Porous structure and hydrophilic-hydrophobic properties of gas diffusion layers of the electrodes in proton-exchange membrane fuel cells

The porous structure and hydrophilic-hydrophobic properties of the gas diffusion layers (GDL) of electrodes on a substrate of carbon paper in proton-exchange membrane fuel cells have been investigated with the methods of standard porosimetry and of pycnometry. GDL containing various fluoroplast concentrations were impregnated with water, and this process has been investigated at 20 and 80 degrees C. The impregnation rate is significantly higher for untreated carbon paper than for teflonated GDL and also increases significantly with increasing temperature. With teflonization of the carbon paper, hydrophilic porosity decreases, while hydrophobic porosity increases. This increase, however, ceases at high fluoroplast concentrations. The concept of hydrophobization effectiveness of the porous carbon substrate of GDL is introduced. It has been established that hydrophobization effectiveness decreases with increasing fluoroplast concentration and depends on the type of suspension. Curves of the angle of wetting of GDL by water versus the pore radius exhibit a minimum. Different values of the angle of wetting of GDL by water in different pores are explained by nonuniform distributions of both fluoroplast particles and hydrophilic surface groups in pores of different dimensions.