Characterization and testing of strontium titanium ferrite-based solid oxide cells for reversible and co-electrolysis operation

This study investigates the electrocatalytic performance and the preliminary durability of SrTi 0.3 Fe 0.7 O 3-δ (STF) and Sr 0.95 (Ti 0.3 Fe 0.63 Ni 0.07 )O 3-δ (STF-Ni) as fuel electrodes for solid oxide cells operated at 750 °C in reversible mode with H 2 /H 2 O and CO/CO 2 mixtures, and in H 2 O/CO 2 co-electrolysis mode. STF-Ni achieved a peak power density of 415 mW/cm 2 under 3 % humidified H 2 , and maintained 96 % of its performance over 96 h of H 2 /H 2 O reversible operation. In co-electrolysis, STF-Ni delivered a maximum current density of 540 mA/cm 2 at 1.4 V, with 15 % performance drop at 1.2 V after 162 h. Reversible operation with CO/CO 2 mixtures proved most challenging, as surface SrCO 3 formation caused significant degradation, and stable performance was reached only on STF-Ni. STF-Ni consistently demonstrated superior stability compared to STF across all the operative modes. A 0D model was utilized to analyze the I/V curves of STF-Ni: a power-law rate for the fuel electrode's kinetics with H 2 and H 2 O mixtures was extracted, and the kinetic insensitivity to the CO 2 amount in co-electrolysis was proved. Complementary characterization using XRD, TPR, SEM, and TEM techniques highlighted the role of exsolution. After exposure to CO 2 , compositional changes in exsolved Ni-Fe nanoparticles were observed, with selective reincorporation of Fe into the perovskite structure. • SOCs with Sr(Ti 0.3 Fe 0.7 Ni 0.07 )O 3-δ (STF-Ni) electrodes for exsolution are tested. • Exsolved Ni-Fe nanoparticles provide stability to the STF-Ni electrodes. • Selective Fe reincorporation in reductive C-containing atmospheres occurs on STF-Ni. • In co-electrolysis H 2 O and H 2 control the reactivity, while CO 2 behaves as an inert.