Hydrogenous solid oxide fuel cells: role and evolution of anode materials

The accelerating depletion of fossil fuel reserves and the growing impact of greenhouse gas emissions underscore the urgent need for sustainable energy carriers. Hydrogen and hydrogen-rich fuels such as ammonia, methane, and methanol, stand out due to their exceptional energy density and low environmental impact when produced from renewable sources. Solid oxide fuel cells (SOFCs) can leverage the high energy density of these hydrogenous fuels and offer high efficiencies by directly utilising these hydrogen-rich fuels over the anode. However, Hydrogenous SOFCs face challenges with these fuels, such as slow kinetics, anode deactivation through nitridation, sulphur and carburation, or stack component compatibility and manufacturing cost. This review presents a historical overview of cermets, perovskites, and high-entropy alloys (HEAs) as anode materials for SOFCs. It aims to provide a comprehensive understanding of why these materials are effective as anodes and to elucidate how improvements to anode design have improved and evolved over time. This review aims to collate the most recent studies into the mechanisms for hydrogenous fuel usage at a fundamental level. Additionally, the latest methodologies combining artificial intelligence and machine learning algorithms to enhance research efficacy within the SOFC field will be discussed. Recent literature highlights the ever-improving viability of directly utilising ammonia, methane, and methanol compared to hydrogen, due to the improvements in the anode. Among all studied anode materials, traditional nickel-based cermet anodes continue to display the highest power densities, albeit at the expense of carbon and sulphur tolerance compared to HEAs. Ultimately, challenges in anode stability and system integration persist, highlighting the need for continued investment and innovation.