Abstract
Sulfur- (S-CNT) and nitrogen-doped (N-CNT) carbon nanotubes have been produced by catalytic chemical vapor deposition (c-CVD) and were subject to an annealing treatment. These CNTs were used as supports for small (≈2 nm) Pt3M (M = Co or Ni) alloyed nanoparticles that have a very homogeneous size distribution (in spite of the high metal loading of ≈40 wt % Pt), using an ionic liquid as a stabilizer. The electrochemical surface area, the activity for the oxygen reduction reaction and the amount of H2O2 generated during the oxygen reduction reaction (ORR) have been evaluated in a rotating ring disk electrode experiment. The Pt3M/N-CNT catalysts revealed excellent electrochemical properties compared to a commercial Pt3Co/Vulcan XC-72 catalyst. The nature of the carbon support plays a key role in determining the properties of the metal nanoparticles, on the preparation of the catalytic layer, and on the electrocatalytic performance in the ORR. On N-CNT supports, the specific activity followed the expected order Pt3Co > Pt3Ni, whereas on the annealed N-CNT support, the order was reversed.
Highlights
Proton exchange membrane fuel cells (PEMFCs) convert chemical energy from the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) into electrical energy
Three kinds of Carbon nanotubes (CNTs) have been produced by catalytic chemical vapor deposition (c-CVD): undoped (CNTs), N-doped (N-CNTs) and S-doped CNT (S-CNTs)
Very regular structures were obtained for the CNT sample (Figure 1a), while the N-CNT sample presented a “bamboolike” structure typically found in N-doped CNTs (Figure 1b) [39], and the structure of the S-doped CNTs presents some alterations, which are different than those observed for the N-CNTs
Summary
Proton exchange membrane fuel cells (PEMFCs) convert chemical energy from the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) into electrical energy. XPS analysis showed the presence of sulfonic acid groups on the surface of N-doped CNTs (Supporting Information File 1, Figure S4b), and the S content increases with the nitrogen content. The TEM images of sample Pt3Co/CNT (Supporting Information File 1, Figure S5b) show that the use of ILs does not result in well-dispersed NPs on this support.
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