Effect of SiO_2 additives on the PEM fuel cell electrode performance

摘要

The Nafion membrane used as an electrolyte in the Polymer Electrolyte Membrane Fuel Cell (PEMFC) needs hydration to retain the proton conductivity. In PEMFC operation the reactant gas needs to be humidified either externally or internally. To reduce the cost, weight and complexities of the PEMFC system, it is beneficial to operate the PMEFC without humidification of the reactant gases because it eliminates the need for a complex gas-humidincation sub-system. In recent years, worldwide R&D efforts have been made to remove the external humidifying unit from the PEMFC system by endowing the membrane electrode assembly (MEA) with self-humidifying ability. Efforts have been made to minimize humidification of the ionic polymer by introducing SiO_2 either in the catalyst layer or on the gas diffusion layer or on the membrane directly. In-house has made two silica powders, 1. Aerogel silica, surface area is 582 m~2/g and 2. Silica powder with surface area of 45 m~2/g is incorporated in the fuel cell electrode. This improves the hydrophilic and protonation properties of the SiO~2 powders when treated with H~2SO~4. Initial experiments under humidified conditions showed that the Silica powder, which was not treated with H~2SO_2 gave marginally lower performance compared to the H~2SO~4 treated sample. The polarization behaviors of the electrode with and without SiO_2 in the catalyst layer were studied. The PEMFC was also studied under different humidity conditions. The electrodes and the PEMFC were characterized by different electrochemical techniques like cyclic voltammetry and Electrochemical Impedance Spectroscopy (EIS). The results are presented in this paper.