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Exploration high-efficient bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of great significance for several renewable energy applications. In this paper, a catalyst composed of Co 9 S 8 and porous carbon (Co 9 S 8 –C) is prepared first via the calcination of Co–S–C based precursor coating on carbon-fibre-paper (CFP) substrate under argon atmosphere. Then, the Co 9 S 8 –C is modified via the decomposition gas of dicyandiamide, thus Co 9 S 8 –N-doped carbon (Co 9 S 8 -NC) catalyst is synthesized. As revealed, the morphology and defect features are effectively modulated by the modification, suggesting the reduced particle sizes of Co 9 S 8 component and obviously improved N proportion and various defects. As a result, Co 9 S 8 -NC represents excellent activities electrocatalytic performances toward OER and ORR, which surpass those of its three counterparts including Co 9 S 8 –C, Co 9 S 8 , and NC. A half-wave potential of 0.86 ​V versus RHE for ORR and a low overpotential of 280 ​mV ​at 10 ​mA ​cm-2 current density for OER are achieved, with the Δ E value of 0.64 ​V. Additionally, the catalyst also demonstrates desirable application prospect for Zn-air battery. The post-treatment method reported here might be utilized widespread to promote the synergistic effects between the Co-contained particles and N-doped carbons in composite catalysts. The DCA post-treatment can produce high amounts of N-doped pore edges, and can simultaneously facilitate the intimate electronic contact between moderately eroded Co 9 S 8 and N-doped carbon matrix thus forming abundant high active coupling Co-N x -C centers. The catalyst demonstrates excellent bifunctional performance for catalyzing OER and ORR. Image 1 • Co 9 S 8 -porous N-doped carbon (NC) catalyst was in-situ synthesized on CFP substrate. • Intimate electronic contact between Co 9 S 8 and NC is achieved through a dicyandiamide post-treatment. • N content is much improved with rich new-formed pyridinic N and interfacial Co–N. • The catalyst exhibits remarkable OER/ORR bifunction and good prospect in flexible Zn-air battery. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • Novel CoSb/NC catalysts are prepared via a novel Sb-modulated strategy. • The feeding amount of Sb salt is tuned to modulate the particle size and pore structure of CoSb/NC catalysts. • CoSb/NC catalysts exhibit enhanced ORR activity and kinetics outperforming the state-of-the-art Pt/C. • CoSb/NC catalysts are electrocatalytically active toward OER. • CoSb/NC catalysts can drive rechargeable Zn-air battery with a high peak power density of 180 mW cm−2. Rational modulation and optimization of structural properties plays a significant role in advancing the electrocatalytic performance of electrocatalysts. In this study, we report a novel Sb-modulated strategy to synthesize novel CoSb/NC catalysts comprised of CoSb alloy supported on nitrogen-doped carbon (denoted as CoSb/NC). Apart from alloying with Co to generate CoSb alloys, we demonstrated that the evaporation of Sb could modulate the particle size and pore structure of CoSb/NC. Such modulation has facilitated the formation of micro/meso-porous structure to accelerate the mass/charge transport and increase the accessibility of active sites, resulting in a highest kinetic current density of 22.6 mA cm−2 at 0.85 V vs. RHE as well as a low Tafel slope of 38 mV dec−1, which even outperforms the state-of-the-art Pt/C. Additionally, CoSb/NC is demonstrated to be electrocatalytic active toward OER with the overpotential to be 430 mV at 10 mA cm−2. Rechargeable Zn-air battery tests reveal that CoSb/NC possesses competitive performance in terms of charge-discharge ability and stability, suggesting its potential application in renewable energy conversion devices. This work provides a novel approach to modulate the structure of nitrogen-doped carbon based materials as efficient oxygen electrocatalysts. [ABSTRACT FROM AUTHOR]

• Co/N-C Zn is prepared via high-temperature gas-transport approach. • The intrinsic structure of Co/ N-C Zn has been greatly modulated by ZnCl 2 treatment. • Co/N-C Zn exhibits enhanced ORR and OER performance. • ORR and OER active sites are determined by control experiments. • Co/N-C Zn can drive liquid and solid-state rechargeable Zn-air battery efficiently. In this study, a facile surface treatment on polypyrrole (PPy) nanofiber with ZnCl 2 solution is employed to fabricate N-doped carbon anchored with metallic Co (denoted as Co/N-C Zn) via gas-transport approach. Structural characterizations reveal that the intrinsic structure of Co/N-C Zn in terms of its morphology, pore structure and defects have been greatly modulated by such a surface treatment, resulting in a higher loading amount of metallic Co, larger surface area and increased pyridinic N and Co-N species as efficient active sites. Benefiting from the structural modulation, Co/N-C Zn exhibits outstanding ORR activity and kinetics with a positive half-wave potential of 0.88 V vs. RHE, a high kinetic current density (J k) value of 36.6 mA cm−2 at 0.85 V vs. RHE, and a small Tafel slope of 55.9 mV dec−1, which even outperforms commercial Pt/C. Moreover, enhanced OER performance is also achieved in Co/N-C Zn , with an overpotential of 280 mV at 10 mA cm−2, surpasses that of commercial RuO 2 (295 mV). Finally, Co/N-C Zn shows promise for substitution of commercial Pt/C and RuO 2 to drive both liquid and solid-state rechargeable Zn-air batteries with high peak power densities of 196 mW cm−2 and 130 mW cm−2. [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]