3D-Zipped Interface: In Situ Covalent-Locking for High Performance of Anion Exchange Membrane Fuel Cells.

Polymer electrolyte membrane fuel cells can generate high power using a potentially green fuel (H2 ) and zero emissions of greenhouse gas (CO2 ). However, significant mass transport resistances in the interface region of the membrane electrode assemblies (MEAs), between the membrane and the catalyst layers remains a barrier to achieving MEAs with high power densities and long-term stabilities. Here, a 3D-interfacial zipping concept is presented to overcome this challenge. Vinylbenzyl-terminated bi-cationic quaternary-ammonium-based polyelectrolyte is employed as both the anionomer in the anion-exchange membrane (AEM) and catalyst layers. A quaternary-ammonium-containing covalently locked interface is formed by thermally induced inter-crosslinking of the terminal vinyl groups. Ex situ evaluation of interfacial bonding strength and in situ durability tests demonstrate that this 3D-zipped interface strategy prevents interfacial delamination without any sacrifice of fuel cell performance. A H2 /O2 AEMFC test demonstration shows promisingly high power densities (1.5 W cm-2 at 70 °C with 100% RH and 0.2 MPa backpressure gas feeds), which can retain performances for at least 120 h at a usefully high current density of 0.6 A cm-2 .

The alkali degradation of LDPE-based radiation-grafted anion-exchange membranes studied using different ex situ methods.

Radiation-grafted anion-exchange membranes (RG-AEM) in alkaline membrane fuel cells (AEMFC) exhibit promising performances (low in situ resistances, high power outputs and reasonably high alkali stabilities). Much research is focused on developing AEMs with enhanced chemical stabilities in the OH--forms at temperatures >60 °C. This study contributes towards this effort by providing a comparison of three different ex situ methods of screening alkali stabilities (where different laboratories conducted experiments on exactly the same batches of RG-AEM). Vinylbenzyl chloride monomer was radiation-grafted onto 25 µm thick low-density polyethylene (LDPE) precursor film in a single batch. This batch of grafted membrane was then split into three sub-batches, which were converted into RG-AEMs via amination with either: trimethylamine (TMA), N-methylpyrrolidine (MPY), or N-methylpiperidine (MPIP). Samples of each RG-AEM (l-AEM-TMA, l-AEM-MPY, and l-AEM-MPIP) were then distributed between the three collaborating institutes for evaluation using each institutes' test protocols. Out of the three head-group chemistries, the l-AEM-TMA generally exhibits the best balance of conductivity and ex situ alkali degradation, especially in lower humidity environments. The l-AEM-TMA also exhibited interestingly high Cl- ion conductivities (ca. 100 mS cm-1) when heated to 80 °C in a relative humidity RH = 95% atmosphere, a measurement frequently overlooked in favour of determining conductivities of RG-AEMs submerged in water (conductivities of submerged RG-AEMs can be suppressed due to excessive water contents and swelling).

Calix[4]arene urea derivatives: The pathway from fundamental studies to the selective removal of fluorides and phosphates from water.

Wet processes of phosphoric acids produce untreated wastewater containing large amounts of fluoride leading to serious environmental problems. This paper reports fundamental studies on two lower rim functionalised calix[4]arene based receptors namely 5, 11, 17, 23 tetra-tert-butyl, 25, 27 bis [diethylphenylurea]ethoxy, 26, 28 dihydroxycalix[4]arene, 1 and 25, 27 bis[diethylphenylurea]ethoxy, 26, 28 dihydroxycalix[4]arene, 2 and their ionic interactions. It is shown that these receptors only interact with fluoride and phosphate in acetonitrile. Their receptive properties are higher for phosphate (2:1 anion:receptor complex) relative to fluoride (1:1 complex). However, thermodynamics shows that these receptors are more selective for fluoride relative to phosphate in the formation of the 1:1 complex. The pathway from fundamental studies to the use of these receptors for removing these anions from water has been tested. The receptive properties of 1 for phosphate are held when the extraction involves aqueous solutions containing individual ions. However, in mixtures containing both anions, the kinetics of the process and the selectivity of 1 for fluoride predominate and as a result, fluoride is better extracted than phosphate. The counter-ion effect on the removal process is assessed from Molecular Simulation studies. The removal of fluoride from phosphate is discussed taking into account existing technologies.