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Ammonia is a prospective carbon-free fuel source for fuel cell systems due to low production cost, ease in liquefaction at ambient temperatures, and high energy density. Furthermore, hydrogen and nitrogen originating from ammonia fuel are expected to have little negative effect on fuel cell performance, while hydrocarbon fuels draws some severe problems at electrodes, such as CO poisoning or carbon deposition in low- and high-temperature fuel cells, respectively.
Several technologies can be considered for the ammonia utilization in fuel cell systems. For the utilization of ammonia fuel, we aim to develop a system combined with ammonia decomposition reactor and solid-state fuel cells such as solid oxide fuel cells (SOFCs) and anion-exchange membrane fuel cells (AEMFCs). Ruthenium catalysts are well-known to promote the decomposition of ammonia to hydrogen and nitrogen, but the limited availability of ruthenium demands new catalyst systems. Nickel catalysts exhibit relatively high activity for this reaction among base metals. In this study, we introduce the development of nickel catalysts supported on metal oxide. The influence of support materials and additives on the catalytic activity for ammonia decomposition was investigated.
SOFCs can also be operated with a direct supply of ammonia fuel to their anode. There are two possible mechanisms for ammonia oxidation over the anode: 1) ammonia can be directly electro-oxidized on the anode, and 2) ammonia catalytically decomposes to nitrogen and hydrogen over the anode, and then the produced hydrogen is electrochemically oxidized. Therefore, the fundamental study on the reaction route of ammonia over the anode was conducted to elucidate its oxidation mechanism.