Effect of SiO2 additives on the PEM fuel cell electrode performance

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-humidification 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 SiO2 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 m2/g and 2. Silica powder with surface area of 45 m2/g is incorporated in the fuel cell electrode. This improves the hydrophilic and protonation properties of the SiO2 powders when treated with H2SO4. Initial experiments under humidified conditions showed that the Silica powder, which was not treated with H2SO4, gave marginally lower performance compared to the H2SO4 treated sample. The polarization behaviors of the electrode with and without SiO2 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.