Energy storage technologies are essential considering the site / location-specific constraints and intermittent nature of renewable sources. Proton-conducting electrolysis cells (PCECs) emerged as a technology for reliable large-scale electricity storage in the form of hydrogen gas. The fabrication of proton-conducting electrolysis cells is associated with numerous constraints during and after the operation, such as electrode layer cracking, delamination, and warpage. The most frequently cited cause of this problem in the literature is a mismatch in the thermal expansion coefficient. According to Andreas et al., this mismatch should not exceed 50% to avoid thermal stress leading to cracks and delamination [1]. A common way to address these issues is to form a cer-cer or a cer-met composite of the electrode and the electrolyte. Hence, in the present work, we focus on incorporating a functional layer as an intermediate layer of cer-cer composite by direct mixing of BaCo0.4Fe0.4Zr0.2O3-δ (BCFZ442) and BaZr0.7Ce0.2Y0.1O3-δ (BZCY721) powders in various ratios (50:50, 70:30, and 90:10 wt %, respectively) and checked their chemical compatibility, sintering behavior, DC electrical properties, and mechanical properties at various sintering temperatures. The so-prepared optimized (10:7:1:: Powder loading: Dispersant loading: Binder solution) functional layer paste screen-printed on both sides of sintered BZCY721 pellets serving as the electrolyte, thus forming symmetric cells after sintering the electrodes. The cross-sectional scanning electron microscopic views collected on the symmetrical cell before and after the operation/measurements showed a good adherence between the electrolyte and the electrode. An electrode/electrolyte interface with a porous structure, availing the accessible path for hydrogen diffusion. The electrochemical impedance of the symmetrical cells was measured in wet air (3% H2O) from 400-700 oC at 50 oC intervals in the frequency range of 0.1 Hz to 1 MHz. The polarization resistance decreases as the temperature increases. After considering electrocatalytic activity and the aforementioned conditions, the 70:30 composition with 3% ethyl cellulose in a binder solution stands out as the most promising candidate with the lowest polarization resistance of 0.99 Ohm-cm-2 & Ea = 0.94 eV to act as a functional layer.
[1] Loken Andreas, Ricote Sandrine, Wachowski Sebastian, Thermal and chemical expansion in proton ceramic electrolytes and compatible electrodes, Crystals, 8(9), 365 (2018)