Thermodynamic Exergy Analysis of PEMFC Systems for System Efficiency and Waste Heat Recovery

Proton Exchange Membrane Fuel Cell (PEMFC) vehicles are emerging as a promising green alternative to fossil fuel and battery-operated electric vehicles. Fuel cells convert the chemical energy of fuel to direct current (DC) through electrochemical reactions, rejecting some heat in the process. This study aims to minimize heat generated during these reactions within the fuel cell stack and utilize it to enhance stack efficiency. Through thermodynamic modeling and exergy analysis, the research focuses on reducing waste heat from exothermic reactions in PEMFC stacks. It investigates using low-temperature waste heat for heating hydrogen and inlet air also examining into how stoichiometry and current density influence heat reduction. Analytical studies were carried out using air stoichiometry ranging from 1.5 to 2 and ambient temperatures typical of Bangalore's climate (15°C to 35°C). The results show that increasing the current density from 1 A/cm² to 1.5 A/cm² significantly raises the hydrogen power requirement and stack power output, however, it leads to a decrease in overall system efficiency, from 57% to 49%, due to higher exergy losses. In addition, as ambient temperature rises from 288.15 K to 308.15 K, reduces the overall efficiency of the system, primarily due to higher auxiliary power consumption. Cathode stoichiometry also plays a crucial role, increasing stoichiometry from 1.5 to 2 resulting in higher compressor power consumption and more waste heat generation. Furthermore, Auxiliary parts like heat exchangers and air compressors require a significant amount of power in which emphasizes the need for system optimization. Heating inlet gases with hot cooling water can boost system efficiency by 1% and save around 2.7 kW of energy. System efficiency could be substantially enhanced by effectively utilizing the stack's waste heat.