Alternative hydrogen carriers for button-cell oxide-ion solid oxide fuel cells: A critical review outlining current status, challenges, and prospects

Solid oxide fuel cells (SOFCs) are emerging as key technologies for enabling low-carbon energy systems due to their high efficiency, environmental friendliness, fuel flexibility, and compatibility with renewable hydrogen carriers. Among the various configurations, button-cell SOFCs based on oxide-ion conductors offer a well-defined platform for investigating fundamental and applied aspects of electrochemical performance. While hydrogen and syngas remain the primary fuels, the high operating temperatures of SOFCs enable the direct utilization of a wide range of alternative fuels. However, comprehensive reviews on this topic are scarce. The present review addresses this gap by critically examining recent progress in the experimental characterization and the corresponding fundamental thermodynamic and kinetic understanding of button-cell SOFCs fuelled by ammonia, ethanol, ethylene glycol, methanol, or toluene. Based on the analysed studies, SOFCs operating with alternative fuels exhibit competitive performance. Ammonia-fed cells achieve peak power densities (PPD) up to ∼2680 mW/cm2at 750 °C, and their stability ranges from 10 h to over 500 h, with isolated cases exceeding 1000 h. Feed gas containing a high concentration of toluene, despite its strong coking propensity, delivered a PPD of ∼14 mW/cm2at 650 °C. Methanol-fuelled SOFCs show a wide PPD range from ∼2 to 2108 mW/cm2, with isolated long-term tests over 1000 h. Ethanol-fed systems reach PPDs between ∼81 and 1370 mW/cm2, depending on operating temperature and anode design. Ethylene glycol demonstrates promising performance, with PPDs up to 1186 mW/cm2at 750 °C and stable operation for 200 h at 400 mA/cm2. Key challenges are identified in the degradation mechanisms of anode materials, long-term stability, and fuel processing. We discuss recent strategies to mitigate these issues, focusing on material innovations and the role of catalytic functionalities in promoting efficient fuel conversion. Promising research directions are addressed to unlock the full potential of button-cell SOFCs as efficient and durable multi-fuel energy conversion devices in next-generation hydrogen-based energy infrastructures.