Transparent fuel cells

It is important to note that this single cell was tested at 100% relative humidity and the cell temperature was 80°C. Spernjak, Prasad, and Advani [87] used a transparent fuel cell (fhe end plafe was made out of polycarbon-afe) to visualize fhe wafer accumulation inside fhe FF channels wifh differenf DL materials. If was observed fhaf, af humidified conditions, the CC (untreated— no PTFE— AvCarbon TM 1071 HCB) was able to perform and remove fhe wafer better fhan a CFP (unfreafed— no PTFE—TCP-lT-60). In facf, if was concluded fhaf wafer was frapped inside the DL when the CFP was used, resulting in flooding of fhe CL. 

In DMFCs, methanol crossover and carbon dioxide gas management are critical issues that have be dealt with. Argyropoulos, Scott, and Taama [98] used a transparent fuel cell (fhe anode end plate was made out of acrylic) to visualize the CO2 evolution and management on the anode side. Both CFPs and CCs were used as anode DLs and it was observed that CFP (Toray carbon paper) was not a suitable material due to its poor gas removal properties. 

Similar observations were presented by Spernjak et al. [87], who also developed a transparent fuel cell to visualize the different behavior of treated and untreated DLs. This cell gave the indication that with treated DLs the water produced at the cathode side emerged as droplets on the surface of the material over the entire visible area. However, with the untreated DLs, water preferred to be in contact with the side walls of the channels with time, the water accumulated and formed films and slugs near the flow field walls. This behavior caused greater water management issues and lower gas transport toward the active catalyst areas. 

Tuber et al. [Ill] used a transparent fuel cell (at 30°C) to visualize both hydrophobic and hydrophilic diffusion layers. They discussed the idea of... 

Through the use of a transparent fuel cell, Spernjak et al. [87] were able to visualize the anode FF plate (and DL without MPL) while operating the fuel cell with a cathode that had MPL on the DL. It was observed that liquid water was present in the anode flow field only when an MPL on the cathode side was used. Again, this is an indication that the cathode side creates a pressure barrier that pushes the water toward the anode. These observations agree with the ones presented mathematically by Weber and Newman [148]. Although they did not do any experimental work, their two-phase fuel cell model concluded that the MPL acts as a valve that pushes water away from the DL toward the anode though the membrane. 

In recent years, the use of transparent fuel cells has increased substantially due to the need for a better understanding of liquid water accumulation on the surface of the DLs and flow through the FF channels. In most transparent cells, either the cathode or the anode (or both) has transparent polycarbonate end plates that act as windows and sit on top of the corresponding FF plates. These plates are normally thin and made out of metal, such as stainless steel or gold-plated brass, and their thickness is equal to the depth of the FF channels (i.e., the charmels are machined all the way through the plate). Thus, the transparent end plate also acts as part of the charmels. 

An example of a transparent PEMFC was presented by Spemjak, Prasad, and Advani [87], who used a 10 cm transparent fuel cell to investigate different cathode DL materials (with and without MPLs) influence on water management. The FF channels had a single-path serpentine design with rectangular channel cross sections 1 mm deep and 0.8 mm wide. In these researchers study, the analyzed images corresponded to those in the lower section of the cathode s active area (closest to the outlet) because most of the water droplets were observed in this area away from the inlet. To observe how different DLs affected the water transport in the anode, this side was also visualized (see Section 4.3.3.2). 

Ge and Wang [226] utilized a transparent fuel cell with two different FF designs—straight and serpentine—in order to study the water accumulation on the anode side of a fuel cell. No water accumulated on top of the DL surfaces in either FF design during all the tests. The literature contains many other examples of transparent cells used as tools to better understand the water transport mechanisms in fuel cells [111,227-232]. 

Transparent fuel cells are also common tools used to visualize and observe the water accumulation inside FFs and on the surfaces of diffusion layers. Liu, Guo, and Ma [227] tested interdigitated and parallel flow fields wifh CFP DLs. It was observed that the former FF design enhanced the mass transfer when the gas flow was forced to pass through the DL. In fact, the water flooding areas in the interdigitated channels were substantially smaller than in the parallel channel. 

In order to study cathode flooding in small fuel cells for portable applications operated at ambient conditions, Tuber et al.81 designed a transparent cell that was only operated at low current densities and at room temperature. The experimental data was then used to confirm a mathematical model of a similar cell. Fig. 4 describes the schematic top and side view of this transparent fuel cell. The setup was placed between a base and a transparent cover plate. While the anodic base plate was fabricated of stainless steel, the cover plate was made up of plexiglass. A rib of stainless steel was inserted into a slot in the cover plate to obtain the necessary electrical connection. It was observed that clogging of flow channels by liquid water was a major cause for low cell performance. When the fuel cell operated at room temperature during startup and outdoor operation, a hydrophilic carbon paper turned out to be more effective compared with a hydrophobic one.81... 

Theodorakakos et al.82 developed a computer model that described the detachment of liquid droplets from solid surfaces. In order to validate the model, a transparent fuel cell was used and then an ex-situ experiment was conducted. This test analyzed... 

Optically transparent fuel cells H2O (liquid), O2, O2 and H2 flow distribution Full flow field flow visualization, real-time data acquisition Modified cells have lower performance than traditional fuel cells... 

Refine software/firmware to accomplish transparent fuel cell stack startup and drive-ofif and enhance reliability. 

Transparent fuel cells [18] can be used to visualize the water inside flow channels. They have the advantage of allowing the use of inexpensive imaging equipment. The major drawback is the necessity of using transparent flow field and housing materials, which have different physical characteristics (contact angle, thermal properties) than commonly used materials. 

Transparent fuel cells [77-84] are widely used to characterize the water removal process on the flow field of a PEM fuel cell. As they allow optical access to the flow field, one can observe the formation of water droplets and the water removal process in the flow channels. A transparent cell usually includes a transparent plastic end plate, a copper plate to serve as the current collector, and a flow field plate on the anode side, cathode side, or both, as shown in Fig. 3.22. For the test setup, a high-speed camera is required to record the status of liquid water in the flow channels. Thus, water flooding at different stages or under various conditions can be recorded, as shown in Fig. 3.23 [81 ]. In this way, the visualization of water transport and removal in a transparent cell can be used to optimize the operating conditions, the structural designs of the flow field and gas diffusion layer, and the screening of materials for the gas diffusion layer. 

Manufticturers Comments 121 C+cure. High density, non-asbestos, no metallic filler. Radar transparent. Fuel cell, fuel barrier. 

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