Carbon nanotube-supported sulfided Rh catalysts for the oxygen reduction reaction

Carbon nanotube (CNT) supported sulfided Rh catalysts were prepared applying three different routes: deposition-precipitation (DP), grafting of colloidal Rh nanoparticles, and polythiophene-assisted synthesis. The catalysts (1.4-1.8wt%) prepared by DP were synthesized on CNTs from RhCl3 using hydrogen peroxide and subsequent exposure to on-line generated H2S followed by heat treatment. The Rh particles were found to be highly dispersed on the CNT surface. Alternatively, RhSx/Rh nanoparticles with four different loadings (4.3-21.9wt%) grafted on carbon nanotubes were prepared through a functionalization of CNTs with short chain thiols and subsequent binding of colloidal Rh nanoparticles onto the thiolated CNTs. All steps of the synthesis were monitored by XPS. Finally, polythiophene/CNT composites were prepared and employed in the preparation of Rh17S15/Rh nanoparticles supported on CNTs. The CNTs with the highest polythiophene loading yielded the highest amount of Rh17S15 after Rh deposition and thermal treatment. The activity and stability of the prepared catalysts were studied towards the oxygen reduction reaction.