Spatial Distribution Of Losses Research Articles

Towards an Impedance-Based Analysis of SOFC-Stacks

This proceeding aims to understand the performance of SOFC stacks using impedance spectroscopy. For the stack analysis, gradients over the active cell area are averaged out, preventing access to local phenomena. Hence, to get better insight into the spatial distribution of losses, single cells with an active electrode area of 1 cm² are characterized at 850 °C based on EIS and DRT-analysis. To ensure an appropriate deconvolution of processes, symmetrical anode and cathode cells are also tested. Next to the ideally contacted cells, metallic interconnecting repeat units are analyzed to study the impact of contacting and gas supply in the stack. The effect of fuel utilization was also investigated by mimicking different locations in the stack. In this contribution, the complex impedance behavior of the stack based on polarization losses will be discussed. The paper also provides disentangled information often lost or averaged out in stacks.

Spatially Resolved Deconvolution of Loss Processes in PEM Fuel Cells

The complex operating behaviour of PEM Fuel Cells is heavily influenced by different non-linear loss processes, which limit the cell performance. Depending on the operating conditions, the different losses change in magnitude and characteristic time constants [1]. During technical operation of large-sized PEM Fuel Cells, gradients in operating conditions occur along the gas channels, resulting in an inhomogeneous current density distribution. This is caused by the locally varying electrochemical activity due to in-plane gradients in concentrations of reactants and reaction products, gas pressure and temperature. Consequently, each loss process occurs locally distributed to a varying degree. Therefore, a profound knowledge about the spatial distribution of losses is essential for optimizing the operating strategy as well as the cell and stack components.The commonly measured I/V characteristics provide only integral information about the overall performance. Thus, the data obtained represent merely the sum of all loss processes averaged over the entire cell area and do not allow detailed conclusions about the respective spatial distribution along the channel.Inevitably, in order to deconvolute the loss processes in the entire area of large sized cells, an approach is required that provides deeper insight in the processes and their interdependencies. For this purpose, an impedance-based methodology is developed that enables a spatially resolved deconvolution of loss processes. It is based on electrochemical impedance spectroscopy (EIS) and an impedance data analysis by the distribution of relaxation times (DRT) [2,3] that is applied to a segmented cell [4] with almost gradient-free segments. By systematically varying operating conditions the different loss processes are identified, quantified and separated with respect to their characteristic frequencies.In this contribution the design of the test bench and the segmented cell will be presented. Furthermore, first results regarding the electrochemical characterization and the impedance-based deconvolution of loss processes in a segmented cell will be discussed. M. Heinzmann et al., J. Power Sources 402, pp. 24-33 (2018).H. Schichlein et al., J. Appl. Electrochem. 32, pp. 875-882 (2002).E. Ivers-Tiffée et al., J. Ceram. Soc. Japan 125, pp. 193-201 (2017).T. Reshetenko et al., J. Electrochem. Soc. 163, pp. F1100-F1106 (2016)

Spatial distribution of losses in growth of trees caused by the feeding of pine shoot beetles Tomicus piniperda and T. minor (Col., Scolytidae) in Scots pine stands growing within range of the influence of a timber yard in southern Poland

This study deals with the assessment of increment losses in Scots pine trees caused by the maturation feeding of pine shoot beetles Tomicus piniperda (L.) and T. minor (Hart.) (Col., Scolytidae) in even-aged stands growing during their entire life span within range of the influence of a sawmill and its timber yard. In spring 2004, on three sample plots, 0.2 ha in size, situated 60, 200, and 500 m from the yard, height and dbh of all trees were measured and increment cores were taken from randomly selected sample trees. An agreement between the spatial distribution of losses in tree increments and the distribution of damage to crowns of investigated stands indicated that the losses resulted from the maturation feeding of pine shoot beetles migrating from the sawmill timber yard. Divergence of growth in the about 25-years-old stand indicated the beginning of intensive feeding of beetles in pine shoots with a high level of probability. In comparison with the control stand the basal area losses in stands growing 60 and 200 m from the beetle source amounted to 57% and 46%, respectively. The difference in the height of trees was as large as almost 100%.