Solid oxide fuel cell (SOFC) is an efficient technology to mitigate impacts of fossil fuels in the environment. SOFCs’ fuel flexibility and electrochemical degradations due to the high operating temperature are associated to the anode. Hence, it is crucial to find thermochemically stable and electrochemically active materials for anode. In situ exsolution can generate strongly engrained and well-distributed transition metal nanoparticles (TMNs) from the B-site of a perovskite oxide. An excellent catalyst for hydrogen reactions, Ni can be exsolved from the thermochemically stable SrTiO_3-δ (STO) host to enhance the activity. However, the exsolution kinetics in this material requires substantial improvement. Herein, to increase the catalytic performance and the Ni-exsolution kinetics, w...[ Read more ]

Solid oxide fuel cell (SOFC) is an efficient technology to mitigate impacts of fossil fuels in the environment. SOFCs’ fuel flexibility and electrochemical degradations due to the high operating temperature are associated to the anode. Hence, it is crucial to find thermochemically stable and electrochemically active materials for anode. In situ exsolution can generate strongly engrained and well-distributed transition metal nanoparticles (TMNs) from the B-site of a perovskite oxide. An excellent catalyst for hydrogen reactions, Ni can be exsolved from the thermochemically stable SrTiO_3-δ (STO) host to enhance the activity. However, the exsolution kinetics in this material requires substantial improvement. Herein, to increase the catalytic performance and the Ni-exsolution kinetics, we investigated various nonmetal substitutional strategies, (i) Si or P in B-site; and (ii) N, S, F, or Cl in O-site. Using ab initio calculations, we show that Si or P substitution in B-site facilitates Ni diffusion and segregation towards the surface through lattice distortion from Si/P-tetrahedral adoption and the nonmetals’ defect charges. Testing different Si and P-substitution levels, we validate theoretical findings related experiments; the area-specific resistance measured at 800 °C in 3% humidified H₂ improves from 0.600 Ω · cm² for Sr_0.8Ti_0.9Ni_0.1O_3−δ (STN) to 0.061 Ωcm² for Sr_0.8Ti_0.85Ni_0.1Si_0.05O_{3⎯ δ} and 0.056 Ω cm² for Sr_0.8Ti_0.85Ni_0.1P_0.05O_{3⎯ δ}. X-ray photoelectron spectroscopy characterizations reveal that nonmetal substitution reduce Ni to a lower oxidation state than STN before exsolution. In turn, this promotes the reduction of Ni during exsolution, which improves the ASR. In STO-derived heteroanionic materials, comparing anion substitutions with ab intio computations, we reveal that F’s defect charge and weak Ni ─ F bond facilitate Ni segregation and diffusion. Moreover, the F-defect shows better stability than other O-site substituents (N, S, or Cl), in alongside it eases oxygen vacancy formation. The electrostatic interactions from F-defect lowers the Ni transportation barrier. Our combined efforts suggest that F is the best choice for anion substitution in this material to improve Ni-exsolution.