Mechanism of chromium poisoning on La_0.5Sr_0.5Co_0.25Fe_0.75O₃ cathode and enhancing chromium tolerance using a novel anion doping strategy

Chromium poisoning the La_1-xSr_xCo_yFe_1-yO₃(LSCF) cathode for solid oxide fuel cells is a severe issue that can lead to its electrochemical performance degradation. To clarify poisoning mechanism of chromium species and develop a novel anion doping strategy with enhancing chromium tolerance, the adsorption behavior of Cr species on LSCF and F-doping LSCF surface are explored by density functional theory (DFT) calculations. Our results indicate that CrO₃ molecule prefers to be adsorbed on the La(Sr)O-terminated surface rather that the Co(Fe)O₂-terminated LSCF(001) surface. The adsorption energies of CrO₃ molecule are much larger than that of O₂ molecules, implies that the CrO₃ is more favorable to absorb on the LSCF surface. Bader charge analysis shows the CrO₃ molecule behaves as an electron acceptor through an adsorption process. The adsorption of Cr atom is a weak physical adsorption for Sr site and La site and the Cr atom chemisorption is found to occur on hollow site and O site. In addition, F-doping efficiently improves chromium tolerance by weakening the adsorption strength of chromium species that poisons LSCF surface and this may be a feasible strategy to develop cathode for high performance solid oxide fuel cells.