Fabrication of gas-diffusion electrodes at various pressures and investigation of synergetic effects of mixed electrocatalysts on oxygen reduction reaction

This work introduces a new method for the construction of gas-diffusion electrodes (GDEs) for fuel cells. Sampled dc voltammetry is used to study the oxygen reduction reaction (ORR) during the rate-determining step. In this study, GDEs are fabricated in two separate stages: pressure processing followed by temperature processing. The GDE that gives the best performance is constructed at a pressure of 60 kF cm(-2), and has a platinum loading of 0.5 mg cm(-2) and 30% polytetra fluoroethylene (PTFE) in the reaction layer. The values of the symmetry factor and exchange current density of this optimal GDE are 0.5279 and 35.16 mA cm(-2), respectively. In order to reduce or eliminate the polarization effect, two types of electrocatalyst (platinum on carbon and platinum on activated charcoal) with different surface areas are combined to create a mixed electrocatalyst. An investigation is made of the electrochemical characteristics of pure samples of each electrocatalyst and mixtures of the two electrocatalysts over a range of mole ratios. The results indicate that, under optimized conditions (a platinum loading of 0.9 mg cm(-2) with a mole fraction of platinum on carbon of 0.8), the exchange current density is 92.55 mA cm-2. The use of a mixed electrocatalyst reduces the concentration polarization of the ORR in the rate-determining step. (C) 2003 Elsevier Science B.V. All rights reserved.