Confinement of CoOx-CoP nanoparticles inside nitrogen doped CNTs: A low-cost ORR electrocatalyst

Abstract

Non-noble metal containing catalysts for oxygen reduction reaction (ORR) are being targeted due to their low cost and availability. The rarity, high-cost, and self-poisoning of noble metals are the main drawbacks for the large-scale applications. Herein, a facile and simple synthetic strategy is adopted to prepare non-noble metal-based nitrogen doped carbon nanotubes (N-CNTs). The cobalt oxides (CoOx) nanoparticles are in-situ encapsulated inside these N-CNTs which are then treated with acid (HCl) and phosphidized to obtain CoOx-CoP/N-CNTs. High resolution transmission electron spectroscopy (HR-TEM) results reveal that the ends of N-CNTs are closed with nanoparticles. X-ray photoelectron spectroscopy (XPS) confirms the presence of cobalt oxide and cobalt phosphide nanoparticles. The catalyst CoOx-CoP/N-CNTs2 demonstrated Eonset and E1/2 of 0.96 V and 0.81 V, respectively in alkaline environment which is very much comparable to the state of art catalyst (20 wt% Pt/C). Acid treatment significantly enhances the electrocatalytic activity for ORR in comparison to material synthesized without prior treatment with acid. The catalyst exhibits excellent durability over 10,000 cycles and methanol tolerance to 0.5 M methanol addition. The enhanced ORR activity is attributed to synergistic effect of carbon matrix and encapsulated nanoparticles.