Co- and Ni- free oxygen electrode performance improvement by electrode/electrolyte interface tuning

One of the present challenges for Solid Oxide Cells (SOC) developers is to produce durable and high performance cell units for high temperature electrolysis applications, utilizing cost efficient raw materials with low recycling costs to reach a large scale industrialization. Nickel and cobalt, which are state-of-the-art compounds in the manufacturing of SOC electrodes, bring critical concerns regarding the need of high conditioning and recycling costs related to their carcinogenic properties. In addition, cobalt is recognized since 2017 as Critical Raw Materials (CRM) for the EU community, due to the high economical risk associated to its supply within Europe (55% of the world’s cobalt being sourced from Central Africa). Use of Co- and Ni- free electrode materials would provide a significant reduction of use of CRM in European SOC manufacturing, and offers SOC cell and stack manufacturers the benefit of a more environmental-friendly and lower cost manufacturing process and the potential of using recycled materials from previous manufacturing. To this end, TNO has undertaken to develop a novel Co- and Ni-free oxygen electrode design based on the (La,Ca,Sr)FeO3 perovskite class of materials. However the removal of nickel and cobalt in the oxygen electrode tends to increase the overpotential of the electrode. Taking into account this last drawback, TNO aims to optimize the performance of this new Co- and Ni-free compounds by microstructural improvement in terms of particle size, porosity and surface roughness. In addition, a novel electrode architecture is proposed by creating a patterned electrode/electrolyte interface, thus enhancing the triple phase boundary density between electrolyte and oxygen electrode. This novel concept is envisaged to improve the electrode performance and to prevent electrode delamination during SOC operations. A higher triple phase boundary density contributes to lower the local partial oxygen pressure between electrolyte and oxygen electrode, known as critical degradation phenomena of the oxygen electrode at high current density under electrolysis conditions. The latest development of the novel Co- and Ni- free oxygen electrode design developed at TNO, within the FCHJU NewSOC project will be presented during the conference