The Synthesis of Cerium Oxide Antioxidant Supported on Silica Nanotube for Polymer Electrolyte Membrane Fuel Cell
Authors: Oh Song I , Lee So Young , Ko Jae Jun , Han Jong Hee , Kim Hyoung-Juhn 
Published: February 2020

To prevent oxidation of the polymer electrolyte membrane (PEM) in the fuel cell, the ability of cerium oxide nanoparticles are well known as free radical scavengers. However the cerium oxide has limited use due to agglomeration and dissolution in the membrane. In this study, the cerium oxide nanoparticles attached to silica nanotube were synthesized, and the membranes containing those antioxidant are prepared. As cerium oxide nanoparticles can be easily embedded within silica nanotubes to form cerium containing materials which can protect cerium oxide nanoparticles from aggregation and can slowly release cerium ions, these materials are predicted to have a more effective application in PEM than conventional cerium oxide nanoparticles.
The synthesis of silica nanotubes is based on the hard templating of rod-like nanocrystals, which are synthesized in reverse micelles of a polyethylene glycol type surfactant in the organic solvent. The deposition of silica using the silica precursor around nanosized rods stabilizes the complex structure and eventually produces silica nanotubes. Silica nanotube having the length of 50 nm and the width of 20 nm is produced and its size can be controlled during manufacture. Cerium oxide particles are grown on the surface of the silica nanotubes using the coupling agent having the silicate. It can be uniformly supported the cerium oxide nanoparticles on the surface of the silica nanotubes. Figure 1 shows the transmission electron microscopy (TEM) including energy dispersive X-ray chemical analysis (EDS) images of silica nanotubes after cerium oxide nanoparticles coating. The EDS elemental analysis confirms that cerium oxide nanoparticles are evenly attached to the surface of silica nanotubes. Also, inductively coupled plasma (ICP) analysis is conducted on the loaded cerium.
The cerium oxide antioxidants supported on silica nanotubes are added to the fluorinated polymer solution at a constant ratio, and then stirred to prepare a membrane. The solution is casting and dried in an oven and then heat-treated. The properties of the prepared membranes are evaluated by proton conductivity, fluoride release rate (FRR), and cerium migration compared to the pristine, the membrane containing cerium oxide and cerium oxide antioxidants supported on silica nanoparticles with a diameter of 50 nm. The results are shown in the Table 1. The proton conductivity increases due to the water diffusion effect of the silica nanotube rather than the silica nanoparticle structure. When the cerium content is the same, the FRR value and cerium migration of the membrane containing the tube structure antioxidant are the lowest.
This is most effective for the tube structure to have cerium dispersion and high surface area. In order to solve the rapid decrease in antioxidant activity due to migration and aggregation, the cerium oxide antioxidants supported on silica nanotubes are expected to significantly enhance the performance of the PEM in fuel cells.

Figure 1