Composition and evaluation of single-layer electrode proton exchange membrane fuel cells for mass transfer analysis

Abstract

Single-layer electrodes (SLEs) were used to replace conventional multi-layer electrodes for proton exchange membrane fuel cells (PEMFCs), and their performance in the analysis of mass transfer in an electrode was evaluated. The cell comprises a polymer electrolyte membrane, catalyst layers, and separators with a microchannel. The removal of conventional microporous and gas diffusion layers has the potential to enhance the through-plane mass transfer efficiency. The biggest challenge is the degradation of in-plane diffusivity of gas and water under ribs. Finding optimum microchannel and SLE structure by evaluating the cell performance under a rib and channel, respectively, is necessary. In this study, two types of cells were developed to obtain a fundamental understanding of gas and water transport in SLE-PEMFCs using microfabrication techniques. One cell had its cathode active area under a microchannel, and the other had it under a rib. A silicon wafer was used as a separator. A microchannel was fabricated on a silicon substrate. A current-collecting layer was coated on the substrate by Au sputtering. The reaction area was determined by the anode electrode, which was buried in the microchannel. The width of both the microchannel and rib was 100 μm. Performance evaluation was conducted using the cells, and the performance was compared under the cathode channel and rib. Results indicated that the overpotential under the rib was much larger than that under the channel. To achieve high performance as an overall cell, a large channel area is preferable. Therefore, performance evaluation was conducted under channels with widths of 50-400 μm. The channel performance over the range of widths studied (50-100 μm) was consistent, although the performance was low for widths above 100 μm. This could be because of the electrical conductivity and delamination of the electrode.

Keywords

• proton exchange membrane fuel cells
• transport phenomena
• single layer electrodes
• catalyst layers
• microchannel
• microfabrication