Synthesis and characterization of a Sr0.95Y0.05TiO3−δ-based hydrogen electrode for reversible solid oxide cells

Abstract

Reversible solid oxide cells (RSOCs) can generate electricity as solid oxide fuel cells (SOFC) facing a shortage of electricity and can also store the electricity as solid oxide electrolysis cells (SOEC) at the time of excessive electricity. The composite Sr_0.95Y_0.05TiO_3−δ–Sm_0.2Ce_0.8O_1.9 (SYT–SDC) as the hydrogen electrode provides a promising alternative for a conventional Ni/YSZ. The possible charge compensation mechanism of SYT is described as Sr_0.95Y_0.05Ti_0.95−2δ⁴⁺Ti_2δ+0.05³⁺O_3−δ. The Ti³⁺ is approximately 11.73% in the reduced SYT by XRD Rietveld refinement, electron paramagnetic resonance (EPR) and thermogravimetry (TG) analysis. Voltage–current curves and impedance spectra are measured as a function of applied voltages to characterize the cells. The bulk resistance (R_o) and the electrode polarization resistance (R_p) at open circuit voltages (OCV) at 750 °C are 9.06 Ω cm² and 10.57 Ω cm², respectively. The R_o values have a small amount of changes with small slopes both in the SOFC (−0.29 Ω cm² V⁻¹) and SOEC mode (0.5 Ω cm² V⁻¹), whereas the R_p values decrease all the time with the increasing voltages at both the SOFC (−2.59 Ω cm² V⁻¹) and SOEC mode (−9.65 Ω cm² V⁻¹), indicating that the electrical conductivity and electro-catalytic property of the SYT-based hydrogen electrode can be improved under the SOEC mode.