Reversible O2 Research Articles

Selective Adsorption of Oxygen from Humid Air in a Metal-Organic Framework with Trigonal Pyramidal Copper(I) Sites.

High or enriched-purity O2 is used in numerous industries and is predominantly produced from the cryogenic distillation of air, an extremely capital- and energy-intensive process. There is significant interest in the development of new approaches for O2-selective air separations, including the use of metal-organic frameworks featuring coordinatively unsaturated metal sites that can selectively bind O2 over N2 via electron transfer. However, most of these materials exhibit appreciable and/or reversible O2 uptake only at low temperatures, and their open metal sites are also potential strong binding sites for the water present in air. Here, we study the framework CuI-MFU-4l (CuxZn5-xCl4-x(btdd)3; H2btdd = bis(1H-1,2,3-triazolo[4,5-b],[4',5'-i])dibenzo[1,4]dioxin), which binds O2 reversibly at ambient temperature. We develop an optimized synthesis for the material to access a high density of trigonal pyramidal CuI sites, and we show that this material reversibly captures O2 from air at 25 °C, even in the presence of water. When exposed to air up to 100% relative humidity, CuI-MFU-4l retains a constant O2 capacity over the course of repeated cycling under dynamic breakthrough conditions. While this material simultaneously adsorbs N2, differences in O2 and N2 desorption kinetics allow for the isolation of high-purity O2 (>99%) under relatively mild regeneration conditions. Spectroscopic, magnetic, and computational analyses reveal that O2 binds to the copper(I) sites to form copper(II)-superoxide moieties that exhibit temperature-dependent side-on and end-on binding modes. Overall, these results suggest that CuI-MFU-4l is a promising material for the separation of O2 from ambient air, even without dehumidification.

The role of oxygen in automotive grade lithium-ion battery cathodes: an atomistic survey of ageing.

The rising demand for high-performance lithium-ion batteries, pivotal to electric transportation, hinges on key materials like the Ni-rich layered oxide LiNixCoyAlzO2 (NCA) used in cathodes. The present study investigates the redox mechanisms, with particular focus on the role of oxygen in commercial NCA electrodes, both fresh and aged under various conditions (aged cells have performed >900 cycles until a cathode capacity retention of ∼80%). Our findings reveal that oxygen participates in charge compensation during NCA delithiation, both through changes in transition metal (TM)-O bond hybridization and formation of partially reversible O2, the latter occurs already below 3.8 V vs. Li/Li+. Aged NCA material undergoes more significant changes in TM-O bond hybridization when cycling above 50% SoC, while reversible O2 formation is maintained. Nickel is found to be redox active throughout the entire delithiation and shows a more classical oxidation state change during cycling with smaller changes in the Ni-O hybridization. By contrast, Co redox activity relies on a stronger change in Co-O hybridization, with only smaller Co oxidation state changes. The Ni-O bond displays an almost twice as large change in its bond length on cycling as the Co-O bond. The Ni-O6 octahedra are similar in size to the Co-O6 octahedra in the delithiated state, but are larger in the lithiated state, a size difference that increases with battery ageing. These contrasting redox activities are reflected directly in structural changes. The NCA material exhibits the formation of nanopores upon ageing, and a possible connection to oxygen redox activity is discussed. The difference in interaction of Ni and Co with oxygen provides a key understanding of the mechanism and the electrochemical instability of Ni-rich layered transition metal oxide electrodes. Our research specifically highlights the significance of the role of oxygen in the electrochemical performance of electric-vehicle-grade NCA electrodes, offering important insights for the creation of next-generation long-lived lithium-ion batteries.

Hydrophobic and Homogeneous Conductive Carbon Matrix for High-Rate Non-Alkaline Zinc-Air Batteries.

Non-alkaline zinc-air batteries (ZABs) that use reversible O2 /ZnO2 chemistry exhibit excellent stability and superior reversibility compared to conventional alkaline ZABs. Unlike alkaline ZABs, ZnO2 discharge products are generated on the surface of the air cathodes in non-alkaline ZABs, requiring more gas-liquid-solid three-phase reaction interfaces. However, the kinetics of reported ZABs based on carbon black (CB) is far from satisfactory due to the insufficient reaction areas. The rational structural design of the air cathode is an effective way to increase active surfaces to further enhance the performance of non-alkaline ZABs. In this study, multi-walled carbon nanotubes (MW-CNTs) with unique mesoporous structures and high pore volumes are selected to replace CB in the air cathode preparation. Due to the larger electrochemically active surface area, superior hydrophobicity, and uniform electroconductibility of MW-CNTs-based cathodes, primary ZABs exhibit high specific capacity (704 mAh gZn-1 ) with a Zn utilization ratio of 85.85% at 1.0mA cm-2 , excellent discharge rate performance, and negligible self-discharge. Furthermore, rechargeable ZABs also demonstrate outstanding rate capability and excellent cycling stability at various current densities. This work provides a fundamental understanding of the criteria for the cathode design of non-alkaline ZABs, thus opening a new pathway for more sustainable ZABs.

Absolutely‐Zero‐Expansion Behavior Enables Ultra‐Long Life for Stationary Energy Storage

AbstractUltra‐long‐life (at least 10 000 cycles) lithium‐ion batteries are very effective for stationary energy‐storage applications. However, even “zero‐strain” materials with small unit‐cell‐volume changes of <1% cannot last for ultra‐long cycles due to gradually accumulated intracrystal strain/stress. Here, Li[Li0.2Cr0.4Ti1.4]O4 is explored as the first absolutely‐zero‐expansion material with unit‐cell‐volume variations of zero during Li+ storage. Its absolutely‐zero‐expansion mechanism is intensively studied, revealing that 16c‐octahedron shrinkage fully offsets 16d‐octahedron expansion through reversible O2− movement. It delivers better cycling stability than, as far as we know, all electrochemical energy‐storage materials previously reported. Its capacity retention at 10 C and 1.0 mg cm−2 after 17 000 cycles reaches 91.5%. When the active‐material loading significantly increases to 6.4 mg cm−2, its capacity retention at 5 C after 500 cycles reaches 95.7%. At an elevated temperature of 45 °C, it not only keeps excellent cycling stability but also exhibits significantly enhanced rate capability. Therefore, Li[Li0.2Cr0.4Ti1.4]O4 is especially suitable for stationary energy storage.

A thermodynamically stable O2-type cathode with reversible O2-P2 phase transition for advanced sodium-ion batteries

Low-cost sodium-ion batteries (SIBs) have shown very promise in the applications of renewable energy and low-speed electric vehicles. The development of a new O2-type cathode in SIBs is very challenging in that this compound is only stable as an intermediate product of P2-type oxides during redox reactions. Here, we report a thermodynamically stable O2-type cathode obtained by Na/Li ion exchange from P2-type oxide in a binary molten salt system. It is demonstrated that the as-prepared O2-type cathode exhibits a highly reversible O2–P2 phase transition during Na+ de-intercalation. The unusual O2–P2 transition has a low volume change of ∼11%, much lower than that of 23.2% for P2–O2 transformation in the P2-type cathode. The lowered lattice volume change of this O2-type cathode gives rise to superior structural stability upon cycling. Therefore, the O2-type cathode possesses a reversible capacity of about 100 mAh/g with a good capacity retention of 87.3% even after 300 cycles at 1C, indicating outstanding long-term cycling stability. These achievements will promote the development new class of cathode materials with high capacity and structural stability for advanced SIBs.

Structure Activity Relationships for Reversible O2 Chemisorption by the Solid Phases of Co(salen) and Co(3F-salen).

The potential of solid-state materials comprising Co(salen) units for concentrating dioxygen from air was recognized over 80 years ago. While the chemisorptive mechanism at the molecular level is largely understood, the bulk crystalline phase plays important, yet unidentified roles. We have reverse crystal-engineered these materials and can for the first time describe the nanostructuring requisite for achieving reversible O2 chemisorption by Co(3R-salen) R = H or F, the simplest and most effective of the many known derivatives of Co(salen). Of the six phases of Co(salen) identified, α-ζ: α = ESACIO, β = VEXLIU, γ, δ, ε, and ζ (this work), only γ, δ, ε, and ζ are capable of reversible O2 binding. Class I materials (phases γ, δ, and ε) are obtained by desorption (40-80 °C, atmospheric pressure) of the co-crystallized solvent from Co(salen)·(solv), solv = CHCl3, CH2Cl2, or 1.5 C6H6. The oxy forms comprise between 1:5 and 1:3 O2:[Co] stoichiometries. Class II materials achieve an apparent maximum of 1:2 O2:Co(salen) stoichiometries. The precursors for the Class II materials comprise [Co(3R-salen)(L)·(H2O)x], R = H, L = pyridine, and x = 0; R = F, L = H2O, and x = 0; R = F, L = pyridine, and x = 0; R = F, L = piperidine, and x = 1. Activation of these depends on the desorption of the apical ligand (L) that templates channels through the crystalline compounds with the Co(3R-salen) molecules interlocked in a Flemish bond brick pattern. The 3F-salen system produces F-lined channels proposed to facilitate O2 transport through the materials through repulsive interactions with the guest O2. We postulate that a moisture dependence of the activity of the Co(3F-salen) series is due to a highly specific binding pocket for locking in water via bifurcated hydrogen bonding to the two coordinated phenolato O atoms and the two ortho F atoms.

Accessible Li Percolation and Extended Oxygen Oxidation Boundary in Rocksalt‐like Cathode Enabled by Initial Li‐deficient Nanostructure

AbstractDisordered rocksalt cathodes have shown attractive electrochemical performance via oxygen redox, but are limited by a necessary Li‐excess level above the percolation threshold (x > 1.09 in LixTM2‐xO2, TM = transition metals) to obtain electrochemical activity. However, a relatively low‐Li content is essential to alleviate excessive oxygen charge compensation in rocksalt oxides. Herein, taking the homogeneous Li2MnO3 and LiMn2O4 as the starting point, disordered rocksalt‐like cathodes are prepared with initial Li‐deficient nanostructures, cation vacancies, and partial spinel‐type structures that provide a solution for the acquisition of fast Li+ percolation channels under Li‐deficient condition. As a result, the prepared sample exhibits high initial discharge capacity (363 mAh g−1) and energy density (1081 Wh kg−1). Advanced spectroscopy and in situ measurements observe highly reversible charge compensation during electrochemical process and assign coupled Mn‐ and O‐related redox contribution. Theoretical calculations also suggest the novel and chemical reversible trapped molecular O2 model in the rocksalt structure with vacancies, demonstrating a dual role of Li‐deficient structure in promoting cationic oxidation and extending reversible oxygen redox boundary. This work is expected to breakthrough the existing ideas of oxygen oxidation and opens up a higher degree of freedom in the design of disordered rocksalt structures.

Modulation of Allosteric Control and Evolution of Hemoglobin.

Allostery arises when a ligand-induced change in shape of a binding site of a protein is coupled to a tertiary/quaternary conformational change with a consequent modulation of functional properties. The two-state allosteric model of Monod, Wyman and Changeux [J. Mol. Biol. 1965; 12, 88-118] is an elegant and effective theory to account for protein regulation and control. Tetrameric hemoglobin (Hb), the oxygen transporter of all vertebrates, has been for decades the ideal system to test for the validity of the MWC theory. The small ligands affecting Hb's behavior (organic phosphates, protons, bicarbonate) are produced by the red blood cell during metabolism. By binding to specific sites, these messengers make Hb sensing the environment and reacting consequently. HbI and HbIV from trout and human HbA are classical cooperative models, being similar yet different. They share many fundamental features, starting with the globin fold and the quaternary assembly, and reversible cooperative O2 binding. Nevertheless, they differ in ligand affinity, binding of allosteric effectors, and stability of the quaternary assembly. Here, we recollect essential functional properties and correlate them to the tertiary and quaternary structures available in the protein databank to infer on the molecular basis of the evolution of oxygen transporters.

Ru-Doping of P2-NaxMn0.75Ni0.25O2-Layered Oxides for High-Energy Na-Ion Battery Cathodes: First-Principles Insights on Activation and Control of Reversible Oxide Redox Chemistry

Design and development of high-energy, efficient, and structurally stable positive electrodes for Na-ion batteries (NIBs) have recently been focusing on layered transition metal oxides (NaxTMO2, 0 < x < 1). When doped with late transition metals, the redox reactions ensuring the charge compensation upon Na+ removal can rely on the direct participation of anionic chemistry, with encouraging outcomes in terms of both energy density and power. However, the control of reversible O2–/O– reactions is still a major issue, as the undesired release of O2 can lead to detrimental effects on cathode capacity and overall cell stability. The fine-tuning of metal–oxygen bond covalency has recently emerged as a promising strategy toward the reversible access of oxygen redox. Following the route paved by Ru-based Li-rich cathode materials, we hereby present a first-principles investigation of a Ru-doped NaxTMO2 (TM = Ru, Ni, and Mn) system and the related structural and electronic properties of interest for NIB applications. We aim to dissect the specific role of each element sublattice in compensating the electronic charge along desodiation, with a major focus on the anionic contribution. The oxygen activity is addressed in the high-voltage range (i.e.,xNa = 0.25), and the underlying mechanism is derived from PBE + U(-D3BJ) calculations. We also discuss the effects of Mn deficiency as a suitable site for the formation of low-energy superoxide species via preferential breaking of the Ni–O bond. Conversely, breaking a Ru–O bond is unlikely to occur, which assesses the key role of the Ru dopant in stabilizing the oxide lattice and enabling the desired reversible conditions. Our results also highlight the oxygen vacancy formation energy as an effective descriptor for different activities toward the O2–/O–/O2 evolution. All these theoretical insights can be useful to drive further experimental efforts toward the optimal design of efficient and high-energy NIB cathodes with enhanced practical reversible capacity.

Semi-flowable Zn semi-solid electrodes as renewable energy carrier for refillable Zn–Air batteries

Today's society relies on energy storage on a day-to-day basis, e.g. match energy production and demand from renewable sources, power a variety of electronics, and enable emerging technologies. As a result, a vast range of energy storage technologies has emerged in the last decades. Among them, rechargeable Zn–Air batteries have held great promises for a long time. However, the severe challenges related to the reversible O2 reactions and poor cyclability at the positive and negative electrodes, respectively, have severely hindered the success of this technology. Herein, electrically-conducting and semi-flowable Zn semi-solid electrodes are proposed to revive the appealing concept of a mechanically–rechargeable alkaline Zn–Air battery, in which the spent negative electrodes are easily substituted at the end of the discharge process (refillable primary battery). In this proof-of-concept study energy densities of ca. 1500 Wh L−1 (1350 Ah Lelectrode−1 and utilization rate of 85%) are achieved thanks to the compromised flowability of the proposed Zn semi-solid electrodes. In this way, semi-solid Zn electrodes become a type of green energy carrier having intrinsic advantages over gas and liquid fuels. Zn semi-flowable electrode can be generated elsewhere using renewable sources, easily stored, transported, and used to produce electricity.

Nonvolatile and Nonflammable Sulfolane-Based Electrolyte Achieving Effective and Safe Operation of the Li–O2 Battery in Open O2 Environment

The Li-O2 battery should operate effectively/safely in an open O2 environment for practical applications, but not trapped in sealed/closed atmosphere. However, the typical use of volatile and flammable electrolyte restricts Li-O2 battery to be able to be running in open O2 environment. We report herein, for the first time, a highly electrochemical reversible Li-O2 battery operated in an open O2 environment, i.e., under the condition of keeping O2 flowing continuously based on a nonvolatile and nonflammable sulfolane (TMS) solvent. The electrochemical irreversibility of Li2O2/O2 conversion and incompatibility between Li metal anodes and electrolyte have been addressed via dissolving LiNO3 in concentrated TMS electrolyte. The tuned electrolyte not only enables a stable solid electrolyte interphase (SEI) with conformal inorganic components (including LiF, LiNxOy, and Li2O) that promotes a uniform Li electro-plating/stripping process but also results in a low charge overpotential, a stable discharge terminal plateau, and reversible O2 generation of the Li-O2 battery conducted in an open O2 environment.

Probing the effect of Mg doping on triclinic Na2Mn3O7 transition metal oxide as cathode material for sodium-ion batteries

Triclinic Na2Mn3O7 has been identified as a promising material for high-capacity sodium-ion batteries. However, the knowledge on the effect of doping of metal ions and structural transformations of Na2Mn3O7 during dis(charge) is limited. Integration of alkali metal-ions, specially Mg2+ can enhance the electrochemical properties in transition metal oxides. Herein, a series of Mg2+ doped triclinic Na2Mn3O7 cathode materials was explored for the first time. Electrochemical analysis revealed that Mg2+ improves specific capacities, and rate capabilities. Ex situ X-ray diffraction (XRD) and Galvanostatic charge discharge cycling (GCD) showed that the triclinic phase reversibly converts into two monoclinic phases at high Na+ insertion levels. Na+ extraction at high potentials is supported by another biphasic region which converts to a major triclinic phase at the end of the charge. GCD, cyclic voltammetry (CV) and ex situ X-ray absorption spectroscopy (XAS) documented that the capacity mainly evolved through a Mn4+/3+ redox couple and a reversible O2-/n− redox reaction. CV and Galvanostatic intermittent titration techniques (GITT) showed that Mg2+ reduces the Na+-vacancy ordering and improves the Na+ diffusion. The 2 mol.% Mg-doped material exhibited a high specific capacity of 143 mAh/g after 30 cycles and a rate capability of 93 mAh/g (at 500 mA/g). GCD analysis demonstrated that O2-/n− redox is remarkably stable up to at least 90 cycles. Full cells made using the 0.5 mol.% Mg-doped material displayed a promising discharge specific capacity of 80 mAh/g. The effects of cation doping into the complex crystal structures, phase transformations during Na+ de(intercalation) and the importance of O2-/n− redox for achieving high capacities were uncovered. The findings of this work will guide the design of novel cathode materials for sodium-ion batteries.

Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2

Summary O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.

Reversible and Broad-Range Oxygen Sensing Based on Purely Organic Long-Lived Photoemitters

The detection of oxygen (O2) by optical sensors is of growing importance, for example, in biology, life science, environmental science, and aerodynamics, where the composition of gases is crucial for many applications. Purely organic optical O2 sensors are very attractive for monitoring food deterioration, biosensing, and biomonitoring, as they can provide continuous, reversible, and nondestructive O2 sensing. However, purely organic optical reversible O2 sensors that can work with a broad O2 concentration range and that have robust reversibility are yet to be realized. We hereby developed a purely organic optical O2 sensor by embedding polyimide-based photoemitters within a poly(vinyl alcohol) (PVA) matrix. The photoemitters are synthesized through one-pot hydrothermal reactions. They have a lifetime of room temperature phosphorescence (RTP) of up to a few microseconds (μs) when they are embedded into the polymer matrix. Our results demonstrate that the photoemitters have higher sensitivity and broader sensing range to O2 if they are synthesized with longer reaction times because they possess a more rigid polyimide structure. The O2 sensor with such optimized photoemitters embedded in the polymer matrix exhibits continuous and broad-range O2 sensing in the range of 0–16% O2. The Stern–Volmer quenching constant (Ksv) was calculated to be 0.2351 kPa–1 for the linear response range of 0–4% O2. Moreover, the O2 sensor can be repetitively used at least 10 times in the linear range (0–4% O2) or beyond the linear range (up to 21% O2). The metal-free, purely organic sensors that enable the continuous and repetitive detection of O2 within a relevant O2 sensing range are appealing especially for monitoring packaged food, biomonitoring, and biosensing.

Identification of Correlation between Cation Disordering and the Anionic Redox Chemistry in Li-Rich Layered Oxides

To satisfy our increasing dependence on the high energy storage electronics, Li-rich layered oxides (Li[LixM1-x]O2, M = Ni, Co, Mn, Ru, Ir, etc) have attracted significant attention as cathode materials for lithium-ion batteries in recent years. This class of cathode materials exhibit promising capacities, up to 300 mAh/g, due to accumulative transition metal and oxygen redox reaction1–5. Additional capacity in this class of Li-rich cathode material is due to the anionic redox which is irreversible or partially reversible oxygen evolution6,7 and reversible O2-/n- redox1,3,4,8. Luo el at.1 demonstrated that the localized electron holes on oxygen coordinated by Mn4+ and Li+ ions is promoted by the relatively more ionic interactions of O-(Mn/Li) than O-(Ni/Co) interactions at the result of the oxygen oxidation. In our previous study2, at least partially reversible oxygen evolution was observed in 0.4Li2MnO3-0.6LiMn0.5Ni0.5O2 by using Rietveld refinement of high resolution powder diffraction patterns. In the case of 4d (Ru) and 5d (Ir) transition metal-based Li-rich cathode materials, reversible anionic redox was confirmed by X-ray photoelectron spectroscopy (XPS)3,4. Even though the participation of oxygen in redox activity in Li2MnO3 results in partial oxygen evolution with irreversible structural changes9, oxygen redox reaction is stabilized by the reversible peroxo-dimers (O2 n-) formation in the Li2MO3-based (M = Ru, Ir) Li-rich cathode materials due to the high covalent metal-oxygen environment in Ru- and Ir-based lithium-rich cathode materials. However, Seo et al.10 identified the structural and chemical origin of the anionic redox activity which preferentially takes place along the Li-O-Li configurations (non-bonding O 2p states) in Li-rich layered oxides and cation-disordered oxides by using ab initio calculations based on DFT. The electrons in Li-O-Li states exist in the higher energy states than those in the other O 2p states owing to their unhybridized O 2p and Li 2s orbitals. Through these significant studies, anionic redox mechanism seems to be well established. In the case of Na2RuO3, extra anionic capacity is enabled in honeycomb-ordered Na2RuO3 due to the ordered intermediate Na1RuO3 phase which can accommodate the frontier orbital reorganization11, meanwhile, transition metal migration into the empty Li sites is closely associated with the anionic redox as a result of the structural disordering in Li1.17Ni0.21Co0.08Mn0.54O2 5 and Li2IrxSn1-xO3 systems12. It is still under debating whether such manifold anionic chemistry will be solved in terms of transition metals (3d, 4d, and 5d) or alkali metals (Li and Na) or bulk and local structure. In addition, the different reaction mechanism is confirmed between multivalent iridium redox (Ir4+/5.5+)12 and cumulative iridium (Ir4+/5+) and oxygen (O2-/n-) redox13 even in the same C2/m space group of Li2IrO3 materials.Herein, redox mechanism of Li2IrO3 was investigated as a model compound for Li-rich cathode material to understand the key structural differences that lead to anionic redox activity through the synchrotron-based analysis. The local environment, not the composition itself in Li-rich materials, is one of the major factors affecting the redox reaction. We demonstrate that the in-plane disordering in the transition metal layer play a critical role in cation migration and anionic redox, and that cation migration also can trigger the anionic redox reactions. These fundamental insights about Li-rich material family are critical for further development of anionic redox-based cathode materials. In-plane ordering in pristine state with the same composition of Li2IrO3 has a major impact on cation migration and reversible anion redox. Based on the experimental data, detailed findings and discussion will be presented in the PRiME 2020.References K. Luo et al., Nat. Chem., 8, 684–691 (2016)S. Muhammad et al., Nano Energy, 21, 172–184 (2016)M. Sathiya et al., Nat. Mater., 12, 827–835 (2013)E. McCalla et al., Science (80-. )., 350, 1516–1521 (2015).W. E. Gent et al., Nat. Commun., 8, 2091 (2017)A. R. Armstrong et al., J. Am. Chem. Soc., 128, 8694–8698 (2006).A. Boulineau, L. Simonin, J. F. Colin, C. Bourbon, and S. Patoux, Nano Lett., 13, 3857–3863 (2013).H. Koga et al., J. Electrochem. Soc., 160, 786–792 (2013).J. R. Croy et al., Chem. Mater., 26, 7091–7098 (2014).D. H. Seo et al., Nat. Chem., 8, 692–697 (2016)B. Mortemard de Boisse et al., Nat. Commun., 7, 11397 (2016)J. Hong et al., Nat. Mater., 18, 256–265 (2019)E. McCalla et al., Science (80-. )., 350, 1516–1521 (2015)

Correlation between Cation Disordering and the Anionic Redox Chemistry in Li-Rich Layered Oxides

To satisfy our increasing dependence on the high energy storage electronics, Li-rich layered oxides (Li[LixM1-x]O2, M = Ni, Co, Mn, Ru, Ir, etc) have attracted significant attention as cathode materials for lithium-ion batteries in recent years. This class of cathode materials exhibit promising capacities, up to 300 mAh/g, due to accumulative transition metal and oxygen redox reaction1–5. Additional capacity in this class of Li-rich cathode material is attributed to the anionic redox which is irreversible or partially reversible oxygen evolution6,7 and reversible O2-/n- redox1,3,4,8. Luo el at.1 demonstrated that the localized electron holes on oxygen coordinated by Mn4+ and Li+ ions is promoted by the relatively more ionic interactions of O-(Mn/Li) than O-(Ni/Co) interactions at the result of the oxygen oxidation. In our previous study2, at least partially reversible oxygen evolution was observed in 0.4Li2MnO3-0.6LiMn0.5Ni0.5O2 by using Reitveld refinement of high resolution powder diffraction patterns. In the case of 4d (Ru) and 5d (Ir) transition metal-based Li-rich cathode materials, reversible anionic redox was confirmed by X-ray photoelectron spectroscopy (XPS)3,4. Even though the participation of oxygen in redox activity in Li2MnO3 results in partial oxygen evolution with irreversible structural changes9, oxygen redox reaction is stabilized by the reversible peroxo-dimers (O2 n-) formation in the Li2MO3-based (M = Ru, Ir) Li-rich cathode materials due to the high covalent metal-oxygen environment in Ru- and Ir-based lithium-rich cathode materials. However, Seo et al.10 identified the structural and chemical origin of the anionic redox activity which preferentially takes place along the Li-O-Li configurations (non-bonding O 2p states) in Li-rich layered oxides and cation-disordered oxides by using ab initio calculations based on DFT. The electrons in Li-O-Li states are higher energy than those in the other O 2p states owing to their unhybridized O 2p and Li 2s orbitals without taking into account the covalency between the transition metal and oxygen. Through the significant research efforts, anionic redox mechanism seems to be well established. In the case of Na2RuO3, extra anionic capacity is enabled in honeycomb-ordered Na2RuO3 due to the ordered intermediate Na1RuO3 phase which can accommodate the frontier orbital reorganization11, meanwhile, transition metal migration into the empty Li sites is closely associated with the anionic redox as a result of the structural disordering in Li1.17Ni0.21Co0.08Mn0.54O2 5 and Li2IrxSn1-xO3 systems12. It is still under debating whether such manifold anionic chemistry will be solved in terms of transition metals (3d, 4d, and 5d) or alkali metals (Li and Na) or bulk and local structure. In addition, the different reaction mechanism is confirmed between multivalent iridium redox (Ir4+/5.5+)12 and cumulative iridium (Ir4+/5+) and oxygen (O2-/n-) redox13 even in the same C2/m space group of Li2IrO3 materials.Herein, redox mechanism of Li2IrO3 was investigated as a model compound for Li-rich cathode material to understand the key structural differences that lead to anionic redox activity through the synchrotron-based analysis. The local environment, not the composition itself in Li-rich materials, is one of the major factors affecting the redox reaction. We demonstrate that the in-plane disordering in the transition metal layer play a critical role in cation migration and anionic redox, and that cation migration also can trigger the anionic redox reactions. These fundamental insights about Li-rich material family are critical for further development of anionic redox-based cathode materials. In-plane ordering in pristine state with the same composition of Li2IrO3 has a major impact on cation migration and reversible anion redox. Based on the experimental data, detailed findings and discussion will be presented in the 237th ECS meeting.

Gas Adsorption of Mixed-Valence Trinuclear Oxothiomolybdenum Glycolates.

Trinuclear oxothiomolybdenum(IV) glycolates (H2glyc, glycolic acid) with 2-methylimidazole (2-mim), 4-methylimidazole (4-mim), and sulfite, Na2[MoIV3(μ3-S)(μ2-O)3(glyc)3(2-mim)3]·1.5H2O (1), (4-Hmim)6[MoIV3(μ3-S)(μ2-O)3(glyc)3(4-mim)3]2[MoVIO2(glyc)2] (2), and Na3(4-Hmim)[MoIV3(μ3-S)(μ2-O)3(SO3)(glyc)3(4-mim)]·8H2O (3), have been isolated in reduced media, where 4-methylimidazole trinuclear oxothiomolybdenum(IV) glycolates in 2 coprecipitate with dioxomolybdenum(VI) glycolate, exhibiting unusual mixed valences of 4+ and 6+. Large downfield shifts of glycolates have been observed in solid-state and solution 13C (1H) NMR spectra with coordination to Mo, indicating obvious dissociation of soluble 1 and 3 in solution. Investigations of the coordination modes and conversions among the three complexes give insight into the reactivities of trinuclear oxothiomolybdenum(IV) complexes. Channels with 3.1 × 7.0 Å2 diameters exist in 2, showing reversible O2 absorption of 65.03 mg at 29.9 bar compared with little or no adsorption of N2, H2, CO2, and CH4 at room temperature, respectively. Moreover, trinuclear 2- or 4-methylimidazole oxothiomolybdenum(IV) glycolates 1 and 3 show only a few adsorptions for O2 under the same conditions.

Structural Transformation in Metal-Organic Frameworks for Reversible Binding of Oxygen.

Polycyclic aromatic derivatives can trap 1 O2 to form endoperoxides (EPOs) for O2 storage and as sources of reactive oxygen species. However, these materials suffer from structural amorphism, which limit both practical applications and fundamental studies on their structural optimization for O2 capture and release. Metal-organic frameworks (MOFs) offer advantages in O2 binding, such as clear structure-performance relationships and precise controllability. Herein, we report the reversible binding of O2 is realized via the chemical transformation between anthracene-based and the corresponding EPO-based MOF. It is shown that anthracene-based MOF, the framework featuring linkers with polycyclic aromatic structure, can rapidly trap 1 O2 to form EPOs and can be restored upon UV irradiation or heating to release O2 . Furthermore, we confirm that photosensitizer-incorporated anthracene-based MOF are promising candidates for reversible O2 carriers controlled by switching Vis/UV irradiation.

Structural Transformation in Metal–Organic Frameworks for Reversible Binding of Oxygen

AbstractPolycyclic aromatic derivatives can trap 1O2 to form endoperoxides (EPOs) for O2 storage and as sources of reactive oxygen species. However, these materials suffer from structural amorphism, which limit both practical applications and fundamental studies on their structural optimization for O2 capture and release. Metal–organic frameworks (MOFs) offer advantages in O2 binding, such as clear structure–performance relationships and precise controllability. Herein, we report the reversible binding of O2 is realized via the chemical transformation between anthracene‐based and the corresponding EPO‐based MOF. It is shown that anthracene‐based MOF, the framework featuring linkers with polycyclic aromatic structure, can rapidly trap 1O2 to form EPOs and can be restored upon UV irradiation or heating to release O2. Furthermore, we confirm that photosensitizer‐incorporated anthracene‐based MOF are promising candidates for reversible O2 carriers controlled by switching Vis/UV irradiation.

Effect of toxic ligands on O2 binding to heme and their toxicity mechanism.

Heme, as the cofactor and active site of Hb, enables Hb to carry out the necessary function required for O2 management for life, that is, reversible O2 binding for transport. In this paper, the microscopic mechanism of heme-associated poisoning has been elucidated from the perspective of electronic interaction by performing first-principles calculations. The results show that the functional groups (-CHO, -COOH, -NO2, -NH2) and CN exhibit a stronger affinity for heme than O2 and are more likely to occupy the O2 binding site, which results in the loss of the ability of heme to carry O2. Moreover, the addition of functional groups, CO and CN to heme at the side site can cause a pronounced enhancement toward the O2 binding characteristics of heme, which prevents heme from releasing O2 to oxygen-consuming tissues as the blood circulates. The reversible O2 binding function of heme is disrupted by the presence of these toxic ligands in the heme binding pocket, which greatly affects O2 transport in the blood. The inability of tissues to obtain O2 leads to tissue hypoxia, which is the main cause of poisoning. Based on the energy, geometry and electronic properties, the hypoxia mechanism proposed by us coincides well with experiment, and the research has the potential to provide a theoretical reference for the relevant areas of bioscience.