Adding a hydrophobic micro-porous layer (MPL) between a gas diffusion layer (GDL) and a catalyst layer (CL) at the cathode of a PEM fuel cell was found capable of improving cell performance. However, how an MPL does this is not well-understood because current techniques are limited in measuring, observing and simulating multiphase pore fluid flow across the full range of pores that vary to a great extent in geometry, topology, surface morphology. In this work, we focused our investigation on estimating flow properties of an MPL volume to assess the limiting effect of strongly hydrophobic sub-micron pores on water transports. We adopted a nano-tomography and pore network flow modelling approach. A pore-structure model, purposely reconstructed from an intact MPL sample using Focused Ion Beam milling and Scanning Electron Microscope (FIB/SEM) previously, was used to extract a realistic pore network. A two-phase pore network flow model, developed recently for simulating the flow of gas, liquid or their mixture in both micrometre and nanometre pores, was applied to the pore network. We firstly tested the validity of the constructed pore network, and then calculated the properties: permeability for both water and selected gases, water entry pressure, and relative permeability. Knudsen diffusion was taken into consideration in calculations when appropriate. Our calculations showed that the water permeability was three orders of magnitude smaller than experimentally measured results reported in the literature, and when the water contact angle increased from 95 degrees to 150 degrees, the water-entry pressure increased from 2.5 MPa to 28 MPa. Thus our results revealed that for a strongly hydrophobic MPL that contains nanometre pores only it would behave like a buffer to water, and therefore the structural preferential paths in an MPL, such as cracks, are likely to be responsible for significant liquid water transport from the CL to the GDL that has been observed experimentally recently. We highlighted the needs for multi-scale modelling of the interplays of liquid water and gas transfer in MPLs that contain variable pores. (C) 2014 Elsevier Ltd. All rights reserved.

Chemical looping combustion (CLC) is an emerging technology for clean combustion of fossil fuels with inherent CO2 capture. In the present work, we investigate the use of iron and manganese based mixed oxides (MnxFe1 (x)-CeO2)supported on CeO2 as oxygen carriers in CLC. The low cost and low toxicity of iron and manganese make them interesting candidates for CLC, but both mono-metallic carriers suffer from issues of low reactivity, and manganese is additionally prone to form undesired spinel structures with typical oxide supports. Mono-and bimetallic oxygen carriers were synthesized across the entire spectrum of compositions from pure Mn to pure Fe (with x = 0, 0.1, 0.33, 0.5, 0.8, 0.9, 1), characterized, and tested in thermogravimetric and fixed-bed reactor studies using H-2 and CH4 as fuels. We find that the use of ceria as support results in stable operation for all compositions of the metal phase, including pure Mn. Bimetallic carriers with high Fe content, which contain a FeMnO3 phase, exhibit an unusual, reversible de-alloying/re-alloying behavior during cyclic redox operation, which precludes any synergistic effects between the two metals and results in slowed reduction kinetics. However, Mn-rich carriers show a pronounced increase in carrier reactivity and selectivity for total oxidation of methane due to the addition of small amounts of Fe, indicating the promise of appropriately designed FeMn carriers as low-cost, environmentally benign oxygen carrier materials for chemical looping combustion. (C) 2014 Elsevier Ltd. All rights reserved.

In this work partial briquetting is employed as a means of biomass densification to allow for biomass inclusion in coking coal blends. The effect of increasing the bulk density was evaluated by comparison with direct addition. Two briquettes of different composition were studied. The influence of the briquettes on the Gieseler plasticity of the coals was determined. It was found that the effect of the binder was not enough to compensate for the decrease in plasticity produced by the inert components of the briquettes. Carbonizations were carried out in a movable wall oven of 17 kg capacity and the quality of the cokes produced was tested by evaluating their mechanical strength, coke reactivity to CO2 and post-reaction strength. In addition, the porosity and ash chemistry of the cokes was determined and an attempt was made to establish a relation between these results and the quality of the cokes. Coke quality results suggest that 10-15 wt.% of briquettes containing biomass can be included in coking blends. (C) 2014 Elsevier Ltd. All rights reserved.

An alternative method is proposed for the determination of calcium in biodiesel samples using square-wave voltammetry and a glassy carbon electrode in a solution containing EDTA. A microwave assisted acid digestion of the biodiesel samples was carried out before analysis. Experimental parameters such as deposition potential, deposition time, frequency, amplitude, step potential, were optimized for the purpose of determination of trace calcium ion in 1 x 10(4) mu mol L-1 ammonium buffer solution (pH 9.4) in the presence of 400 mu mol L-1 of EDTA. Under optimal conditions, the limit of detection was 1.6 x 10(-3) mu mol L-1 for Ca2+ with a 2 min preconcentration time. In addition, the EDTA/GCE displayed good reproducibility (CV maximum of 0.70%) and accuracy (recovery around 102%) making it suitable for the determination of Ca2+ in real biodiesel sample. (C) 2013 Elsevier Ltd. All rights reserved.

Hydrogen produced from the conversion of hydrocarbons or alcohols contains variable amounts of CO that should be removed for some applications such as feeding low-temperature polymer electrolyte membrane fuel cells (PEMFCs). The CO preferential oxidation reaction (PROX) is particularly well-suited for hydrogen purification for portable and on-board applications. In this work, the synthesis and characterization by XRF, BET, XRD, Raman spectroscopy and H-2-TPR of a gold catalyst supported on a copper-cerium mixed oxide (AuCeCu) for the PROX reaction are presented. The comparison of this catalyst with the copper-cerium mixed oxide (CeCu) revealed that the experimental procedure used for the deposition of gold gave rise to the loss of reducible material by copper lixiviation. However, the AuCeCu solid was more active for CO oxidation at low temperature. A kinetic study has been carried over the AuCeCu catalyst for the PROX reaction and compared with that of the CeCu catalyst. The main difference between the models affected the contribution of the CO adsorption term. This fact may be related to the surface electronic activity produced by the interaction of the cationic species in the AuCeCu solid, able to create more active sites for the CO adsorption and activation in the presence of gold. (C) 2013 Elsevier Ltd. All rights reserved.

Dimethyl ether (DME) is the simplest ether and it is used as an alternative fuel or fuel additive to reduce toxic emissions from combustion processes. The effects of DME on n-butane oxidation were investigated for two different concentrations of DME in the fuel mixture (i.e., 20% and 50%) and two different fuel-rich equivalence ratios (i.e., 2.6 and 3.0) using detailed chemical kinetic modeling. Reactor model was selected as atmospheric-pressure, adiabatic, tubular reactor, operated under laminar flow conditions. The concentration profiles of major, minor, and trace species were obtained for n-butane/DME/oxygen/argon at six different reactor inlet temperatures, and the results were compared with those attained for pure n-butane oxidation case (n-butane/oxygen/argon). Dimethyl ether addition decreased formations of various toxic species such as carbon monoxide, aromatic species, and polycyclic aromatic hydrocarbons, while it increased the formations of formaldehyde and acetaldehyde. Increasing equivalence ratio increased the formations of carbon monoxide, methane, aromatic species, and polycyclic aromatic hydrocarbons, while its effects on formaldehyde and acetaldehyde were not pronounced under the conditions studied. (C) 2012 Elsevier Ltd. All rights reserved.