Effective anchoring of Pt-nanoparticles onto sulfonated polyelectrolyte-wrapped carbon nanotubes for use as a fuel cell electrocatalyst

Abstract

Sulfonated polymers, such as sulfonated polysulfone and sulfonated polyimide, are promising candidates as a future polyelectrolyte for polymer electrolyte fuel cells (PEFCs). In PEFC cell systems, the same polyelectrolyte material is often added to the electrocatalyst layer as the ionic path. We selected partially sulfonated poly(arylene thioethersulfone) (SPTES) and poly[(2,2′-benzidinedisulfonicacid)-alt-(1,4,5,8-naphthalenetetracarboxylic dianhydride)] (BDSA-NTDA) as the electrolytes and wrapped multi-walled carbon nanotubes (MWNTs) with the materials to which platinum nanoparticles (Pt) were attached onto the polyelectrolyte layer to fabricate new electrocatalysts. In these electrocatalysts, the MWNT and Pt serve as the electron path and reaction site, respectively. For both polyelectrolytes, Pt-nanoparticles <5 nm in diameter with a narrow size distribution were observed to be homogeneously dispersed on the polymer-wrapped MWNTs. The electrochemical measurements revealed that MWNT/SPTES/Pt and MWNT/BDSA-NTDA/Pt possessed electrochemically active surface areas (ECSA) of 42.3 and 35.6 m2/g of Pt, respectively. Such a high ECSA efficiency ensures the use of these composites for the preparation of a future electrocatalyst. Sulfonated polymers are promising polyelectrolyte for polymer electrolyte fuel cells (PEFCs) in the next generation. We found that the sulfonated polyelectrolyte can wrap multi-walled carbon nanotubes (MWNTs). After the reduction of Pt salt in the presence of the polyelectrolyte-wrapped MWNTs, Pt-nanoparticles below 5 nm in diameter with a narrow distribution were found to be homogeneously loaded. The composites are composed from the electron conductor, proton conductor and the catalyst metal, which are all necessary for the electrocatalyst for fuel cell and are promising materials for PEFC in the next generation.