Carbon nanotube-supported binary silver-based nanocatalysts for oxygen reduction reaction in alkaline media

• MWCNT-supported binary Ag–Me (Me = Co, Cu, Ni, Sn) nanocatalysts were prepared.
• Ag8Co2/MWCNT showed the best electroactivity for ORR in alkaline media.
• ORR takes place via a 4-electron reaction on these binary catalysts.
• These catalysts present stable electroactivity for ORR.
• The catalysts are electrochemically inactive to methanol oxidation.

Multi-walled carbon nanotube (MWCNT)-supported silver nanocatalyst Ag/MWCNT and binary silver-based nanocatalysts Agx–Mey/MWCNT (molar ratio x:y = 9:1, 8:2, 7:3; Me = Co, Cu, Ni, Sn) have been synthesized by using the NaBH4 reduction method. All catalysts have been studied in terms of structure and morphology by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Their electrocatalytic activity for oxygen reduction reaction (ORR) in 1 mol L−1 NaOH solution has been investigated with the linear scanning voltammetry on a rotating disk electrode. Results show that in terms of the ORR current density, Ag8Co2/MWCNT is the best among the three binary Ag–Co/MWCNT catalysts, Ag9Cu1/MWCNT is the best among the three binary Ag–Cu/MWCNT catalysts, Ag9Ni1/MWCNT is the best among the three binary Ag–Ni/MWCNT catalysts, and Ag9Sn1/MWCNT is the best among the three Ag–Sn/MWCNT catalysts. Their ORR current density follows the order: Ag8Co2/MWCNT > Ag9Ni1/MWCNT > Ag9Cu1/MWCNT > Ag9Sn1/MWCNT > Ag/MWCNT. The onset potential of ORR on the Ag8Co2/MWCNT is 0.005 V, which is slightly higher than that on the Ag/MWCNT. However, the Ag8Co2/MWCNT exhibits a much higher ORR diffusion current density of 3.16 mA cm−2@−0.3 V at 1600 rpm than the Ag/MWCNT. A four-electron reaction of ORR on the as-synthesized binary Ag-based catalysts is more dominant than a two-electron reaction. In addition, these catalysts are electrochemically inactive to methanol oxidation, showing high alcohol-tolerance.