Tailoring A Poly(ether sulfone) Bipolar Membrane: Osmotic-Energy Generator with High Power Density.

Osmotic energy, obtained through different concentrations of salt solutions, is recognized as a form of a sustainable energy source. In the past years, membranes derived from asymmetric aromatic compounds have attracted attention because of their low cost and high performance in osmotic energy conversion. The membrane formation process, charging state, functional groups, membrane thickness, and the ion-exchange capacity of the membrane could affect the power generation performance. Among asymmetric membranes, a bipolar membrane could largely promote the ion transport. Here, two polymers with the same poly(ether sulfone) main chain but opposite charges were synthesized to prepare bipolar membranes by a nonsolvent-induced phase separation (NIPS) and spin-coating (SC) method. The maximum power density of the bipolar membrane reaches about 6.2 W m-2 under a 50-fold salinity gradient, and this result can serve as a reference for the design of bipolar membranes for osmotic energy conversion systems.

Modification of sulfonated poly(arylene ether nitrile) proton exchange membranes by poly(ethylene-co-vinyl alcohol).

The modification of the physicochemical properties of sulfonated poly(arylene ether nitrile) (SPAEN) proton exchange membranes was demonstrated by poly(ethylene-co-vinyl alcohol) (EVOH) doping (named SPAEN-x%). By controlling the temperature during membrane preparation, the side reactions of the sulfonic acid groups to form sulfonic acid esters were effectively prevented, greatly reducing the proton conductivity of the membranes. Due to the flexible chain of EVOH, SPAEN-8% showed a relatively high elongation of 30.2%, which enhanced the aromatic polymers' flexibility. The SPAEN-2% membrane exhibited proton conductivity of 166, 55, and 9.6 mS cm-1 at 95%, 70%, and 50% relative humidity, respectively, higher than those of the other SPAEN-x% membranes and even comparable to that of Nafion 212. The water uptake, morphological study, and through-plane proton conductivity of the membranes were studied and discussed. The results suggest that EVOH doping can be used as an effective strategy to improve SPAEN-based proton exchange membranes' performance.

Phosphonate poly(vinylbenzyl chloride)-Modified Sulfonated poly(aryl ether nitrile) for Blend Proton Exchange Membranes: Enhanced Mechanical and Electrochemical Properties.

Blend proton exchange membranes (BPEMs) were prepared by blending sulfonated poly(aryl ether nitrile) (SPAEN) with phosphorylated poly(vinylbenzyl chloride) (PPVBC) and named as SPM-x%, where x refers to the proportion of PPVBC to the weight of SPAEN. The chemical complexation interaction between the phosphoric acid and sulfonic acid groups in the PPVBC-SPAEN system resulted in BPEMs with reduced water uptake and enhanced mechanical properties compared to SPAEN proton exchange membranes. Furthermore, the flame retardancy of the PPVBC improved the thermal stability of the BPEMs. Despite a decrease in ion exchange capacity, the proton conductivity of the BPEMs in the through-plane direction was significantly enhanced due to the introduction of phosphoric acid groups, especially in low relative humidity (RH) environments. The measured proton conductivity of SPM-8% was 147, 98, and 28 mS cm-1 under 95%, 70%, and 50% RH, respectively, which is higher than that of the unmodified SPAEN membrane and other SPM-x% membranes. Additionally, the morphology and anisotropy of the membrane proton conductivities were analyzed and discussed. Overall, the results indicated that PPVBC doping can effectively enhance the mechanical and electrochemical properties of SPAEN membranes.

Ionic Crosslinking-Induced Nanochannels: Nanophase Separation for Ion Transport Promotion.

Charge-governed ion transport is crucial to numerous industries, and the advanced membrane is the essential component. In nature, the efficient and selective ion transport is mainly governed by the charged ion channels located in cell membrane, indicating the architecture with functional differentiation. Inspired by this architecture, a membrane by ionic crosslinking sulfonated poly(arylene ether ketone) and imidazolium-functionalized poly(arylene ether sulfone) is designed and fabricated to make full use of the charges. This ionic crosslinking is designed to realize nanophase separation to aggregate the ion pathways in the membrane, which results in excellent ion selectivity and high ion conductivity. With the excellent ion transport behavior, ionic crosslinking membrane shows great potential in osmotic energy conversion, which maximum power density can be up to 16.72 W m-2 . This design of ionic crosslinking-induced nanophase separation offers a roadmap for ion transport promotion.