Mixed Transition‐Metal Oxides: Design,Synthesis, and Energy‐Related Applications

A promising family of mixed transition‐metal oxides (MTMOs) (designated as A_xB_3‐xO₄; A, B=Co, Ni, Zn, Mn, Fe, etc.) with stoichiometric or even non‐stoichiometric compositions, typically in a spinel structure, has recently attracted increasing research interest worldwide. Benefiting from their remarkable electrochemical properties, these MTMOs will play significant roles for low‐cost and environmentally friendly energy storage/conversion technologies. In this Review, we summarize recent research advances in the rational design and efficient synthesis of MTMOs with controlled shapes, sizes, compositions, and micro‐/nanostructures, along with their applications as electrode materials for lithium‐ion batteries and electrochemical capacitors, and efficient electrocatalysts for the oxygen reduction reaction in metal–air batteries and fuel cells. Some future trends and prospects to further develop advanced MTMOs for next‐generation electrochemical energy storage/conversion systems are also presented.     

3d-Transition metal doped spinels as high-voltage cathode materials for rechargeable lithium-ion batteries

Finding appropriate positive electrode materials for Li-ion batteries is the next big step for their application in emerging fields like stationary energy storage and electromobility. Among the potential materials 3d-transition metal doped spinels exhibit a high operating voltage and, therefore, are highly promising cathode materials which could meet the requirements regarding energy and power density to make Li-ion batteries the system of choice for the above mentioned applications. The compounds considered here include substituted Mn-based spinels such as LiM_0.5Mn_1.5O₄ (M = Ni, Co, Fe), LiCrMnO₄ and LiCrTiO₄. In this review, the recent researches conducted on these spinel materials are summarized. These include different routes of synthesis, structural studies, electrode preparation, electrochemical performance and mechanism of Li-extraction/insertion, thermal stability as well as degradation mechanisms. Note that even though the Ni-, Co-, and Fe-doped materials share the same chemical formula, the oxidation state distributions as well as the operating voltages are different among them. Furthermore, apart from the initial structural similarity, the Li-intercalation takes place through different mechanisms in different materials. In addition, this difference in mechanism is found to have considerable influence on the long-term cycling stability of the material. The routes to improve the electrochemical performance of some of the above candidates are discussed. Further emphasis is given to the parameters that limit their application in current technology, and strategies to overcome them are addressed.     

Bridging X-ray computed tomography and computational modeling for electrochemical energy-conversion and –storage

X-ray imaging techniques are powerful tools for understanding morphology, transport and even reactions within the electrochemical energy systems. Transmission X-ray microscopy (TXM) and X-ray computed tomography (CT) have been widely used in ex-situ studies to probe morphology of electrochemical energy materials. Emerging operando studies highlight the possibility of imaging energy materials and devices under realistic operating conditions. We present an overview of recent advances in the X-ray CT methods with application to fuel cells, batteries and other energy technologies, and describe how the information obtained with multimodal imaging is used within the multi-scale computational models. Overall, the progress in imaging outran the modeling progress, and current models are limited in their utility to incorporate vast amount of multimodal image data.     

钴基双金属氧化物的制备及其在电化学储能领域的应用

钴基双金属氧化物MCo₂O₄（M=Ni、Zn、Mn等）既继承了单一钴金属氧化物（Co₃O₄、CoO等）高比容量的优点,又引入了新的改性金属元素用于改善其导电性差、倍率性能不佳等缺点,是一种潜在的新型电化学储能材料。本文分类介绍了NiCo₂O₄、ZnCo₂O₄、MnCo₂O₄等钴基双金属氧化物及其复合物的现有研究（包括制备方法、形貌结构、颗粒尺寸及其电化学性能）,阐述了改性手段的可能性机理,并对钴基双金属氧化物后续研究提出了一些看法。     

钴基双金属氧化物的制备及其在电化学储能领域的应

钴基双金属氧化物MCo₂O₄（M=Ni、Zn、Mn等）既继承了单一钴金属氧化物（Co₃O₄、CoO等）高比容量的优点,又引入了新的改性金属元素用于改善其导电性差、倍率性能不佳等缺点,是一种潜在的新型电化学储能材料。本文分类介绍了NiCo₂O₄、ZnCo₂O₄、MnCo₂O₄等钴基双金属氧化物及其复合物的现有研究（包括制备方法、形貌结构、颗粒尺寸及其电化学性能）,阐述了改性手段的可能性机理,并对钴基双金属氧化物后续研究提出了一些看法。     

Recent Advances in Porous Carbon Materials for Electrochemical Energy Storage

Climate change and the energy crisis have promoted the rapid development of electrochemical energy‐storage devices. Owing to many intriguing physicochemical properties, such as excellent chemical stability, high electronic conductivity, and a large specific surface area, porous carbon materials have always been considering as a promising candidate for electrochemical energy storage. To date, a wide variety of porous carbon materials based upon molecular design, pore control, and compositional tailoring have been proposed for energy‐storage applications. This focus review summarizes recent advances in the synthesis of various porous carbon materials from the view of energy storage, particularly in the past three years. Their applications in representative electrochemical energy‐storage devices, such as lithium‐ion batteries, supercapacitors, and lithium‐ion hybrid capacitors, are discussed in this review, with a look forward to offer some inspiration and guidelines for the exploitation of advanced carbon‐based energy‐storage materials.     

Recent advances of transition metal oxalate-based micro- and nanomaterials for electrochemical energy storage: a review

A key challenge in the development of electrochemical energy storage (EES) is the design and engineering of electrode materials for electrochemical reactions. Transition metal oxalates (TMOxs) have been widely used in various EES applications due to their low cost, simple synthesis, and excellent electrochemical performance. In this review, the recent advances in the design and engineering of transition metal oxalate-based micro- and nanomaterials for EES are summarized. Specifically, the survey will focus on three types of micro- and nano-scale TMOxs (monometallic, bimetallic, and trimetallic TMOxs), their composites (TMOx-metal oxide, TMOx-hydroxide, TMOx-GO, and TMOx-MOFs composites), and derivatives, including transition metal oxides (TiO₂, V₂O₅, Mn_xO_y, Co₃O₄, NiO, CuO, and Nb₂O₅), multi-transition metal oxides (MCo₂O₄ (M = Ni, Cu, and Zn), NiMn₂O₄, and N_xO_y-M_xO_y), transition metal sulfide (NiS₂), and carbon materials (ordinary carbon, GO and their composites), within the context of their intrinsic structure and corresponding electrochemical performance. A range of experimental variables will be carefully analyzed, such as sample synthesis, crystal structure, and electrochemical reaction mechanism. The applications of these materials as EES electrodes are then featured for supercapacitors (SCs) and lithium-ion batteries (LIBs). We conclude the review with a perspective of future research prospects and challenges.     

Recent Advances on Nitrogen-Doped Porous Carbons Towards Electrochemical Supercapacitor Applications

Due to ever-increasing global energy demands and dwindling resources, there is a growing need to develop materials that can fulfil the World's pressing energy requirements. Electrochemical energy storage devices have gained significant interest due to their exceptional storage properties, where the electrode material is a crucial determinant of device performance. Hence, it is essential to develop 3-D hierarchical materials at low cost with precisely controlled porosity and composition to achieve high energy storage capabilities. After presenting the brief updates on porous carbons (PCs), then this review will focus on the nitrogen (N) doped porous carbon materials (NPC) for electrochemical supercapacitors as the NPCs play a vital role in supercapacitor applications in the field of energy storage. Therefore, this review highlights recent advances in NPCs, including developments in the synthesis of NPCs that have created new methods for controlling their morphology, composition, and pore structure, which can significantly enhance their electrochemical performance. The investigated N-doped materials a wide range of specific surface areas, ranging from 181.5 to 3709 m² g⁻¹, signifies a substantial increase in the available electrochemically active surface area, which is crucial for efficient energy storage. Moreover, these materials display notable specific capacitance values, ranging from 58.7 to 754.4 F g⁻¹, highlighting their remarkable capability to effectively store electrical energy. The outstanding electrochemical performance of these materials is attributed to the synergy between heteroatoms, particularly N, and the carbon framework in N-doped porous carbons. This synergy brings about several beneficial effects including, enhanced pseudo-capacitance, improved electrical conductivity, and increased electrochemically active surface area. As a result, these materials emerge as promising candidates for high-performance supercapacitor electrodes. The challenges and outlook in NPCs for supercapacitor applications are also presented. Overall, this review will provide valuable insights for researchers in electrochemical energy storage and offers a basis for fabricating highly effective and feasible supercapacitor electrodes.     

Hierarchically Porous Organic Materials Derived From Copolymers: Preparation and Electrochemical Applications

Abstract

Compared to conventional porous materials with a uniform pore size distribution, hierarchical ones containing interconnected macro-, meso-, and micropores have greatly enhanced material performance due to the increased specific surface area and mass transfer. Copolymer is a good candidate used for construction of such hierarchically porous structures, resulting from its tunable segment composition, unique phase separation, and self-assembly, etc. Hierarchically porous materials derived from copolymers can be served as a versatile support for many reactive molecules. Furthermore, hierarchically porous carbon materials (HPCMs) can also be prepared by carbonization of copolymers, one segment of which is converted to carbon while the other segment is responsible for the pore formation after its removal by pyrolysis. The obtained hierarchically porous copolymers or carbon materials have promising electrochemical applications especially in energy conversion and storage. In the present review, recent advances in preparation of hierarchically porous materials (HPMs) derived from copolymers are reviewed, and their electrochemical applications in supercapacitors, lithium-ion batteries, fuel cells, electrochemical biosensors, and electrocatalysis are also introduced. The rational design and control for the hierarchically porous microstructures are described deeply from the molecular level. Also, the relationship between the micro-structure and the electrochemical performance is revealed. This review can provide us a better understanding of both theory and experiment for the preparation of hierarchically porous organic materials and their electrochemical applications.     

Strategies for constructing manganese-based oxide electrode materials for aqueous rechargeable zinc-ion batteries

Commercial lithium-ion batteries(LIBs) have been widely used in various energy storage systems. However, many unfavorable factors of LIBs have prompted researchers to turn their attention to the development of emerging secondary batteries. Aqueous zinc ion batteries(AZIBs) present some prominent advantages with environmental friendliness, low cost and convenient operation feature. Mn O2electrode is the first to be discovered as promising cathode material. So far, manganese-based oxides have made...     

Molybdenum Disulfide Based Nanomaterials for Rechargeable Batteries

The rapid development of electrochemical energy storage systems requires new electrode materials with high performance. As a two-dimensional material, molybdenum disulfide (MoS₂) has attracted increasing interest in energy storage applications due to its layered structure, tunable physical and chemical properties, and high capacity. In this review, the atomic structures and properties of different phases of MoS₂ are first introduced. Then, typical synthetic methods for MoS₂ and MoS₂-based composites are presented. Furthermore, the recent progress in the design of diverse MoS₂-based micro/nanostructures for rechargeable batteries, including lithium-ion, lithium-sulfur, sodium-ion, potassium-ion, and multivalent-ion batteries, is overviewed. Additionally, the roles of advanced in situ/operando techniques and theoretical calculations in elucidating fundamental insights into the structural and electrochemical processes taking place in these materials during battery operation are illustrated. Finally, a perspective is given on how the properties of MoS₂-based electrode materials are further improved and how they can find widespread application in the next-generation electrochemical energy-storage systems.     

The rods-like manganese dioxide films grown on nickel foam for electrochemical capacitor applications

MnO₂ films grown on nickel foam (NF) with a desirable 3D structure are investigated as electrochemical pseudocapacitor materials for potential energy storage applications. The prepared MnO₂ films are characterized by X-ray diffraction, FT-IR and scanning electron microscopy. Results indicate that the products are typical hexagonal ?-MnO₂ with a uniform nanorod structure. The electrochemical measurements showed that the MnO₂ films with rods-like morphology have excellent electrochemical performances and its specific capacitance value as single electrode is up to 664 F g^?1 at a discharge current density of 5.5 A g^?1, which is higher than that of most reported corresponding materials. The specific capacitance retention ratio is 76.7% at the current density range from 5.5 to 30 A g^?1. Furthermore, we found that the deposition conditions such as deposition potential and deposition mass have a pronounced effect on their electrochemical activities.     

Enzymatic electrosynthesis as an emerging electrochemical synthesis platform

Enzymatic electrosynthesis (EES), combining enzymatic catalysis and electrochemical techniques for the production of desired chemicals, has gained prominence because of its use of clean electrical energy inputs and highly specific enzyme biocatalysts and its capability of performing complicated reactions with high yield. In this review, we summarize the most recent state-of-the-art advances in EES and recognize that the research emphasis has shifted from CO₂ reduction to the utilization of N₂ and the synthesis of high-value products. Particular attention is given to the energy sources for powering EES, including direct electrical energy, light energy, and chemical energy obtained from self-powered biosystems. Enzyme-based hybrid systems integrated with microbial or chemical approaches are also presented. Finally, key challenges and future directions of EES are discussed briefly.     

Preparation and characterization of Ni(dpedt)(pddt) and Ni(dpedt)(pddt)·CS2, where dpedt is diphenylethylenedithiolate and pddt is 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate

The unsymmetrical nickel 1,2-dithiolene complex based on diphenylethylenedithiolate (dpedt) and 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate (pddt) was prepared and characterized. Depending on the conditions of crystallization, it is possible to obtain the complex in two different crystalline forms. X-ray structure studies recognize these forms as Ni(dpedt)(pddt) and Ni(dpedt)(pddt)·CS₂. The experimental optical and electrochemical parameters are in a good agreement with the calculated ones, using the corresponding parameters of the symmetrical complexes, Ni(dpedt)₂ and Ni(pddt)₂. The HOMO and LUMO energy levels, obtained from optical and electrochemical measurements, are very close to the Fermi energy of (metallic) Au. The chemical and electrochemical properties of both forms showed that they are stable in air and could be candidate materials for optics and electronics.     

Carbon Nanofibers Decorated with Molybdenum Disulfide Nanosheets: Synergistic Lithium Storage and Enhanced Electrochemical Performance

Traditional lithium‐ion batteries that are based on layered Li intercalation electrode materials are limited by the intrinsically low theoretical capacities of both electrodes and cannot meet the increasing demand for energy. A facile route for the synthesis of a new type of composite nanofibers, namely carbon nanofibers decorated with molybdenum disulfide sheets (CNFs@MoS₂), is now reported. A synergistic effect was observed for the two‐component anode, triggering new electrochemical processes for lithium storage, with a persistent oxidation from Mo (or MoS₂) to MoS₃ in the repeated charge processes, leading to an ascending capacity upon cycling. The composite exhibits unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior high‐rate capability, suggesting its potential application in high‐energy lithium‐ion batteries.     

One‐dimensional Nanomaterial Electrocatalysts for CO2 Fixation

Electroreduction of CO₂ into valuable molecules or fuels is a sustainable pathway for CO₂ reduction as well as energy storage. However, the premature development stage of electrocatalysts with high activity, selectivity, and durability still remains a significant bottleneck that hinders this field. One‐dimensional (1D) nanomaterials, including nanorods, nanotubes, nanoribbons, nanowires, and nanofibers, are generally considered as high‐activity and stable electromaterials, due to their unique uniform structures, orientated electronic and mass transport, and rigid tolerance to stress variation. During the past several years, 1D nanomaterials and nanostructures have been extensively studied due to their potentials in serving as CO₂ electroreduction catalysts. In this minireview, recent studies and advances in 1D nanomaterials for CO₂ eletroreduction are summarized, from the viewpoints of both computational and experimental aspects. Based on the composition, the 1D nanomaterials are studied in four categories, including metals, transition‐metal oxides/nitrides, transition‐metal chalcogenides, and carbon‐based materials. Different parameters in tuning 1D materials are also summarized and discussed, such as the crystal facets, grain boundaries, heteroatoms doping, additives and the electrochemical tuning effects. Finally, the challenges and prospects in this direction will be discussed.     

A novel electrochemical noise sensor applied to detect food safety

A novel electrochemical noise (EN) sensor was elaborately designed to detect the metal residue in energy drinks. By calculating the characteristic parameter, noise resistance R _n, obtained from the EN data, the tin and iron residue can be semiquantitatively evaluated. In addition, R _n was further compared with the inductively coupled plasma mass spectrometer (ICP-MS) results. Accordingly, an interesting relationship was found between the EN data and ICP-MS results. The experimental results reveal that R _n can indirectly reflect the corrosion-induced metal release from the packaging materials; a lower R _n means a higher metal release. This electrochemical sensor has potential applications in evaluating food safety because of its fast, economic and in-situ features.     

Promoting CO2 electroreduction on boron-doped diamond electrodes: Challenges and trends

CO₂ electroreduction (eCO₂R) into fuel products is a promising technology to mitigate the effects of greenhouse gas emissions and store renewable energy. The main metal-based electrocatalysts widely employed in CO₂ reduction are characterized by high overpotentials, low stability, and unsatisfactory selectivity. As a result, a growing interest in the use of boron-doped diamond (BDD)-based electrocatalysts have been observed due to its excellent properties. This review sheds light on the techniques applied toward the eCO₂R on BDD surface and the effects of the operational conditions. Particular emphasis will be given on recent advances made in the quest for enhancing the performance of BDD in eCO₂R through its modification with defects insertion or functionalization with metal-based materials. The review will also present a brief overview of the challenges and directions of future research with respect to the development of different electrochemical systems for eCO₂R on BDD electrodes.     

Recent developments on layered 3d-transtition metal oxide cathode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) are now intensively developed as a cost-effective technology alternative to lithium-ion batteries (LIBs) for large-scale energy storage because of their various advantages such as huge abundance of sodium resources, highly safe and significantly low cost. Among many other cathode materials, layered 3d-transition metal oxides (LTMO-Na_xMO₂, x ≤ 1 and M = Co, Ni, Mn, Cr, Cu, Fe and V) have gained an enormous interest and attractive attention among researchers because of their low-cost, high energy density and ease of synthesis. In addition, LTMOs offer higher reversible capacities because of relatively lower molecular weights; however, complex phase transformations limit their cycling life. Based on the previous research, it was examined that the crystalline phase of LTMO highly influences the electrochemical performance of SIBs; therefore, this review mainly focuses on the latest advances of various crystalline phases such as P2-type, P3-type, O3-type and biphase/multiphase materials and its strength as well as future prospects and challenges.     

Electrocatalytic conversion of CO2 to liquid fuels using nanocarbon-based electrodes

Recent advances on the use of nanocarbon-based electrodes for the electrocatalytic conversion of gaseous streams of CO₂ to liquid fuels are discussed in this perspective paper. A novel gas-phase electrocatalytic cell, different from the typical electrochemical systems working in liquid phase, was developed. There are several advantages to work in gas phase, e.g. no need to recover the products from a liquid phase and no problems of CO₂ solubility, etc. Operating under these conditions and using electrodes based on metal nanoparticles supported over carbon nanotube (CNT) type materials, long C-chain products (in particular isopropanol under optimized conditions, but also hydrocarbons up to C8–C9) were obtained from the reduction of CO₂. Pt-CNT are more stable and give in some cases a higher productivity, but Fe-CNT, particular using N-doped carbon nanotubes, give excellent properties and are preferable to noble-metal-based electrocatalysts for the lower cost. The control of the localization of metal particles at the inner or outer surface of CNT is an importact factor for the product distribution. The nature of the nanocarbon substrate also plays a relevant role in enhancing the productivity and tuning the selectivity towards long C-chain products. The electrodes for the electrocatalytic conversion of CO₂ are part of a photoelectrocatalytic (PEC) solar cell concept, aimed to develop knowledge for the new generation artificial leaf-type solar cells which can use sunlight and water to convert CO₂ to fuels and chemicals. The CO₂ reduction to liquid fuels by solar energy is a good attempt to introduce renewables into the existing energy and chemical infrastructures, having a higher energy density and easier transport/storage than other competing solutions (i.e. H₂).