Preparation and characterization of Juglans regia shell-based nanofluid for enhanced cooling in polymer electrolyte membrane fuel cells

Proton Exchange Membrane Fuel Cells (PEMFCs) encounter tremendous thermal management issues owing to the poor heat dissipation capability of traditional coolants such as water and ethylene glycol. These cause dehydration of the membrane, overheating, and loss of system efficiency. To overcome this, bio-based nanofluids of Juglans regia shell (JRS), a readily available carbon-rich agricultural waste, were synthesized and dispersed in 70:30 water:ethylene glycol (W:EG) base fluid at 0.1, 0.3, and 0.5 vol% concentrations. At 0.5 vol%, the JRS nanofluid improved the thermal conductivity by around 11 % (up to 0.468 W/m·K) and retained electrical conductivity at lower values (29.43 μS/cm) in contrast to metal-based counterparts, minimizing the possibility of electrical interference in PEMFCs. Viscosity was moderately improved to 3.41 mPa s at 70 °C, while specific heat was retained at the same value as the base fluid (3.351 kJ/kg·K). Sedimentation tests demonstrated good dispersion stability up to 15 days without the need for surfactants. This research proposes the potential of JRS-based nanofluids as a green, cost-effective coolant, consistent with the principles of circular economy, while providing better thermal performance and system compatibility for PEMFC applications.