Zn-air batteries have attracted significant attention because of their high energy density, environmental friendliness, safety, and low cost. The air cathode of is one of the most expensive cell ...components and a key factor in determining the performance of Zn-air batteries. As a fuel, O
2
availability to the air cathode is determined by the level of both its dissolution and diffusion in an electrolyte, whereby electrocatalysis happens in the three-phase interface where the catalyst, electrolyte, and O
2
meet. Maximizing the performance of air cathodes by rational design of the catalyst structure is of significant importance. To date, various electrocatalysts, including heteroatom-doped carbon, transition metal nitrides/oxides/sulfides, and perovskite oxides, have been developed with outstanding oxygen reduction reaction and oxygen evolution activity. More and more researchers are trying to apply electrocatalysts into Zn-air battery prototypes. The aim of this review is to afford a better understanding of air cathodes and provide guidelines to the researchers for the design and construction of high-performance, easy-to-use cathodes for metal-air batteries.
This review addresses the importance of the air-electrode structure and the microstructures of the catalyst for rechargeable zinc-air batteries.
Two-dimensional (2D) metal-organic framework (MOF) nanosheets have been recently regarded as the model electrocatalysts due to their porous structure, fast mass and ion transfer through the ...thickness, and large portion of exposed active metal centers. Combining them with electrically conductive 2D nanosheets is anticipated to achieve further improved performance in electrocatalysis. In this work, we in situ hybridized 2D cobalt 1,4-benzenedicarboxylate (CoBDC) with Ti3C2Tx (the MXene phase) nanosheets via an interdiffusion reaction-assisted process. The resulting hybrid material was applied in the oxygen evolution reaction and achieved a current density of 10 mA cm-2 at a potential of 1.64 V vs reversible hydrogen electrode and a Tafel slope of 48.2 mV dec-1 in 0.1 M KOH. These results outperform those obtained by the standard IrO2-based catalyst and are comparable with or even better than those achieved by the previously reported state-of-the-art transition-metal-based catalysts. While the CoBDC layer provided the highly porous structure and large active surface area, the electrically conductive and hydrophilic Ti3C2Tx nanosheets enabled the rapid charge and ion transfer across the well-defined Ti3C2Tx-CoBDC interface and facilitated the access of aqueous electrolyte to the catalytically active CoBDC surfaces. The hybrid nanosheets were further fabricated into an air cathode for a rechargeable zinc-air battery, which was successfully used to power a light-emitting diode. We believe that the in situ hybridization of MXenes and 2D MOFs with interface control will provide more opportunities for their use in energy-based applications.
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IJS, KILJ, NUK, PNG, UL, UM
We present two different ways to fabricate nitrogen-doped graphene (N-graphene) and demonstrate its use as a metal-free catalyst to study the catalytic active center for the oxygen reduction reaction ...(ORR). N-graphene was produced by annealing of graphene oxide (G-O) under ammonia or by annealing of a N-containing polymer/reduced graphene oxide (RG-O) composite (polyaniline/RG-O or polypyrrole/RG-O). The effects of the N precursors and annealing temperature on the performance of the catalyst were investigated. The bonding state of the N atom was found to have a significant effect on the selectivity and catalytic activity for ORR. Annealing of G-O with ammonia preferentially formed graphitic N and pyridinic N centers, while annealing of polyaniline/RG-O and polypyrrole/RG-O tended to generate pyridinic and pyrrolic N moieties, respectively. Most importantly, the electrocatalytic activity of the catalyst was found to be dependent on the graphitic N content which determined the limiting current density, while the pyridinic N content improved the onset potential for ORR. However, the total N content in the graphene-based non-precious metal catalyst does not play an important role in the ORR process.
N-doped hollow carbon nanospheres (NHCS) with mesoporous carbon shells is selected as nanoreactors and encapsulated with few-layered MoS2 nanosheets to monitor its electrochemical properties and ...structural conversion in long-term cycling. Mesoporous walls of NHCS can facilitate electrolyte penetration and provide conductive shells for superior mass diffusion and charge transfer. When serving as SIB anodes, MoS2@NHCS has a capacity value of 371 mAh g-1 at 1 A g-1 with a capacity retention of 94.9% after 100 cycles which is higher than powder form MoS2 and is among the highest values of earlier reported MoS2 electrodes. The origin of gradual capacity decay of MoS2@NHCS anodes in-between 50 to 150 cycles has been investigated. Transmission electron microscopy and ex-situ X-ray diffraction have shown significant morphology change of space-confined MoS2 and the production of MoO3 together with oxygen-deficient MoOx after continuous charge/discharge test. After long-term cycle test of MoS2@NHCS, the ratios of Mo6+ and Mo5+ increased significantly with the decreasing of Mo4+ ratio, while the sulfur from MoS2 transformed from S2− to SO42−. This work highlight the phase transformation and composition change of MoS2 for MoS2-based anode in long-duration charge/discharge tests.
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•Few-layered MoS2 nanosheets spaced-confined in N-doped hollow carbon nanospheres (NHCS) as sodium-ion battery anodes.•MoS2@NHCS has a capacity value of 371 mAh g-1 at 1 A g-1 with a capacity retention of 94.9% after 100 cycles.•The sodiation of MoS2 nanosheets created irreversible phase and composition change with sodiation mechanism in long-term cycling proposed.•After long-term cycling, the ratios of Mo6+ and Mo5+ of MoS2@NHCS increased significantly with the decreasing of Mo4+ratio.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Besides catalyzing the oxygen reduction and evolution, the catalyst structure of O2-electrodes plays an important role in the mass transfer and reversible conversion of the discharge products. This ...review provides a comprehensive overview of the O2-electrodes for Li-O2 batteries, with an emphasis on the electrodes synthesis, working mechanism and overall performance evaluation.
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•Challenges and future of the hierarchical O2-cathode for nonaqueous Li-O2 batteries.•The charge and discharge mechanism for Li-O2 batteries and O2-cathode performance evaluation.•The recent significant research progress in the hierarchically structured O2-cathode for Li-O2 battery.•The catalysts selection and state-of-the-art electrode structure design for Li-O2 cathodes.
In the last decade, Li-O2 batteries have been a research focus due to its ultrahigh energy density as chemical power sources and being rechargeable through oxygen reduction and evolution reactions. Besides catalyzing the oxygen reduction and evolution, the rationally designed air-cathode to accommodate the insoluble discharge products and allow efficient transfer of reactants is critical for Li-O2 batteries. To date, the development of a wide variety of electrocatalyst has driven the application-directed research in Li-O2 batteries. This review provides a comprehensive overview of the O2-electrodes for Li-O2 batteries, with an emphasis on the O2-electrodes synthesis, working mechanism, and overall performance evaluation. The aim of this review is to afford a better understanding of Li-O2 cathodes and to provide guidelines for researchers to design and construct high-performance, easy-to-use cathodes for Li-O2 batteries.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this paper, using Ni3S2@MoS2 as an example, we report the successful design and synthesis of a novel hybrid core/shell metal sulfides with a conductive Ni3S2 core by a green, scalable and one-step ...solution strategy. When they are tested as supercapacitor electrodes, the Ni3S2@MoS2 heterostructure exhibits about 2 times the capacitance (848Fg−1) compared to the pristine Ni3S2 sample (425Fg−1), excellent rate capability (46.6% capacity retention at 20Ag−1) and outstanding cycling stability (91% retention after 2000 cycles). The enhancement is ascribed to the robust hierarchical core/shell structures which provide an increased reaction area and a close contact of electrolyte with the active material. In addition, a highly conductive 1D core material endows the quick transport of electrons along Ni3S2 nanorods to Ni foam. It is prospected that such novel hybrids can offer great potential promise in large-scale energy storage device applications.
One-dimensional hierarchical Ni3S2@MoS2 core/shell nanorod arrays on Ni foam synthesized using a one-step hydrothermal method exhibit a higher specific capacitance with better cycling performance than bare Ni3S2 sample. Display omitted
•A facile but powerful method is designed to grow Ni3S2@MoS2 core/shell nanoarrays on Ni foam.•Ni3S2@MoS2 heterostructure exhibits better performance than bare Ni3S2 sample.•Such novel hybrids can offer great potential promise in large-scale energy storage applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Many researchers have used nitrogen (N) as a dopant and/or N-containing functional groups to enhance the capacitance of carbon electrodes of electrical double layer (EDL) capacitors. However, the ...physical mechanism(s) giving rise to the interfacial capacitance of the N-containing carbon electrodes is not well understood. Here, we show that the area-normalized capacitance of lightly N-doped activated graphene with similar porous structure increased from 6 mu F cm super(-2) to 22 mu F cm super(-2) with 0 at%, and 2.3 at% N-doping, respectively. The quantum capacitance of pristine single layer graphene and various N-doped graphene was measured and a trend of upwards shifts of the Dirac Point with increasing N concentration was observed. The increase in bulk capacitance with increasing N concentration, and the increase of the quantum capacitance in the N-doped monolayer graphene versuspristine monolayer graphene suggests that the increase in the EDL type of capacitance of many, if not all, N-doped carbon electrodes studied to date, is primarily due to the modification of the electronic structure of the graphene by the N dopant. It was further found that the quantum capacitance is closely related to the N dopant concentration and N-doping provides an effective way to increase the density of the states of monolayer graphene.
Graphene exhibits many unique electronic properties owing to its linear dispersive electronic band structure around the Dirac point, making it one of the most studied materials in the last 5‐6 years. ...However, for many applications of graphene, further tuning its electronic band structure is necessary and has been extensively studied ever since graphene was first isolated experimentally. Here we review the major progresses made in electronic structure engineering of graphene, namely by electric and magnetic fields, chemical intercalation and adsorption, stacking geometry, edge‐chirality, defects, as well as strain.
Tuning the electronic band structure of graphene is of great importance for its application in electronic devices. In this paper, we review the recent progress in electronic structure engineering of graphene, by applying electric and magnetic fields, introducing chemical intercalation and adsorption, changing stacking geometry and edge structure, introducing defects, as well as applying strain.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A lightweight, flexible, and highly efficient energy management strategy is highly desirable for flexible electronic devices to meet a rapidly growing demand. Herein, Ni–Co–S nanosheet array is ...successfully deposited on graphene foam (Ni–Co–S/GF) by a one‐step electrochemical method. The Ni–Co–S/GF composed of Ni–Co–S nanosheet array which is vertically aligned to GF and provides a large interfacial area for redox reactions with optimum interstitials facilitates the ions diffusion. The Ni–Co–S/GF electrodes have high specific capacitance values of 2918 and 2364 F g−1 at current densities of 1 and 20 A g−1, respectively. Using such hierarchical Ni–Co–S/GF as the cathode, a flexible asymmetric supercapacitor (ASC) is further fabricated with polypyrrple(PPy)/GF as the anode. The flexible asymmetric supercapacitors have maximum operation potential window of 1.65 V, and energy densities of 79.3 and 37.7 Wh kg−1 when the power densities are 825.0 and 16100 W kg−1, respectively. It's worth nothing that the ASC cells have robust flexibility with performance well maintained when the devices were bent to different angles from 180° to 15° at a duration of 5 min. The efficient electrochemical deposition method of Ni–Co–S with a preferred orientation of nanosheet arrays is applicable for the flexible energy storage devices.
The Ni–Co–S nanosheet arrays have been successfully deposited on 3D porous graphene by electrochemical method, which presents excellent electrochemical performance. Flexible, robust supercapacitor devices with Ni–Co–S/graphene foam cathode and polypyrrole/graphene foam anode have been demonstrated with their electrochemical performance systematically evaluated.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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