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Journal ArticleDOI

Monodisperse cobalt sulfides embedded within nitrogen-doped carbon nanoflakes: an efficient and stable electrocatalyst for the oxygen reduction reaction

19 Jul 2016-Journal of Materials Chemistry (The Royal Society of Chemistry)-Vol. 4, Iss: 29, pp 11342-11350
TL;DR: In this paper, the authors reported the designed synthesis of Co9S8 and nitrogen doped hollow carbon sphere composites by carbonization of metanilic anions within the confinement of two-dimensional galleries of hollow spherical cobalt-aluminum layered double hydroxides.
Abstract: Unique hollow hybrid structures composed of well-dispersed catalyst nanoparticles embedded in a carbon matrix offer great advantages for constructing advanced supported catalysts. Herein, we report the designed synthesis of Co9S8 and nitrogen doped hollow carbon sphere (Co9S8/NHCS) composites by carbonization of metanilic anions within the confinement of two-dimensional galleries of hollow spherical cobalt–aluminum layered double hydroxides. The Co9S8/NHCS composites are composed of numerous porous carbon nanoflakes, and monodisperse Co9S8 nanoparticles are embedded within the carbon nanoflakes. Electrochemical measurements show that the Co9S8/NHCS catalysts prepared at 900 °C exhibit superior oxygen reduction reaction (ORR) activity, resulting in the highest ORR performance to date among all transition metal sulfide-based ORR catalysts in both alkaline and acidic electrolytes. This interlayer confined reaction approach may provide an efficient platform for the synthesis of other functional materials for alternative applications.
Citations
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Journal ArticleDOI
TL;DR: Mixed metal sulfides (MMS) have attracted increased attention as promising electrode materials for electrochemical energy storage and conversion systems including lithium-ion batteries (LIBs), SIBs, hybrid supercapacitors (HSCs), metal-air batteries (MABs), and water splitting as discussed by the authors.
Abstract: Mixed metal sulfides (MMSs) have attracted increased attention as promising electrode materials for electrochemical energy storage and conversion systems including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), hybrid supercapacitors (HSCs), metal–air batteries (MABs), and water splitting. Compared with monometal sulfides, MMSs exhibit greatly enhanced electrochemical performance, which is largely originated from their higher electronic conductivity and richer redox reactions. In this review, recent progresses in the rational design and synthesis of diverse MMS-based micro/nanostructures with controlled morphologies, sizes, and compositions for LIBs, SIBs, HSCs, MABs, and water splitting are summarized. In particular, nanostructuring, synthesis of nanocomposites with carbonaceous materials and fabrication of 3D MMS-based electrodes are demonstrated to be three effective approaches for improving the electrochemical performance of MMS-based electrode materials. Furthermore, some potential challenges as well as prospects are discussed to further advance the development of MMS-based electrode materials for next-generation electrochemical energy storage and conversion systems.

640 citations

Journal ArticleDOI
TL;DR: In this paper, a review mainly focuses on the opening of 2D materials and their subsequent applications in energy conversion and storage fields, expecting the development of such a new class of materials, namely expanded 2D Materials.
Abstract: The development of two-dimensional (2D) materials is experiencing a renaissance since the adventure of graphene. 2D materials typically exhibit strong in-plane covalent bonding and weak out-of-plane van der Waals interactions through the interlayer gap. Opening 2D materials is an effective way to alter the physical and chemical properties, such as band gap, conductivity, optical property, thermoelectric property, photovoltaic property and superconductivity. A larger interlayer distance means more accessible active sites for catalysis, an ion-accessible surface in the interlayer space, which may greatly enhance the performance of 2D materials for energy conversion and storage. Moreover, opening 2D materials by intercalation can change the band filling state and the Fermi level. This review mainly focuses on the opening of 2D materials and their subsequent applications in energy conversion and storage fields, expecting to promote the development of such a new class of materials, namely expanded 2D materials. The exciting progresses of these expanded materials made in both energy conversion and storage devices including solar cells, thermoelectric devices, electrocatalyst, supercapacitors and rechargeable batteries, is presented and discussed in depth. Furthermore, prospects and further developments in these exciting fields of the expanded 2D materials are also commented.

273 citations

Journal ArticleDOI
01 Aug 2018-Small
TL;DR: Recent advances of air electrodes from bifunctional catalysts to architectures are summarized, and their advantages and disadvantages are discussed to underline the importance of progress in the evolution of bifunctionsal air electrodes.
Abstract: Large-scale application of renewable energy and rapid development of electric vehicles have brought unprecedented demand for advanced energy-storage/conversion technologies and equipment Rechargeable zinc (Zn)-air batteries represent one of the most promising candidates because of their high energy density, safety, environmental friendliness, and low cost The air electrode plays a key role in managing the many complex physical and chemical processes occurring on it to achieve high performance of Zn-air batteries Herein, recent advances of air electrodes from bifunctional catalysts to architectures are summarized, and their advantages and disadvantages are discussed to underline the importance of progress in the evolution of bifunctional air electrodes Finally, some challenges and the direction of future research are provided for the optimized design of bifunctional air electrodes to achieve high performance of rechargeable Zn-air batteries

157 citations

Journal ArticleDOI
TL;DR: In this paper, the inverse-opal-structured hybrid of N, S-codoped carbon-confined Co9S8 nanoparticles for high-efficient bifunctional electrocatalysts at air-cathode and polyacrylamide-co-polyacrylic acid alkalinous hydrogel of high ion-conductivity and water holding power for solid electrolyte, on-chip all-solid-state rechargeable Zn-air batteries (OAR-ZABs) are developed.
Abstract: Through the combination of inverse-opal-structured hybrids of N, S-codoped-carbon-confined Co9S8 nanoparticles for high-efficient bifunctional electrocatalysts at air-cathode and polyacrylamide-co-polyacrylic acid alkalinous hydrogel of high ion-conductivity and water holding power for solid electrolyte, on-chip all-solid-state rechargeable Zn-air batteries (OAR-ZABs) are developed. The OAR-ZABs acquire a higher open circuit potential of 1.408 V, larger specific capacity of 738 mA h g−1, and better rechargeability (105 cycles/35 h) compared with most reported devices employing traditional PVA basic hydrogel electrolyte. The exhibited areal/specific energy densities (7.53 mW h cm−2/900.4 Wh kg−1) also outperform the values of competitors such as micro-supercapacitors (≤0.01 mW h cm−2) and Li-ion batteries (≤200 Wh kg−1). Furthermore, the reasonable in-plane electrode deployment endows the OAR-ZABs with good coplanar integration capability and high flexibility, allowing in-plane series/parallel connection to output required voltage/current and working stably at different bending angles. Combined with the other advantages including its miniaturization and the inherent security of employed hydrogel electrolyte, the OAR-ZABs are ideally suitable for wearable applications. As a demo, a flexible OAR-ZABs array in series connection is fabricated and conformally sewed on clothes, being safely used to charge the smart phone or light the safety warning device. All these make them competitive micro-power sources for wearable microelectronics.

143 citations

References
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Journal ArticleDOI
06 Feb 2009-Science
TL;DR: It is reported that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells.
Abstract: The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of –80 millivolts and a current density of 4.1 milliamps per square centimeter at –0.22 volts, compared with –85 millivolts and 1.1 milliamps per square centimeter at –0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.

6,370 citations

Journal ArticleDOI
22 Apr 2011-Science
TL;DR: A family of non–precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power.
Abstract: The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non-precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).

3,464 citations

Journal Article
TL;DR: In this article, a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power.
Abstract: Fuel cell catalysts synthesized from abundant metals approach the performance and durability of platinum at lower cost. The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non–precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non–precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).

2,974 citations

Journal ArticleDOI
TL;DR: It is shown that few-walled carbon nanotubes, following outer wall exfoliation via oxidation and high-temperature reaction with ammonia, can act as an oxygen reduction reaction electrocatalyst in both acidic and alkaline solutions.
Abstract: Oxygen reduction reaction catalysts based on precious metals such as platinum or its alloys are routinely used in fuel cells because of their high activity. Carbon-supported materials containing metals such as iron or cobalt as well as nitrogen impurities have been proposed to increase scalability and reduce costs, but these alternatives usually suffer from low activity and/or gradual deactivation during use. Here, we show that few-walled carbon nanotubes, following outer wall exfoliation via oxidation and high-temperature reaction with ammonia, can act as an oxygen reduction reaction electrocatalyst in both acidic and alkaline solutions. Under a unique oxidation condition, the outer walls of the few-walled carbon nanotubes are partially unzipped, creating nanoscale sheets of graphene attached to the inner tubes. The graphene sheets contain extremely small amounts of irons originated from nanotube growth seeds, and nitrogen impurities, which facilitate the formation of catalytic sites and boost the activity of the catalyst, as revealed by atomic-scale microscopy and electron energy loss spectroscopy. Whereas the graphene sheets formed from the unzipped part of the outer wall of the nanotubes are responsible for the catalytic activity, the inner walls remain intact and retain their electrical conductivity, which facilitates charge transport during electrocatalysis.

1,471 citations

Journal ArticleDOI
TL;DR: The distinct properties resulting from various dopants, different doping levels and configurations, and synergistic effects from co-dopants are emphasized, hoping to assist a better understanding of doped graphene materials.
Abstract: Heteroatom doping can endow graphene with various new or improved electromagnetic, physicochemical, optical, and structural properties. This greatly extends the arsenal of graphene materials and their potential for a spectrum of applications. Considering the latest developments, we comprehensively and critically discuss the syntheses, properties and emerging applications of the growing family of heteroatom-doped graphene materials. The advantages, disadvantages, and preferential doping features of current synthesis approaches are compared, aiming to provide clues for developing new and controllable synthetic routes. We emphasize the distinct properties resulting from various dopants, different doping levels and configurations, and synergistic effects from co-dopants, hoping to assist a better understanding of doped graphene materials. The mechanisms underlying their advantageous uses for energy storage, energy conversion, sensing, and gas storage are highlighted, aiming to stimulate more competent applications.

1,440 citations