Nanofluids as a coolant for polymer electrolyte membrane fuel cells: Recent trends, challenges, and future perspectives

In this comprehensive review, we critically examine the application of nanofluids as coolants in PEMFCs, explicitly focusing on elucidating their thermal efficiency enhancement mechanisms. In addition to the existing research, the significant areas critically reviewed include the influence of nanoparticle size and concentration, surface modification techniques, characterization methods, nanofluid stability under different conditions, nanofluid behavior in various flow regimes, and the impact of nanofluids on system performance and efficiency. A meticulous analysis of the most recent studies involving single nanofluids (Al2O3, SiO2, TiO2, ZnO, BN) and hybrid nanofluids (CuFeAl, Al2O3:SiO2, Bio glycol+Al2O3:SiO2, TiO2:SiO2) underscores their potential to revolutionize PEMFC cooling systems. Findings reveal that nanofluids exhibit remarkable enhancements in heat transfer, offering a 20-27% reduction in radiator size compared to traditional coolants. The science underpinning this enhancement is multifaceted, characterized by self-deionization phenomena, nanoparticle dispersion stability via Brownian motion, and unprecedented inter-atomic interactions. Notably, nanofluids effectively eliminate particle sedimentation and coagulation, ensuring sustained heat transfer performance over extended operational periods. However, several challenges are observed, such as the limited exploration of electrical conductivity, which occurred because of the correlation between the net-charge influence of the suspended particle and electrical double layer (EDL) behavior. Furthermore, understanding and utilizing smart nanofluids and nanobubbles demand rigorous investigation for optimal cooling strategies. Future research should focus on standardizing nanofluid synthesis and characterization protocols, elucidating the underlying heat transfer mechanisms, addressing cost and scalability issues, and ensuring nanofluids' durability in PEMFCs. The review's timeliness lies in its relevance to the current advancements and challenges in the field, offering valuable insights for researchers and practitioners working in the thermal management of PEMFC.