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In this work, the through-plane porosity distributions of paper and felt gas diffusion layers (GDLs) treated with micro-porous layers (MPLs) are measured using microscale computed tomography. The porosity distributions of the GDL microstructure and cracked MPL coating are analyzed and presented independently. In the MPL core region, the porosity of the cracked MPL is found to steadily decrease towards the catalyst layer side. Through comparison, the extent to which the MPL penetrates the GDL is also observed. From cross-sectional images of the MPL treated GDL, crack locations were found to correspond with adjacent fibre locations, indicating that fibres can influence the presence of cracks in the MPL. We also present the through-plane combined porosity distribution for the GDL and cracked MPL, which can be employed for predictive modelling of liquid water transport in the polymer electrolyte membrane fuel cell (PEMFC). [ABSTRACT FROM AUTHOR]

Besides major NADH-, succinate-, and other substrate oxidase reactions resulting in four-electron reduction of oxygen to water, the mitochondrial respiratory chain catalyzes one-electron reduction of oxygen to superoxide radicalfollowed by formation of hydrogen peroxide. In this paper the superoxide generation by Complex I in tightly coupled bovine heart submitochondrial particles is quantitatively characterized.The rate of superoxide formation during-controlled respiration with succinate depends linearly on oxygen concentration and contributes approximately 0.4% of the overall oxidase activity at saturating (0.25 mM) oxygen. The major part of one-electron oxygen reduction during succinate oxidation (~80%) proceeds via Complex I at the expense of its-dependent reduction (reverse electron transfer). At saturating NADH the rate offormation is substantially smaller than that with succinate as the substrate. In contrast to NADH oxidase,the rate-substrate concentration dependence for the superoxide production shows a maximum at low (~50 µM)concentrations of NADH. NAD+ and NADH inhibit the succinate-supported superoxide generation. Deactivation of Complex I results in almost complete loss of its NADH-ubiquinone reductase activity and in increase in NADH-dependent superoxide generation. A model is proposed according to which complex I has two redox active nucleotide binding sites.One site (F) serves as an entry for the NADH oxidation and the other one (R) serves as an exit during either the succinate-supported NAD+ reduction or superoxide generation or NADH-ferricyanide reductase reaction. [ABSTRACT FROM AUTHOR]