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Table of Content

    20 March 2024, Volume 7 Issue 1
    PGM-Free Biomass-Derived Electrocatalysts for Oxygen Reduction in Energy Conversion Devices: Promising Materials
    Stefano Zago, Laura C. Scarpetta Pizo, José H. Zagal, Linlin Li, Stefania Specchia
    2024, 7(1):  1.  doi:10.1007/s41918-023-00197-3
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    Biomass is a low-cost, abundant and renewable resource that can be used to manufacture porous carbon-based materials for a variety of applications. Different mesoporous carbon supports can be obtained from the various synthetic approaches that are aimed at increasing the specific surface area and functionalization. Currently, most of the biomass is used for energy recovery. The circular economy approach could lead to the development of cheap and sustainable materials, and turning of wastes into a precious resource. In this review, we provide the recent advances in the field of electrochemistry for porous carbon materials derived from biomass, which offers wider applications in proton exchange membrane fuel cells (PEMFCs), anion exchange membrane fuel cells (AEMFCs) and Zn-air batteries (ZABs). The focus is on understanding the required properties of the materials and the role of synthetic pathways in platinum group metal (PGM) free electrocatalysts. The most promising materials are evaluated towards the oxygen reduction reaction (ORR) in PEMFC, AEMFC, and ZAB. The results achieved showed that the expected performances on these energy conversion devices still lack for deployment in practice, especially if compared with commercially available PGM-free electrocatalysts. This review article provides insights on how to improve the actual electrocatalytic activity of biomass-derived materials.
    Polyethylene Oxide-Based Composite Solid Electrolytes for Lithium Batteries: Current Progress, Low-Temperature and High-Voltage Limitations, and Prospects
    Xin Su, Xiao Pei Xu, Zhao Qi Ji, Ji Wu, Fei Ma, Li Zhen Fan
    2024, 7(1):  2.  doi:10.1007/s41918-023-00204-7
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    Lithium-ion batteries (LIBs) are considered to be one of the most promising power sources for mobile electronic products, portable power devices and vehicles due to their superior environmental friendliness, excellent energy density, negligible memory effect, good charge/discharge rates, stable cycling life, and efficient electrochemical energy conversion, which distinguish it from other power devices. However, the flammable and volatile organic solvents in carbonate-containing liquid electrolytes can leach, resulting in thermal runaway and interface reactions, thus significantly limiting its application. The use of polymer solid electrolytes is an effective way to solve this safety issues, among which poly (ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) have attracted much attention because of their stable mechanical properties, ease of fabrication, excellent electrochemical and thermal stability. Unfortunately, PEO-SPEs with their low room-temperature ionic conductivity, narrow electrochemical windows, poor interface stability, and uncontrollable growth of lithium dendrites cannot meet the demand for high energy density in future LIBs. Therefore, this review firstly describes the ion transport mechanisms and challenges that are crucial for PEO-SPEs, and then provides a comprehensive review of current approaches to address the challenges, including novel and efficient lithium salts, additives, composite electrolytes, stable solid electrolyte interfaces, 3-D lithium metals and alloys, cathode protection layers and multi-layer electrolytes. Finally, future research directions are proposed for the stable operation of PEO-SPEs at room temperature and high voltage, which is imperative for the commercialization of safe and high energy density LIBs.
    Research Progress on the Solid Electrolyte of Solid-State Sodium-Ion Batteries
    Shuzhi Zhao, Haiying Che, Suli Chen, Haixiang Tao, Jianping Liao, Xiao Zhen Liao, Zi Feng Ma
    2024, 7(1):  3.  doi:10.1007/s41918-023-00196-4
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    Because sodium-ion batteries are relatively inexpensive, they have gained significant traction as large-scale energy storage devices instead of lithium-ion batteries in recent years. However, sodium-ion batteries have a lower energy density than lithium-ion batteries because sodium-ion batteries have not been as well developed as lithium-ion batteries. Solid-state batteries using solid electrolytes have a higher energy density than liquid batteries in regard to applications with sodium-ion batteries, making them more suitable for energy storage systems than liquid batteries. Due to their low ionic conductivity, solid electrolytes are currently unable to achieve comparable performance to liquid electrolytes at room temperature. In this review, we discuss the advancements in SSEs applied to sodium-ion batteries in recent years, including inorganic solid electrolytes, such as Na–β-Al2O3, NASICON and Na3PS4, polymer solid electrolytes based on PEO, PVDF-HFP and PAN, and plastic crystal solid electrolytes mainly composed of succinonitrile. Additionally, appropriate solutions for low ionic conductivity, a narrow electrochemical stability window and poor contact with electrodes, which are the significant flaws in current SSEs, are discussed in this review.
    Free-Standing Single-Atom Catalyst-Based Electrodes for CO2 Reduction
    M. Nur Hossain, Lei Zhang, Roberto Neagu, Xiaolin Li, Enoch Rassachack
    2024, 7(1):  5.  doi:10.1007/s41918-023-00193-7
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    Electrochemical CO2 reduction technology could solve the CO2-induced climate warming by electrochemically converting atmospheric CO2 back into fuel, essentially recycling it and building a low carbon emission economy. However, the electrochemical CO2 reduction reaction (CO2RR) poses a significant challenge due to the highly stable and linear CO2 molecules, in addition to a proton-coupled multi-electron transfer process. Thus, highly active catalysts, placed on activity bolstering materials, and permeable electrodes are crucial for CO2RR. Single-atom catalysts (SACs) have recently garnered increasing interest in the electrocatalysis community due to their potentially high mass efficiency and cost benefits (every atom is an active center, resulting in nearly 100% utilization) and adjustable selectivity (higher uniformity of the active sites compared to nanoparticles). However, preserving the accessibility and activity of the SACs inside the electrode poses major materials development and electrode design challenges. A conventional layered structure SAC electrode typically consists of a gas diffusion layer (GDL), a microporous layer (MPL) and a SAC catalyst layer (SACCL), fabricated by using a powder bonding process. However, this process usually encounters issues such as delamination and instability of SACs due to the weak binder-catalyst-support interface. Conversely, the free-standing SAC electrode design has the potential to overcome these issues by eliminating the GDL, MPL, and need of a binder, in contrast to the powder bonding process. This work first reviews the latest developments in experimental and modeling studies of powdered SAC electrode by the traditional powder bonding process. Next, it examines the development towards the free-standing SAC electrode for high-performance electrochemical reduction of CO2. The synthesis-structure-fabrication-performance relationships of SAC-based materials and associated electrodes are analyzed. Furthermore, the article presents future challenges and perspectives for high-performance SAC electrodes for CO2RR.
    Solving the Singlet Oxygen Puzzle in Metal-O2 Batteries: Current Progress and Future Directions
    Yaying Dou, Shuochao Xing, Zhang Zhang, Zhen Zhou
    2024, 7(1):  6.  doi:10.1007/s41918-023-00201-w
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    The development of aprotic alkali metal-oxygen batteries has shown promise due to their high theoretical specific energy, which is supported by the exergonic oxygen electrochemistry. However, practical realization of these batteries has been impeded by parasitic reactions that compromise their rechargeability, efficiency, and cycle life. Recent research has identified highly reactive singlet oxygen (1O2) as the main cause of degradation, which has led to a focus on understanding and harnessing this reactive species. This review provides a summary of current knowledge on the formation mechanisms of 1O2, identifies knowledge gaps that need to be addressed in the future, and discusses the implications of contaminants and battery components for 1O2 formation. The review also covers recent advances in deactivating and taming 1O2, and explains the mechanisms that underpin these strategies. We conclude with perspectives on the remaining challenges and future research opportunities in the field of 1O2-related (electro)chemistry in metal-oxygen batteries.
    Recent Advances in Redox Flow Batteries Employing Metal Coordination Complexes as Redox-Active Species
    Bin Liu, Yiju Li, Guocheng Jia, Tianshou Zhao
    2024, 7(1):  7.  doi:10.1007/s41918-023-00205-6
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    Redox flow batteries (RFBs) that employ sustainable, abundant, and structure-tunable redox-active species are of great interest for large-scale energy storage. As a vital class of redox-active species, metal coordination complexes (MCCs) possessing the properties of both the organic ligands and transition metal ion centers are attracting increasing attention due to the advantages of multielectron charge transfer, high structural tailorability, and reduced material crossover. Herein, we present a critical overview of RFBs that employ MCCs as redox-active materials in both aqueous and nonaqueous mediums. The progress is comprehensively summarized, including the design strategies, solubility characteristics, electrochemical properties, and battery cycling performance of MCCs. Emphasis is placed on the ligand selection and modification strategies used to tune the critical properties of MCCs, including their redox potential, solubility, cycling stability, and electron transfer redox reactions, to achieve stable cycled RFBs with a high energy density. Furthermore, we discuss the current challenges and perspectives related to the development of MCC-based RFBs for large-scale energy storage implementations.
    Electrochemical Carbon Dioxide Reduction in Acidic Media
    Zhe Yao, Xiaomeng He, Rui Lin
    2024, 7(1):  8.  doi:10.1007/s41918-024-00210-3
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    The electrochemical reduction of carbon dioxide (CO2RR) stands as an enticing approach for the production of essential chemicals and feedstocks, storing clean electric energy and mitigating greenhouse gas emissions. Recent years have witnessed remarkable breakthroughs in CO2RR, enhancing its performance and transitioning related research from laboratory settings toward industrial realization. However, the journey of CO2RR development is not devoid of challenges, including issues like mass transfer limitation, salt accumulation, and flooding phenomena. Remarkably, recent studies have unveiled a promising avenue by conducting CO2RR in an acidic environment, effectively circumventing these challenges and presenting novel opportunities. In this review, we embark on a reassessment of H-cells and flow cells, delving into their opportunities, challenges, strengths, and weaknesses. Additionally, we compile recent advancements in CO2RR under acidic conditions, elucidating the performance metrics and strategies embraced by pertinent research. Subsequently, we propose three pivotal concerns in acidic CO2RR: ① balancing the competition between CO2RR and hydrogen evolution reaction (HER), ② enhancing the selectivity, and ③ exploring industrial applications. And finally, we delve into the core factors influencing the performance of CO2RR in acid: local pH, cation effects, and catalyst design. Building upon these strategies, challenges, and insights, prospects are proposed for the future trajectory of CO2RR development.
    Advanced Electrode Structures for Proton Exchange Membrane Fuel Cells: Current Status and Path Forward
    Gaoqiang Yang, ChungHyuk Lee, Xiaoxiao Qiao, Siddharth Komini Babu, Ulises Martinez, Jacob S. Spendelow
    2024, 7(1):  9.  doi:10.1007/s41918-023-00208-3
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    Proton exchange membrane fuel cells (PEMFCs) have demonstrated their viability as a promising candidate for clean energy applications. However, performance of conventional PEMFC electrodes, especially the cathode electrode, suffers from low catalyst utilization and sluggish mass transport due to the randomly distributed components and tortuous transport pathways. Development of alternative architectures in which the electrode structure is controlled across a range of length scales provides a promising path toward overcoming these limitations. Here, we provide a comprehensive review of recent research and development of advanced electrode structures, organized by decreasing length-scale from the millimeter-scale to the nanometer-scale. Specifically, advanced electrode structures are categorized into five unique architectures for specific functions: (1) macro-patterned electrodes for enhanced macro-scale mass transport, (2) micro-patterned electrodes for enhanced micro-scale mass transport, (3) electrospun electrodes with fiber-based morphology for enhanced in-plane proton transport and through-plane O2 transport, (4) enhanced-porosity electrodes for improved oxygen transport through selective inclusion of void space, and (5) catalyst film electrodes for elimination of carbon corrosion and ionomer poisoning. The PEMFC performance results achieved from each alternative electrode structure are presented and tabulated for comparison with conventional electrode architectures. Moreover, analysis of mechanisms by which new electrode structures can improve performance is presented and discussed. Finally, an overview of current limitations and future research needs is presented to guide the development of electrode structures for next generation PEMFCs.
    Emerging Atomically Precise Metal Nanoclusters and Ultrasmall Nanoparticles for Efficient Electrochemical Energy Catalysis: Synthesis Strategies and Surface/Interface Engineering
    Mingjie Wu, Fang Dong, Yingkui Yang, Xun Cui, Xueqin Liu, Yunhai Zhu, Dongsheng Li, Sasha Omanovic, Shuhui Sun, Gaixia Zhang
    2024, 7(1):  10.  doi:10.1007/s41918-024-00217-w
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    Atomically precise metal nanocluster and ultrasmall nanoparticle catalysts have garnered significant interest in electrocatalysis applications due to their unique geometric and electronic structures. As an intermediate state between single-atom catalysts (SACs) and nanoparticles in size, nanoclusters with specific low nuclearity provide designated metallic states with multiple atoms or surface sites for the adsorption and transformation of reactants/intermediates. The unique catalytic properties of nanoclusters offer a novel platform for designing effective and efficient electrocatalysts, potentially surpassing the SACs in certain catalytic reactions. This review summarizes and discusses the latest progress of nanoclusters and ultrasmall nanoparticles for various electrocatalysis applications, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), CO2 reduction reaction (CO2RR), nitrogen reduction reaction (NRR), hydrogen evolution reaction (HER), various chemicals oxidation reaction (COR), etc. Specifically, this review highlights surface/interface chemical modification strategies and structure-properties relationships, drawing from the atomic-level insights to determine electrocatalytic performance. Lastly, we present the challenges and opportunities associated with nanocluster or ultrasmall nanoparticle electrocatalysts.