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Development of economical, stable and high-efficient electrocatalysts gives vital incentives to promote the large-scale implementation of clean energy devices. Transition metal sulfides and carbon materials provide broad platforms for design of highly active electrocatalysts thanks to their flexibility, high electrical conductivity, and possessing various catalytically active sites towards different reaction systems. Herein, a ternary-component MoS 2 –Co 9 S 8 -NC nanohybrid is synthesized, in which Co 9 S 8 , MoS 2 , and N-doped carbon (NC) are integrated with each other. Owing to forming abundant varied active centers including Co 9 S 8 –MoS 2 heterojunctions, and Co–N, Mo–N coupling centers locating at the contact interfaces between transition metal sulfides and N-doped carbon, the hybrid demonstrates greatly enhanced performances towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Such hybrid represents low overpotentials of 95 mV and 230 mV to achieve 10 mA cm−2 current density for HER and OER in 1.0 M KOH, respectively, and demonstrates favorable prospects for large-scale applications in overall water splitting. Image 1 • MoS 2 –Co 9 S 8 -NC is prepared via a facile precursor-solution-based process. • There are abundant MoS 2 /Co 9 S 8 , Co 9 S 8 /NC and MoS 2 /NC hetero-interfaces. • Abundant interfaces in MoS 2 –Co 9 S 8 -NC facilitate HER and OER performances. • Metal-N bonds are formed at Co 9 S 8 /NC and MoS 2 /NC interfaces with N doping. [ABSTRACT FROM AUTHOR]

The particle size and dispersity of metal particles are key factors affecting the activity of electrocatalysts. Herein, employing N-doped carbon fiber as support, we report a facile gas-phase transport strategy for the synthesis of a series of transition metal nanoparticles (denoted as M/N-CF, M = Co, Cu, Mn, Ni, Fe). The current synthesis strategy not only yields metal nanoparticles with ultra-small size (∼5 nm) and good monodispersity, but also introduces a porous nanostructure with large surface area (730 m2 g−1) and rich M-N species. When used for catalyzing oxygen reduction reaction, all the M/N-CF catalysts adopt a highly efficient 4e− ORR pathway, reaching a most positive half-wave potential of 0.87 V vs. RHE for Mn/N-CF, quite approaching that of commercial Pt/C (0.88 V vs. RHE). Among them, Co/N-CF can also catalyze oxygen evolution reaction in an overpotential of 380 mV at 10 mA cm−2, approaching that of commercial RuO 2 (295 mV). Furthermore, as air electrode for rechargeable Zn-air battery, Co/N-CF based device achieves a high power density (163 mW cm−2) and good long-term cycling stability (over 50 h at 10 mA cm−2), suggesting the potential application of M/N-CF catalysts in energy conversion and storage systems. Image 1 • A facile and universal gas-phase transport strategy is presented to synthesize a series of transition metal based oxygen electrocatalysts (M/N-CF). • M/N-CF catalysts possess a porous nanostructure with large surface area and rich M − N species. • All the M/N-CF catalysts can catalyze ORR in a highly efficient 4e− ORR pathway. • Co/N-CF can simultaneously catalyze ORR and OER, achieving a high power density (163 mW cm−2) and good long-term cycling stability as air electrode in Zn-air battery. [ABSTRACT FROM AUTHOR]