Steam electrolysis in solid oxide electrolytic cells using a cermet of copper and gadolinia doped ceria cathode

Rising concerns on CO2 emissions and depletion of fossil fuels have led to the quest for developing technologies that aim to produce hydrogen via renewables-powered zero-emission electrolytic pathways. Solid oxide electrolytic cell (SOEC) is such an emerging technology since it is expected to produce higher electric efficiency compared to other state-of-the-art electrolysers like proton exchange membrane (PEM) and alkaline electrolytic cell (AEL). However, SOEC technology is limited by a dearth of high-temperature redox stable electrocatalyti-cally active cathode materials and is currently relying mainly on the materials used as fuel electrodes in solid oxide fuel cells (SOFC). This work investigates the electrochemical performance of three different cathodes comprising cermets of copper and gadolinia doped ceria (Cu-GDC) for steam electrolysis at 800 degrees C in tubular SOEC under varying steam flow conditions and applied voltages. Remarkably, a polarisation resistance as low as 0.42 omega cm2 was obtained at 1.60 V with a corresponding Faradaic efficiency more than 95%. A comparison of the trends depicted by current density versus steam flow rate clearly indicated that at any operating temperature, optimum steam flow rate required for maximum current density was governed by the concentration of electrocatalytically active sites. Similarly, a comparison of the voltage-current characteristics of both the cells revealed that Cu content as low as 30 wt% can impart sufficient electronic conductivity as well as catalytic activity to achieve current densities only 15-20% lower than what is obtained with 70 wt% Cu. Finally, 90 min short-term testing of both the cells at 1.60 V under 23% H2/77% steam (v/v) indicated no signs of performance degradation.