Design Strategies for Alkaline Exchange Membrane-Electrode Assemblies: Optimization for Fuel Cells and Electrolyzers.

Production of hydrocarbon-based, alkaline exchange, membrane-electrode assemblies (MEA's) for fuel cells and electrolyzers is examined via catalyst-coated membrane (CCM) and gas-diffusion electrode (GDE) fabrication routes. The inability effectively to hot-press hydrocarbon-based ion-exchange polymers (ionomers) risks performance limitations due to poor interfacial contact, especially between GDE and membrane. The addition of an ionomeric interlayer is shown greatly to improve the intimacy of contact between GDE and membrane, as determined by ex situ through-plane MEA impedance measurements, indicated by a strong decrease in the frequency of the high-frequency zero phase angle of the complex impedance, and confirmed in situ with device performance tests. The best interfacial contact is achieved with CCM's, with the contact impedance decreasing, and device performance increasing, in the order GDE >> GDE+Interlayer > CCM. The GDE+interlayer fabrication approach is further examined with respect to hydrogen crossover and alkaline membrane electrolyzer cell performance. An interlayer strongly reduces the rate of hydrogen crossover without strongly decreasing electrolyzer performance, while crosslinking the ionomeric layer further reduces the crossover rate though also limiting device performance. The approach can be applied and built upon to improve the design and production of alkaline, and more generally, hydrocarbon-based MEA's and exchange membrane devices.

A low-loading Ru-rich anode catalyst for high-power anion exchange membrane fuel cells.

Herein, we report a Ru-rich anode catalyst for alkaline exchange membrane fuel cells. The fuel cell with such a RuPdIr/C anode and Ag-based cathode attained a peak power density close to 1 W cm-2 with only 0.2 mg cm-2 anode precious group metal loading, reaching the highest mass activity reported for this technology.

A Pd/C-CeO2 Anode Catalyst for High-Performance Platinum-Free Anion Exchange Membrane Fuel Cells.

One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM-FCs). The anion exchange membrane fuel cell (AEM-FC) has long been proposed as a solution as non-Pt metals may be employed. Despite this, few examples of Pt-free AEM-FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt-free AEM-FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt-free AEM-FC that employs a mixed carbon-CeO2 supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM-FC tests run on dry H2 and pure air show peak power densities of more than 500 mW cm(-2) .

Influence of the structure and composition of mono- and dialkyl phosphate mixtures on aluminum complex organogels.

The rheological properties and structure of organogels formed by the in situ complexation and self-assembly of aluminum isopropoxide and didodecyl phosphate surfactant in decane are investigated as mono-n-dodecyl phosphoric acid and bis(2-ethylhexyl) phosphoric acid complexing agents are added. At low loadings, the bulky bis(2-ethylhexyl) additive disrupts the physical gel structure by changing the packing around the aluminum centers, weakening the transition from viscoelastic fluid to physical network of branched cylinders, and completely suppresses gelation at high loadings. Monododecyl phosphate affects coordination at the Al center. At low substitution, it shifts the composition at which the transition to a physical gel occurs while simultaneously improving long-term stability. Structures deduced from the rheological response are confirmed by small-angle neutron scattering, which shows that the aggregates are locally cylindrical and molecularly thin at all compositions studied, although the cross section of the cylinders depends on the alkyl chain structure and composition of the organic phosphate mixtures.

Osmotic pressure and phase boundary determination of multiphase systems by analytical ultracentrifugation.

We show that analytical ultracentrifugation can be applied to derive full equations of state of colloids in a single sedimentation equilibrium experiment, by determination of single-phase boundaries as well as of osmotic pressure versus concentration at fixed temperatures. A continuous dependence of the osmotic pressure, over orders of magnitude between at least approximately 10(1) and 10(4) Pa, and a wide concentration range, are determined in agreement with standard theoretical considerations. Two model experimental colloidal systems are investigated: For a well-known synthetic clay system (laponite), it is shown that two regimes-counter-ion ideal gas and interacting double layers-can easily be identified in the equation of state, whereas metastable glass- or microphase-separated gel states previously encountered in osmotic stress measurements of laponite are circumvented. For the case of rigid, crystallized catanionic bilayers, single phase domains can be identified. Osmotic pressure results in this case disagree with results obtained using the classical osmotic stress technique, as a result of sample adhesion to the ultracentrifuge cell windows and uncertainty due to possible micromolar ion contamination.

Competitive surface adsorption of solvent molecules and compactness of agglomeration in calcium hydroxide nanoparticles.

Calcium hydroxide forms unstable reactive nanoparticles that are stabilized when they are dispersed in ethylene glycol or 2-propanol. The aggregation behavior of these particles was investigated by contrast-variation small-angle neutron scattering (SANS), combined with small-angle X-ray scattering (SAXS). Nanoparticles on the order of 100 nm were found to aggregate into mass-fractal superstructures in 2-propanol, while forming more compact agglomerated aggregates with surface fractal behavior in ethylene glycol. Commensurate specific surface areas evaluated at the Porod limit were more than an order of magnitude greater in 2-propanol (approximately 200 m2.g(-1)) than in ethylene glycol (approximately 7 m2.g(-1)). This profound microstructural evolution, observed in similar solvents, is shown to arise from competitive solvent adsorption. The composition of the first solvent layer on the particles is determined over the full range of mixed solvent compositions and is shown to follow a quantifiable thermodynamic equilibrium, determined via contrast-variation SANS, that favors ethylene glycol over 2-propanol in the surface layer by about 1.4 kJ.mol(-1) with respect to the bulk solvent composition.