Nitrogen-doped graphene nanosheets as cathode materials with excellent electrocatalytic activity for high capacity lithium-oxygen batteries

Novel and Highly Sensitive Electrochemical Sensor for the Determination of Oxytetracycline Based on Fluorine-Doped Activated Carbon and Hydrophobic Deep Eutectic Solvents

Residues of oxytetracycline (OTC), a veterinary antibiotic and growth promoter, can be present in animal-derived foods; their consumption is harmful to human health and their presence must therefore be detected and regulated. However, the maximum residue limit is low, and consequently highly sensitive and accurate detectors are required to detect the residues. In this study, a novel highly sensitive electrochemical sensor for the detection of OTC was developed using a screen-printed electrode modified with fluorine-doped activated carbon (F-AC/SPE) combined with a novel deep eutectic solvent (DES). The modification of activated carbon by doping with fluorine atoms (F-AC) enhanced the adsorption and electrical activity of the activated carbon. The novel hydrophobic DES was prepared from tetrabutylammonium bromide (TBABr) and a fatty acid (malonic acid) using a green synthesis method. The addition of the DES increased the electrochemical response of F-AC for OTC detection; furthermore, it induced preconcentration of OTC, which increased its detectability. The electrostatic interactions between DES and OTC as well as the adsorption of OTC on the surface of the modified electrode through H-bonding and π-π interactions helped in OTC detection, which was quantified based on the decrease in the anodic peak potential (E _pa = 0.3 V) of AC. The electrochemical behavior of the modified electrode was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Under optimum conditions, the calibration plot of OTC exhibited a linear response in the range 5-1500 μg L^-1, with a detection limit of 1.74 μg L^-1. The fabricated electrochemical sensor was successfully applied to determine the OTC in shrimp pond and shrimp samples with recoveries of 83.8-100.5% and 93.3-104.5%, respectively. In addition to the high sensitivity of OTC detection, the proposed electrochemical sensor is simple, cost-effective, and environmentally friendly.

A Review of High-Energy Density Lithium-Air Battery Technology: Investigating the Effect of Oxides and Nanocatalysts

In vehicles that require a lot of electricity, such as electric vehicles, it is necessary to use high-energy batteries. Among the developed batteries, the lithium-ion battery has shown better performance. This battery has an energy density of 10 equal to that of a lithium-ion battery and uses air oxygen as the active material of the cathode and anode like a lithium-ion battery made of lithium metal. The cathode used in these batteries must have special properties such as strong catalytic activity and high conductivity, and nanotechnology has greatly helped to improve the materials used in the cathode of lithium-air batteries. The importance of proper catalyst distribution and the relationship between the oxide product and the catalyst and the indirect effect of the ORR catalyst on the OER reaction is not present in the fuel cell. The maximum capacity of lithium-air battery theory using graphene under optimal electron conduction conditions and the experimental maximum obtained for graphene by optimizing the structure geometry, examples of structural engineering using carbon fiber and carbon nanotubes in cathode fabrication with the ability to perform the reaction properly while providing space for lithium oxide placement, are examined. This article describes the mechanism of this battery, and its components are examined. The challenges of using this battery and the application of nanotechnology to solve these challenges are also discussed.

Design Principles of Nitrogen-doped Graphene Nanoribbons as Highly Effective Bifunctional Catalysts for Li - O2 Batteries

Li-O2 batteries are promising candidates in fields demanding high capacities like electric vehicles due to their superior theoretical energy density in contrast to lithium-ion batteries. However, oxygen reduction reaction (ORR)...

Single-side functionalized graphene as promising cathode catalysts in nonaqueous lithium-oxygen batteries

High-performance cathode catalysts are always desirable for nonaqueous lithium-oxygen (Li-O₂) batteries. Using density functional theory calculations, the structural, electronic, and magnetic properties of SSX-Gr with different C/X ratios (X = H or F) are systematically studied. Then, a detailed mechanism on the dissociation of O₂ and the migration of Li on the SSX-Gr is revealed, based on which C₆X and C₈X are confirmed as the potential candidates as cathode catalysts. The studies on reaction pathways suggest that the four-electron pathway is the more possible catalytic pathway for the selected SSX-Gr. The free energy diagrams for discharging and charging processes catalyzed by SSX-Gr reveal that C₆F exhibits the highest application potential due to its considerably low oxygen reduction overpotential (0.83 V) and oxygen evolution overpotential (1.47 V). The extra spins induced by single-side functionalization endow graphene with the electrocatalytic activity.

Application of functionalized graphene in Li-O2 batteries

Li-O₂ batteries (LOB) are considered as one of the most promising energy storage devices using renewable electricity to power electric vehicles because of its exceptionally high energy density. Carbon materials have been widely employed in LOB for its light weight and facile availability. In particular, graphene is a suitable candidate due to its unique two-dimensional structure, high conductivities, large specific surface areas, and good stability at high charge potential. However, the intrinsic catalytic activity of graphene is insufficient for the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in LOB. Therefore, various surface functionalization schemes for graphene have been developed to tailor the surface chemistry of graphene. In this review, the properties and performances of functionalized graphene cathodes are discussed from theoretical and experimental aspects, including heteroatomic doping, oxygen functional group modifications, and catalyst decoration. Heteroatomic doping breaks electric neutrality of sp² carbon of graphene, which forms electron-deficient or electron-rich sites. Oxygen functional groups mainly create defective edges on graphene oxides with C-O, C=O, and -COO-. Catalyst decoration is widely attempted by various transition and precious metal and metal oxides. These induced reactive sites usually improve the ORR and/or OER in LOB by manipulating the adsorption energies of O₂, LiO₂, Li₂O₂, and promoting electron transportation of cathode. In addition, functionalized graphene is used in anode and separators to prevent shuttle effect of redox mediators and suppress growth of Li dendrite.

Polyelemental Nanoparticles as Catalysts for a Li-O2 Battery

The development of highly efficient catalysts in the cathodes of rechargeable Li-O₂ batteries is a considerable challenge. Polyelemental catalysts consisting of two or more kinds of hybridized catalysts are particularly interesting because the combination of the electrochemical properties of each catalyst component can significantly facilitate oxygen evolution and oxygen reduction reactions. Despite the recent advances that have been made in this field, the number of elements in the catalysts has been largely limited to two metals. In this study, we demonstrate the electrochemical behavior of Li-O₂ batteries containing a wide range of catalytic element combinations. Fourteen different combinations with single, binary, ternary, and quaternary combinations of Pt, Pd, Au, and Ru were prepared on carbon nanofibers (CNFs) via a joule heating route. Importantly, the Li-O₂ battery performance could be significantly improved when using a polyelemental catalyst with four elements. The cathode containing quaternary nanoparticles (Pt-Pd-Au-Ru) exhibited a reduced overpotential (0.45 V) and a high discharge capacity based on total cathode weight at 9130 mAh g^-1, which was ∼3 times higher than that of the pristine CNF electrode. This superior electrochemical performance is be attributed to an increased catalytic activity associated with an enhanced O₂ adsorbability by the quaternary nanoparticles.

An Overview of Engineered Graphene-Based Cathodes: Boosting Oxygen Reduction and Evolution Reactions in Lithium- and Sodium-Oxygen Batteries

The depletion of fossil fuels, the rapid evolution of the global economy, and high living standards require the development of new energy-storage systems that can meet the needs of the world's population. Metal-oxygen batteries (M=Li, Na) arise, therefore, as promising alternatives to widely used lithium-ion batteries, due to their high theoretical energy density, which approaches that of gasoline. Although significant progress has been made in recent years, there are still several challenges to overcome to reach the final commercialization of this technology. One of the most limiting and challenging factors is the development of bifunctional cathodes towards oxygen reduction and evolution reactions. In this sense, graphene, which is very promising and tunable, has been widely explored by the research community as a key material for this technology. Herein, a wide literature overview is presented and analyzed with the aim of guiding future research in this field.

2 D Materials for Electrochemical Energy Storage: Design, Preparation, and Application

Electrochemical energy storage is a promising route to relieve the increasing energy and environment crises, owing to its high efficiency and environmentally friendly nature. However, it is still challenging to realize its widespread application because of unsatisfactory electrode materials, with either high cost or poor activity and new electrode materials are urgently needed. Two-dimensional (2 D) materials are possible candidates, owing to their unique geometry and physicochemical properties. This Review summarizes the latest advances in the development of 2 D materials for electrochemical energy storage. Computational investigation and design of 2 D materials are first introduced, and then preparation methods are presented in detail. Next, the application of such materials in supercapacitors, alkali metal-ion batteries, and metal-air batteries are summarized comprehensively. Finally, the challenges and perspectives are discussed to offer a guideline for future exploration of high-efficiency 2 D materials for electrochemical energy storage.

Defect Engineering on Electrode Materials for Rechargeable Batteries

The reasonable design of electrode materials for rechargeable batteries plays an important role in promoting the development of renewable energy technology. With the in-depth understanding of the mechanisms underlying electrode reactions and the rapid development of advanced technology, the performance of batteries has significantly been optimized through the introduction of defect engineering on electrode materials. A large number of coordination unsaturated sites can be exposed by defect construction in electrode materials, which play a crucial role in electrochemical reactions. Herein, recent advances regarding defect engineering in electrode materials for rechargeable batteries are systematically summarized, with a special focus on the application of metal-ion batteries, lithium-sulfur batteries, and metal-air batteries. The defects can not only effectively promote ion diffusion and charge transfer but also provide more storage/adsorption/active sites for guest ions and intermediate species, thus improving the performance of batteries. Moreover, the existing challenges and future development prospects are forecast, and the electrode materials are further optimized through defect engineering to promote the development of the battery industry.

Room-temperature reduction of NO2 in a Li-NO2 battery: a proof of concept

Although considerable effort has been devoted to purifying nitrogen oxides (NO_x), it is still challenging to effectively reduce NO_x at room temperature and ambient pressure without catalysts. In this study, as a proof-of-concept, we have for the first time demonstrated the room-temperature reduction of nitrogen dioxide (NO₂) using a rechargeable lithium-nitrogen dioxide (Li-NO₂) battery. The battery shows a capacity of 884 mAh g^-1 at 50 mA g^-1 (an actual energy density of 666 Wh kg^-1) and a promising electrochemical Faraday efficiency (FE) of 67%. The unique properties of Li-NO₂ rechargeable batteries not only provide a way to reduce and recycle NO₂ but also highlight the potential of oxidative air pollutants as energy sources for next-generation electrochemical energy storage (EES) systems.

Mechanism of Ionic Impedance Growth for Palladium-Containing CNT Electrodes in Lithium-Oxygen Battery Electrodes and its Contribution to Battery Failure

The electrochemical oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) and on CNT (carbon nanotube) cathode with a palladium catalyst, palladium-coated CNT (PC-CNT), and palladium-filled CNT (PF-CNT) are assessed in an ether-based electrolyte solution in order to fabricate a lithium-oxygen battery with high specific energy. The electrochemical properties of the CNT cathodes were studied using electrochemical impedance spectroscopy (EIS). Palladium-filled cathodes displayed better performance as compared to the palladium-coated ones due to the shielding of the catalysts. The mechanism of the improvement was associated to the reduction of the rate of resistances growth in the batteries, especially the ionic resistances in the electrolyte and electrodes. The scanning electron microscopy (SEM) and spectroscopy were used to analyze the products of the reaction that were adsorbed on the electrode surface of the battery, which was fabricated using palladium-coated and palladium-filled CNTs as cathodes and an ether-based electrolyte.

New Class of Electrocatalysts Based on 2D Transition Metal Dichalcogenides in Ionic Liquid

The optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics of different elementary reaction steps, non-Nernstian behavior, and electronic structure of the catalyst. This indicates that the currently utilized classes of electrocatalysts may not be adequate for future needs. This study reports on synthesis and characterization of a new class of materials based on 2D transition metal dichalcogenides including sulfides, selenides, and tellurides of group V and VI transition metals that exhibit excellent catalytic performance for both oxygen reduction and evolution reactions in an aprotic medium with Li salts. The reaction rates are much higher for these materials than previously reported catalysts for these reactions. The reasons for the high activity are found to be the metal edges with adiabatic electron transfer capability and a cocatalyst effect involving an ionic-liquid electrolyte. These new materials are expected to have high activity for other core electrocatalytic reactions and open the way for advances in energy storage and catalysis.

Self-Nitrogen-Doped Carbon from Plant Waste as an Oxygen Electrode Material with Exceptional Capacity and Cycling Stability for Lithium-Oxygen Batteries

To promote the development of electric automobiles, high energy density and high-power batteries are urgently needed. More and more attention has been paid to look for high-performance cathode catalysts for Li-O₂ batteries. However, the sluggish kinetic reaction, the stacking of electrical insulation product of Li₂O₂, and the undesired parasitic reaction restrict their capacity and present poor cycling performance. Here, we prepared nitrogen self-doped activated carbons (N-PIACs) derived from the plant waste (poplar inflorescence) through the activation and slow pyrolysis carbonization method, exhibiting several advantages. The materials presented a three-dimensional interconnecting pore structure and a high surface area. Besides, defects and functional groups doped by nitrogen as active sites improved electrochemical catalysis activity. The Li∥N-PIACs-O₂ battery delivered a high specific capacity of 12060 mAh/g, which was 2.3 times that of the pristine plant waste-based Li-O₂ battery (N-PICs). In addition, it presented more excellent cycling stability than other common carbon materials. In this study, we developed a functional carbon nanomaterial from cheap natural materials, which might become a highly attractive subject, indicating that this strategy could strengthen the properties of Li-O₂ batteries.

New Application of Waste Citrus Maxima Peel-Derived Carbon as an Oxygen Electrode Material for Lithium Oxygen Batteries

Recently, lithium oxygen battery has become a promising candidate to satisfy the current large-energy-storage devices demand because of its amazing theoretical energy density. However, it still faces problems such as poor reversibility and short cycle life. Here, citrus maxima peel (CMP) was used as a precursor to prepare activated and Fe-loading carbon (CMPACs and CMPACs-Fe, respectively) via pyrolysis in nitrogen atmosphere at 900 °C, in which KOH was added as an activator. Electrochemical measurements show that CMPAC-based Li-O₂ battery possesses high specific capacity of 7800 mA h/g, steady cycling performance of 466 cycles with a corresponding Coulombic efficiency of 92.5%, good rate capability, and reversibility. Besides, CMPACs-Fe-based O₂ electrode delivers even lower overpotential in both charge and discharge processes. We conclude that these excellent electrochemical performances of CMPACs and CMPACs-Fe-based O₂ electrode benefit from their cellular porous structure, plenty of active sites, and large specific surface area (900 and 768 m²/g), which suggest that these biomass-derived porous carbons might become promising candidates to achieve efficient lithium oxygen battery.

CxNy particles@N-doped porous graphene: a novel cathode catalyst with a remarkable cyclability for Li-O2 batteries

Despite the intrinsic advantages of ultra-high theoretical capacity and energy density of lithium-O2 batteries, there remain several critical issues to be resolved, especially the two concerning poor cyclability and rate capability. In this work, CxNy particles@N-doped porous graphene (CxNy@NPG) with a novel three-dimensional architecture is successfully synthesized via a simple template method and employed as the cathode catalyst of Li-O2 batteries. It is surprisingly found that the as-synthesized CxNy@NPG cathode not only demonstrates a remarkable cycling performance of 200 cycles at 1000 mA g-1 but also an intriguing high-rate capability with 8892 mA h g-1 at 1000 mA g-1, both of which can be attributed to a synergistic effect between the unique 3D porous structure and an effective N-doping. Specifically, it is believed that the unique porous 3D structure will, on one hand, build numerous microchannels, thus facilitating rapid O2 diffusion, and on the other hand, provide sufficient storage space to accommodate adequate discharge products. Indispensably, it is also believed that the N-doped porous graphene enables improved bifunctional catalytic activities towards both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), thus decreasing the discharge/charge overpotential, and reducing undesired side reactions. It is anticipated that the new 3D porous CxNy@NPG provides an inspiring route to design long cycling and high-rate performance cathodes for Li-O2 batteries.

Strategies toward High-Performance Cathode Materials for Lithium-Oxygen Batteries

Rechargeable aprotic lithium (Li)-O₂ batteries with high theoretical energy densities are regarded as promising next-generation energy storage devices and have attracted considerable interest recently. However, these batteries still suffer from many critical issues, such as low capacity, poor cycle life, and low round-trip efficiency, rendering the practical application of these batteries rather sluggish. Cathode catalysts with high oxygen reduction reaction (ORR) and evolution reaction activities are of particular importance for addressing these issues and consequently promoting the application of Li-O₂ batteries. Thus, the rational design and preparation of the catalysts with high ORR activity, good electronic conductivity, and decent chemical/electrochemical stability are still challenging. In this Review, the strategies are outlined including the rational selection of catalytic species, the introduction of a 3D porous structure, the formation of functional composites, and the heteroatom doping which succeeded in the design of high-performance cathode catalysts for stable Li-O₂ batteries. Perspectives on enhancing the overall electrochemical performance of Li-O₂ batteries based on the optimization of the properties and reliability of each part of the battery are also made. This Review sheds some new light on the design of highly active cathode catalysts and the development of high-performance lithium-O₂ batteries.

Doped boron nitride surfaces: potential metal free bifunctional catalysts for non-aqueous Li-O2 batteries

The development of novel cathode catalysts is crucial for the practical application of lithium-oxygen (Li-O2) batteries. In this paper, we have evaluated the catalytic mechanism and activity of doped hexagonal boron nitride (h-BN) surfaces as cathode catalysts for nonaqueous Li-O2 batteries. From the free energy diagrams it is evident that the CN doped h-BN surface shows the best catalytic activity among the others and this arises due to its considerably lower oxygen reduction reaction (ORR) overpotential and lower oxygen evolution reaction (OER) overpotential. This is due to the weaker binding of the first product (LiO2) and stronger binding with the inserted Li atom. The computations predict that among the considered doped h-BN surfaces, the CN doped h-BN surface can be an efficient metal-free cathode material for nonaqueous Li-O2 batteries.

Long-life sodium/carbon fluoride batteries with flexible, binder-free fluorinated mesocarbon microbead film electrodes

Flexible, binder-free F-MCMB film electrodes enhance the cycle stability and achieve the longest lifespan reported thus far in sodium batteries.

Platinum-free, graphene based anodes and air cathodes for single chamber microbial fuel cells

Microbial fuel cells (MFCs) exploit the ability of microorganisms to generate electrical power during metabolism of substrates. However, the low efficiency of extracellular electron transfer from cells to the anode and the use of expensive rare metals as catalysts, such as platinum, limit their application and scalability. In this study we investigate the use of pristine graphene based electrodes at both the anode and the cathode of a MFC for efficient electrical energy production from the metabolically versatile bacterium Rhodopseudomonas palustris CGA009. We achieve a volumetric peak power output (PV) of up to 3.51 ± 0.50 W m-3 using graphene based aerogel anodes with a surface area of 8.2 m2 g-1. We demonstrate that enhanced MFC output arises from the interplay of the improved surface area, enhanced conductivity, and catalytic surface groups of the graphene based electrode. In addition, we show a 500-fold increase in PV to 1.3 ± 0.23 W m-3 when using a graphene coated stainless steel (SS) air cathode, compared to an uncoated SS cathode, demonstrating the feasibility of a platinum-free, graphene catalysed MFCs. Finally, we show a direct application for microwatt-consuming electronics by connecting several of these coin sized devices in series to power a digital clock.

Solvent-Free Mechanochemical Synthesis of Nitrogen-Doped Nanoporous Carbon for Electrochemical Energy Storage

Nitrogen-doped nanoporous carbons were synthesized by a solvent-free mechanochemically induced one-pot synthesis. This facile approach involves the mechanochemical treatment and carbonization of three solid materials: potassium carbonate, urea, and lignin, which is a waste product from pulp industry. The resulting nitrogen-doped porous carbons offer a very high specific surface area up to 3000 m²  g^-1 and large pore volume up to 2 cm³  g^-1 . The mechanochemical reaction and the impact of activation and functionalization are investigated by nitrogen and water physisorption and high-resolution X-ray photoelectron spectroscopy (XPS). Our N-doped carbons are highly suitable for electrochemical energy storage as supercapacitor electrodes, showing high specific capacitances in aqueous 1 m Li₂ SO₄ electrolyte (177 F g^-1 ), organic 1 m tetraethylammonium tetrafluoroborate in acetonitrile (147 F g^-1 ), and an ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate; 192 F g^-1 ). This new mechanochemical pathway synergistically combines attractive energy-storage ratings with a scalable, time-efficient, cost-effective, and environmentally favorable synthesis.

Ultrahigh-Capacity Lithium-Oxygen Batteries Enabled by Dry-Pressed Holey Graphene Air Cathodes

Lithium-oxygen (Li-O₂) batteries have the highest theoretical energy density of all the Li-based energy storage systems, but many challenges prevent them from practical use. A major obstacle is the sluggish performance of the air cathode, where both oxygen reduction (discharge) and oxygen evolution (charge) reactions occur. Recently, there have been significant advances in the development of graphene-based air cathode materials with a large surface area and catalytically active for both oxygen reduction and evolution reactions, especially with additional catalysts or dopants. However, most studies reported so far have examined air cathodes with a limited areal mass loading rarely exceeding 1 mg/cm². Despite the high gravimetric capacity values achieved, the actual (areal) capacities of those batteries were far from sufficient for practical applications. Here, we present the fabrication, performance, and mechanistic investigations of high-mass-loading (up to 10 mg/cm²) graphene-based air electrodes for high-performance Li-O₂ batteries. Such air electrodes could be easily prepared within minutes under solvent-free and binder-free conditions by compression-molding holey graphene materials because of their unique dry compressibility associated with in-plane holes on the graphene sheet. Li-O₂ batteries with high air cathode mass loadings thus prepared exhibited excellent gravimetric capacity as well as ultrahigh areal capacity (as high as ∼40 mAh/cm²). The batteries were also cycled at a high curtailing areal capacity (2 mAh/cm²) and showed a better cycling stability for ultrathick cathodes than their thinner counterparts. Detailed post-mortem analyses of the electrodes clearly revealed the battery failure mechanisms under both primary and secondary modes, arising from the oxygen diffusion blockage and the catalytic site deactivation, respectively. These results strongly suggest that the dry-pressed holey graphene electrodes are a highly viable architectural platform for high-capacity, high-performance air cathodes in Li-O₂ batteries of practical significance.

Ultralong Cycle Life Achieved by a Natural Plant: Miscanthus × giganteus for Lithium Oxygen Batteries

Large energy-storage systems and electric vehicles require energy devices with high power and high energy density. Lithium oxygen (Li-O₂) batteries could achieve high energy density, but they are still facing problems such as low practical capacity and poor cyclability. Here, we prepare activated carbons (MGACs) based on the natural plant Miscanthus × giganteus (MG) through slow pyrolysis. It possesses a large surface area, plenty of active sites, and high porosity, which are beneficial to the utilization of oxygen electrode in Li-O₂ batteries. The MGACs-based oxygen electrode delivers a high specific capacity of 9400 mAh/g at 0.02 mA/cm², and long cycle life of 601 cycles (with a cutoff capacity of 500 mAh/g) and 295 cycles (with a cutoff capacity of 1000 mAh/g) at 0.2 mA/cm², respectively. Additionally, the material exhibits high rate capability and high reversibility, which is a promising candidate for the application in Li-O₂ batteries.

Perovskite-type La0.8Sr0.2Co0.8Fe0.2O3 with uniform dispersion on N-doped reduced graphene oxide as an efficient bi-functional Li–O2 battery cathode

A composite cathode including N-rGO with homogeneously dispersed perovskite La_0.8Sr_0.2Co_0.8Fe_0.2O₃ on the surface is studied.

NiMn2O4 as an efficient cathode catalyst for rechargeable lithium–air batteries

Intermediate spinel structured NiMn₂O₄-FT performs better than normal spinel oxide NiMn₂O₄-PH as a cathode bi-functional catalyst for Li–air batteries.

Monolayer germanium monochalcogenides (GeS/GeSe) as cathode catalysts in nonaqueous Li–O2batteries

The possibility of using 2D-GeSe/GeS as a cathode catalyst for nonaqueous Li–O₂batteries is computationally confirmed.

A highly efficient bifunctional heterogeneous catalyst for morphological control of discharged products in Na–air batteries

Heterogeneous compounds of Co₃O₄ and liquid ferrocene as an air catalyst show an excellent cycle performance of up to 570 cycles.

Facile Synthesis of Boron-Doped rGO as Cathode Material for High Energy Li-O2 Batteries

To improve the electrochemical performance of the high energy Li-O2 batteries, it is important to design and construct a suitable and effective oxygen-breathing cathode. Herein, a three-dimensional (3D) porous boron-doped reduction graphite oxide (B-rGO) material with a hierarchical structure has been prepared by a facile freeze-drying method. In this design, boric acid as the boron source helps to form the 3D porous structure, owing to its cross-linking and pore-forming function. This architecture facilitates the rapid oxygen diffusion and electrolyte penetration in the electrode. Meanwhile, the boron-oxygen functional groups linking to the carbon surface or edge serve as additional reaction sites to activate the ORR process. It is vital that boron atoms have been doped into the carbon lattices to greatly activate the electrons in the carbon π system, which is beneficial for fast charge under large current densities. Density functional theory calculation demonstrates that B-rGO exhibits much stronger interactions with Li5O6 clusters, so that B-rGO more effectively activates Li-O bonds to decompose Li2O2 during charge than rGO does. With B-rGO as a catalytic substrate, the Li-O2 battery achieves a high discharge capacity and excellent rate capability. Moreover, catalysts could be added into the B-rGO substrate to further lower the overpotential and enhance the cycling performance in future.

First-Principles Design of Graphene-Based Active Catalysts for Oxygen Reduction and Evolution Reactions in the Aprotic Li-O2 Battery

Using first-principles density functional theory (DFT) calculations, we demonstrate that catalytic activities toward oxygen reduction and evolution reactions (ORR and OER) in a Li-O2 battery can be substantially improved with graphene-based materials. We accomplish the goal by calculating free energy diagrams for the redox reactions of oxygen to identify a rate-determining step controlling the overpotentials. We unveil that the catalytic performance is well described by the adsorption energies of the intermediates LiO2 and Li2O2 and propose that graphene-based materials can be substantially optimized through either by N doping or encapsulating Cu(111) single crystals. Furthermore, our systematic approach with DFT calculations applied to design of optimum catalysts enables screening of promising candidates for the oxygen electrochemistry leading to considerable improvement of efficiency of a range of renewable energy devices.

Cathode Based on Molybdenum Disulfide Nanoflakes for Lithium-Oxygen Batteries

Lithium-oxygen (Li-O2) batteries have been recognized as an emerging technology for energy storage systems owing to their high theoretical specific energy. One challenge is to find an electrolyte/cathode system that is efficient, stable, and cost-effective. We present such a system based on molybdenum disulfide (MoS2) nanoflakes combined with an ionic liquid (IL) that work together as an effective cocatalyst for discharge and charge in a Li-O2 battery. Cyclic voltammetry results show superior catalytic performance for this cocatalyst for both oxygen reduction and evolution reactions compared to Au and Pt catalysts. It also performs remarkably well in the Li-O2 battery system with 85% round-trip efficiency and reversibility up to 50 cycles. Density functional calculations provide a mechanistic understanding of the MoS2 nanoflakes/IL system. The cocatalyst reported in this work could open the way for exploiting the unique properties of ionic liquids in Li-air batteries in combination with nanostructured MoS2 as a cathode material.