Synthesis of the block sulfonated poly(ether ether ketone)s (S-PEEKs) materials for proton exchange membrane

Constructing anhydrous proton exchange membranes based on cadmium telluride nanocrystal-doped sulfonated poly(ether ether ketone)/polyurethane composites

Cadmium telluride (CdTe) nanocrystals with thiol stabilizers have been applied widely in the fields of energy storage and transformation. The aim of this work is to develop anhydrous proton exchange membranes (PEMs) by introducing CdTe nanocrystals bearing thioglycolic acid (tga) or mercaptopropionic acid (mpa) stabilizers into sulfonated poly(ether ether ketone) (SPEEK) and polyurethane (PU) systems. In the prepared SPEEK/PU/CdTe membranes, CdTe nanocrystals could provide desirable properties such as improving mechanical strength and enhancing proton conductivity by combining with phosphoric acid (PA) molecules. Successful preparation of SPEEK/PU/CdTe/PA membranes was demonstrated by the identification of high and stable proton conductivity and satisfactory thermal/chemical stability and mechanical properties. The fine appearance of membranes revealed uniform dispersion of components. Measurements of properties showed that the SPEEK(74%)/PU/CdTe-mpa(20/60/20)/100%PA membrane as a candidate anhydrous PEM is promising for use in high-temperature proton exchange membrane fuel cells. Specifically, the recommended membrane showed a proton conductivity of 1.18 × 10^-1 S cm^-1 at 160 °C and 3.96 × 10^-2 S cm^-1 at 100 °C, lasting for 600 h, and a tensile stress of 14.6 MPa at room temperature. Mixing inorganic CdTe nanocrystals with polymers to form inorganic/organic composite membranes is effective for producing anhydrous PEMs with cheaper polymers without functional groups to conduct protons.

Surface modification of Nafion membranes by ion implantation to reduce methanol crossover in direct methanol fuel cells

The surface of Nafion membranes was modified by light ion implantation to reduce methanol crossover without affecting bulk membrane properties.

Separators used in microbial electrochemical technologies: Current status and future prospects

Microbial electrochemical technologies (METs) are emerging green processes producing useful products from renewable sources without causing environmental pollution and treating wastes. The separator, an important part of METs that greatly affects the latter's performance, is commonly made of Nafion proton exchange membrane (PEM). However, many problems have been identified associated with the Nafion PEM such as high cost of membrane, significant oxygen and substrate crossovers, and transport of cations other than protons protons and biofouling. A variety of materials have been offered as alternative separators such as ion-exchange membranes, salt bridges, glass fibers, composite membranes and porous materials. It has been claimed that low cost porous materials perform better than PEM. These include J-cloth, nylon filter, glass fiber mat, non-woven cloth, earthen pot and ceramics that enable non-ion selective charge transfer. This paper provides an up-to-date review on porous separators and plots directions for future studies.

Temperature- and humidity-controlled SAXS analysis of proton-conductive ionomer membranes for fuel cells

We report herein temperature- and humidity-controlled small-angle X-ray scattering (SAXS) analyses of proton-conductive ionomer membranes. The morphological changes of perfluorosulfonic acid polymers (Nafion and Aquivion) and sulfonated aromatic block copolymers (SPE-bl-1 and SPK-bl-1) were investigated and compared under conditions relevant to fuel cell operation. For the perfluorinated ionomer membranes, water molecules were preferentially incorporated into ionic clusters, resulting in phase separation and formation of ion channels. In contrast, for the aromatic ionomer membranes, wetting led to randomization of the ionic clusters. The results describe the differences in the proton-conducting behavior between the fluorinated and nonfluorinated ionomer membranes, and their dependence on the humidity.

Sulfonated poly(ether ether ketone) and sulfonated poly(1,4-phenylene ether ether sulfone) membranes for vanadium redox flow batteries

Nafion is a currently used as a proton exchange membrane in vanadium redox flow batteries (VRBs). It is an excellent proton-conducting and fully hydrated membrane, but it is costly. In order to reduce the cost of the membrane used in VRBs and to reduce vanadium permeability across the membrane, sulfonated poly(ether ether ketone) (S-PEEK) and sulfonated poly(1,4-phenylene ether ether sulfone) (S-PPEES) membranes were fabricated and studied as a function of the sulfonation reaction time. The increase in the degree of sulfonation from 46 to 86% induced increases in the water uptake, ion exchange capacity, proton conductivity, and vanadium permeability. The vanadium permeability coefficients of S-PEEK and S-PPEES membranes are in the range of 0–24.95 × 10–7 cm2 min–1, which are significantly lower than that of Nafion 117, which is 30.84 × 10–7 cm2 min–1. The proton conductivity of S-PEEK in our study is nine times higher than sulfonated poly(arylene ether ketone) in a previous work and more suitable for using in VRBs.

Structure-morphology-property relationships of non-perfluorinated proton-conducting membranes

A fundamental understanding of structure-morphology-property relationships of proton exchange membranes (PEMs) is crucial in order to improve the cost, performance, and durability of PEM fuel cells (PEMFCs). In this context, there has been an explosion over the past five years in the volume of research carried out in the area of non-perfluorinated, proton-conducting polymer membranes, with a particular emphasis on exploiting phase behavior associated with block and graft copolymers. This progress report highlights a selection of interesting studies in the area that have appeared since 2005, which illustrate the effects of factors such as acid and water contents and morphology upon proton conduction. It concludes with an outlook on future directions.