Technical challenges and enhancement strategies for transitioning PEMFCs from H2-air to H2-O2

Compared to other types of air-independent propulsion (AIP) technologies, proton exchange membrane fuel cells (PEMFCs) are gaining increasing recognition for applications in enclosed environments without air, such as underwater and aerospace scenarios. This is attributed to their large power density and silent operation. Although PEMFCs have reached a level of maturity in terrestrial applications nowadays, transitioning them from air supply (H2-air) to pure oxygen supply (H2-O2) still presents numerous technical challenges, as indicated by our literature review and analysis. These challenges primarily involve redesigning key materials, water and thermal management techniques, and system configurations at various scales, ranging from micro to macro levels. First, the oxygen-rich environments and higher operational voltage of H2-O2 PEMFCs will inevitably accelerate the corrosion rate of all PEMFCs components. Secondly, the active water and thermal management techniques adopted in H2-air PEMFCs no longer meet the requirements of energy efficiency and compactness in enclosed environments. Finally, current hydrogen sources technologies limit mission durations due to their relatively low energy storage density, and air compressors commonly used in H2-air PEMFCs are not compatible with H2-O2 PEMFCs. The nature of enclosed environments also necessitates more rigorous approaches to safety in system integration. This review systematically summarizes comprehensive enhancement strategies aimed at addressing these challenges. Developing anti-corrosive catalysts and supports in the catalyst layer, membrane, gas diffusion layer (GDL), and bipolar plate (BPP) can mitigate their degradation to prolong the lifespan of H2-O2 PEMFCs. Passive water and thermal management techniques are also essential for making PEMFCs practical in enclosed environments. Furthermore, advanced hydrogen and oxygen sources technologies are crucial for increasing energy storage density, and safety design is paramount for the urgent advancement of H2-O2 PEMFCs technology. These strategies are believed to accelerate the application of H2-O2 PEMFCs in enclosed environments and have been proven to be effective.