Statistical investigations of basis weight and thickness distribution of continuously produced fuel cell electrodes

The presented work is focused on the investigation of catalyst basis weight scattering in direct methanol fuel cell electrodes produced by a roll-to-roll process. For the manufacturing of highly efficient electrodes the statistical variance of the catalyst basis weight should be as small as possible. The dependencies between the variances of the catalyst basis weight, substrate basis weight, substrate thickness, and electrode basis weight are inferred from theoretical considerations. A commercial substrate is coated with catalyst dispersion by a continuous knife coating process to manufacture the electrodes. The basis weight and thickness of the substrate and the electrode are investigated ex-situ. The distribution of the measurands enables the determination of an estimator for the expected value and the variance which are used to calculate the variance of the catalyst basis weight. The main finding of the investigations is that different impacts on the distribution of the catalyst basis weight exist. A construction fault in the coating knife of the employed coating machine causes a gradient in the catalyst layer. After removing this fault it can be proved that a periodic structure in the substrate basis weight and thickness is responsible for a large contribution to the catalyst basis weight variance. (C) 2013 Elsevier B.V. All rights reserved.