Enhancing the Faradaic Efficiency in Proton-Conducting Ceramic Electrolysis Cells (PCECs) for Hydrogen Production: Influence of Electrolyte Thickness and Operating Conditions

Abstract

Proton-conducting Ceramic Cells (PCCs) operating at intermediate temperatures (350 °C–700 °C) offer unique advantages like fast kinetics, improved thermodynamics, and low-degradation. However, the mixed ionic-electronic conductivity in their ceramic electrolytes causes electronic leakage, reducing overall cell performance. Increasing electrolyte thicknesses can mitigate electronic leakage by extending the migration path for electronic charge carriers. Furthermore, it affects the concentration gradients of charge carriers and helps to reduce localized electronic conductivity in the electrolyte, thereby mitigating electronic leakage. Conversely, increased electrolyte thickness also increases proton migration resistances. This study examines how the electrolyte thickness (7, 17, and 28 μm) affects PCC performance in fuel cell and electrolysis applications. Maximum fuel cell performance was achieved with a 17 μm thick electrolyte, ideally balancing reduced electronic leakage and increased ohmic losses. In electrolysis, however, the 28 μm thick electrolyte showed better faradaic efficiencies leading to superior electrolysis performance at low current densities (< 1 A‧cm −2 ). Additionally, increased steam partial pressures, higher temperatures, and lower current densities further improved electrolysis efficiency, emphasizing the benefit of endothermic operation of PCCs for converting industrial waste heat into chemical energy. A 560-hour durability test in electrolysis mode revealed a relatively high degradation rate (∼196 mV‧kh −1 ), emphasizing the need for enhanced stability in PCC configurations. In SPCCs, electronic leakage currents increase with thinner electrolytes. Optimal fuel cell performance was achieved with a 17 μm thick electrolyte. Thicker electrolytes (28 μm) showed superior electrolysis performance (<1 A‧cm −2 ). Faradaic efficiency decreases with increasing anodic overpotentials. Higher temperatures yield more hydrogen production at a constant current density.