Improved Anode Two-Phase Mass Transfer Management of Direct Methanol Fuel Cell by the Application of Graphene Aerogel

The main purpose of this paper is to utilize the intrinsic hydrophobicity and microstructure of graphene aerogel to construct a novel anode two-phase mass transfer structure for passive micro direct methanol fuel cell. Compared with its traditional counterpart composed of carbon black and poly(tetrafluoroethylene), the anode gas diffusion layer based on graphene aerogel holds some greatly improved microstructures, which contributes to an excellent gas liquid mass transfer management. During discharge, smaller, more evenly distributed bubbles of CO2 fill in the pores of the three-dimensional structure of graphene aerogel and form a convection in the opposite direction of methanol transport, increasing the mass transfer resistance of methanol without causing a loss of effective reaction area. A methanol crossover test system is specifically designed to verify the effect of CO2 on reducing methanol crossover under operation. As a result, an increase of more than 20% in the output power density and a significant increase of the operating methanol concentration are achieved without additional structures. Moreover, the energy density of the micro direct methanol fuel cell with the novel anode gas diffusion layer is almost 3 times that of the one with commercial gas diffusion layer, which greatly enhances its utility in portable devices.