Polyelectrolyte multilayer catalysts in electrospun bipolar membranes

Abstract

Here we utilize the layer-by-layer (LbL) technique to homogenously integrate polyelectrolyte (PE) multilayers with multiple different catalytic functionalities inside an electrospun BPM without forming an electrically and/or ionically non-conductive catalyst layer. BPMs were fabricated by coating an electrospun cation exchange layer alternately with polyethyleneimine (PEI)-poly (acrylic acid) (PAA), followed by hot-pressing between pristine electrospun anion and cation exchange layers. This resulted in a BPM having a thin entangled 3D junction with high surface area and well-integrated catalysts. Optical reflectometry shows that the amount of PE catalysts inside the BPM can be controlled by tuning coating parameters such as the amount of bilayers and the ionic strength of the coating solution, where especially a higher ionic strength resulted in a significantly higher mass adsorption. The BPMs coated at higher ionic strength (500 mM NaCl) showed the lowest water dissociation potential of 0.84 V. Furthermore, it was found that incorporating the PE multilayers diminished the effect of the electric field and that the catalytic activity becomes more dominant in facilitating the water dissociation reaction. The advantage of creating a 3D junction using electrospinning in combination with the versatility of the LbL deposition technique allows for further optimization to create high performance BPMs that can be tailored to specific applications.