Hard/Soft Template Synthesis of Mesoporous TiO2/Carbon Supports for Fuel Cells
Authors: Jones Allison , Montiel Gonzalo , Viva Federico , Trevani Liliana 
Published: February 2020

Mesoporous carbons (MC) are attractive catalyst supports for polymer electrolyte membrane fuel cells (PEMFCs) applications because of their low cost, high surface area, good electrical conductivity, and high chemical stability under normal operating conditions.[1] However, carbon corrosion in the cathode compartment can result in a significant reduction in the catalyst electrochemical active surface area (ECSA), that it will negatively impact in the fuel cell performance.[2] Hence, alternative catalyst substrates with a greater chemical stability under acidic and oxidizing conditions have captured significant attention in recent years. [3,4]

Among the most promising materials for PEMFCs are carbon nanotubes (CNTs), graphene, and hybrid core/shell metal oxide/mesoporous carbons (MOx/MC). Unfortunately, CNTs and graphene are still too expensive for this application, while studies on hybrid supports, in the case of metal oxides, were limited to low metal oxide contents due to the reduction on surface area observed after the deposition of metal oxide nanoparticles.[5,6]

For that reason, the use of ordered mesoporous carbons obtained by carbonization of polymeric materials synthesized in the presence of soft-templates such as surfactants or polyelectrolytes[7] or silica nanoparticles as hard-templates[1] is quite attractive. It can contribute to produce chemically stable materials with an adequate surface area and pore size distribution, and these properties can be modified by merely varying the synthesis and carbonization conditions.[1,4,7]

In this study, the effort was oriented to develop mesoporous carbons (MC), and hybrid TiO2/MC catalyst supports with high surface area and tailored micro-mesoporous structure. Carbon materials were obtained by carbonization of a resorcinol-formaldehyde resin synthesized in the presence of silica nanoparticles and poly(diallyldimethylammonium) chloride, a polyelectrolyte as soft template. The deposition of TiO2 nanoparticles was carried out using a sol-gel method that has shown to result in the formation of core/shell TiO2/carbon nanocomposite structures with low TiO2 segregation.[5,6] Both, MC and TiO2/MC substrates were decorated with Pt or PtRu catalyst nanoparticles using standard impregnation methods.
The materials were characterized using standard methods (XRD, XPS, TEM, SEM, TGA, ICP-OES, and Raman spectroscopy). The catalytic activity of Pt and PtRu nanoparticles toward the oxygen reduction reaction (ORR), and the oxidation of methanol (MOR) was investigated using a number of electrochemical techniques in a three-electrode cell configuration.
The improvement in the catalytic activity of Pt toward the ORR and the chemical stability were both assigned to the high BET surface area of the starting carbon materials (> 500 m2/g) that allowed working with high TiO2 loadings while still keeping a reasonable electrical conductivity. The high TiO2 content seems to improve the catalyst distribution on the support, and the contact between the TiO2 and Pt nanoparticles. Preliminary results for the oxidation of methanol on PtRu/TiO2/MC also show a significant improvement when compared to Pt/MC and Pt/TiO2/MC, but the changes are less significant when compared with PtRu/MC, however more studies are underway to confirm these findings.

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