Pt electrocatalysts supported on multiwalled carbon nanotube (Pt/MWCNT) nanocomposites have been synthesized by a rapid intermittent microwave irradiation (IMI) technique for polymer electrolyte and direct methanol fuel cells (PEFCs and DMFCs), using H(2)PtCl(6) as Pt precursor. The Pt/MWCNT nanocomposites are characterized by XRD, XPS, and TEM. The results indicate that Pt particle size and distribution on the MWCNT support are affected significantly by the oxidation treatment of MWCNTs, the IMI procedure, and the MWCNT tube diameter or surface area. The PtO(x) (x = 1, 2) species was first deposited on the surface of MWCNTs by the IMI and subsequently reduced to Pt(0) with refluxing in the presence of HCOOH. Pt/MWCNT nanocomposites synthesized by this IMI method have achieved extremely uniform dispersed Pt nanoparticles with a particle size of approximately 3 nm. Electrochemical measurement indicates that Pt/MWCNT nanocomposites synthesized by the IMI method display a significantly higher electrochemically active area and higher catalytic activity for the methanol oxidation reaction in comparison to a commercial Pt/C catalyst.

Perfluorosulfonic polymers such as Nafion are the most common membrane electrolytes used in polymer electrolyte and direct methanol fuel cells (PEFCs and DMFCs) owing to their high proton conductivity and good chemical and thermal stability. However, methanol readily migrates from the anode, through the Nafion membrane, to the cathode, reducing the open-circuit potential (OCP) by as much as 0.15-0.2 V and poisoning the electrocatalysts at the cathode.[1] Methanol crossover seriously retards the technological development of DMFCs. Thus, there has been extensive research activity in the modification of Nafion-based membranes to reduce the methanol crossover through, for example, the in situ polymerization of Nafion with poly(1-methylpyrrole), [2] and the development of composite membranes such as Nafion-silica, [3,4] Nafion-zirconium phosphate, [5] Nafion-cesium ions, [6] and Nafion-poly(furfuryl alcohol) nanocomposite membranes.[7]The modification of Nafion membranes reduces the methanol crossover and, in general, improves the performance of DMFCs. To achieve significant reduction in the methanol permeability, the oxide content has to be high (e.g., 20 wt % silica in the case of the Nafion-silica composite [3] ). This, in turn, reduces the proton conductivity and the mechanical properties are also seriously affected owing to the significant alteration of the membrane microstructure. Sandwiching a Pd thin film between Nafion membranes, [8] depositing a Pd and/or Pd-Cu alloy thin film on the surface of a Nafion membrane, [9][10][11] or depositing Pd nanoparticles through ion exchange followed by chemical reduction, [12] have been shown to reduce the methanol crossover. Unfortunately, the Pd thin film increased the overall cell resistance. The dispersed Pd particles in the membrane altered its microstructure, resulting in reduced cell performance and stability. Various multilayer membrane structures have also been investigated with the aim of suppressing methanol crossover. Yang and Manthiram studied the methanol crossover and conductivity of Nafion membranes with a thin barrier layer of sulfonated poly(ether ether ketone) (SPEEK).[13] Si et al. developed trilayer membranes composed of one central methanol barrier layer and two conductive layers to suppress the methanol crossover. [14] Casting non-conductive polymers such as poly(vinyl alcohol) (PVA) onto Nafion membranes can also reduce the methanol crossover. [15] However, in all these cases, the proton conductivity also decreased significantly due to the addition of a relatively thick barrier layer. The sequential adsorption of oppositely charged polyelectrolytes by layer-by-layer (LbL) self-assembly is an efficient method for obtaining multilayer thin films. This technique has progressed significantly since the pioneering work by Decher et al. [16,17] In this technique, two oppositely charged polyelectrolytes dissolved in aqueous solution are alternately deposited on a support surface by means of electrostatic attraction. After each dipping cycle, the surface cha...

A simple method was developed to prepare ultra‐low Pt loading membrane electrode assembly (MEA) using vertically aligned carbon nanotubes (VACNTs) as highly ordered catalyst support for PEM fuel cells application. In the method, VACNTs were directly grown on the cheap household aluminum foil by plasma enhanced chemical vapor deposition (PECVD), using Fe/Co bimetallic catalyst. By depositing a Pt thin layer on VACNTs/Al and subsequent hot pressing, Pt/VACNTs can be 100% transferred from Al foil onto polymer electrolyte membrane for the fabrication of MEA. The whole transfer process does not need any chemical removal and destroy membrane. The PEM fuel cell with the MEA fabricated using this method showed an excellent performance with ultra‐low Pt loading down to 35 μg cm−2 which was comparable to that of the commercial Pt catalyst on carbon powder with 400 μg cm−2. To the best of our knowledge, for the first time, we identified that it is possible to substantially reduce the Pt loading one order by application of order‐structured electrode based on VACNTs as Pt catalysts support, compared with the traditional random electrode at a comparable performance through experimental and mathematical methods.