Highly selective porous separator with thin skin layer for alkaline water electrolysis

© 2022Advanced porous separators with thin selective skin layers to reduce the hydrogen permeation are developed for applications in alkaline water electrolysis. A thin skin layer based on crosslinked polyvinyl alcohol (cPVA) is fabricated on a porous substrate by a facile and scalable ultrasonic spray coating process. As the number of ultrasonic spraying cycles increases, the resulting separator demonstrates a decrease in the large-diameter pore fraction, an increase in the bubble-point pressure, and a reduction in the hydrogen permeability without a significant increase in the areal resistance. As a result, the optimized separator with a cPVA skin layer combines a low ionic resistance of 0.267 Ω cm2, a high bubble point pressure of 2.71 bar, and a low hydrogen permeability of 1.12 × 10−11 mol cm−2 s−1 bar−1. The electrolytic cell assembled with cPVAZ-30 achieves current densities of 861 mA cm−2 and 1890 mA cm−2 at 2.0 V and 2.6 V, respectively, in a 30 wt% KOH electrolyte solution at 80 °C.Y

Poly(ethylene-co-vinyl acetate)/polyimide/poly(ethylene-co-vinyl acetate) tri-layer porous separator with high conductivity and tailored thermal shutdown function for application in sodium-ion batteries

A poly (ethylene-co-vinyl acetate) (EVA)/polyimide (PI)/EVA (PIE) tri-layer separator with thermal stability and a shutdown function is fabricated for use in sodium-ion battery (SIB) applications. Porous EVA layers are coated on both sides of an electrospun-PI, acting as a supporting layer, through a dip-coating process accompanying a thermally induced phase separation in which polyethylene-block-poly (ethylene glycol) is used as a polymeric pore generator to obtain an open porous morphology. Excellent thermal stability of the PIE tri-layer separator is demonstrated, with two simultaneous incompatible thermal behaviors, i.e., a negligible thermal shrinkage of up to 200 degrees C, and a rapid thermal shutdown at approximately 100 degrees C. In addition, the PIE tri-layer separator shows a higher ionic conductivity and larger electrolyte uptake of the sodium liquid electrolyte than a commercial olefin separator, leading to better cycling performance when assembled into SIB coin cells. All these outstanding properties of PIE tri-layer separator demonstrate that its promise as a candidate separator for use in SIBs.y

Perfluorocyclobutyl-containing multiblock copolymers to induce enhanced hydrophilic/hydrophobic phase separation and high proton conductivity at low humidity

A multiblock copolymer containing a highly sulfonated poly(phenylene sulfide sulfone) (sPPSS) hydrophilic oligomer and a partially fluorinated perfluorocyclobutyl (PFCB)-containing hydrophobic oligomer was synthesized. The sharp contrast between the hydrophilic and hydrophobic moieties induced a well-developed phase separation, which was observed in the transmission electron microscopy (TEM) images within the polymer electrolyte membrane (PEM). The increased chain mobility from the flexible ether and PFCB groups afforded facile thermal annealing of the membrane. Thermal annealing induced polymer chain packing of the hydrophobic moieties, enhancing the hydrophilic/hydrophobic phase separation. The fabricated membranes exhibited higher proton conductivity compared with those of conventional hydrocarbon PEM possessing a random copolymer architecture, while their dimensional swelling was suppressed. Additionally, under low humidification (a relative humidity (RH) of 50%), the sulfonated-fluorinated membrane achieved a high proton conductivity of up to 41.9 mScm(-1). A high adhesion strength of 32.7 mNem(-1) was also observed, indicating strong interfacial compatibility in the membrane electrode assembly (MEA) due to its structural affinity for the contacting perfluorosulfonated binder. The enhanced hydrophilic/hydrophobic phase separations facilitated fuel cell performances of 1.13 and 0.61 Acm(-2) at 0.6 V and 65 degrees C under 100% and 50% RH conditions, respectively, in addition to achieving stable chemical and physical durabilities.N