(378t) Experimental Optimization of Design Parameters of Cylindrical PEM Fuel Cell and Diagnosis of Its Performance Degradation

Proton Exchange Membrane (PEM) fuel cells have the potential to replace secondary batteries in portable applications. However, the heavy subsystems, expensive components like graphite plates and titanium end plates are the barriers for its commercialization in this sector. This has led to the development of air-breathing cylindrical PEM (c-PEM) fuel cells, which eliminate the need for graphite plates and titanium endplates. The preliminary design of a air-breathing cylindrical fuel cell delivers a performance of 300 mA/cm² @ 0.6 V. Since the design parameters of this cell have not been optimized, there is still considerable scope for improving performance.

One of the design parameters that can affect the cylindrical cell performance is cathode open area. Larger open area for cathode will increase the path length for electrons in gas diffusion layer and the smaller open area will increase the mass transport loss by reducing the oxygen access to the cathode. Decreasing the cathode open area will also increase the rib thickness of cathode current collector, which will lead to the improper distribution of oxygen over the cathode. The orientation of cathode opening is another parameter which can influence the cell performance. Horizontal slots in the cathode will obstruct the free fall of water droplets produced on the cathode. The generated water molecules can stick to the rib of the cathode current collector and prevent the oxygen molecules from reaching the cathode catalyst layer. On the other hand, vertical slots in the cathode current collector will provide less number of sites for water molecules to stick to its rib. The geometry of the cathode opening can also affect the cell performance because the hydraulic diameter of the cathode opening is dependent on its geometry. The first part of the talk will focus on the optimization of c-PEM fuel cell design parameters such as cathode open area, orientation and geometry of cathode opening.

During the initial testing of the cell, it was observed that the cell performance degrades over time even when the cell is not in operation. The reason for this performance degradation can be due to the cathode in c-PEM fuel cells being always open to atmosphere, unlike planar fuel cells. This can give rise to two problems, one is the higher rate of water evaporation from the membrane and the other is the corrosion of carbon support. Loss of water from the membrane will increase the ohmic resistance of the cell and the carbon support corrosion can decrease the electrochemically active surface (ECSA) of the electrode. The second part of this talk will be dedicated to the development of a test protocol incorporating impedance and ECSA measurements to identify the reason behind this performance degradation. A solution strategy will also be developed to improve the durability of c-PEM fuel cells.