Eivind Morten Skou

Thermal stability of styrene grafted and sulfonated proton conducting membranes based on poly(vinylidene fluoride)

The thermal stability of styrene grafted and sulfonated poly(vinylidene fluoride), PVDF-g-PSSA, proton conducting membranes has been studied using thermal gravimetric analysis in combination with mass spectrometry and thermochromatography. The matrix polymer, PVDF, and the non-sulfonated counterpart, PVDF-g-PS, were studied as reference materials. It was found that the degradation of the PVDF-g-PS membrane proceeds in two steps starting atca. 340 °C with the evolution of degradation products typical of polystyrene. The PVDF-g-PSSA membranes are stable to around 270 °C even in a strongly oxidising atmosphere. The degradation starts with the simultaneous evolution of water and sulfur dioxide. The polystyrene grafts start decomposing at 340 oC in the PVDF-g-PSSA membranes. Thus the membranes are suitable for tests in electrochemical applications at elevated temperatures.

SiC nanocrystals as Pt catalyst supports for fuel cell applications

A robust catalyst support is pivotal to Proton Exchange Membrane Fuel Cells (PEMFCs) to overcome challenges such as catalyst support corrosion, low catalyst utilization and overall capital cost. SiC is a promising candidate material which could be applied as a catalyst support in PEMFCs. SiC nanocrystals are here synthesized using nano-porous carbon black (Vulcan® XC-72) as a template using two different reactions, which result in particle sizes in the ranges of 50–150 nm (SiC-SPR) and 25–35 nm (SiC-NS). Pt nano-catalysts of size 5–8 nm and 4–5 nm have successfully been uniformly deposited on the nanocrystals of SiC-SPR and SiC-NS by the polyol method. The SiC substrates are subjected to an acid treatment to introduce the surface groups, which help to anchor the Pt nano-catalysts. These SiC based catalysts have been found to have a higher electrochemical activity than commercially available Vulcan based catalysts (BASF & HISPEC). These promising results signal a new era of SiC based catalysts for fuel cell applications.

Perovskites as Cathodes for Nitric Oxide Reduction

Using cone shaped electrodes, the electrochemical reduction of nitric oxide and oxygen has been investigated by cyclic voltammetry on an oxygen overstoichiometric (La{sub 0.85}Sr{sub 0.15}MnO{sub 3+{delta}}), and an oxygen stoichiometric (La{sub 0.85}Sr{sub 0.15}CoO{sub 3{minus}{delta}}) perovskite over the temperature range 300--500 C. An oxygen ion-conducting 10% gadolinium-doped cerium oxide is used as electrolyte. It is shown that the reduction of nitric oxide proceeds rapidly on La{sub 0.85}Sr{sub 0.15}MnO{sub 3+{delta}} compared to the oxygen reduction while the oxygen reduction on La{sub 0.85}Sr{sub 0.15}CoO{sub 3{minus}{delta}} is faster than the nitric oxide reduction.

Solid state electrolyte membranes for direct methanol fuel cells

Abstract Solid state electrolyte membranes for direct methanol fuel cells were prepared from proton conductors and a polymer binder. The most promising proton conductor was tin oxide-containing mordenite, the conductivity of which was retained in the membranes. The diffusion of methanol across the membranes and the solvent uptake were lower than for commercial electrolyte membranes.

Electrochemical reduction of NO and O2 on Cu/CuO

The electrochemical reduction of NO and O2 on a Cu-point electrode covered with a surface layer of CuO is investigated in an electrochemical cell with a gadolinium doped cerium oxide oxygen ion conducting electrolyte in the temperature interval 300–500 ∘C. It is shown that the reduction of NO on CuO is possible at a lower overvoltage than it is in the case of the reduction of O2. The results indicate that the reduction of NO on CuO is not inhibited in the presence of O2 and that the reduction of NO can be selectively performed on a CuO-electrode.

Effect of incineration temperature on phosphorus availability in bio-ash from manure.

In the near future phosphorus (P) will be a limited resource in high demand. This will increase the incentives for recycling P in animal manure. In this study the dry‐matter‐rich fraction from slurry separation was incinerated and the P availability of the ash fraction examined. The aim was to adjust incineration temperature to support a high plant‐availability of P in ash. The plant‐availability of P was approximately halved when the incineration temperature was increased from 400 to 700 °C. This decrease in plant‐availability was probably due to the formation of hydroxyapatite. Incineration temperatures should therefore be kept below 700 °C to ensure a high fertilizer efficiency of P in ash. This may conflict with the energy production, which is optimal at temperatures above 800 °C. An alternative to incineration may therefore be thermal gasification of the dry‐matter‐rich fraction, which can be carried out efficiently at lower temperatures.

Oxygen reduction and methanol oxidation behaviour of SiC based Pt nanocatalysts for proton exchange membrane fuel cells

Research with proton exchange membrane fuel cells has demonstrated their potential as important providers of clean energy. The commercialization of this type of fuel cell needs a breakthrough in the electrocatalyst technology to reduce the relatively large amount of noble metal platinum used with the present carbon based substrates. We have recently examined suitably sized silicon carbide (SiC) particles as catalyst supports for fuel cells based on the stable chemical and mechanical properties of this material. In the present study, we have continued our work with studies of the oxygen reduction and methanol oxidation reactions of SiC supported catalysts and measured them against commercially available carbon based catalysts. The deconvolution of the hydrogen desorption signals in CV cycles shows a higher contribution of Pt (110) and Pt (111) peaks compared to Pt (100) for SiC based supports than for carbon based commercial catalysts, when HClO4 is used as an electrolyte. The Pt (110) and Pt (111) facets are shown to have higher electrochemical activities than Pt (100) facets. To the best of our knowledge, methanol oxidation studies and the comparison of peak deconvolutions of the H desorption region in CV cyclic studies are reported here for the first time for SiC based catalysts. The reaction kinetics for the oxygen reduction and for methanol oxidation with Pt/SiC are observed to be similar to the carbon based catalysts. The SiC based catalyst shows a higher specific surface activity than BASF (Pt/C) for methanol oxidation and oxygen reduction while the mass activity values are comparable.

Electrochemical Stability and Postmortem Studies of Pt/SiC Catalysts for Polymer Electrolyte Membrane Fuel Cells

In the presented work, the electrochemical stability of platinized silicon carbide is studied. Postmortem transmission electron microscopy and X-ray photoelectron spectroscopy were used to document the change in the morphology and structure upon potential cycling of Pt/SiC catalysts. Two different potential cycle aging tests were used in order to accelerate the support corrosion, simulating start-up/shutdown and load cycling. On the basis of the results, we draw two main conclusions. First, platinized silicon carbide exhibits improved electrochemical stability over platinized active carbons. Second, silicon carbide undergoes at least mild oxidation if not even silicon leaching.

Understanding the Role of Gelatin as a Pretreating Agent for Use in Li-Ion Batteries

The effect of gelatin on irreversible charge consumption (charge loss) of graphite electrodes due to solid electrolyte interphase formation is studied. Three graphite types from Timcal SA are examined: Timrex KS44, Timrex SFG44, and Timrex E-SLX50. It is shown that in all cases gelatin treatment leads to a decrease in irreversible charge losses with respect to untreated samples. The effect of gelatin treatment is compared to that of. mild oxidation of graphites. Furthermore, it is shown that gelatin is electrochemically stable; the charge associated with gelatin degradation is not higher than cci. I mAh/g. Using differential electrochemical mass spectrometry it is shown that gelatin-treated samples release CO 2 at voltages negative to +0.5 V vs. metallic lithium. This might serve as an additional explanation for the beneficial role of gelatin with respect to irreversible losses of lithium in the first few cycles of graphite electrode operation.

Electrochemical Performance and Durability of Carbon Supported Pt Catalyst in Contact with Aqueous and Polymeric Proton Conductors

Significant differences in catalyst performance and durability are often observed between the use of a liquid electrolyte (e.g., sulfuric acid), and a solid polymer electrolyte (e.g., Nafion). To understand this phenomenon, we studied the electrochemical behavior of a commercially available carbon supported platinum catalyst in four different electrode structures: catalyst powder (CP), catalyst ionomer electrode (CIE), half membrane electrode assembly (HMEA), and full membrane electrode assembly (FMEA) in both ex situ and in situ experiments under a simulated start/stop cycle. We found that the catalyst performance and stability are very much influenced by the presence of the Nafion ionomers. The proton conducting phase provided by the ionomer and the self-assembled electrode structure render the catalysts a higher utilization and better stability. This is probably due to an enhanced dispersion, an improved proton-catalyst interface, the restriction of catalyst particle aggregation, and the improved stability of the ionomer phase especially after the lamination. Therefore, an innovative electrode HMEA design for ex-situ catalyst characterization is proposed. The electrode structure is identical to the one used in a real fuel cell, where the protons transport takes place solely through solid state proton conducting phase.