Performance assessment of a molten hydroxide direct carbon fuel cell-based hybrid system coupled with a two-stage thermoelectric generator

Abstract

A new hybrid system model is proposed to harvest the waste heat produced by a molten hydroxide direct carbon fuel cell (MHDCFC) for additional electricity production via a two-stage thermoelectric generator (TTEG), in which the TTEG considers Thomson effect combined with Peltier, Joule and Fourier heat conduction. Mathematical expressions for the energy efficiency, power output, exergy efficiency and exergy destruction rate of hybrid system, MHDCFC and TTEG are analytically obtained by considering the polarization losses in MHDCFC, regenerative losses, heat-conduction losses and Joule heat in TTEG, and heat leakage from MHDCFC to environment. The energetic and exergetic performance features and the optimum operating ranges for the MHDCFC/TTEG hybrid system are revealed. The attainable maximum power output density and the corresponding energy efficiency and exergy efficiency of the proposed hybrid system are, respectively, 55.4 %, 8.7 % and 8.8 % greater than that of a standalone MHDCFC, while the exergy destruction rate is decreased by 7.2 %. In addition, the effects of some decisive operation conditions and design parameters on the MHDCFC/TTEG hybrid system performance are studied.