Nafion/PTFE and zirconium phosphate modified Nafion/PTFE composite membranes for direct methanol fuel cells

Composite Polymers Development and Application for Polymer Electrolyte Membrane Technologies-A Review

Nafion membranes are still the dominating material used in the polymer electrolyte membrane (PEM) technologies. They are widely used in several applications thanks to their excellent properties: high proton conductivity and high chemical stability in both oxidation and reduction environment. However, they have several technical challenges: reactants permeability, which results in reduced performance, dependence on water content to perform preventing the operation at higher temperatures or low humidity levels, and chemical degradation. This paper reviews novel composite membranes that have been developed for PEM applications, including direct methanol fuel cells (DMFCs), hydrogen PEM fuel cells (PEMFCs), and water electrolysers (PEMWEs), aiming at overcoming the drawbacks of the commercial Nafion membranes. It provides a broad overview of the Nafion-based membranes, with organic and inorganic fillers, and non-fluorinated membranes available in the literature for which various main properties (proton conductivity, crossover, maximum power density, and thermal stability) are reported. The studies on composite membranes demonstrate that they are suitable for PEM applications and can potentially compete with Nafion membranes in terms of performance and lifetime.

Preparation and properties of branched sulfonated poly(arylene ether ketone)/polytetrafluoroethylene composite materials for proton exchange membranes

Branched sulfonated poly(arylene ether ketone)s (BSPAEKs) exhibit excellent oxidative stability and solubility, making them suitable for proton exchange membranes (PEMs).

Universal electrode interface for electrocatalytic oxidation of liquid fuels

Electrocatalytic oxidations of liquid fuels from alcohols, carboxylic acids, and aldehydes were realized on a universal electrode interface. Such an interface was fabricated using carbon nanotubes (CNTs) as the catalyst support and palladium nanoparticles (Pd NPs) as the electrocatalysts. The Pd NPs/CNTs nanocomposite was synthesized using the ethylene glycol reduction method. It was characterized using transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, voltammetry, and impedance. On the Pd NPs/CNTs nanocomposite coated electrode, the oxidations of those liquid fuels occur similarly in two steps: the oxidations of freshly chemisorbed species in the forward (positive-potential) scan and then, in the reverse scan (negative-potential), the oxidations of the incompletely oxidized carbonaceous species formed during the forward scan. The oxidation charges were adopted to study their oxidation mechanisms and oxidation efficiencies. The oxidation efficiency follows the order of aldehyde (formaldehyde) > carboxylic acid (formic acid) > alcohols (ethanol > methanol > glycol > propanol). Such a Pd NPs/CNTs nanocomposite coated electrode is thus promising to be applied as the anode for the facilitation of direct fuel cells.

Promising aquivion composite membranes based on fluoroalkyl zirconium phosphate for fuel cell applications

Layered zirconium phosphate (ZP) that bears fluorinated alkyl chains bonded covalently to the layers (ZPR) was used as a nanofiller in membranes based on a short-side-chain perfluorosulfonic acid (PFSA) to mechanically reinforce the PFSA hydrophobic component. Compared to the pristine PFSA, membranes with a ZPR loading up to 30 wt% show enhanced mechanical properties, and the largest improvement of elastic modulus (E) and yield stress (σY ) are observed for the 10 wt% ZPR membrane: ΔE/E up to 90% and ΔσY /σY up 70% at 70°C and 80% relative humidity (RH). In the RH range 50-95%, the in-plane conductivity of the composite membranes reaches 0.43 S cm(-1) for 10 wt% ZPR at 110°C and is on average 30% higher than the conductivity of the pristine PFSA. The 10 wt % ZPR membrane is as hydrated as the neat PFSA membrane at 50% RH but becomes progressively less hydrated with increasing RH both at 80 and 110°C. The fuel cell performance of this membrane, at 80°C and 30% RH, is better than that of the unmodified PFSA.

High yield precipitation of crystalline α-zirconium phosphate from oxalic acid solutions

Microcrystalline zirconium phosphate (ZrP) has been synthesized by precipitating a Zr(IV) salt (i.e., zirconium propionate, chloride, or oxide chloride) with H(3)PO(4) from aqueous solutions of oxalic acid (H(2)C(2)O(4)) at 80 °C. Independent of the Zr(IV) salt, crystalline materials have been obtained with reaction yields >90% and reaction time of one day for the following molar ratios: H(3)PO(4)/Zr = 6 and H(2)C(2)O(4)/Zr = 10. The material prepared from Zr propionate (ZrP(prop)) has been further investigated by scanning electron microscopy, thermogravimetry, and ion exchange titrations. Structural characterization has been performed by X-ray powder diffraction and solid state (1)H-(31)P 2D correlation NMR experiments. Structural parameters obtained by Rietveld analysis of powder diffraction data agree with those reported in the literature for single crystal determinations. Moreover, NMR data show that the closest proton environment of the phosphorus atom in ZrP(prop) is the same as in ZrP samples of similar crystallinity prepared according to literature methods.