Silver Nanoparticle/Multiwalled Carbon Nanotube Hybrid as an Efficient Electrocatalyst for the Oxygen Reduction Reaction in Alkaline Medium

A straightforward approach is employed to synthesize silver nanoparticle/multiwalled carbon nanotube (Ag/MWNTs) hybrids through the direct reduction of silver nitrate in the presence of MWNTs, where Ag nanoparticles capped with tris(hydroxymethyl)phosphine oxide (d=2.9nm) are uniformly deposited on MWNTs. The as-synthesized Ag/MWNTs hybrids exhibit high catalytic activity toward the oxygen reduction, which increases with the loading amount of Ag nanoparticles. Rotating disk electrode and rotating ring-disk electrode analyses further indicate that the Ag/MWNTs hybrids follow the same four-electron pathway towards the oxygen reduction reaction as the Pt/C catalyst, and the Ag/MWNTs hybrid (22.8wt.%) manifests comparable catalytic activity to the 20% Pt/C catalyst, together with superior long-term stability and methanol tolerance, demonstrating the potential application on direct methanol fuel cells as an effective oxygen reduction catalyst.