It is a critical challenge to construct efficient precious-metal-free bifunctional oxygen electrocatalysts for fuel cell and metal-air batteries via structural and component engineering. Herein, a one-dimensional mesoporous double-layered tubular structure, where CoS nanocrystals are incorporated into nitrogen, sulfur codoped carbon, is successfully synthesized via the coordinated-assisted polymerization and sacrificial template methods. The double-layered tubular structure provides for a large electrochemically active surface area and promotes fast mass transfer. Cobalt oxides/oxyhydroxides, which are evolved from the sulfides during the catalytic processes, as the main active sites efficiently catalyze the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), in cooperation with the Co-N-C and heteroatom-induced active sites. Hence, it demonstrates excellent bifunctional electrocatalytic activity with the overvoltage between the OER potential at 10 mA cm ( E) and ORR half-wave potential ( E) of 0.707 V, which is superior to most of precious-metal-free bifunctional oxygen electrocatalysts reported recently, as well as the state-of-art Pt/C and RuO catalysts.

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We report a self-template and facile pyrolysis method to synthesize Fe/Fe3C-decorated metal–nitrogen–carbon mesoporous nanospheres, of which preserved plum-like and hollow structures can be simply engineered via controlling the thickness of the outermost polydopamine layer in the precursors. The preserved plum-like structure is demonstrated to show a large electrochemically active surface area and facilitate fast charge transfer, in comparison with the hollow one. The catalytic activities of metal–nitrogen–carbon and nitrogen-doped carbon active sites in the outer carbon layer toward oxygen reduction are improved under the activation of the encased Fe species. Hence, preserved plum-like structures exhibit excellent catalytic kinetics toward the oxygen reduction reaction in alkaline media. The mass activity of 21.0 mA mgcatalyst –1 at 0.9 V vs RHE is achieved and the half-wave potential is 50 mV more positive than that of the Pt/C catalyst with the same mass loading. Moreover, the outer carbon layer endows the tolerance of strong acidic and alkaline environments, resulting in good durability. Our study proposes a simple strategy for the rational design of novel transition metal carbide-based catalysts, making it a promising candidate for replacing platinum-group metal catalysts in low-temperature fuel cells.

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