Performance analyses of a combined system consisting of high-temperature polymer electrolyte membrane fuel cells and thermally regenerative electrochemical cycles

Abstract

High-temperature polymer electrolyte membrane fuel cells have a promising prospect in combined heat and power applications because their relatively high operating temperature. In this paper, a new combined system comprised of a high-temperature polymer electrolyte membrane fuel cell, a regenerator and a thermally regenerative electrochemical cycle subsystem is proposed, where the thermally regenerative electrochemical cycle subsystem further converts the waste heat from the high-temperature polymer electrolyte membrane fuel cell into electricity. Considering various electrochemically and thermodynamically irreversible losses within each subsystem and between them, mathematical formulas for power output, energy efficiency, exergy destruction rate and exergy efficiency of the combined system are formulated. The energetic and exergetic performance characteristics of the combined system are revealed and the optimum operating ranges are determined using maximum power density as objective function. Results show that the maximum output power density of the proposed system is improved by 15.6% compared with that of a single high-temperature polymer electrolyte membrane fuel cell, and its corresponding energy efficiency and exergy efficiency are also increased by 8.5% and 11.7%, respectively. Moreover, the effects of decisive operating conditions and designing parameters on the combined system performance are discussed in detail.