CO2/H2o High Temperature Co-Electrolysis Using LaFeO3-Based Oxide Cathode

Abstract

An increasing awareness of severe environmental impact has been seriously concerned due to the increasing demand for energy, the diminishing resources of fossil fuels, and the tremendous effects on climate change. An important indication is from global warming effect, caused by effluent greenhouse gas emission (mainly CO2). Therefore, efficient management and utilisation of CO2 and energy (generation and storage) are required attention urgently. Co-electrolysis of steam and CO2in a solid state electrolysis cells (SOECs) is a promising strategy, which may provide an approach to not only effectively reduce climate impact, but also produce useful fuels (such as syngas and hydrocarbon source) through waste heat. Thus, this allows the conversion of electricity into a fuel, while giving new opportunities for efficient and effective use of energy. Ni-based cermet materials are usually used as fuel electrodes for SOECs, while constant circulation of reducing gas (H2 or CO) is required in order to prevent the oxidation of the metallic phase, which can lead to an issue of long-term operation. In addition, the stability of the conventional cathodes applied in electrolyser is still required to be much improved. Hence, decrease in degradation rate is essential for the application of high-temperature electrolyser. Therefore, utilisation of oxides as fuel electrodes has been highly suggested instead of metallic based electrodes. Previous our study has reported a promising LaFeO3-based perovskite material as a fuel electrode for CO2 electrolysis, showing a good activity and cell performance for CO2 reduction without carbon formation.[ 1 ] In this study, we further investigate co-electrolysis of CO2 and steam, using LSGM and LaFeO3-based materials for the electrolyte and cathode, respectively. Galvanostatic measurements and electrochemical impedance spectroscopy has been conducted to investigate the cell performance. A comparable current density of over ~0.61 A/cm2 has been achieved at ~1.6 V and 800°C. This study was focused on the formation of the syngas CO/H2 in operation. The content of the product gases was measured by gas chromatography installed with a thermal conductive detector. As Ni-based cermet is used as a cathode, a H2-enriched gas composition was formed particularly at < 800°C because of the dominant electrolysis of H2O and water-gas shift reaction (CO+H2O↔CO2+H2). However, in case of LaFeO3-based perovskite oxide cathode, a reasonable electrolysis current was achieved and the CO/H2 ratio in product was similar to the CO2/H2O in feeding composition. This suggests that LaFeO3-based oxide is active to CO2 electrolysis and presents low activity for water-gas shift reaction. Therefore, using LaFeO3-based oxide as a cathode of a co-electrolyser may be feasible for the control of CO/H2 ratio. [1] T. Ishihara, K.-T. Wu, S. Wang, ECS Trans. 2015, 66, 197.