Search Results (18)

With unique 4f electronic shells, rare earth metal-based catalysts have been attracting tremendous attention in electrocatalysis, including oxygen reduction reaction (ORR). In particular, atomically dispersed Ce/CeO₂-based catalysts have been explored extensively due to several unique features. This review article provides a comprehensive understanding of (i) the significance of the effect of Ce high-spin state on ORR activity enhancement on the Pt and non-pt electrocatalysts, (ii) the spatially confining and stabilizing effect of ceria on the generation of atomically dispersed transition metal-based catalysts, (iii) experimental and theoretical evidence of the effect of Ce³⁺ ↔ Ce⁴⁺ redox pain on radical scavenging, (iv) the effect of the Ce 4f electrons on the d-band center and electron transfer between Ce to the N-doped carbon and transition metal catalysts for enhanced ORR activity, and (v) the effect of Pt/CeO₂/carbon heterojunctions on the stability of the Pt/CeO₂/carbon electrocatalyst for ORR. Among several strategies of synthesizing Ce/CeO₂ electrocatalysts, the metal–organic framework (MOF)-derived catalysts are being perused extensively due to the tendency of Ce to readily coordinate with O- and N-containing ligands, which upon undergoing pyrolysis, results in the formation of high surface area, porous carbon networks with atomically dispersed metallic/clusters/nanoparticles of Ce active sites. This review paper provides an overview of recent advancements regarding Ce/CeO₂-based catalysts derived from the MOF precursor for ORR in fuel cells and metal–air battery applications and we conclude with insights into key issues and future development directions. Full article

III-nitrides are crucial materials for solar flow batteries due to their versatile properties. In contrast to the well-studied MOVPE reaction mechanism for AlN and GaN, few works report gas-phase mechanistic studies on the growth of InN. To better understand the reaction thermodynamics, this work revisited the gas-phase reactions involved in metal–organic vapor-phase epitaxy (abbreviated as MOVPE) growth of InN. Utilizing the M06-2X function in conjunction with Pople’s triple-ζ split-valence basis set with polarization functions, this work recharacterized all stationary points reported in previous literature and compared the differences between the structures and reaction energies. For the reaction pathways which do not include a transition state, rigorous constrained geometry optimizations were utilized to scan the PES connecting the reactants and products in adduct formation and XMIn (M, D, T) pyrolysis, confirming that there are no TSs in these pathways, which is in agreement with the previous findings. A comprehensive bonding analysis indicates that in TMIn:NH₃, the In-N demonstrates strong coordinate bond characteristics, whereas in DMIn:NH₃ and MMIn:NH₃, the interactions between the Lewis acid and base fragments lean toward electrostatic attraction. Additionally, the NBO computations show that the H radical can facilitate the migration of electrons that are originally distributed between the In-C bonds in XMIn. Based on this finding, novel reaction pathways were also investigated. When the H radical approaches MMInNH₂, MMIn:NH₃ rather than MMInHNH₂ will generate and this is followed by the elimination of CH₄ via two parallel paths. Considering the abundance of H₂ in the environment, this work also examines the reactions between H₂ and XMIn. The Mulliken charge distributions indicated that intermolecular electron transfer mainly occurs between the In atom and N atom whiling forming (DMInNH₂)₂, whereas it predominately occurs between the In atom and the N atom intramolecularly when generating (DMInNH₂)₃. Full article

Organic materials have emerged as promising candidates for cathode materials in lithium-ion batteries and supercapacitors, offering unique properties and advantages over traditional inorganic counterparts. This review investigates the use of organic compounds as cathode materials in energy storage devices, focusing on their application in lithium-ion batteries and supercapacitors. The review covers various types of organic materials, organosulfur compounds, organic free radical compounds, organic carbonyl compounds, conducting polymers, and imine compounds. The advantages, challenges, and ongoing developments in this area are examined and the potential of organic cathode materials to achieve higher energy density, improved cycling stability, and environmental sustainability is highlighted. The comprehensive analysis of organic cathode materials provides insights into their electrochemical performance, electrode reaction mechanisms, and design strategies such as molecular structure modification, hybridization with inorganic components, porous architectures, conductive additives, electrolyte optimization, binder selection, and electrode architecture to improve their efficiency and performance. In addition, future research in the field of organic cathode materials should focus on addressing current limitations such as low energy density, cycling stability, poor discharge capability, potential safety concerns and improving their performance. To do this, it will be necessary to improve structural stability, conductivity, cycle life, and capacity fading, explore new redox-active organic compounds, and pave the way for the next generation of high-performance energy storage devices. For organic cathode materials to be commercially viable, it is also essential to develop scalable and economical manufacturing processes. Full article

7,7′,8,8′-tetracyanoquinodimethane (TCNQ) is one of the most widely used effective surface electron acceptors in organic electronics and sensors, which opens up a very interesting field in electrochemical applications. In this review article, we outline the historical context of electrochemically stable selective electrode materials based on TCNQ and its derivatives and their development, their electrochemical characteristics, and the experimental aspects of their electrochemical applications. TCNQ-modified electrodes are characterized by long-term stability, reproducibility, and a low detection limit compared to other sensors; thus, their use can increase determination speed and flexibility and reduce investigation costs. TCNQ and its derivatives can also be successfully combined with other detector materials for cancer-related clinical diagnostic testing. Examples of simple, rapid, and sensitive detection procedures for various analytes are provided. Applications of new electrochemically stable TCNQ-based metal/covalent–organic hybrid frameworks, with exceptionally large surface areas, tunable pore sizes, diverse functionality, and high electrical conductivity, are also presented. As a result, they also offer enormous potential as revolutionary catalysts, drug carrier systems, and smart materials, as well as for use in gas storage. The use of TCNQ compounds as promising active electrode materials in high-power organic batteries/energy storage devices is discussed. We hope that the information featured in this review will provide readers with a good understanding of the chemistry of TCNQ and, more importantly, help to find good ways to prepare new micro-/nanoelectrode materials for rational sensor design. Full article

Redox flow batteries (RFBs) have attracted significant attention as a promising electrochemical energy storage technology, offering various advantages such as grid-scale electricity production with variable intermittent electricity delivery, enhanced safety compared to metal-ion batteries, decoupled energy and power density, and simplified manufacturing processes. For this review, we exclusively focus on organic, non-aqueous redox flow batteries. Specifically, we address the most recent progress and the major challenges related to the design and synthesis of robust redox-active organic compounds. An extensive examination of the synthesis and characterization of a wide spectrum of redox-active molecules, focusing particularly on derivatives of posolytes such as quinone, nitroxyl radicals, dialkoxybenzenes, and phenothiazine and negolytes such as viologen and pyridiniums, is provided. We explore the incorporation of various functional groups as documented in the references, aiming to enhance the chemical and electrochemical stability, as well as the solubility, of both the neutral and radical states of redox-active molecules. Additionally, we offer a comprehensive assessment of the cell-cycling performance exhibited by these redox-active molecules. Full article

Lithium–sulfur (Li–S) batteries hold great promise in the field of power and energy storage due to their high theoretical capacity and energy density. However, the “shuttle effect” that originates from the dissolution of intermediate lithium polysulfides (LiPSs) during the charging and discharging process is prone to causing continuous irreversible capacity loss, which restricts the practical development. Beyond the traditional Li–S batteries based on the dissolution-diffusion mechanism, novel Li–S batteries based on solid-phase conversion exhibit superior cycling stability owing to the absolute prevention of polysulfides shuttling. Radically eliminating the formation of polysulfides in cathodes or cutting off their diffusion in electrolytes are the two main ways to achieve solid-phase conversion. Generally, direct transformation of sulfur to final Li₂S without polysulfides participation tends to occur in short-chain sulfur polymers or special molecular forms of sulfur substances, while specific regulations of liquid electrolytes with solvating structure or solid-state electrolytes can effectively suppressing the polysulfides dissolution. In this review, we systematically organized and summarized the structures and approaches to achieve solid-phase conversion, introduce their preparation methods, discuss their advantages and disadvantages, and analyze the factors and effects of different structures on battery performances. Finally, the problems demanding a prompt solution for the practical development of solid-phase conversion-based Li–S batteries, as well as their future development direction, are suggested. Full article

The need for environmentally benign portable energy storage drives research on organic batteries and catalytic systems. These systems are a promising replacement for commonly used energy storage devices that rely on limited resources such as lithium and rare earth metals. The redox-active TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl) fragment is a popular component of organic systems, as its benefits include remarkable electrochemical performance and decent physical properties. TEMPO is also known to be an efficient catalyst for alcohol oxidation, oxygen reduction, and various complex organic reactions. It can be attached to various aliphatic and conductive polymers to form high-loading catalysis systems. The performance and efficiency of TEMPO-containing materials strongly depend on the molecular structure, and thus rational design of such compounds is vital for successful implementation. We discuss synthetic approaches for producing electroactive polymers based on conductive and non-conductive backbones with organic radical substituents, fundamental aspects of electrochemistry of such materials, and their application in energy storage devices, such as batteries, redox-flow cells, and electrocatalytic systems. We compare the performance of the materials with different architectures, providing an overview of diverse charge interactions for hybrid materials, and presenting promising research opportunities for the future of this area. Full article

Multifunctional molecular materials have attracted material scientists for several years as they are promising materials for the future generation of electronic devices. Careful selection of their molecular building blocks allows for the combination and/or even interplay of different physical properties in the same crystal lattice. Incorporation of redox activity in these networks is one of the most appealing and recent synthetic strategies used to enhance magnetic and/or conducting and/or optical properties. Quinone derivatives are excellent redox-active linkers, widely used for various applications such as electrode materials, flow batteries, pseudo-capacitors, etc. Quinones undergo a reversible two-electron redox reaction to form hydroquinone dianions via intermediate semiquinone radical formation. Moreover, the possibility to functionalize the six-membered ring of the quinone by various substituents/functional groups make them excellent molecular building blocks for the construction of multifunctional tunable metal-organic frameworks (MOFs). An overview of the recent advances on benzoquinone-based MOFs, with a particular focus on key examples where magnetic and/or conducting properties are tuned/switched, even simultaneously, by playing with redox activity, is herein envisioned. Full article

Flexible cross-linked anion exchange membranes (AEMs) based on poly (p-phenylene oxide) grafted with N-spirocyclic quaternary ammonium cations were synthesized via UV-induced free-radical polymerization by using diallylpiperidinium chloride as an ionic monomer. Five membranes with ion exchange capacity (IEC) varying between 1.5 to 2.8 mmol Cl⁻·g⁻¹ polymer were obtained and the correlation between IEC, water uptake, state of water in the membrane and ionic conductivity was studied. In the second part of this study, the influence of properties of four of these membranes on cell cycling stability and performance was investigated in an aqueous organic redox flow battery (AORFB) employing dimethyl viologen (MV) and N,N,N-2,2,6,6-heptamethylpiperidinyl oxy-4-ammonium chloride (TMA-TEMPO). The influence of membrane properties on cell cycling stability and performance was studied. At low-current density (20 mA·cm⁻²), the best capacity retention was obtained with lower IEC membranes for which the water uptake, freezable water and TMA-TEMPO and MV crossover are low. However, at a high current density (80 mA·cm⁻²), membrane resistance plays an important role and a membrane with moderate IEC, more precisely, moderate ion conductivity and water uptake was found to maintain the best overall cell performance. The results in this work contribute to the basic understanding of the relationship between membrane properties and cell performance, providing insights guiding the development of advanced membranes to improve the efficiency and power capability for AORFB systems. Full article

Li-O₂ batteries represent a promising rechargeable battery candidate to answer the energy challenges our world is facing, thanks to their ultrahigh theoretical energy density. However, the poor cycling stability of the Li-O₂ system and, overall, important safety issues due to the formation of Li dendrites, combined with the use of organic liquid electrolytes and O₂ cross-over, inhibit their practical applications. As a solution to these various issues, we propose a composite gel polymer electrolyte consisting of a highly cross-linked polymer matrix, containing a dextrin-based nanosponge and activated with a liquid electrolyte. The polymer matrix, easily obtained by thermally activated one pot free radical polymerization in bulk, allows to limit dendrite nucleation and growth thanks to its cross-linked structure. At the same time, the nanosponge limits the O₂ cross-over and avoids the formation of crystalline domains in the polymer matrix, which, combined with the liquid electrolyte, allows a good ionic conductivity at room temperature. Such a composite gel polymer electrolyte, tested in a cell containing Li metal as anode and a simple commercial gas diffusion layer, without any catalyst, as cathode demonstrates a full capacity of 5.05 mAh cm⁻² as well as improved reversibility upon cycling, compared to a cell containing liquid electrolyte. Full article

Environmentally persistent free radicals (EPFRs) can be detected in ambient PM_2.5, cigarette smoke, and soils and are formed through combustion and thermal processing of organic materials. The hazards of EPFRs are largely unknown. In this study, we assess the developmental toxicity of EPFRs and the ability of TEMPOL (4-Hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl) to protect against such hazards using zebrafish embryos. Particles containing EPFRs were acquired by dosing dichlorobenzene (DCB) vapor on the Cab-o-sil/5% CuO particles at 230 °C in vacuo (referred to as DCB-230). The particles were suspended in ultrapure water to make 1 mg/mL of stock solution from which series dilution was undertaken to obtain 10, 20, 30, 40, 50, 60, 80, and 100 µg/mL final test solutions, which were then placed in individual wells with a 4 h postfertilization (hpf) zebrafish embryo. Plates were run in duplicate to obtain a sample size of 24 animals per concentration; 12 embryos were exposed per concentration per plate. Statistical analysis of the morphology endpoints was performed. We investigated overt toxicity responses to DCB-230 in a 22-endpoint battery that included developing zebrafish from 24–120 hpf. Exposure to concentrations greater than 60 µg/mL of DCB-230 induced high mortality in the developmental zebrafish model. Exposure to EPFRs induced developmental hazards that were closely related to the concentrations of free radicals and EPFRs. The potential protective effects of TEMPOL against EPFRs’ toxicity in zebrafish were investigated. Exposure to EPFRs plus TEMPOL shifted the concentration to an induced 50% adverse effect (EC50), from 23.6 to 30.8 µg/mL, which verifies TEMPOL’s protective effect against EPFRs in the early phase of zebrafish development. Full article

Since environmental pollution by emerging organic contaminants is one of the most important problems, gaining ground year after year, the development of decontamination technologies of water systems is now imperative. Advanced oxidation processes (AOPs) with the formation of highly reactive radicals can provide attractive technologies for the degradation of organic pollutants in water systems. Among several AOPs that can be applied for the formation of active radicals, this review study focus on sulfate radical based-AOPs (SR-AOPs) through the heterogeneous catalytic activation of persulfate (PS) or peroxymonosulfate (PMS) using perovskite and spinel oxides as catalysts. Perovskites and spinels are currently receiving high attention and being used in substantial applications in the above research area. The widespread use of these materials is based mainly in the possibilities offered by their structure as it is possible to introduce into their structures different metal cations or to partially substitute them, without however destroying their structure. In this way a battery of catalysts with variable catalytic activities can be obtained. Due to the fact that Co ions have been reported to be one of the best activators of PMS, special emphasis has been placed on perovskite/spinel catalysts containing cobalt in their structure for the degradation of organic pollutants through heterogeneous catalysis. Among spinel materials, spinel ferrites (MFe₂O₄) are the most used catalysts for heterogeneous activation of PMS. Specifically, catalysts with cobalt ion in the A position were reported to be more efficient as PMS activators for the degradation of most organic pollutants compared with other transition metal catalysts. Substituted or immobilized catalysts show high rates of degradation, stability over a wider pH area and also address better the phenomena of secondary contamination by metal leaching, thus an effective method to upgrade catalytic performance. Full article

A three-fold symmetric trioxotriangulene derivative with three pyridyl groups as coordinating sites was designed and synthesized. In a cyclic voltammetry measurement, the trioxotriangulene skeleton exhibited a multi-stage redox ability from neutral radical to radical tetra-anion species. In the zinc complex of monoanion species, three pyridyl groups coordinated to the zinc ion to build up a two-dimensional coordination network with a cavity larger than 12 Å in diameter. This complex was utilized as a cathode active material of a lithium ion battery, and it exhibited a capacity of ca. 60 mAh g⁻¹ per the weight of the active material with a stable cycling performance up to 1000 cycles. This work shows that the coordination network formed by the trioxotriangulene-based ligand was effective in the improvement of cycle performance of the organic rechargeable battery. Full article

A novel nitroxyl radical polymer poly(TEMPO-acrylamide-co-sodium styrene sulfonate) (abbreviated as poly(TAm-co-SSS)) was synthesized using 4-acrylamido-2,2,6,6- tetramethylpiperidine (AATP) copolymerized with styrene sulfonate sodium (SSS). AATP was synthesized through a substitution reaction of acryloyl chloride. Meanwhile, poly(4-acrylamido-2,2,6,6-tetramethylpiperidine-1-nitroxyl radical) (PTAm) was prepared as a control sample. Then, the structures of products were characterized by nuclear magnetic resonance spectroscopy (¹H-NMR), Fourier transform infrared spectroscopy (FT-IR), high performance liquid chromatography-mass spectrometry (HPLC-MS), differential scanning calorimetry (DSC), X-Ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR), respectively. Additionally, the electrochemical impedance spectra (EIS) and the charge-discharge cycling properties were studied. The results demonstrated that the poly(TAm-co-SSS) with the side group of sodium sulfonate adjacent to TEMPO group exhibits a better charge-discharge cycling stability than that of the PTAm. Moreover, the charge specific capacity of the poly(TAm-co-SSS) is larger than that of the PTAm. Besides, the first coulombic efficiency of poly(TAm-co-SSS) is higher in comparison with that of PTAm. These superior electrochemical performances were ascribed to the synergistic effect of sulfonate ions group and nitroxyl radical structure, which benefits the improvement of charge carrier transportation of the nitroxyl radical polymers. Consequently, the nitroxyl radical poly(TAm-co-SSS) is promising for use in organic radical battery materials, based on the good electrochemical properties. Full article

Redox-active polymer networks based on stable nitroxide radicals are a very promising class of materials to be used in the so-called organic radical batteries. In order to obtain fast-charging and high power electrodes, however, excellent ionic conductivity inside the electrode material is required to allow easy diffusion of ions and fast redox reactions. In this contribution, we investigated redox-active poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) chains cross-linked through ionic liquid-like 1,2,3-triazolium groups. Different networks were prepared in which the amount of cross-linker and the counter-anion associated to the 1,2,3-triazolium group were varied. The ionic conductivities of the different polymer networks were first measured in the solid state by electrochemical impedance spectroscopy at different temperatures, and an increased ionic conductivity was measured when 1,2,3-triazolium groups were present in the network. The effects of the chemical nature of the counterions associated to the 1,2,3-triazolium groups and of the crosslinking density were then studied. The best ionic conductivities were obtained when bis (trifluoromethane)sulfonamide (TFSI) counter-anions were used, and when the crosslinking density of the TFSI-containing gel was higher. Finally, those ion-conducting gels were loaded with free LiTFSI and the transference number of lithium ions was accordingly measured. The good ionic conductivities and lithium ions transference numbers measured for the investigated redox-active gels make them ideal candidates for application as electrode materials for either organic radical batteries or pseudo-capacitors energy storage devices. Full article