Ammonia will play a pivotal role in the future of zero carbon emitted sustainable fuel. The development of inexpensive efficient catalysts for ammonia electro-oxidation (AEO) is essential to its success. This study provides evidence that nanoparticles of earth-abundant elements, e.g., MoC, encapsulated in a doped-graphene shell (DG-MoC), are promising cocatalysts of Pt for AEO which significantly improve the catalyst cost and activity in comparison to the state-of-the-art platinum. DG-MoC, DG-MoC-supported Pt (Pt/DG-MoC), and nitrogen-doped-graphene (NG) catalysts were synthesized and characterized by Brunauer–Emmett–Teller (BET) surface area analysis, electrochemical techniques, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX), scanning transmission electron microscopy (STEM), and electron energy loss (EEL) spectroscopy. The XRD analysis of DG-MoC disclosed that the presence of α-MoC1–x microscopy techniques demonstrates a close vicinity of Pt and MoC nanoparticles in Pt/DG-MoC. We report, for the first time, that Pt/DG-MoC particles reveal a large synergistic effect for AEO activity, while DG-MoC and NG showed no activity. Pt/DG-MoC gave a higher current density, lower half- and peak- potentials (28 mV and 14 mV, respectively), and greater resilience to ammonia poisoning than Pt/C as shown in the fall in the peak current density in the second voltammogram, i.e, approximately 3.6% compared to 20.7% for Pt/C. The XPS spectrum of the catalysts explained the source of this synergistic effect.