PrSrFe_0.9Cu_0.1O₄ (PSFCu1), and PrSrFe_0.8Cu_0.2O₄ (PSFCu2), have been successfully synthesized and employed as semiconductors in reversible solid oxide cells (R-SOCs). Following an H₂ reduction treatment at 700 °C, in situ precipitation of Fe or Fe–Cu alloy occurs on the surface of these materials, concurrently inducing a phase transformation. Both Cu doping and the reduction process enhance the concentration of oxygen vacancies, ultimately enhancing oxygen mobility. It shows that the single cell utilizing PSFCu2 as the semiconductor demonstrates superior performance in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes, with H₂-30%H₂O and O₂ serving as the fuel and oxidant, respectively. Furthermore, the Nyquist plots obtained from equivalent symmetrical cells indicate that PSFCu2 exhibits the most favorable oxygen reduction reaction (ORR) activity, with the rate-determining step (RDS) being the reduction of oxygen atoms to the oxygen atoms to O^–. Conversely, in the case of the hydrogen oxidation reaction (HOR), the reduced PSFCu2 displays the best performance, with H₂ adsorption and dissociation identified as the RDS for this process.