Electrocatalysis of oxygen reduction on multi-walled carbon nanotube supported Ru-based catalysts in alkaline media

• Binary RuNi and RuSn catalysts were synthesised for ORR.
• The nanoparticle catalysts were supported on MWCNTs and Vulcan carbon (XC-72R).
• MWCNTs supports caused to ORR activity enhancement of binary catalysts.
• RuNi/MWCNTs showed the highest ORR activity.

Ru and bimetallic Ru-M (M = Ni and Sn) nanoparticles were supported on the multi-walled carbon nanotubes (MWCNTs) and Vulcan carbon (XC-72). Morphology of nanoparticles was investigated by scanning electron microscopy (SEM). The kinetics and mechanism of the oxygen reduction reaction (ORR) were analyzed in 0.1 M NaOH solution. From rotating disk electrode (RDE) studies, it was found that the number of electrons (n) involved in the ORR depends on the alloy compositions. For single Ru nanoparticles, n was 2 and for alloy nanoparticles the value of n increases almost to 4. The number of electrons transferred was calculated 3.88 for RuNi/MWCNTs. The prepared nanoparticles were used as the active catalyst of gas diffusion electrodes (GDEs). The electrocatalytic performance of the GDEs was investigated by cyclic voltammetery (CV), AC impedance spectroscopy (EIS) and chronoamperometery methods. The RuNi/MWCNs indicated the lowest charge transfer resistance in the whole range of applied potentials. According to the electrochemical measurements, the Ru-M/MWCNT catalysts displayed significantly higher performance than the Ru-M/C catalysts.