Bimetallic nanoparticles with extremely uniform dispersion on conductive-carbon supports are very much in need to improve the kinetics of sluggish electrochemical reactions relevant to fuel cell applications. Here, bimetallic platinum-cobalt (26.7 wt% Pt + 2.8 wt% Co on reduced graphene oxide with atomic composition of platinum-to-cobalt as 3:1) and platinum-nickel (26.8 wt% Pt + 2.8 wt% Ni on reduced graphene oxide support with atomic composition of platinum-to-nickel as 3:1) nanoparticles with high degree of uniform dispersion (average particle sizes of about 1-2.25 nm) on graphene oxide in its partially reduced form ('rGO') were fabricated by a simple one-pot chemical-based reduction method. A pomegranate peel extract was utilized to neutralize the high acidic graphene oxide (GO) formed during the chemical exfoliation of natural graphite and used along with metal precursors during the chemical reduction to achieve well-dispersed Pt3Ni/rGO and Pt3Co/rGO nanoparticles. The efficiencies towards electrocatalytic oxygen reduction reaction (ORR) of the synthesized catalysts were tested in different media (acidic and basic). In acidic medium, the ORR activity descriptors like mass-specific and area-specific current density as well potential at half-wave (E-1/2) are considerably higher for Pt3Ni/rGO nano catalysts than Pt3Co/rGO, Pt/rGO and Pt/C electrocatalysts. Interestingly, in basic medium the Pt3Co/rGO exhibit higher ORR activity among the other catalysts tested. The general facile fabrication strategy shown in this work is promising to extend to prepare other mono, bi and ternary metallic nanoparticles with high uniformity on carbon-based substrates to utilize as highly advanced electrocatalysts. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.