Vertically aligned carbon nanotube electrodes for high current density operating proton exchange membrane fuel cells

• Electrodes for PEMFCs were prepared using vertically aligned carbon nanotubes (CNTs).
• The electrodes enabled high performance (2.6 A cm−2) with low Pt loading (0.1 mg cm−2).
• The wavy CNTs did not make agglomeration during the wet manufacturing process.
• Vertically aligning was important for manufacturing but was irrelevant for performance.

We successfully developed cathode electrodes for polymer electrolyte membrane fuel cells (PEMFC) that enable operation at high current densities by incorporating vertically aligned carbon nanotubes (CNTs) as the catalyst support; additionally, we prepared 236 cm2 membrane electrodes assemblies (MEAs) for vehicular use. The electrode structure improved the mass transport of reactants, i.e. oxygen, proton, electron and water, in systems performing at a 2.6 A cm−2 current density and 0.6 V with extremely low platinum (Pt) loading at the cathode (0.1 mg cm−2). The improved mass transport caused the 70 mV dec−1 Tafel slope to continue up to 1.0 A cm−2. The mass transport was improved because the pores were continuous, the catalyst support materials did not agglomerate and the catalyst layer made good electrical contact with the microporous layer. Utilizing wavy coil-shaped CNTs was also crucial. These CNTs displayed anti-agglomerative characteristics during the wet manufacturing process and maintained a continuous pore structure framing the layered catalyst structure. Because the CNTs had elastic characteristics, they might fill the space between catalyst and microporous layers to prevent flooding. However, the compressed CNTs in the cells were no longer vertically aligned. Therefore, vertically aligning the nanotubes was important during the MEA manufacturing process but was irrelevant for cell performance.