High Performance of Anion Exchange Membrane Fuel Cells By Introducing Hydrophobic Carbon Nanotube Diffusion Layer
Authors: Zhang Zijie , Zeng Lin 
Published: December 2024

In recent years, anion exchange membrane fuel cells have garnered significant attention due to their ability to utilize low platinum group metal catalysts, thereby reducing manufacturing costs. In contrast to proton exchange membrane fuel cells, anion exchange membrane fuel cells have a distinctive operational characteristic where they produce water at the anode electrode while consuming water on the cathode electrode. The primary challenge hindering their advancement is managing water, specifically addressing the uneven distribution of water between the anode and cathode. As one of the crucial components of the fuel cell, the gas diffusion layer conducts electrons from the catalytic layer to the bipolar plate, transports reaction gases to the catalytic layer for electrochemical reactions, and removes excess water and waste heat generated on the anode electrode. Carbon nanotubes have high specific surface area, superior electrical conductivity, excellent mechanical properties, and inherent hydrophobicity due to their high degree of graphitization, and are considered to be promising materials for optimizing mass transport within gas diffusion layers. Abundant carbon nanotubes are synthesized in situ on carbon fibers to create a three-dimensional network structure, which not only provides more attachment sites for catalytic particles but also facilitates the electron flow path by interlacing carbon nanotubes within the catalytic layer.

In this work, the iron-cobalt catalyst was uniformly sprayed onto the gas diffusion substrate through ultrasonic spraying technology. The carbon source atmosphere was ionized and deposited under plasma radio frequency to synthesize abundant carbon nanotubes in the radial direction of the carbon fibers. Contact angle measurements revealed that the carbon nanotube-modified gas diffusion layer exhibited an approximate contact angle of 145°, which was significantly greater than that of the commercial gas diffusion media. Experimental research results indicated that, under various lower relative humidity conditions, when the cathode and anode inlet flow rates were set at 0.3 L/min and 0.5 L/min, respectively, the peak power generated by the membrane electrode assembled with the carbon nanotube-modified gas diffusion layer reached 988.9 mW/cm². This represents a substantial 27.1% increase compared to the performance achieved using the commercial gas diffusion layer. Upon further increasing the cathode and anode inlet flow rates to 0.6 L/min and 1 L/min, respectively, and operating under different higher relative humidity conditions, the membrane electrode assembled with the carbon nanotube-modified gas diffusion layer exhibited a peak power of 1031.7 mW/cm². In stark contrast, the commercial gas diffusion layer achieved only 760.6 mW/cm² under similar conditions. Through equivalent circuit and electrochemical impedance test analysis, it can be seen that the carbon nanotube-modified gas diffusion layer can effectively improve concentration polarization loss and ohmic polarization loss.