Srco3

The RSrCoFeO₆ (R =
Sm, Eu) samples were prepared by using the solid-state
reaction process. First, the precursor oxides Sm₂O₃ (Alfa Aesar, 99.9% REO), Eu₂O₃ (Alfa
Aesar, 99.9% REO), SrCO₃ (Merck), Co₂O₃ (Merck, >99%), and Fe₂O₃ (Merck, >99%)
were
mixed in the proper stoichiometric ratio. Afterward, we placed the
mixture together with 20 zirconia balls (∼5 mm diameter) in
a Retsch PM100 planetary ball mill at 450 rpm for 30 min (dry without
a medium). Finally, the powder was thermally treated for 12 h at 1100
°C in an air atmosphere, thus obtaining the final compounds.

The SCZO perovskite oxide material was prepared by a conventional solid-state synthesis method (Sakbodin et al., 2016 (link)). In the synthesis process, stoichiometric amounts of strontium carbonate (SrCO₃, ≥99.9% purity, Sigma-Aldrich), cerium oxide (CeO₂, 99.9% purity, Alfa Aesar), and zirconium oxide (ZrO₂, 99.9% purity, Inframat) were ball-milled to ensure even mixing of the starting chemicals. In order to obtain homogeneous solution in the ball milling process, ethanol (200 proof, Pharmco) and milling media (yttria-stabilized zirconia) were adequately added. The resultant slurry was ball milled for 24 h, followed by drying and grinding into fine powder and then calcination at 1573 K for 10 h. The as-obtained material was SCZO perovskite ceramic powder and was directly used in the catalysis tests.
The Fe/SiO₂ catalyst material was prepared by fusing iron silicate (Fe₂SiO₄) and quartz particles (SiO₂, BDH) at 1973 K for 6 h in stagnant air in a high-temperature furnace (MTI Corporation KSL1700X), as reported in our previous work (Sakbodin et al., 2016 (link)). The iron silicate was synthesized in the lab following a reported procedure (DeAngelis et al., 2012 (link)). Before the fusing process, the Fe₂SiO₄ and quartz particles were mixed and ball milled for 12 h. After cooling to room temperature, the resultant product was crushed and sieved to 40–80 mesh.

All composite oxides were synthesized with solid state method. Powders of SrCO₃, IrO₂, TiO₂, and Co₃O₄ from Sigma-Aldrich Corporation were used as raw materials. Briefly, stoichiometry amount of raw materials were weighted and then mixed in mortar. The mixed precursors were finally calcined with box furnaces in ambient air. A sintering condition of 850 °C for 12 h, 1100 °C for 12° h, and 1200 °C for 12 h is applied for m-SrIrO₃, SrCo_0.9Ir_0.1O_3−δ, and SrCo_0.9Ti_0.1O_3−δ respectively.

The GDC target (Ce_0.8Gd_0.2O_2 − δ) for pulsed laser deposition was prepared from powder (Treibacher, Austria) by isostatical pressing and subsequent sintering at 1550 °C for 5 h. The STFO (SrTi_0.7Fe_0.3O_3 − δ) powder was prepared by solid state reaction from SrCO₃ (99.99% pure, Sigma-Aldrich), TiO₂ (99.99% pure, Sigma Aldrich), and Fe₂O₃ (99.98% pure, Sigma Aldrich). The educts were thoroughly mixed, calcined at 800 °C, ground, again calcined at 1000 °C, and—after a further grinding step—isostatically pressed and sintered at 1250 °C. The phase purity of both targets was confirmed by X-ray diffraction. STFO and GDC thin films were deposited on (100)-oriented yttria stabilized zirconia single crystals (YSZ, 9.5 mol% Y₂O₃ in ZrO₂, supplier: CrysTec, Germany) by pulsed laser deposition (PLD) using a KrF excimer-laser (Lambda COMPexPro 201 F, 248 nm wavelength). The deposition of 200 nm thin films was carried out in 4 × 10^− 2 mbar of pure oxygen with a pulse repetition rate of 5 Hz and a nominal pulse energy of 400 mJ. The substrate temperature during the deposition was controlled by a pyrometer (Heitronics, Germany) and was 650 °C.

Si-incorporated perovskite samples were prepared by a ball-milling-assisted solid-state reaction approach. Freshly dried chemicals of SrCO₃, Co₃O₄ and SiO₂ (Sigma-Aldrich) were weighted according to the stoichiometric ratio of SrCo_1–ySi_yO_3–δ (y = 0.00, 0.03, 0.05, 0.07 and 0.10) with different intentional Si-doping levels. The precursory powders were then mixed in an acetone medium for 1 h using a high-energy ball mill (Planetary Mono Mill, Pulverisette 6, Fritisch) at a rotation of 400 rpm. The as-obtained mixtures were dried, pressed into pellets and subjected to calcination in air under ambient pressure at 1000–1200 °C for 24 h with intermediate grindings. The actual composition of each sample after calcination was analysed by XRD (Supplementary Tables 1 and 2).

The Ba_xSr_1−xTi_1−yFe_yO_3−δ samples with x = 0, 0.2, 0.5 and y = 0.1, 0.8, were synthesized by a two-step solid-state route. Stoichiometric amounts of BaCO₃, SrCO₃, TiO₂ and Fe₂O₃ powders (Sigma Aldrich, >99.9% purity) were mixed in an agate mortar for 30 min. Mixed powders were uniaxially pressed into 12 mm diameter round pellets under 400 MPa pressure. The pellets were calcined at 1000 °C in air for 12 h (3 °C min⁻¹ heating/cooling rate). In the next step, the pellets were crushed, ground, re-pelletized under 400 MPa pressure and sintered at 1100 °C for 24 h. In the further text, the samples will be denoted as BXSTFY, where X and Y are the molar percentages of barium and iron, e.g. Ba_0.5Sr_0.5Ti_0.9Fe_0.1O_3−δ – B50STF10.

1393B20 and B12.5MgSr were prepared from analytical grade Na₂CO₃, NH₄H₂PO₄, CaCO₃, MgO, SrCO₃, H₃BO₃ (Sigma Aldrich, St Louis, MO, USA), K₂CO₃ (Alfa Aesar, Haverhill, MA, USA) and Belgian quartz sand. 1393B20 and B12.5MgSr were melted in 60 g batches in a platinum crucible for 30 min at 1450 °C and 1300 °C, respectively. Melting was done in air atmosphere in LHT 02/17 LB Speed electric furnace (Nabertherm GmbH, Lilienthal, Germany). The molten glasses were casted and annealed in electric muffle furnace (Nabertherm L 3/12). The glasses were annealed for at least 6 h at 500 °C.
The casted glasses were first crushed and milled using a planetary ball mill (Fritsch GmbH, Idar-Oberstein, Germany). Then powders were sieved (Gilson Company, Inc., Ohio, USA) to particle size < 38 µm. The nominal oxide compositions of the glasses are given in Table 1.Table 1

Nominal glass composition (mol %)

	SiO2	B2O3	P2O5	Na2O	K2O	CaO	MgO	SrO
1393B20	43.68	10.92	1.7	6	7.9	22.1	7.7	0
B12.5MgSr	47.12	6.73	1.72	22.66	0	6.77	5	10