Cold-starts of a polymer electrolyte fuel cell (PEFC), isothermally maintained at various subfreezing temperatures, were visualized using high resolution dynamic in-plane neutron imaging. The results obtained aim to bring new knowledge about the water accumulation mechanisms leading to the voltage drop usually observed in isothermal mode after a given working time, also called voltage failure. In particular, the data presented should be useful for comparison to simulation predictions provided by modeling studies. As main result, water in a condensed phase was observed to accumulate not only in the membrane-electrode-assembly (MEA), but also in the cathode gas diffusion layer (GDL) at −15 • C and even in the cathode gas channels at −10 • C. Moreover, approximately 400 cold-starts were realized without neutron imaging and revealed stochastic distributions of working times. The presence of water in super-cooled state is discussed and finally retained as only valid explanation of the results obtained. Additionally, the sudden freezing of super-cooled water is thought to cause the rapid water accumulation observed in the MEA during the voltage failure.

The analysis of a large body of heavy ion fusion reaction data with medium-heavy projectiles (6 < or = Z < or = 18) and actinide targets suggests a disappearance of the 3n exit channel with increasing atomic number of the projectile. Here, we report a measurement of the excitation function of the reaction (248)Cm ((26)Mg,xn)(274-x)Hs and the observation of the new nuclide (271)Hs produced in the 3n evaporation channel at a beam energy well below the Bass fusion barrier with a cross section comparable to the maxima of the 4n and 5n channels. This indicates the possible discovery of new neutron-rich transactinide nuclei using relatively light heavy ion beams of the most neutron-rich stable isotopes and actinide targets.

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A method combining (2)H labeling of different sources of H atoms (hydrogen, water vapor) with neutron imaging for the analysis of transport parameters in the bulk and at the interfaces of Nafion polymer electrolyte membranes is proposed. The use of different isotope compositions in the steady state allows evaluation of the relation between bulk and interface transport parameters, but relies on literature data for evaluating absolute values. By using transients of isotope composition, absolute values of these parameters including the self-diffusion coefficient of H can be extracted, making this method an attractive alternative to self-diffusion measurements using nuclear magnetic resonance (NMR), allowing measurements in precisely controlled conditions in real fuel cell structures. First measurements were realized on samples with and without electrodes and we report values of the self-diffusion coefficient of the same order of magnitude as values measured using NMR, although with slightly higher numbers. In our particular case, lower interfacial exchange rates for water transport were observed for samples with an electrode.

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