The Influence of Channel Wettability on Two-Phase Flow and Polymer Electrolyte Membrane Fuel Cell Performance

Abstract

Water management is one of the critical issues affecting polymer electrolyte membrane fuel cell (PEMFC) performance, durability and cost. Modifying the surface wettability of flow field channels in PEMFC can improve the water management and consequently the fuel cell performance. In the present work, an ex-situ investigation of the effects of channels with different surface wettability on the two phase-flow characteristics has been conducted. Horizontal graphite channel (slightly hydrophobic) and other four channels coated with polytetrafluoroethylene (PTFE) (hydrophobic), silica/Polydimethylsiloxane (PDMS) (superhydrophobic), silica/PDMS at the bottom wall but with the side walls being raw graphite (combined surface wettability channel), and silica coated channel (superhydrophilic), are tested and visualized at room temperature and atmospheric pressure. Pressure drop measurements and two-phase flow visualization using high speed camera have been performed. Superhydrophobic channel has shown desirable positive effect on the two-phase flow and on the PEMFC's performance compared with the other channels, especially at high current densities.

Modeling of liquid water transport in a proton exchange membrane fuel cell gas flow channel with dynamic wettability

“…Water droplet transport on the channel surface is observed to have an elliptic spreading shape (or elliptic contact line) on the surface with a continuous change in the local contact angle (from the advancing to the receding angles) from the leading to the trailing edge of the water droplet . The elliptic water spreading shape on the surface, as shown in Figure , can be described by …”

“…It was found that easier water movement on the surface was obtained as the size of the silica particle in the coating material was increased, although the static contact angles measured on the solid surface with different coatings were almost the same. Therefore, sliding angle is another parameter for the description of the surface dynamic wettability associated with the water transport on the surface . As shown in Figure B, the sliding angle is normally measured as the angle of the surface inclination at which liquid starts to slide on the surface under gravity, and it represents relative easiness of a liquid droplet moving on a surface under a driving force.…”

Water Transport and Removal in PEMFC Gas Flow Channel with Various Water Droplet Locations and Channel Surface Wettability

“…Similarly, the wave-like fluctuation of the water droplet shape (or height along z direction) can also be explained by the asymmetric air velocity or air shear force acting on the water droplet. Under such a kind of air shear force, water droplet can even roll on the hydrophobic surface, which has been observed in the experimental study [32]. In order to better clarify the advantage of the improved model, simulations are also carried out with the no-slip boundary condition for comparisons.…”

Biomimetic flow fields for proton exchange membrane fuel cells: A review of design trends

“…Owejan et al [144] demonstrated that a hydrophobic coating on flow field channels were retaining a higher amount of liquid water. However, Al Shakhshir et al [145] found out that despite the fact that both hydrophobic or hydrophilic treatment was reducing the overall pressure drop, the cell voltage with a parallel flow field and hydrophilic channels was more stable than that of the untreated channel, and that the hydrophobic treatment was decreasing the cell performance. The advantages of hydrophilic channels were shown by Lu et al [146], where it was found that more uniform water and gas flow distribution and a more desirable film flow regime was achieved by hydrophilically coated gas channels.…”