Robert C. T. Slade

Alkaline anion-exchange radiation-grafted membranes for possible electrochemical application in fuel cells

Vinylbenzyl chloride was grafted onto PVDF and FEP polymer films using radiation-grafting methodology. Subsequent reaction with trimethylamine and ion-exchange with potassium hydroxide yields alkaline anion-exchange membranes that are capable of conducting hydroxide ions; such membranes may be suitable for use in low temperature direct methanol fuel cells for portable devices. The PVDF based materials underwent an undesirable degradation and were found to be less suitable for this class of membrane. FEP-based materials exhibited superior structural stability, conductivities up to 0.02 S cm−1 at room temperature, and good retention of ion-exchange capacities when treated in water at 60 °C.

The radiation-grafting of vinylbenzyl chloride onto poly(hexafluoropropylene-co-tetrafluoroethylene) films with subsequent conversion to alkaline anion-exchange membranes: optimisation of the experimental conditions and characterisation

Poly(hexafluoropropylene-co-tetrafluoroethylene) (FEP) was successfully radiation-grafted with vinylbenzyl chloride (VBC). Subsequent amination with trimethylamine followed by ion exchange with aqueous hydroxide yielded alkaline anion-exchange membranes (AAEMs). Experimental parameters were established for maximising the degree of grafting (d.o.g.); the optimum treatment duration for maximum amination was also established. The graft penetration at different degrees of grafting was investigated and related to the grafting conditions. The stabilities of the grafted membranes and the final AAEMs were thoroughly investigated using thermogravimetry and differential thermal analysis (TG/DTA). The ion-exchange capacities (IECs), water uptake levels, and thicknesses of the AAEMs were measured. These AAEMs have potential for application in low-temperature fuel cell systems.

Comparison of PVDF- and FEP-based radiation-grafted alkaline anion-exchange membranes for use in low temperature portable DMFCs

Vinylbenzyl chloride has been radiation grafted onto both PVDF and FEP fluoropolymer films; subsequent amination and ion-exchange to give the hydroxide ion forms yield anion-exchange membranes suitable for use in low temperature direct methanol fuel cells for portable applications.

A Carbon Dioxide Tolerant Aqueous‐Electrolyte‐Free Anion‐Exchange Membrane Alkaline Fuel Cell

Despite over a century of study and decades of intensive research, few fuel cell products have appeared on the market. The major inhibitor to mass commercialisation is cost. H2/air alkaline fuel cells (AFCs) containing KOH(aq) electrolyte promise the lowest cost devices, with the ability to use non-Pt catalysts. The fundamental problem with AFCs is that the KOH(aq) electrolyte reacts with CO2 (cathode air supply) to form carbonate species, which lowers cell performance and lifetime (formation of carbonate precipitates in electrodes and reduction of OH concentration in electrolyte). However, the carbonate content of a aqueous-electrolyte-free (metal-cation-free) alkaline anion-exchange membrane (AAEM), that was pre-exchanged to the CO3 form, decreased when operated in H2/air and methanol/air fuel cells. This remarkable result is contrary to prior wisdom; AAEMs inherently prevent carbonate performance losses when incorporated into AFCs. This experiment was made possible only by the recent breakthrough development of an alkaline interface ionomer, which allows fabrication of membrane electrode assemblies that do not require incorporation of metal hydroxides species to perform well.

An alkaline polymer electrochemical interface: a breakthrough in application of alkaline anion-exchange membranes in fuel cells

A novel alkaline polymer has been developed as an interfacial material for use in the preparation of metal-cation-free alkaline membrane electrode assemblies (MEAs) for all-solid-state alkaline fuel cells (AFCs) with long-term performance stability.

Factors affecting the performance of microbial fuel cells for sulfur pollutants removal

A microbial fuel cell (MFC) has been developed for removal of sulfur-based pollutants and can be used for simultaneous wastewater treatment and electricity generation. This fuel cell uses an activated carbon cloth+carbon fibre veil composite anode, air-breathing dual cathodes and the sulfate-reducing species Desulfovibrio desulfuricans. 1.16gdm(-3) sulfite and 0.97gdm(-3) thiosulfate were removed from the wastewater at 22 degrees C, representing sulfite and thiosulfate removal conversions of 91% and 86%, respectively. The anode potential was controlled by the concentration of sulfide in the compartment. The performance of the cathode assembly was affected by the concentration of protons in the cation-exchanging ionomer with which the electrocatalyst is co-bound at the three-phase (air, catalyst and support) boundary.

Investigation of protonic conduction in Yb- and Y-doped barium zirconates

Barium zirconate ceramics doped with Y and Yb, BaMxZr1 − xO3 − α (M = Yb, Y), are perovskite single phases and exhibit protonic conduction in moist nitrogen atmospheres at temperatures 500 < T (°C) < 1000. Samples with x = 0.10 have been investigated by ac and dc electrochemical techniques. Conductivities with Yb as dopant were larger, by a factor ≈ 10, than those with Y as dopant. Conductivities for Yb-doped samples (e.g. σb (750 °C) ≈ 2 × 10− 4 S cm−1) are lower than those reported for analogous cerates. Throughout the experimental temperature range, the apparent conductivity found in dc studies (summing resistances due to the electrolyte and electrode-electrolyte interfacial phenomena) was lower, by a temperature independent factor ≈ 2, than the conductivity determined by ac techniques.

Nanocomposite materials: polyaniline-intercalated layered double hydroxides

Open lamellar systems such as layered double hydroxides (LDHs) can be used to generate new intercalation compounds. We report the synthesis of nanocomposite materials consisting of organopolymer molecules encapsulated between ultra-thin mixed-metal hydroxide sheets which are propped apart by spacers [terephthalate or hexacyanoferrate(II) ions acting as pillars]. The oxidising host matrixes [Cu(1 –x)2+Crx3+(OH)2]·[(C6H4-1,4-(CO2)2)x/22–·nH2O] and [Cu(1 –x)2+Alx3+(OH)2]·[(Fe(CN)6)x/44–·nH2O] were used as hosts for the interlamellar oxidative polymerisation of aniline. The materials were prepared using chimie douce pathways and characterised by conventional physical techniques (XRD, FTIR, TG, DTA), which indicated the presence of polyaniline molecules and the retention of the host framework after incorporation of the organopolymer.

PdNi hollow nanoparticles for improved electrocatalytic oxygen reduction in alkaline environments

Palladium-nickel (PdNi) hollow nanoparticles were synthesized via a modified galvanic replacement method using Ni nanoparticles as sacrificial templates in an aqueous medium. X-ray diffraction and transmission electron microscopy show that the as-synthesized nanoparticles are alloyed nanostructures and have hollow interiors with an average particle size of 30 nm and shell thickness of 5 nm. Compared with the commercially available Pt/C or Pd/C catalysts, the synthesized PdNi/C has superior electrocatalytic performance towards the oxygen reduction reaction, which makes it a promising electrocatalyst for alkaline anion exchange membrane fuel cells and alkali-based air-batteries. The electrocatalyst is finally examined in a H2/O2 alkaline anion exchange membrane fuel cell; the results show that such electrocatalysts could work in a real fuel cell application as a more efficient catalyst than state-of-the-art commercially available Pt/C.

Systematic examination of hydrogen ion conduction in rare-earth doped barium cerate ceramics

Protonic conduction is demonstrated in doped perovskites BaCe1−xMxO3−α (M=Y, Yb, Nd, Gd, La; x=0.05, 0.10) at high temperature in a moist atmosphere. Conduction by protons was confirmed by EMF measurements on various gas cells using specimen ceramics as the solid electrolyte membrane separating moist and “dry” nitrogen atmospheres. Electrical conductivity (σ) measurements were carried out in the temperature range T=600–900°C using complex impedance techniques. A depressed semicircle in the impedance plane plots at T<700°C (and absent at higher temperatures) was assigned to interfacial (electrode/ electrolyte) charge transfer resistance. Plots of log (σT) versus 1/T showed Arrhenius behaviour in all cases. The highest electrical conductivities were those for Yb and Gd doped ceramics. It is postulated that water molecules react to fill vacant oxygen sites in the doped perovskites, thereby generating hydroxide ions (Oo+V∼o+H2O⇒2(OH)o), with the proton able to migrate between sites corresponding to attachment to adjacent oxygens.