Recent advances in electrocatalysts for non-aqueous Li-O2 batteries

As one of the next-generation energy-storage devices,Li-O₂ battery has become the main research direction for the academic researchers due to its characteristics of environmental friendship,relatively simple structures,high energy density of 3500 Wh/kg and low cost.However,Li-O₂ battery cannot be commercialized on a large scale because of the challenging issues including high-efficient electro-catalysts,membranes,Li-based anode and so on.In this review,we focused on the recent development of electrocatalyst materials as cathodes for the non-aqueous Li-O₂ batteries which are relatively simpler than other Li-O₂ batteries' structures.Electrocatalysts were summarized including noble metals,nano-carbon materials,transition metals and their hybrids.We points out that the challenges of preparation high-efficient catalysts not only require high catalytic activity and conductivity,but also have novel nanoarchitectures with large interface and porous volume for LiOx storage.Furthermore,the further investigation of reaction mechanism and advanced in situ analysis technologies are welcome in the coming work.     

Recent advances in carbon-based electrocatalysts for oxygen reduction reaction

Fuel cells are one of the most promising clean energy devices to substitute for fossil fuel in the future to alleviate energy crisis and environmental pollution.As the key reaction on the cathode in the fuel cells,oxygen reduction reaction(ORR) still requires efficient noble metal catalysts such as the comme rcial Pt/C to boost the reaction for its sluggish kinetics.Therefore,it is critical to design earth-abundant carbonbased catalysts with high efficiency and long-term stability to replace the...     

Recent advances in metal-organic frameworks for oxygen evolution reaction electrocatalysts

The anodic oxygen evolution reaction(OER) can be combined with various cathodic reactions to enable the electrochemical synthesis of diverse chemicals and fuels, particularly in water electrolysis for hydrogen production. It is however exhibiting a high overpotential due to the sluggish four-electron transfer process, which is considered the decisive reaction in energy conversion systems. In recent years, metal-organic frameworks(MOFs) have emerged as the ideal catalysts for accelerating OER. Th...     

Recent advances in cathodes for all-solid-state lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have been regarded as the candidate for the next-generation energy storage system due to the high theoretical specific capacity (1675 mAh/g), energy density (2600 Wh/kg) and the abundance of elemental sulfur, but the application of Li-S batteries is impeded by a series of problems. Recently, all-solid-state Li-S batteries (ASSLSBs) have drawn great attention because many drawbacks such as safety issues caused by metallic lithium anodes and organic liquid electrolytes can be overcome through the use of solid-state electrolytes (SEs). However, not only the problems brought by sulfur cathodes still exist, but more trouble arouses from the interfaces between SEs and cathodes, hampering the practical application of ASSLSBs. Therefore, in order to deal with the problems, enormous endeavors have been done on ASSLSB cathodes during the past few decades, including engineering of cathode active materials, cathode host materials, cathode binder materials and cathode structures. In this review, the electrochemical mechanism and existing problems of ASSLSBs are briefly introduced. Subsequently, the strategies for developing cathode materials and designing cathode structures are presented. Then there follows a brief discussion of SE problems and expectations, and finally, the challenges and perspectives of ASSLSBs are summarized.     

Metal–organic framework based bifunctional oxygen electrocatalysts for rechargeable zinc–air batteries: current progress and prospects

Zinc–air batteries (ZABs) are regarded as ideal candidates for next-generation energy storage equipment due to their high energy density, non-toxicity, high safety, and environmental friendliness. However, the slow oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics on the air cathode limit their efficiency and the development of highly efficient, low cost and stable bifunctional electrocatalysts is still challenging. Metal–Organic Framework (MOF) based bifunctional oxygen electrocatalysts have been demonstrated as promising alternative catalysts due to the regular structure, tunable chemistry, high specific surface area, and simple and easy preparation of MOFs, and great progress has been made in this area. Herein, we summarize the latest research progress of MOF-based bifunctional oxygen electrocatalysts for ZABs, including pristine MOFs, derivatives of MOFs and MOF composites. The effects of the catalysts'' composites, morphologies, specific surface areas and active sites on catalytic performances are specifically addressed to reveal the underlying mechanisms for different catalytic activity of MOF based catalysts. Finally, the main challenges and prospects for developing advanced MOF-based bifunctional electrocatalysts are proposed.

The research progress of MOF-based bifunctional oxygen electrocatalysts for zinc–air batteries is reviewed and the main challenges and prospects for developing advanced MOF-based bifunctional electrocatalysts are proposed.     

Recent advances in defect electrocatalysts: Preparation and characterization

the types and strategies used to prepare defect electrocatalysts will continue to be studied and developed as new defective materials are generated.4. Characterization of defectsThis review briefly summarizes recent progress in defect electrocatalysts, and the synthesis strategies and characterization techniques for defects are systematically discussed. Although challenges in the characterization of defect structures in the electrocatalytic reaction process remain, the dynamic evolution of defect sites is predicted to be helpful for designing and preparing high-performance electrocatalysts for commercial applications. Furthermore, due to an insufficient understanding of the defect-structureproperty relationships, future possibilities for the reasonable design of defect electrocatalysts to obtain desirable performance are suggested.     

Recent advances in electrospun electrode materials for sodium-ion batteries

Sodium-ion batteries(SIBs)have been considered as an ideal choice for the next generation large-scale energy storage applications owing to the rich sodium resources and the analogous working principle to that of lithium-ion batteries(LIBs).Nevertheless,the larger size and heavier mass of Na⁺ion than those of Li⁺ion often lead to sluggish reaction kinetics and inferior cycling life in SIBs compared to the LIB counterparts.The pursuit of promising electrode materials that can accommodate the rapid and stable Na-ion insertion/extraction is the key to promoting the development of SIBs toward a commercial prosperity.One-dimensional(1 D)nanomaterials demonstrate great prospects in boosting the rate and cycling performances because of their large active surface areas,high endurance for deformation stress,short ions diffusion channels,and oriented electrons transfer paths.Electrospinning,as a versatile synthetic technology,features the advantages of controllable preparation,easy operation,and mass production,has been widely applied to fabricate the 1 D nanostructured electrode materials for SIBs.In this review,we comprehensively summarize the recent advances in the sodium-storage cathode and anode materials prepared by electrospinning,discuss the effects of modulating the spinning parameters on the materials’micro/nano-structures,and elucidate the structure-performance correlations of the tailored electrodes.Finally,the future directions to harvest more breakthroughs in electrospun Na-storage materials are pointed out.     

Recent advances in solid-state beyond lithium batteries

Journal of Solid State Electrochemistry - As battery technologies are in continuous development, and especially due to the rapid growth in vehicle electrification, which requires large (e.g.,...     

Recent advances in charge mechanism of noble metal-based cathodes for Li-O2 batteries

Lithium-oxygen(Li-O₂ ) batteries are considered as the next generation for energy storages systems due to the higher theoretical energy density than that of Li-ion batteries. However, the high charge overpotential caused by the insulated Li₂O₂ results in low energy efficiency, side reaction from electrolyte and cathode, and therefore poor battery performance. Designing noble metal-based catalysts can be an effective strategy to develop high-performance Li-O_2...     

Hierarchical NiCo2O4 nanorods as an efficient cathode catalyst for rechargeable non-aqueous Li–O2 batteries

NiCo₂O₄ nanorods were synthesized by a hydrothermal method followed by low temperature calcination. FESEM and TEM analyses confirmed that the as-prepared materials consist of a hierarchical nanorod structure. When applied as cathode catalysts in rechargeable Li–O₂ batteries, NiCo₂O₄ nanorods exhibited a superior catalytic activity, including low charge over-potential, high discharge capacity and high-rate capability.     

CO2-adsorbent spongy electrode for non-aqueous Li–O2 batteries

Regulation of the Li₂CO₃ byproduct is the most critical challenge in the field of non-aqueous Li–O₂ batteries.Although considerable efforts have been devoted to preventing Li₂CO₃ formation,no approaches have suggested the ultimate solution of utilizing the clean Li₂O₂ reaction instead of that of Li₂CO₃.Even if extremely pure O₂ is used in a Li–O₂ cell,its complete elimination is impossible,eventually generating CO₂ gas during charge.In this paper,we present the new concept of a CO₂-adsorbent spongy electrode(CASE),which is designed to trap the evolved CO₂ using adsorption materials.Various candidates composed of amine functional groups(–NH2)for capturing CO₂ were screened,with quadrapurebenzylamine(QPBZA)exhibiting superior CO₂-adsorbing ability among the proposed candidates.Accordingly,we fabricated the CASE by sandwiching QPBZA between porous carbon layers,which facilitated the transport of gaseous products.The new electrode was demonstrated to effectively capture the evolved CO₂ during charge,therefore altering the reaction pathways to the ideal case.It is highly advantageous to mitigate the undesirable CO₂ incorporation in the next discharge,resulting in improved cyclability.This novel concept of a CO₂-sponging electrode provides an alternative route to the realization of practically meaningful Li–O₂ batteries.     

Recent advances in interlayer and separator engineering for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have great potential in next-generation energy storage due to its high theoretical specific capacity and energy density.However,...     

Recent advances in oxygen electrocatalysts based on tunable structural polymers

Due to their high energy density, great safety and eco-friendliness, zinc-air batteries (ZABs) attract much attention. During the process of charging and discharging, the two key processes viz. oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) limit their efficiency. In general, the noble metal-based electrocatalysts (ORR: platinum (Pt); OER: iridium (IV) oxide [IrO₂] and ruthenium oxide [RuO₂]) have long been used. Nonetheless, these noble metal electrocatalysts also have their limitations owing to high cost and poor stability. As alternatives, polymers are found to be most promising on account of their tunable structure, uniform network, high surface morphology and strong durability. Polymers are capable catalysts. In this review, recent advances as well as insight into the architecture of covalent organic polymers (COPs), metal coordination polymers (MCPs) and pyrolysis-free polymers (PFPs) are duly outlined.     

Recent advances of composite electrolytes for solid-state Li batteries

All-solid-state lithium batteries(ASSLBs) are recognized as high energy density batteries system without safety issues within the next generation of batteries. The development of solid electrolytes is the crucial step of ASSLBs. The composite electrolyte has stable physical and electrochemical characteristics, and its comprehensive performance surpasses the individual solid electrolyte, bringing unique vitality to the solid electrolyte. However, their intrinsic weakness limits the development of...     

Recent advances of vanadium-based cathode materials for zinc-ion batteries

Zn-ion batteries (ZIBs) have gained great attention as promising next-generation power sources, because of their low cost, enviable safety and high theoretical capacity. Recently, massive researches have been devoted to vanadium-based materials as cathodes in ZIBs, owing to their multiple valence states, competitive gravimetric energy density, but the capacity degradation, sluggish kinetics, low operating voltage hinder further optimization of their performance in ZIBs. This review summarizes recent progress to increase the interlayer spacing, structural stability, and the diffusion ability of the guest Zn ions, including the insertion of different ions, introduction of defects, design of diverse morphologies, the combination of other materials. We also focus on approaches to promoting the valuable performance of vanadium-based cathodes, along with the related ongoing scientific challenges and limitations. Finally, the future perspectives and research directions of vanadium-based aqueous ZIBs are provided.     

Recent advances in spinel-type electrocatalysts for bifunctional oxygen reduction and oxygen evolution reactions

The demand for efficient and environmentally-benign electrocatalysts that help availably harness the renewable energy resources is growing rapidly. In recent years, increasing insights into the design of water electrolysers, fuel cells, and metal–air batteries emerge in response to the need for developing sustainable energy carriers, in which the oxygen evolution reaction and the oxygen reduction reaction play key roles. However, both reactions suffer from sluggish kinetics that restricts the reactivity. Therefore, it is vital to probe into the structure of the catalysts to exploit high-performance bifunctional oxygen electrocatalysts. Spinel-type catalysts are a class of materials with advantages of versatility, low toxicity, low expense, high abundance, flexible ion arrangement, and multivalence structure. In this review, we afford a basic overview of spinel-type materials and then introduce the relevant theoretical principles for electrocatalytic activity, following that we shed light on the structure–property relationship strategies for spinel-type catalysts including electronic structure, microstructure, phase and composition regulation,and coupling with electrically conductive supports. We elaborate the relationship between structure and property, in order to provide some insights into the design of spinel-type bifunctional oxygen electrocatalysts.     

Recent advances for Zn-gas batteries beyond Zn-air/oxygen battery

Zn-gas batteries have attracted great attention in the area of energy conversion and storage owing to their high theoretical energy density in the past decades. In addition to the most widely researched Zn-air/oxygen battery, other novel Zn-gas batteries such as Zn-CO₂, Zn-N₂ and Zn-NO batteries as “killing two birds with one stone” strategy have emerged to provide energy power and upgrade the pollutant/useless gases simultaneously. This technology becomes more appealing as a low-cost and controllable method to produce value-added chemicals and fuels (such as CO, HCOO^?, CH₄, NH₃) at the cathode driven by surplus electricity. However, there is an absence of a guide for the selection of catalyst and the construction of energy system. Herein, we overview recent achievements in typical Zn-gas batteries beyond Zn-air/oxygen, mainly including Zn-CO₂, Zn-N₂ and Zn-NO batteries. The energy storage mechanism of these novel Zn-gas batteries has been clearly elaborated. Then, the produced value-added chemicals and the design of cathodic catalyst materials are summarized. Lastly, the remaining challenges and possible directions of Zn-gas batteries, such as highly reduced products, high yield rate and remarkable battery performance, in the future are discussed.     

Electrical conductivity in Li2O2 and its role in determining capacity limitations in non-aqueous Li-O2 batteries

Non-aqueous Li-air or Li-O(2) cells show considerable promise as a very high energy density battery couple. Such cells, however, show sudden death at capacities far below their theoretical capacity and this, among other problems, limits their practicality. In this paper, we show that this sudden death arises from limited charge transport through the growing Li(2)O(2) film to the Li(2)O(2)-electrolyte interface, and this limitation defines a critical film thickness, above which it is not possible to support electrochemistry at the Li(2)O(2)-electrolyte interface. We report both electrochemical experiments using a reversible internal redox couple and a first principles metal-insulator-metal charge transport model to probe the electrical conductivity through Li(2)O(2) films produced during Li-O(2) discharge. Both experiment and theory show a "sudden death" in charge transport when film thickness is ~5 to 10 nm. The theoretical model shows that this occurs when the tunneling current through the film can no longer support the electrochemical current. Thus, engineering charge transport through Li(2)O(2) is a serious challenge if Li-O(2) batteries are ever to reach their potential.     

Electrochemical oxidation of solid Li2O2 in non-aqueous electrolyte using peroxide complexing additives for lithium–air batteries

Using the anion receptor tris(penftafluorophenyl) borane as an additive to non-aqueous electrolytes, the solubility of solid Li₂O₂ can be dramatically increased through the Lewis acid–base interaction between boron and peroxide. The complexed boron-peroxide ions can be electrochemically oxidized with much better kinetics than the oxidation of solid Li₂O₂ on a carbon powder microelectrode. This discovery could lead to a new avenue for the development of high capacity, high rate, rechargeable, Li–Air batteries.