Researchers at the University of British Columbia (UBC) have used a plasma pre-treatment to achieve through-plane wettability of carbon layers in a fuel cell electrode. A paper on their work is published in the journal Applied Surface Science.
Porous carbon based layers have become standard electrode materials in many energy conversion and storage applications. Generally, the overall performance of the system is influenced by the wetting properties of the pore structure. For example, fully wetted pore structures are desirable for the porous carbon layer used in supercapacitors. The high surface area maximizes the charge stored at the solid-liquid (S-L) interface. For the proton exchange membrane fuel cells (PEMFCs), an optimal balance of water level is critical for high performance and durability.
On one hand, sufficient water content is required to hydrate the membrane to maintain high proton conductivity. Thus the reactant gas supplied to the fuel cell is often humidified to minimize ohmic losses. On the other hand, excess water produced from the electrochemical reaction at the cathode must be removed in order to prevent water accumulation at the porous carbon layer (PTL). Excessive liquid water can block the pores of the catalyst layer and porous transport layer, thus impeding the transport of reactant gas to the active sites.
… In this work, we report for the first time a combination of electrochemical, optical and surface structural analysis towards understanding the impacts of a single-step fast and low-power plasma treatment of a commercial PTL on the performance of PEMFC. An in-house opto- electrochemical technique is used to show the extent of wettability alteration on the top and bottom surface of the treated layers using the electrochemical double layer capacitance as the key metric.—Zahiri et al.
The researchers exposed the surface of a fuel-cell electrode, which contains porous layers of carbon, to ionized oxygen gas for one minute. The treatment deposited varying amounts of oxygen-carrying molecules, which attract water, on the surface.
The upper layers received the most molecules and the next layers received progressively fewer molecules. By creating this gradually decreasing wettability, the water is drawn down from the upper layers through to the bottom layers, from where it exits the cell. The structure of the carbon layer itself remains unchanged.
Our results show that plasma treatment is effective in facilitating water transport in a PEM fuel cell. Other water transport strategies like hydrophobic or water-repelling coatings are too costly or too complex to be viable.—first author Beniamin Zahiri
Plasma treatment also can be easily integrated in the manufacturing of fuel cell components, according to the researchers.
The team is currently exploring other applications of plasma treatment. According to Mérida, plasma treatments can work on other porous materials used in energy storage. They can also be integrated into caustic soda-based industries, a market valued at US$80 billion.
Beniamin Zahiri, Rigoberto Miranda Felix, Ainsleigh Hill, Chun Haow Kung, Trishank Sharma, Jesus Diaz Real, Walter Mérida (2018) “ Through-plane wettability tuning of fibrous carbon layers via O2 plasma treatment for enhanced water management,” Applied Surface Science, Volume 458, Pages 32-42, doi: 10.1016/j.apsusc.2018.07.005