The production of octahedral Pt3Ni/C electrocatalysts with several carbon substrates (Ketjen black, Graphene, and Vulcan XC-72R) via solid-state chemistry was investigated. Different carbon substrates influenced the shape and alloy of Pt3Ni nanoparticles, with octahedral morphology and alloy metal preferred to develop on Ketjen black and Graphene, whereas spherical shape and bi-metallic metal preferred to grow on Vulcan. In addition, the shape was determined to be controlled during the reduction process, where the H2:CO ratio played a significant role in regulating octahedral morphology and executing the ORR activity. At an H2:CO ratio of 1:3, the Pt3Ni/Ketjen black had the greatest ORR activity for both mass activity (1.02 A mgPt-1) and specific activity (5.09 mA cm-2) which were 16.5 and 66.1 times greater than commercial Pt/C catalysts (0.062 A mgPt-1 and 0.077 mA cm-2). Whereas the H2:CO composition that demonstrated the best ORR activity of Pt3Ni onto Graphene and Vulcan XC-72R was 1:1. The catalysts were examined using an accelerated durability test (ADT) with 4000 voltage cycles, and it was discovered that the Pt3Ni /Ketjen catalyst performed the best in terms of ORR stability and durability.