Current Density Distribution Mapping in PEM Fuel Cells as An Instrument for Operational Measurements

Abstract

A newly developed measurement system for current density distribution mapping has enabled a new approach for operational measurements in proton exchange membrane fuel cells (PEMFC). Taking into account previously constructed measurement systems, a method based on a multi layer printed circuit board was chosen for the development of the new system. This type of system consists of a sensor, a special electronic device and the control and visualization PC. For the acquisition of the current density distribution values, a sensor device was designed and installed within a multilayer printed circuit board with integrated shunt resistors. Varying shunt values can be taken into consideration with a newly developed and evaluated calibration method. The sensor device was integrated in a PEM fuel cell stack to prove the functionality of the whole measurement system. A software application was implemented to visualize and save the measurement values. Its functionality was verified by operational measurements within a PEMFC system. Measurement accuracy and possible negative reactions of the sensor device during PEMFC operation are discussed in detail in this paper. The developed system enables operational measurements for different operating phases of PEM fuel cells. Additionally, this can be seen as a basis for new opportunities of optimization for fuel cell design and operation modes.

Modification of gas diffusion layers properties to improve water management

“…Thereby, both tested patterns behave similarly suggesting that in the used co-flow configuration only a small change of MPL's hydrophobicity is sufficient to obtain significantly more homogeneous current density distribution. In this context, it may be stated that a more homogeneous current density distributions would likely extend the life time of the fuel cell, as mentioned in [23,24]. It should be noted that the water management is influenced by many effects, e.g., water removal due to high reactant flow rate [25] or GDL oxidation by substances as hydrogen peroxide and sulfuric acid degrades fuel cell operation [16,26].…”

Results of Current Density Distribution Mapping in PEM Fuel Cells Dependent on Operation Parameters

“…The sensor unit is arranged on a printed circuit board (PCB in Figure 1) consisting of a shunt matrix with 112 elements to determine the local current densities. The shunt resistors have a low temperature coefficient (below 0.13% between 20 and 80 °C), are low ohmic (with a resistor value tolerance of 1%), and are embedded in a solid epoxy resin layer and connected by buried vias to the 112 segments which are in contact with the adjacent bipolar-and cooling plates [10]. A high resolution 15 bit ΣΔ-Analogue-Digital-Converter ensures the accuracy of the digitization with a sufficient sampling time of 4 Hz.…”

“…A CDM board is integrated between the two central cells [10], which maps the distribution of the electricity production over the active area. The characteristics of the CDM are presented in Table 1.…”

“…A high resolution 15 bit ΣΔ-Analogue-Digital-Converter ensures the accuracy of the digitization with a sufficient sampling time of 4 Hz. Furthermore each segment is calibrated with a calibration tool with an accuracy of 0.2% for the measured currents [10].…”

“…The technical demands like resolution, sample time and the measurement principle were discussed in detail in [10]. The new hardware CDM system was field-tested for two years with various starts and stops, offline periods, varied operation parameters and a deep analysis of the current density profile, the cell voltages, the humidity balance and general performance and degradation.…”