Controllable dry synthesis of binder-free nanostructured platinum electrocatalysts supported on multi-walled carbon nanotubes and their performance in the oxygen reduction reaction

Different platinum nanostructures were synthesized by pulsed laser ablation (PLA) of a pure Pt target, a byproduct-free and solvent-free synthesis technique. The Pt nanostructures were directly deposited on multiwalled carbon nanotubes (MWCNT) pre-grown on a stainless steel (SS) mesh by chemical vapor deposition. Performing PLA at different background gas pressures (10-5 to 10 Torr, argon) and laser pulse energies (20 to 66 mJ pulse-1) led to a range of coating morphologies containing very low Pt loadings (14 to 35 mu g cm-2), from the uniform and dense nanoparticle thin coatings at low pressure to highly porous granular coatings at higher pressure. Increasing the background gas pressure led to an increase in primary Pt nanoparticle size from 2.0 +/- 0.2 nm to 2.8 +/- 0.8 nm. XPS results showed a positive shift in the Pt 4f7/2 binding energies with lowering the PLA pressure and laser energy, which was linked to the formation of smaller Pt nanoparticles. The presence of Pt (111), (200), (220), and (311) was confirmed by SAED patterns in the Pt nanostructures. The electrocatalytic performance of these binder-free Pt/MWCNT/SS structures was evaluated in the oxygen reduction reaction (ORR) in an alkaline medium, in both the rotating disk electrode (RDE) and gas diffusion electrode (GDE) configurations. In the RDE setup, all Pt/MWCNT/SS electrocatalysts were found to yield a higher specific ORR activity than the commercial Pt/C thin film, while in the GDE setup the Pt/MWCNT/SS electrode with the lowest Pt loading and highest surface area yielded the highest ORR specific activity.