Solid oxide fuel cells (SOFCs) represent one of the cleanest and most efficient options for the direct conversion of a wide variety of fuels to electricity. For example, SOFCs powered by natural gas are ideally suited for distributed power generation. However, the commercialization of SOFC technologies hinges on breakthroughs in materials development to dramatically reduce the cost while enhancing performance and durability. One of the critical obstacles to achieving high-performance SOFC systems is the cathodes for oxygen reduction reaction (ORR), which perform poorly at low temperatures and degrade over time under operating conditions. Here a comprehensive review of the latest advances in the development of SOFC cathodes is presented: complex oxides without alkaline earth metal elements (because these elements could be vulnerable to phase segregation and contaminant poisoning). Various strategies are discussed for enhancing ORR activity while minimizing the effect of contaminant on electrode durability. Furthermore, some of the critical challenges are briefly highlighted and the prospects for future-generation SOFC cathodes are discussed. A good understanding of the latest advances and remaining challenges in searching for highly active SOFC cathodes with robust tolerance to contaminants may provide useful guidance for the rational design of new materials and structures for commercially viable SOFC technologies.

Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements

In the past decade, intensive research on proton-conducting oxide materials has provided a basis for the development of intermediate-temperature protonic ceramic electrochemical cells, which constitute a real alternative to conventional cells based on oxygen-conducting electrolytes. To achieve both high efficiency and excellent performance, not only electrolytes but also electrode materials should be carefully selected considering their functional properties. Compared to the traditional ABO3 perovskite electrode materials, Ln2NiO4+δ with a layered structure has unique advantages (high chemical stability, mechanical compatibility, improved oxygen transport, and hydration ability), and thus is now becoming a hot topic in this field, offering both scientific and practical interests. However, a comprehensive and in-depth review is still lacking in the literature to date. Accordingly, this work presents a comprehensive overview of the prospects of layered nickelates (Ln2NiO4+δ, where Ln = La, Nd, and Pr) as one of the most attractive oxygen (steam) electrode materials for protonic ceramic electrochemical cells. In particular, the crystalline features, defect structure, stability, chemical properties, and mechanical compatibility of this class of materials, contributing to their transport functionality, are discussed with the primary emphasis on revealing the relationship between the composition of the materials and their properties. The presented systematic results reveal the main strategies regarding the utilisation of Ln2NiO4+δ-based electrodes and existing gaps related to fundamental and applied research aspects.

Recent advances in layered Ln2NiO4+δ nickelates: fundamentals and prospects of their applications in protonic ceramic fuel and electrolysis cells

La2 − xPrxNiO4 + δ as suitable cathodes for metal supported SOFCs

Oxygen transport properties of Ca-doped Pr2NiO4

This chapter reviews recent advances in developing intermediate-temperature solid oxide fuel cells; oxygen and hydrogen separation membranes; and methods for obtaining advanced oxide, nanocomposite, and nanostructured materials for such devices. All the materials were synthesized by novel methods and characterized by sophisticated techniques. High ionic conductivity and improved oxygen/protonic mobility and surface reactivity were demonstrated. A new approach to building the functional layers was developed. A high-power density of single-button fuel cells in the intermediate-temperature range was reached. Oxygen and hydrogen separation membranes demonstrated promising and stable performance due to fast ionic transport and high catalytic activity of the materials concerned.

Kazuya Wakai

Papers

Thermodynamic analyses of structural phase transition of Pr2NiO4+δ involving variation of oxygen content

Analysis of structural phase transition behavior of Ln2NiO4 + δ (Ln: Nd, Pr) with variation of oxygen content