Gas Diffusion Electrode With Large Amounts of Gas Diffusion Channel Using Hydrophobic Carbon Fiber: For Oxygen Reduction Reaction at Gas/Liquid Interfaces

For a gas diffusion cathode for oxygen reduction reaction (ORR) in aqueous alkaline electrolyte, it is important to create networks for O2 gas diffusion, electronic conduction, and liquid-phase OH− transport in the cathode at once. In this study, we succeeded to fabricate a promising cathode using hydrophobic vapor grown carbon fibers (VGCF-Xs), instead of hydrophobic carbon blacks (CBs), as additives to its active layer (AL). Mercury porosimetry, as well as electrochemical impedance spectroscopy, showed that porosity of the cathode gradually increased with increasing the amount of the carbon fibers. In other words, addition of larger amount of the carbon fibers creates better O2 gas diffusion channels. Also, the activation polarization resistance for the ORR increased as the carbon fibers' amount from 0 to 0.03–0.04 g and then dropped. In consequence, the cathode with 0.03 g of the carbon fibers exhibited the highest ORR performance among the prepared cathodes.