Upgrading phosphoric acid fuel cell waste heat through isopropanol-acetone-hydrogen chemical heat pump for storage purposes

Abstract

The inherent electrochemical reaction mechanism of phosphoric acid fuel cells (PAFCs) results in a substantial portion of hydrogen energy being released as waste heat, which adversely affects energy efficiency, operational stability, and economic viability. In this study, we propose a novel hybrid system that integrates an isopropanol-acetone-hydrogen chemical heat pump to capture and convert this waste heat for storage purposes. A steady-state, system-level model is developed based on electrochemical and thermodynamic principles to predict the system’s performance by quantifying irreversible losses arising from energy transfer and conversion processes. Simulation results indicate that the hybrid system achieves a peak output power density of 5448.07 W m^–2, an energy efficiency of 47.02 %, and an exergy efficiency of 50.03 %, corresponding to improvements of 16.26 %, 10.17 %, and 10.09 %, respectively, compared to a standalone PAFC at 473 K. Exhaustive parametric studies show that increases in operating temperature, charge transfer coefficient, and exchange current density of the fuel cell positively improves overall output performance. Conversely, output performance diminishes as electrolyte thickness or the pre-reaction hydrogen-to-acetone molar ratio increases. Local sensitivity analysis identifies electrolyte thickness as the key parameter influencing hybrid system efficiency, underscoring its critical importance for optimization efforts.