Metallic Ni3N Quantum Dots as a Synergistic Promoter for NiO Nanosheet toward Efficient Oxygen Reduction Electrocatalysis

The development of efficient and stable transition-metal-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells is highly desirable, yet a great challenge remains. Here, we report novel Ni3N quantum dot (QD)/NiO heterostructure material, fabricated by immobilization of metallic Ni3N QDs onto the surface of NiO nanosheet, as a highly active and durable electrocatalyst for efficient oxygen reduction performance. The electrochemical characterizations and theoretical calculations reveal that a strong interface coupling effect in Ni3N QDs/NiO heterostructure is realized by the interfacial hetero Ni species, synergistically accelerating the dissociation of adsorbed water molecules and reductive kinetics of adsorbed oxygen molecules during the ORR process. Hence, the developed Ni3N QDs/NiO heterostructure yields prominent oxygen reduction performance with a small half-wave potential (E1/2) of 0.76 V and high kinetic current density (Jk) of 15.4 mA cm–2 at 0.7 V, much superior to those of NiO nanosheet (0.65 V; 0.81 mA cm–2) and comparable to those of commercial Pt/C catalyst (0.80 V; 13 mA cm–2). In addition, the catalyst shows long-term catalytic stability with robust methanol tolerance, serving as a promising noble-metal-free ORR catalyst for fuel cells.