Segmented current collector

To measure the current distribution in a hydrogen PEFC, Brown et al. ° and Cleghorn et al. ° employed the printed circuit board approach using a segmented current collector, anode catalyst, and anode GDL. This approach was further refined by Bender et al. ° to improve ease of use and quality of information measured. Weiser et al. ° developed a technique utilizing a magnetic loop array embedded in the current collector plate and showed that cell compression can drastically affect the local current density. Stumper et al."° demonstrated three methods for the determination of current density distribution of a hydrogen PEFC. First, the partial membrane elec-... 

Wieser et al. [17] proposed the use of an array of Hall sensors with a segmented current collector and flow field for local current density measurements. The authors used unsegmented electrodes in their study. The use of numerous Hall sensors can significantly complicate the experimental setup, making experimentation expensive and tedious. Moreover, interference from neighboring segments is also possible. 

Localized AC impedance and current distributions were measured by Brett et al." on a single linear channel with the segmented cathode current collector plate. Figure 26 shows their measured current density and membrane resistance distributions along the... 

Gasket Anode Printed Circuit Board Segmented Flow-Field Current Collector... 

As outlined above, the segmentation of MEA electrodes is a key process to implement the concept of integrated fabrication of micro fuel cells which consists of merely three foils. Figure 7-15 shows the electrical characterisation of the serial interconnected three cell demonstrator. Approximately 40 mA can be drained at 1.5 V. To illustrate the importance of MEA patterning a fuel cell has been assembled with three serial interconnected current collector structures according to Figure 7-9 but with a continuous piece of MEA. 

Figure 8.2 depicts the various components of a commercial cell. Each segment and boundary represents unique considerations for good cell operation. For instance, the boundary of the current collector with the active mass involves the conductivity of the active mass and the current dishibution (collection) within the porous electrode sducture of the active mass. These are intertwined with the electrolyte being common to all components and a key consideration in developing a safe high-performance commercial cell. Safe cell designs alone are not sufficient criteria for a safe commercial cell. The productions operations must not introduce defects that... 

Figure 11.7 Step-by-step instructions for installing the copper current collectors, (a) Adhere copper flat wire to the anode (Step 4) (b) staple the copper flat wire to the anode, with one copper conductor dedicated for each carbon fabric segment (Step 6) (c) trim the copper flat wire flush to the anode (Step 7) (d) seal copper flat wire with waterproof sealant (Step 11-16) (e) seal the staples on the other side of the anode (Step 17).

Fig. 1 Segmented FIB/SEM images of electrode films with varying porosities. White represents active material domains, light gray represents carbon domains, black represents pore domains, and the top dark gray and bottom gray represent the exterior volume and current collector respectively. Reprinted with permission from reference [2]. Reproduced with the permission of the Electrochemical Society...

FIGURE 3.18 Photograph of a PCB segmented electrode with a seven-channel serpentine flow field current collector used on the anode side of the cell (a) and a close-up of the PCB (b), showing the flow channels [72],... 

Especially, segment-in-series type stacks will have large current collection loss if the electrode has low conductivity. Even for planar stacks, the electrons may not be supplied sufficiently to the place if the current collection points are separated. Generally, electronic conductivity higher than 100 S cm is preferred for a SOFC electrode. If the electronic conductivity is 10 S cm and the electrode thickness is 50 pm, the resistance to transport electrons to the distance of 1 mm is as high as 2 cm Because area-specific resistance of a practical cell is below 1 Q cm , it will cause constriction of the current into the vicinity of the current collector. 

Noponen and co-workers [46, 47] and Giilzow et al. [48] used a collector plate consisting of electrically insulated metal blocks measuring the current flow across each segment individually. Identical contact pressure for each block has to be assured in order to provide uniform contact resistance. 

Bipolar transistors are realized using either an npn- or pnp-junction sequence. The different segments of the device are named as collector, base, and emitter electrode, respectively. In order to operate the transistor, one of the junctions is forward biased, while the other is biased in reverse. Using a small control current over the base electrode, a significant current between the collector and emitter electrodes is enabled. 

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