Review of direct ammonia solid oxide fuel cells: Low temperature cell structure and ammonia decomposition strategies

Ammonia is a promising zero-carbon fuel with features that include a high hydrogen density and ease of storing and transporting. Solid oxide fuel cells (SOFCs) are efficient and clean energy conversion devices. Direct ammonia fuel SOFCs (DA-SOFCs) possess evident cost effectiveness and practicality. The efficient and compact DA-SOFCs is ideal for electric power and transportation applications. At medium-high temperatures (700–1000 °C), the use of ammonia in traditional SOFCs can achieve performance close to hydrogen. However, high temperatures are detrimental to the long - term stability and commercialization of the cell. Thus, low temperature DA-SOFCs (<600 °C) are attractive for low cost and commercialization. But low ammonia decomposition rate and high polarization at low temperatures hindering their progress. Our objective is to present the progress on low temperature SOFCs and ammonia decomposition catalysts over the two decades, including advanced DA-SOFCs performance, characteristics of low temperature induced performance loss, high-performance cell structures, and ammonia decomposition catalysts. The implementation strategies of low operating temperature DA-SOFCs are introduced, including low polarization cell structures, such as semiconductor ion membrane fuel cells (SIMFCs) and hydrogen-permeable metal supported thin film fuel cells (HMFCs), are applied to enhance the low temperature performance. High-entropy alloys, alkaline promoters and hydrogen-permeable metal supports are utilized to increase the ammonia decomposition rate. This review is a state - of - the - art survey of DA-SOFCs, covering performance, materials, techniques, and basic principles, focusing on the implementation and prospects of low temperature DA-SOFCs.