Platinum nanoparticles loaded on pristine and boron oxide modified carbon nano-onions for enhanced ammonia electrooxidation in alkaline direct ammonia fuel cells

• Carbon nano onions were synthesized using a flame pyrolysis method. • Platinum-based electrocatalysts were prepared by alcohol reduction method. • Boron oxide modifications facilitated the attachment of Pt onto the CNO. • The Pt/B-CNO exhibit high current density for ammonia electro-oxidation. Well dispersed ultrafine platinum nanoparticles (Pt NPs) loaded on pristine (p-CNOs) and boron oxide modified carbon nano-onions (B-CNOs) were successfully synthesized by the ethylene glycol reduction method. The obtained materials showed the presence of the face centered cubic structure of Pt with an average particle size of 4.6 ± 0.9 nm (p-CNOs) and 4.4 ± 0.5 nm (B-CNOs) under the alcohol reduction conditions. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of C, O, B, and Pt on the surface of the CNOs. Transmission electron microscopy images showed that the addition of B and Pt onto the surface of CNOs did not alter their morphology. The electrochemical catalytic performance of Pt/p-CNO, unwashed (uw) Pt/B-CNO, washed (w) Pt/B-CNO and commercial Pt/C nanocatalysts were evaluated towards ammonia oxidation in alkaline electrolyte. The Pt/B-CNOuw hybrid nanocatalysts showed enhanced catalytic activity, better stability, and fast charge transfer for ammonia oxidation reactions as compared to Pt/B-CNOw, Pt/p-CNO and the commercial Pt/C hybrids. The improved electrocatalytic activity of the Pt/B-CNOuw hybrid is ascribed to an increase of the electronic conductivity of the carbon nano onions by boron oxide and the enhancement of the interaction with water due to the boron on the support, which could contribute to the oxidation of intermediate products from the ammonia electro-oxidation.