On the stability in alkaline conditions and electrochemical performance of A2BO4-type cathodes for liquid fuel cells

Abstract

Typical direct liquid fuel cells (DLFCs) use a liquid fuel and O₂ as the oxidant. However, for applications where O₂ is not available (e.g., space and underwater), the gas has been replaced by H₂O₂ as a liquid oxidant. This work presents a study of various ceramic disc electrodes with K₂NiO₄ structure and nominal compositions La₂NiO₄, La₂CuO₄, La_1.9Pr_0.1CuO₄, La_1.9Sr_0.1CuO₄, La_1.8Ce_0.2NiO₄, La_1.9Pr_0.1NiO₄, La_1.8Pr_0.2NiO₄ and La_1.9Sr_0.1NiO₄ to assess their stability and activity for the hydrogen peroxide reduction reaction (HPRR) in alkaline media. Stability tests conducted in 2 M NaOH show that Ni and Cu are readily dissolved, as occurs for substituting elements such as Sr, in agreement with calculated Pourbaix diagrams. Such degradation affects the surface of the materials, which is depleted of transition metals. This has consequences for the ORR and HPRR activity due to formation of a La-rich passivation layer on the surface. Only La₂CuO₄ and La_1.8Ce_0.2NiO₄ display HPRR activity at around −0.25 V vs. RHE. An attempt is made to correlate the composition, chemical stability and electrochemical behaviour of these materials based on known molecular-orbital models proposed for the oxygen reduction reaction.