Three-Dimensional Nanofibrous Air Electrode Assembled With Carbon Nanotubes-Bridged Hollow Fe2O3 Nanoparticles for High-Performance Lithium-Oxygen Batteries

Room-Temperature Flexible CNT/Fe2O3 Film Sensor for ppb-Level H2S Detection

Carbon nanotubes (CNTs) had room temperature response, large surface area, and excellent mechanical properties, making them favorable for the design of flexible, wearable, and portable gas sensors. However, CNTs were lacking in response and selective response to different gases, such as H2S. Here, we demonstrated a flexible H2S ppb-level gas sensor based on a carbon nanotube/amorphous Fe2O3 (CNT/Fe2O3) film at room temperature, which was fabricated via a simple one-step solvent-thermal method. The CNT/Fe2O3 film gas sensor exhibited a high selective response to H2S (with a response of 55.1% to 100 ppb H2S), rapid reversible response at room temperature (with a response time of ∼127 s to 100 ppb H2S), and low limit of detection to about 2 ppb. Additionally, the CNT/Fe2O3 film maintained good sensing performance under various bending conditions and could be further fabricated into the fiber gas sensor device via wet stretching, retaining response at the ppb level (with a response of 18.6% to 100 ppb H2S). This research on a flexible gas sensor device based on the CNT film/fiber opened up new possibilities for wearable portable electronic device applications.

Solid-Liquid-Gas Management for Low-Cost Hydrogen Gas Batteries

Aqueous nickel-hydrogen gas (Ni-H₂) batteries with excellent durability (>10,000 cycles) are important candidates for grid-scale energy storage but are hampered by the high-cost Pt electrode with limited performance. Herein, we report a low-cost nickel-molybdenum (NiMo) alloy as an efficient bifunctional hydrogen evolution and oxidation reaction (HER/HOR) catalyst for Ni-H₂ batteries in alkaline electrolytes. The NiMo alloy demonstrates a high HOR mass-specific kinetic current of 28.8 mA mg^-1 at 50 mV as well as a low HER overpotential of 45 mV at a current density of 10 mA cm^-2, which is better than most nonprecious metal catalysts. Furthermore, we apply a solid-liquid-gas management strategy to constitute a conductive, hydrophobic network of NiMo using multiwalled carbon nanotubes (NiMo-hydrophobic MWCNT) in the electrode to accelerate HER/HOR activities for much improved Ni-H₂ battery performance. As a result, Ni-H₂ cells based on the NiMo-hydrophobic MWCNT electrode show a high energy density of 118 Wh kg^-1 and a low cost of only 67.5 $ kWh^-1. With the low cost, high energy density, excellent durability, and improved energy efficiency, the Ni-H₂ cells show great potential for practical grid-scale energy storage.

Recent Advancements in Chalcogenides for Electrochemical Energy Storage Applications

Energy storage has become increasingly important as a study area in recent decades. A growing number of academics are focusing their attention on developing and researching innovative materials for use in energy storage systems to promote sustainable development goals. This is due to the finite supply of traditional energy sources, such as oil, coal, and natural gas, and escalating regional tensions. Because of these issues, sustainable renewable energy sources have been touted as an alternative to nonrenewable fuels. Deployment of renewable energy sources requires efficient and reliable energy storage devices due to their intermittent nature. High-performance electrochemical energy storage technologies with high power and energy densities are heralded to be the next-generation storage devices. Transition metal chalcogenides (TMCs) have sparked interest among electrode materials because of their intriguing electrochemical properties. Researchers have revealed a variety of modifications to improve their electrochemical performance in energy storage. However, a stronger link between the type of change and the resulting electrochemical performance is still desired. This review examines the synthesis of chalcogenides for electrochemical energy storage devices, their limitations, and the importance of the modification method, followed by a detailed discussion of several modification procedures and how they have helped to improve their electrochemical performance. We also discussed chalcogenides and their composites in batteries and supercapacitors applications. Furthermore, this review discusses the subject’s current challenges as well as potential future opportunities.

Recent Advances in Nanoscale Based Electrocatalysts for Metal-Air Battery, Fuel Cell and Water-Splitting Applications: An Overview

Metal-air batteries and fuel cells are considered the most promising highly efficient energy storage systems because they possess long life cycles, high carbon monoxide (CO) tolerance, and low fuel crossover ability. The use of energy storage technology in the transport segment holds great promise for producing green and clean energy with lesser greenhouse gas (GHG) emissions. In recent years, nanoscale based electrocatalysts have shown remarkable electrocatalytic performance towards the construction of sustainable energy-related devices/applications, including fuel cells, metal-air battery and water-splitting processes. This review summarises the recent advancement in the development of nanoscale-based electrocatalysts and their energy-related electrocatalytic applications. Further, we focus on different synthetic approaches employed to fabricate the nanomaterial catalysts and also their size, shape and morphological related electrocatalytic performances. Following this, we discuss the catalytic reaction mechanism of the electrochemical energy generation process, which provides close insight to develop a more efficient catalyst. Moreover, we outline the future perspectives and challenges pertaining to the development of highly efficient nanoscale-based electrocatalysts for green energy storage technology.

Synthesis and Characterisation of Cobalt Ferrite Coatings for Oxygen Evolution Reaction

In this paper, two novel procedures based on powder sedimentation, thermal treatment, and galvanostatic deposition were proposed for the preparation of porous cobalt ferrite (CoFe2O4) coatings with a metallic and organic binder for use as catalysts in the oxygen evolution reaction (OER). The electrochemical properties of the obtained electrode materials were determined as well, using both dc and ac methods. It was found that cobalt ferrite coatings show excellent electrocatalytic properties towards the oxygen evolution reaction (OER) with overpotential measured at a current density of 10 mAcm−2 from 287 to 295 mV and a Tafel slope of 35–45 mVdec−1. It was shown that the increase in the apparent activity of the CoFe2O4 coatings with an organic binder results mainly from a large electrochemically active area. Incorporation of the nickel binder between the CoFe2O4 particles causes an increase in both the conductivity and the electrochemically active area. The Tafel slopes indicate that the same rate-determining step controls the OER for all obtained coatings. Furthermore, it was shown that the CoFe2O4 electrodes exhibit no significant activity decrease after 28 h of oxygen evolution. The proposed coating preparation procedures open a new path to develop high-performance OER electrocatalysts.

Operando NMR characterization of a metal-air battery using a double-compartment cell design

Applying operando investigations is becoming essential for acquiring fundamental insights into the reaction mechanisms and phenomena at stake in batteries currently under development. The capability of a real-time characterization of the charge/discharge electrochemical pathways and the reactivity of the electrolyte is critical to decipher the underlying chemistries and improve the battery performance. Yet, adapting operando techniques for new chemistries such as metal-oxygen (i.e. metal-air) batteries introduces challenges in the cell design due notably to the requirements of an oxygen gas supply at the cathode. Herein a simple operando cell is presented with a two-compartment cylindrical cell design for NMR spectroscopy. The design is discussed and evaluated. Operando⁷Li static NMR characterization on a Li-O₂ battery was performed as a proof-of-concept. The productions of Li₂O₂, mossy Li/Li dendrites and other irreversible parasitic lithium compounds were captured in the charge/discharge processes, demonstrating the capability of tracking the evolution of the anodic and cathodic chemistry in metal-oxygen batteries.

Free-Standing Carbon Nanofibers Protected by a Thin Metallic Iridium Layer for Extended Life-Cycle Li-Oxygen Batteries

It is evident that the exhaustive use of fossil fuels for decades has significantly contributed to global warming and environmental pollution. To mitigate the harm on the environment, lithium-oxygen batteries (LOBs) with a high theoretical energy density (3458 Wh kg^-1Li₂O₂) compared to that of Li-ion batteries (LIBs) have been considered as an attractive alternative to fossil fuels. For this purpose, porous carbon materials have been utilized as promising air cathodes owing to their low cost, lightness, easy fabrication process, and high performance. However, the challenge thus far lies in the uncontrollable formation of Li₂CO₃ at the interface between carbon and Li₂O₂, which is detrimental to the stable electrochemical performance of carbon-based cathodes in LOBs. In this work, we successfully protected the surface of the free-standing carbon nanofibers (CNFs) by coating it with a layer of iridium metal through direct sputtering (CNFs@Ir), which significantly improved the lifespan of LOBs. Moreover, the Ir would play a secondary role as an electrochemical catalyst. This all-in-one cathode was evaluated for the formation and decomposition of Li₂O₂ during (dis)charging processes. Compared with bare CNFs, the CNFs@Ir cathode showed two times longer lifespan with 0.2 V_Li lower overpotentials for the oxygen evolution reaction. We quantitatively calculated the contents of CO₃^2- in Li₂CO₃ formed on the different surfaces of the bare CNFs (63% reduced) and the protected CNFs@Ir (78% reduced) cathodes after charging. The protective effects and the reaction mechanism were elucidated by ex situ analyses, including scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy.

Three-dimensional mesoporous γ-Fe2O3@carbon nanofiber network as high performance anode material for lithium- and sodium-ion batteries

Electrode materials that can function well in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) are desirable for electrochemical energy storage applications, especially under high rate. In this work, a three-dimensional (3D) mesoporous γ-Fe₂O₃@carbon nanofiber (γ-Fe₂O₃@CNF) mat has been successfully synthesized by sol-gel based electrospinning and carbonization. It delivers a specific capacity of 820 mAh g^-1 at 0.5 C after 250 cycles, 430 mAh g^-1 at 6 C after 1000 cycles, and 222 mAh g^-1 at ultrahigh rate of 60 C for LIBs, while for SIBs it delivers a specific capacity of 360 mAh g^-1 at 1 C after 1000 cycles and 130 mAh g^-1 at 60 C. Besides, the result of ex situ microstructure examination shows the polycrystalline nature of γ-Fe₂O₃ nanoparticle still exists in LIB even after 1000 cycles, while it vanishes in SIB, suggesting that the relatively larger volume expansion occurred during Na⁺ insertion/deinsertion, resulting in pulverization of the particles. The CNFs maintained their pristine 3D network structure after the charge/discharge, which demonstrated the critical role of a robust conductive electrode in promoting fast Li⁺/Na⁺ transportation. More importantly, they act as an electrical bridge between Li⁺/Na⁺ and γ-Fe₂O₃ nanoparticles, therefore suppressing the cell impedance growth and γ-Fe₂O₃ volume expansion, resulting in the enhancement in both cyclic and rate capability.

Gallium Nitride Nanoparticles Embedded in a Carbon Nanofiber Anode for Ultralong-Cycle-Life Lithium-Ion Batteries

Recently, gallium (Ga), one of the liquid metals (LMs), has been explored with special attention because of its liquid phase nature as a self-healing agent and Li storage characteristics. The current challenge that restricts the practical use of Ga is handling Ga easily without loss and understanding its reaction behavior in Li-ion batteries. One solution that helps to address the problem associated with liquid phases is to make solid phases such as gallium oxides and nitrides as starting materials for a stable conversion reaction. Here, we have successfully incorporated GaN nanoparticles into carbon confiners [1D carbon nanofibers (CNFs) with the outermost carbon coating layer] as an anode for the Li-ion battery. By preserving liquid Ga derived from GaN after the conversion reaction in conductive walls, long-term cycling performance (over 5000 cycles) is achievable. This work provides an insight into the LM-relevant materials/carbon composite in the area of the rechargeable battery.

Cathode Local Curvature Affects Lithium Peroxide Growth in Li-O2 Batteries

The growth of lithium peroxide (Li₂O₂) in cathodes determines the performance of lithium-oxygen batteries (LOBs). The factor affecting the Li₂O₂ growth position is of great importance. Here, three hollow carbon spheres with diameters of 200 nm, 500 nm, and 2 μm, corresponding to different curvatures of 10, 4, and 1, respectively, are prepared as LOB cathodes. It is found that the larger the curvature, the more difficult it is for Li₂O₂ to grow inside the hollow sphere. Increasing the discharge current density can promote the growth of Li₂O₂ onto a highly curved concave substrate. Therefore, to maximize the battery performance, the applied current density and the local curvature of the porous cathode need to match to optimize the pore space utilization and meanwhile to enhance the interface charge transfer between Li₂O₂ and electrode. The revealed relationship among the local curvature of the porous electrode, Li₂O₂ deposition position, and battery performance is valuable to the topography design of the LOB cathode.

Free-Standing Three-Dimensional CuCo2S4 Nanosheet Array with High Catalytic Activity as an Efficient Oxygen Electrode for Lithium-Oxygen Batteries

In this work, a novel free-standing CuCo₂S₄ nanosheet cathode (CuCo₂S₄@Ni) with high catalytic activity is fabricated for aprotic lithium-oxygen (Li-O₂) battery. This deliberately designed oxygen electrode is found to yield lower overpotential (0.82 V), improved specific capacity (9673 mA h g^-1 at 100 mA g^-1), and enhanced cycle life (164 cycles) as compared to the traditional carbonaceous electrode. The improved performance can be ascribed to the superb spinel structure of CuCo₂S₄, in which both Cu and Co exhibit more abundant redox properties, improving oxygen reduction reaction and oxygen evolution reaction kinetics effectively and boosting the electrochemical reactions. Furthermore, the well-designed architecture also plays a critical role in the improved performance. Encouraged by the excellent catalytic activity of this free-standing cathode, large-scale pouch-type Li-O₂ cell based on CuCo₂S₄@Ni cathode is fabricated and can work under different bending and twisting conditions. This free-standing electrode provides a new strategy for developing Li-O₂ batteries with excellent performance and flexible wearable devices.

Three-Dimensional Interconnected Network Architecture with Homogeneously Dispersed Carbon Nanotubes and Layered MoS2 as a Highly Efficient Cathode Catalyst for Lithium-Oxygen Battery

The structure and catalytic activity of the oxygen electrode determine the overall electrochemical performance of lithium-oxygen (Li-O₂) batteries. Here, a three-dimensional (3D) porous interconnected network structure combined with ultrathin MoS₂ nanosheets with homogeneously dispersed CNTs (MoS₂/CNTs) was synthesized via a one-step hydrothermal reaction. The 3D interconnected architecture can efficiently promote the diffusion of O₂ and Li ions as well as impregnation of electrolyte and provide more abundant storage space for the accommodation of discharge products, while the incorporation of uniformly dispersed CNTs improves the electronic conductivity and maintains the integrity of the cathode structure. Therefore, the Li-O₂ battery based on MoS₂/CNTs achieves improved performance with the low overpotentials (discharge/charge overpotentials of approximately 0.29 and 1.05 V), a high discharge specific capacity of 6904 mA h g^-1 at a rate of 200 mA g^-1, and excellent cycling stability (132 cycles). Experimental studies reveal that the improved electrochemical performance can be ascribed to the synergistic advantages of electronic conductive CNTs and excellent catalytic activity of the MoS₂ nanosheets. Moreover, the unique 3D interconnected network structure can effectively facilitate fast charge transfer kinetics and a facile mass transport pathway. These encouraging performances demonstrate the metal sulfide catalyst as a promising catalytic material of oxygen electrodes for Li-O₂ batteries.