Use Co- and Ni-Free Air Electrode in Solid Oxide Cell Manufacturing for Electrolysis and Fuel Cell Applications
Authors: Ferchaud Claire Julie , Berkel Frans , Berkeveld Loek , Heijink-Smith Miranda , Veldhuis Jakobert , van Wees Hans 
Published: July 2021

The production of durable and high performance Solid Oxide Cells (SOC) units for electrolysis (SOE) and fuel cell (SOFC) applications, using cost efficient raw materials with low recycling cost is one of the main challenges for SOC developers to reach a large scale industrialization. Nickel and cobalt, state-of-the-art compounds in the manufacturing of SOC electrodes, require costly safety management during the manufacturing and recycling processes due to their carcinogenic properties. Cobalt, also recognized since 2017 as Critical Raw Materials (CRM) for the EU community, presents also a high economical risk for European SOC manufacturers, regarding its supply (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 cell and stack developers the benefit of a more environmental-friendly and lower cost manufacturing process, and the potential of using recycled materials from previous manufacturing.

Within the European project NewSOC, TNO develops Co- and Ni-free air electrode materials based on the (La, Ca, Sr)FeO3 perovskite class of materials for SOE and SOFC applications. The electrochemical performances of different Co-free compounds were measured and compared to the state-of-the-art electrode materials (e.g. La0.6Sr0.4Co0.2Fe0.8O3-
d) to achieve the performance targets as defined within the NewSOC project:

Area Specific Resistance (ASR) < 0.5 ohm.cm2 for Low-Temperature operations at 650°C

Operations at high current densities (1 A/cm2) for SOFC and SOE operations

Low degradation rates under SOFC and SOE operations and SOFC/SOE cycles (< 1%/kh)

Stability upon thermal cycling (< 0.2 mV%/cycles) and redox stability

The removal of nickel and cobalt in the oxygen electrode tends to increase the overpotential of the air electrode, with ASR values = 0.6-0.9 ohm.cm2 and maximum current density < 1 A/cm2 for operation at 650°C. Taking this drawback into account, TNO addresses the performance optimization of the Co- and Ni-free air electrode compounds by developing a novel air electrode architectures based on Co-free air electrode materials. The envisaged electrode architecture aims to enhance the triple phase boundary density at the Co- and Ni- free air electrode/electrolyte interface by creating a gradient composite electrode on top of a patterned porous barrier layer. This novel concept is also envisaged to improve the electrode performance and 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. During the conference, the last development of the novel Co- and Ni- free air electrode design developed at TNO will be presented.

Figure 1