David J. Manko

High energy efficiency and high power density proton exchange membrane fuel cells: Electrode kinetics and mass transport

Abstract The development of proton exchange membrane (PEM) fuel cell power plants with high energy efficiencies and high power densities is gaining momentum because of the vital need of such high levels of performance for extraterrestrial (space, underwater) and terrestrial (power source for electric vehicles) applications. Since 1987, considerable progress has been made in achieving energy efficiencies of about 60% at a current density of 200 mA/cm2 and high power densities (⪢ 1 W/cm2) in PEM fuel cells with high (4 mg/cm2) or low (0.4 mg/cm2) platinum loadings in electrodes. This article focuses on: (i) methods to obtain these high levels of performance with low Pt loading electrodes — by proton conductor impregnation into electrodes, localization of Pt near front surface; (ii) a novel microelectrode technique which yields electrode kinetic parameters for oxygen reduction and mass transport parameters; (iii) demonstration of lack of water transport from anode to cathode; (iv) modeling analysis of PEM fuel cell for comparison with experimental results and predicting further improvements in performance; (v) recommendations of needed R&D for achieving the above goals.

High power density proton-exchange membrane fuel cells

Abstract Proton-exchange membrane (PEM) fuel cells use a perfluorosulfonic acid solid polymer film as an electrolyte which simplifies water and electrolyte management. Their thin electrolyte layers give efficient systems of low weight, and their materials of construction show extremely long laboratory lifetimes. Their high reliability and their suitability for use in a microgravity environment makes them particularly attractive as a substitute for batteries in satellites utilizing high power, high energy-density electrochemical energy storage systems. In this investigation, the Dow experimental PEM (XUS-13204.10) and unsupported high platinum loading electrodes yielded very high power densities, of the order of 2.5 W cm−2. A platinum black loading of 5 mg cm−2 was found to be optimum. On extending the three-dimensional reaction zone of fuel cell electrodes by impregnating solid-polymer electrolyte into the electrode structures, Nafion® was found to give better performance than the Dow experimental PEM. The depth of penetration of the solid polymer electrolyte into electrode structures was 50–70% of the thickness of the platinum-catalyzed active layer. However, the degree of platinum utilization was only 16.6% and the roughness factor of a typical electrode was 274.