Highly active bimetallic nanocatalysts (Pd/Ag and Pd/ZnO) decorated nitrogen-doped onion-like carbon nanoparticles for enhanced methanol oxidation in alkaline media

Abstract

Nitrogen-doped onion-like carbons (N-OLCNs) rich with defective sites are synthesized using a flame pyrolysis method, using acetonitrile as both carbon and nitrogen sources. Bimetallic (Pd/Ag and Pd/ZnO) electrocatalysts prepared in a one-pot method using sodium borohydride as a reducing agent, are supported on the N-OLCNs. X-ray diffraction data shows the formation of Pd/Ag and Pd/ZnO supported on the N-OLCNs surface. Transmission electron microscopy analysis confirms the existence of well-dispersed, spherically shaped Pd/Ag (16.9 ± 4.8 nm) and Pd/ZnO (10.4 ± 1.0 nm) on the surface of the N-OLCNs. Pd/N-OLCN, Pd/Ag/N-OLCN, Pd/ZnO/N-OLCN, and a Pd/C electrocatalyst are studied in the methanol oxidation reaction (MOR). Incorporating Ag and ZnO improves the Pd/N-OLCN physiochemical properties and catalytic performance towards MOR in alkaline electrolyte. The Pd/Ag/N-OLCN and Pd/ZnO/N-OLCN electrocatalysts exhibit superior anti-poisoning tolerance, better electrocatalytic stability, and fast charge transfer resistance as compared to monometallic Pd/N-OLCN and Pd/C electrocatalysts in MOR. It is proposed that the electron transfer from the Ag species to the Pd modified the active sites of Pd by increasing the electron density at Pd and hence promoting the desorption of methanol. Furthermore, the improved catalytic performance could also be related to a strong metal-support interaction. • N -OLCNs with rich defective sites were synthesized using a flame pyrolysis method. • Pd-based electrocatalysts were prepared by the sodium borohydride reduction method. • Nitrogen doping facilitated the attachment of Pd, Ag, and ZnO onto the OLCNs. • The catalysts exhibit superior catalytic activity and excellent stability in MOR.