Recent advances in solid polymer electrolyte fuel cell technology with low platinum loading electrodes

Abstract

There is great enthusiasm for the development of high power density fuel cell systems for defense and civilian applications. Taking into consideration the main causes for efficiency losses--activation, mass transport and ohmic overpotentials--the only fuel cell systems capable of achieving high power densities are the ones with alkaline and solid polymer electrolyte. High power densities (0.8 W/cm2 at 0. Even higher power densitiesHistorically, the first type of fuel cell system to find a major application (auxiliary power source in the Gemini Space Vehicles) is the one with solid polymer electrolyte as the electrolyte. These fuel cell systems were developed by the General Electric Company. Since the sixties, great strides have been made in increasing the power density from 50 mW/cm2 to about 2-3 W/cmz. The latter performance was achieved at Ballard Technologies Corporation which used practically the same technology as General Electric CompanylUnited Technologies Corporation--Hamilton Standard. The platinum loading in these fuel cells is 4 mg/cm2 on each electrode.Research and Development at Los Alamos National Laboratory and in our laboratory has led to the attainment of high power densities (zl watt/cm2> in solid polymer electrolyte fuel cells with ten times lower platinum loading in the electrodes (i .e., 0.4 mg/cm2>. used to attain these goals are as follows:The necessary criteria and the methods (1) Extension of the three dimensional reaction zone by the impregnation of a proton conductor (i.e., the ion-exchange membrane) into the electrode structure. Hot pressing of the proton-exchange membrane and electrodes at a temperature above the glass transition temperature and at a pressure of 50 atm. Adequate humidification of the reactant gases by passing these gases through humidification chambers set at temperatures of 10°C for H2 and 5OC for oxygen or air higher than the cell temperature. Enhancement of the electrode kinetics of the hydrogen oxidation and the oxygen reduction reactions and particularly of the mass transport rates of the reactant gases to the electrode by operation at elevated temperatures and pressures, say 95OC and 5 atm. Localization of the platinum near the front surface of the electrode to reduce the thickness of the active layer and provide a higher concentration of platinum sites on the front surface to reduce mass transport and ohmic overpotentials within the porous electrode and at the electrodelelectrolyte interface.( 2 )

Preparation of High‐Platinum‐Utilization Gas Diffusion Electrodes for Proton‐Exchange‐Membrane Fuel Cells

“…These electrodes contained -0.5 mg Pt/cm 2 and included a sputtered platinum layer of -0.05 mg Pt/cm 2. Presently, sputter deposition of platinum is not considered to be an economically viable alternative for fabricating electrodes on a large scale, and wetchemical alternatives are being considered (5).…”

Design of High-Ionic Conductivity Electrodes for Direct Methanol Fuel Cells

“…They found that the best performing electrodes, based on polarization curves, have a Nafion loading of approximately 30 % by mass. The polarization data was subjected to Tafel analysis [14] to fit the polarization curve as:…”

Research of Proton Exchange Membrane Fuel Cell Modeling on Concentration Polarization under Variable-Temperature Operating Conditions

“…Owing to its theoretical significance, this model has been widely used to describe the concentration overvoltage of PEMFCs [8]. In 1989, a simplified semi-empirical model for describing the PEMFC volt-ampere characteristics was first proposed by Srinivasan from Los Alamos National Laboratory in the United States [9]. The model of open-circuit voltage was obtained by Gibbs free energy theory, the activated overvoltage was expressed by the Tafel equation summarized from experimental rules and the ohmic overvoltage was represented by the slope of the linear region of a polarization curve.…”