Performance Improvement of a Direct Carbon Fuel Cell through an Irreversible Vacuum Thermionic Generator

A novel hybrid system consisting of a direct carbon fuel cell (DCFC), a thermionic generator (TIG), and a regenerator is developed to recover the exhaust heat from the fuel cell. Expressions for the power output and efficiency of subsystems and the hybrid system are derived. Based on the energy balance equation, the area matching problem between the DCFC and the TIG is discussed and solved. By considering the main irreversibilities, the influences of the DCFC’s current density and the TIG’s voltage on the performance of the hybrid system are revealed. The maximum power output density and the corresponding efficiency of the hybrid system are, respectively, equal to 379 W/m² and 36%. To enhance the maximum power density of the single DCFC, the optimal regions of the main parameters are determined.