Resolving Oil-to-Water Channel Leakage in Bijels: On the Road to a 3D Janus Porous Material
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Hydrogen fuel cells are essential in the transition to sustainable electricity, since the output of renewable energy sources fluctuates over time. The conversion from chemical to electrical energy is performed by a proton-exchange membrane fuel cell (PEMFC). PEMFCs suffer from lowered efficiency due to water flooding, which hinders the diffusion of the oxygen reactant at the cathode. Hydrophilic and hydrophobic regions in the gas diffusion layer (GDL) improve the mass transport of these two chemicals. A bicontinuous interfacially jammed emulsion gel (bijel) offers two interwoven, fully continuous pore systems of oil and water. Our goal is to phase-selectively hydrophobize the bijel scaffold to create a Janus porous medium, which could serve as a GDL. The hydrophobized channel network facilitates oxygen diffusion, while the untreated pores remain hydrophilic and allow for the transport of water. Bijels are promising candidates to become the first material to extend the asymmetric Janus character to 3 dimensions. Solvent Transfer-Induced Phase Separation (STrIPS) is used for the continuous fabrication of bijel-based templates with sub-micron domains. The system is characterized with scanning electron microscopy (SEM) and confocal microscopy. The present work shows that the hydrophobic character of the particles causes any oil to leak into the water channel. The rate of flooding depends on the oil viscosity. Consequently, the loss of phase-distinction inhibits phase-selective hydrophobization. The removal of oil residue and surfactant from the aqueous phase via electro-osmosis is a promising solution to circumvent the structural degradation which impedes the fabrication of Janus bijels. The application of bijels into a Janus porous GDL would raise the efficiency of mass transport and thereby increase the power density of hydrogen fuel cells.