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A multi-walled carbon nanotubes supported carbon dots co-doped with boron and nitrogen as high-efficiency oxygen reduction catalysts was synthesized through hydrothermal reaction and calcination. Pyridine N and BC 3 act with synergy to significantly enhance catalytic activity. The B atom of BCO 2 can be appropriately combined with O intermediates such as OH or H 2 O to promote adsorption on the catalyst. [Display omitted] Cost-effective production of metal-free catalysts for the oxygen-reduction reaction (ORR), to supersede Pt-based catalysts, is challenging. Here, a three-dimensional nanocatalyst was prepared by compounding multi-wall carbon nanotubes (MWCNTs) with easily modified and doped carbon dots (CDs) as sources of B and N. The catalyst has high conductivity and a large specific surface area similar to the MWCNTs, allowing exposure of many CDs with rich edge active sites and enhancing electron transfer. The catalyst exhibits excellent ORR performance, with 0.92 V of E onset vs reversible hydrogen electrode (RHE). The E 1/2 value exhibits a reduction of 50 mV compared with that of Pt/C (0.85 V) with a limited current density of 5.95 mA cm−2. The enhanced catalytic performance is attributed to the synergy of pyridine N and BC 3. This work describes a simple and economical strategy for metal-free catalysts, and promotes the development of such catalysts for metal-air batteries and fuel cells. [ABSTRACT FROM AUTHOR]

The development of highly active oxygen reduction reaction (ORR) catalysts with low-loading of precious metals is imperative but remains a great challenge. Herein, Pd/B,N-CDs@CNT composite catalysts was designed with Pd nanoparticles immobilized on hybrid support composed of B,N-doped carbon dots (B,N-CDs) and the multi-wall carbon nanotubes (CNT) using a simple methanol reduction method. The deposited Pd nanoparticles exhibit clean surface, low crystallinity and surface distortion. The Pd/B,N-CDs@CNT catalyst shows significantly enhanced ORR activity, with the mass activity about 5–6 times higher than that of commercial Pt/C. Thus prominent ORR performance is mainly attributed to the unique microstructure of Pd nanoparticles. Moreover, the composited B,N-CDs and the doped B, N heteroatoms further improve the ORR performance, in which B,N-CDs supply more absorption sites, the formation of N–Pd facilitates the electron transfer, B doping can promote the adsorption of oxygenated species and weaken the strong interaction between Pd and C. Furthermore, the B, N co-doping plays a synergistic effect. This strategy provides a simple and mild method for designing highly efficient electrocatalysts with ultra-low precious metals in alkaline electrolytes. [Display omitted] • Pd nanoparticles were deposited on B,N-CDs@CNT hybrid by a simple methanol reduction. • The composited B,N-CDs act as a doping source of B, N into CNT. • The Pd nanoparticles show clean surface, low crystallinity and surface distortion. • The Pd/B,N-CDs@CNT shows prominent ORR activity outperforming commercial Pt/C. • The ORR performance is attributed to the unique microstructure of Pd nanoparticles and support effect. [ABSTRACT FROM AUTHOR]