Spontaneous Disproportionation Research Articles

High Efficiency Alkaline Iodine Batteries with Multi‐Electron Transfer Enabled by Bi/Bi2O3 Redox Mediator

The multi‐electron transfer I‐/IO3‐ redox couple is attractive for high energy aqueous batteries. Shifting from an acidic to an alkaline electrolyte significantly enhances the IO3‐ formation kinetics due to the spontaneous disproportionation reaction, while the alkaline environment also offers more favorable Zn anode compatibility. However, sluggish kinetics during the reduction of IO3‐ persists in both acidic and alkaline electrolytes, compromising the energy efficiency of this glorious redox couple. Here, we establish the fundamental redox mechanism of the I‐/IO3‐ couple in alkaline electrolytes for the first time and propose that Bi/Bi2O3 acts as a redox mediator (RM) to “catalyze” the reduction of IO3‐. This mediation significantly reduces the voltage gap between charge/discharge from 1.6 V to 1 V with improved conversion efficiency and rate capability. By pairing the Zn anode and the Bi/Bi2O3 RM cathode, the full battery with I‐/IO3‐ redox mechanism achieves high areal capacity of 12 mAh cm‐2 and stable operation at 5 mAh cm‐2 for over 400 cycles.

High Efficiency Alkaline Iodine Batteries with Multi-Electron Transfer Enabled by Bi/Bi2O3 Redox Mediator.

The multi-electron transfer I-/IO3- redox couple is attractive for high energy aqueous batteries. Shifting from an acidic to an alkaline electrolyte significantly enhances the IO3- formation kinetics due to the spontaneous disproportionation reaction, while the alkaline environment also offers more favorable Zn anode compatibility. However, sluggish kinetics during the reduction of IO3- persists in both acidic and alkaline electrolytes, compromising the energy efficiency of this glorious redox couple. Here, we establish the fundamental redox mechanism of the I-/IO3- couple in alkaline electrolytes for the first time and propose that Bi/Bi2O3 acts as a redox mediator (RM) to "catalyze" the reduction of IO3-. This mediation significantly reduces the voltage gap between charge/discharge from 1.6 V to 1 V with improved conversion efficiency and rate capability. By pairing the Zn anode and the Bi/Bi2O3 RM cathode, the full battery with I-/IO3- redox mechanism achieves high areal capacity of 12 mAh cm-2 and stable operation at 5 mAh cm-2 for over 400 cycles.

Disproportionation and Transalkylation of Phenol and Dimethylphenol on Zeolite Catalysts

AbstractSubstantial amounts of phenolic compounds are present in medium‐low temperature coal tar (MLCT), of which dimethylphenol (DMP) is not as valuable to be utilized as the more abundant cresol due to its complex composition and difficulty in isolation. In this study, the disproportionation and transalkylation reactions of MLCT‐related model compound, i.e., 2,6‐DMP, in phenol over zeolite catalysts are investigated using a fixed‐bed reactor for sustainable new option to utilize MLCT‐derived phenolic mixtures. Reactivity is promoted at high temperatures and associated with zeolite acidity and pore structure. Since disproportionation and transalkylation reactions have certain spatial requirements, the micropores of MFI‐type zeolite may cause spatial barriers that make it difficult to carry out the reactions. MCM‐22, characterized by MWW‐type zeolite, maximized the conversion of 2,6‐DMP due to its strong Bronsted acidity and large mesopore volume. FAU‐type zeolite HY with a 3D large 12‐ring through‐channel shows relatively small spatial confinement and certain molecular sieving ability, which enables bimolecular reactions while allowing cresols to flow out of the pores efficiently to obtain the highest cresol selectivity. The addition of phenol significantly inhibits the spontaneous disproportionation of 2,6‐DMP to tricresol. Besides, o‐cresol dominate the cresol products, suggesting that the selectivity of o‐cresol is kinetically controlled.

A DFT study of the antioxidant potency of α-tocopherol and its derivatives: PMHC, Trolox, and α-CEHC

In this research, antioxidant potency (in terms of peroxyl radical scavenging and catalytic iron ions sequestration) of α-tocopherol and its analogues, has been theoretically investigated. A DFT based kinetic estimation of HOO• radical scavenging potency of PMHC (lipophilic α-TOH derivative) and Trolox (hydrophilic α-TOH derivative) was performed in eight solvents of different polarity. Calculations employing M06-2X functional, accompanied by 6-311++G(d,p) basis set and SMD solvation model, were found as more accurate in reproducing experimentally determined rate constants than M05-2X functional. Rate constant of Trolox in pentyl ethanoate also was estimated by using Snelgrove−Ingold equation and Abraham’s β2H solvent parameter. Scavenging of CH3OO• and HOO• radicals, which is influenced by location, orientation, and dynamics of α-TOH and its derivatives in the membrane lipid bilayer, was estimated by using M06-2X functional. Position of α-TOH phenolic OH group is opposite to that of its metabolite α-CEHC: α-TOH’s OH group is located at the membrane-water interface, and α-CEHC’s OH group is deeply buried into the bilayer. In the aqueous phase both fHAT and SET were investigated, and inside the bilayer only fHAT was considered as feasible. The spontaneous disproportionation of HOO•/O2•− in aqueous solutions should be taken into account to predict potency of antioxidant in scavenging of HOO• radicals. Iron chelating ability of α-TOH and α-CEHC was also investigated. Obtained results indicate α-CEHC, α-tocopherol final catabolite, as more potent scavenger of CH3OO• and HOO• radicals and iron ions chelator than the parent molecule.

Green polyaspartic acid as a novel permanganate activator for enhanced degradation of organic contaminants: Role of reactive Mn(III) species

Attention has been long focused on enhancing permanganate (Mn(VII)) oxidation capacity for eliminating organic contaminants via generating active manganese intermediates (AMnIs). Nevertheless, limited consideration has been given to the unnecessary consumption of Mn(VII) due to the spontaneous disproportionation of AMnIs during their formation. In this work, we innovatively introduced green polyaspartic acid (PASP) as both reducing and chelating agents to activate Mn(VII) to enhance the oxidation capacity and utilization efficiency of Mn(VII). Multiple lines of evidence suggest that Mn(III), existing as Mn(III)-PASP complex, was generated and dominated the degradation of bisphenol A (BPA) in the Mn(VII)/PASP system. The stabilized Mn(III) species enabled Mn(VII) utilization efficiency in the Mn(VII)/PASP system to be higher than that in Mn(VII) alone. Moreover, the electrophilic Mn(III) species was verified to mainly attack the inclusive benzene ring and isopropyl group to realize BPA oxidation and its toxicity reduction in the Mn(VII)/PASP system. In addition, the Mn(VII)/PASP system showed the potential for selectively oxidizing organic contaminants bearing phenol and aniline moieties in real waters without interference from most of coexisting water matrices. This work brightens an overlooked route to both high oxidation capacity and efficient Mn(VII) utilization in the Mn(VII)-based oxidation processes.

A Self‐Charging Aluminum Battery Enabled by Spontaneous Disproportionation Reaction

AbstractHerein, a self‐charging mechanism of rechargeable aluminum (Al) batteries with Chevrel phase molybdenum sulfide (Mo6S8) cathode is reported. The results unambiguously reveal that the self‐charging is a spontaneous disproportionation of Al intercalated Mo6S8 originated from the dynamic shift of Al between occupied sites during Al intercalating and resting. The theoretical study indicates that the fully Al intercalated Mo6S8 in the format of Al4/3Mo6S8 is kinetically accessible driven by electrochemical overpotential but thermodynamically unstable due to the repulsion between Al3+ cations. This mechanism is a true self‐charging with no input of any form of energy, thus distinctly superior to the previously reported self‐charging mechanisms. Based on this discovery, a semi‐flow AlMo6S8 battery is designed and demonstrated with long‐lasting discharge capability and high capacity.

Engineering d-p orbital hybridization for high-stable lithium manganate cathode

Spinel LiMn2O4 is a prevalent cathode material due to its environmental benignities and high operating voltage. Nevertheless, capacity attenuation and structural collapse are still inevitable, caused by the native Jahn–Teller distortion and spontaneous disproportionation of Mn3+. Hereby, LiMn2O4 cathode with stable crystallographic structure is rationally designed based on valence-bond theory with introduction of Ru dopant. The enhanced orbital hybridization between Mn 3d and O 2p is successfully achieved owing to the reinforcing band coherency of Mn–O aroused from the electrostatic interaction between Mn and Ru atoms. Notably, the robust crystal structure framework is effectively reconstructed, which is beneficial for ameliorating phase evolution and inhibiting structural degradation substantiated by the state-of-the-art synchrotron X-ray absorption spectroscopy and in-situ X-ray diffraction. Concomitantly, LiO4 tetrahedron is effectively weakened, further facilitating the rapid Li+ diffusion kinetics intensively confirmed by theoretical calculations and electrochemical tests. Remarkably, the as-designed Ru-doped LiMn2O4 manifests splendid long cycling stability, affording a respectable capacity retention of 88.2 % after 200 loops. Given this, the intriguing work might inaugurate an explicit direction for rationally tuning the orbital hybridization towards advanced electrodes in alkali metal batteries.

Disproportionation of Pharmaceutical Salts: pHmax and Phase-Solubility/pH Variance.

A multiphasic mass action equilibrium model is used to show that the critical pH in the acid-base disproportionation of a solid salt into its corresponding solid free-base form in aqueous suspensions, widely known as "pHmax", is incompletely interpreted. It is shown that the traditional thermodynamic model does not predict the invariance of pH and solubility during the salt-to-free-base conversion process in an alkalimetric titration. Rather, the conversion entails a range of pH and solubility values, depending on the amount of added excess salt above that needed to form a saturated solution. A more precise definition is proposed for pHmax (pH at the maximum solubility of a eutectic mixture), and three new terms are introduced: pHmin (pH at the minimum solubility of the eutectic mixture), pHδ (disproportionation invariant pH within the eutectic, i.e., the equilibrium pH of a spontaneously disproportionating salt slurry), and pHγ (Gibbs pH at which disproportionation yields equimolar amounts of excess salt and excess free-base solids within the eutectic). Two test compounds with reported multiple salts and the free-base solubility values were selected to illustrate the expanded concepts, the bases WR-122455 and RPR-127963. Also, dibasic calcium phosphate was selected as an ionizable test excipient. The salts are designated in the study as μ-type, when they are thermodynamically stable with respect to spontaneous disproportionation in pure water (e.g., WR-122455 salts), and δ-type, when they are predicted to spontaneously disproportionate in pure water (e.g., RPR-127963 salts). In an alkalimetric titration, when an acidified suspension of a salt of a basic molecule is titrated with a strong base (e.g., NaOH), the passage across the eutectic domain (bounded by pHmax and pHmin) is often characterized by (a) minimum in ionic strength either at pHmax (μ-type salt) or pHδ (δ-type salt) and (b) maximum buffer capacity at pHγ. When the alkalimetric titration is performed with a large excess of added salt, a wide eutectic domain forms: pHmax and pHδ remain invariant, but pHmin and pHγ shift substantially in pH. The acid-base mass action model described here can be useful in predicting the stability of salt formulations in mixtures with excipients that can act as pH modifiers.

Proton-Induced Disproportionation of Jahn-Teller-Active Transition-Metal Ions in Oxides Due to Electronically Driven Lattice Instability.

The interfacial chemical reactivity of Jahn-Teller-active transition-metal oxides remains an enigmatic area, often leading to uncontrollable phase transformations in the oxide-based technological applications. In particular, the higher tendency of unwanted transition-metal-ion dissolution and side-reactions in Jahn-Teller-active oxides is accompanied by performance degradation in many electrochemical systems, for example, lithium-ion batteries. We show here that the fundamental electronic structure instability that leads to Jahn-Teller (lattice) distortion in an octahedral ligand field is the active chemical driving force for the spontaneous disproportionation, phase transformation, and metal-ion dissolution in transition-metal oxides upon exposure to protons. On the basis of electronic structure analyses and 18O isotope labeling, we present a mechanism comprising a coupled acid-base/redox reaction that leads to a proton-induced disproportionation of Jahn-Teller-active transition-metal ions, as exemplified by the broad classes of respective oxides.

Thermodynamic stability of borophene, B2O3 and other B1−xOx sheets

The recent discovery of borophene, a two-dimensional allotrope of boron, raises many questions about its structure and its chemical and physical properties. Boron has a high chemical affinity to oxygen but little is known about the oxidation behaviour of borophene. Here we use first principles calculations to study the phase diagram of free-standing, two-dimensional B1−xOx for compositions ranging from x = 0 to x = 0.6, which correspond to borophene and sheets, respectively. Our results indicate that no stable compounds except borophene and sheets exist. Intermediate compositions are heterogeneous mixtures of borophene and . Other hypothetical crystals such as are unfavorable and some of them underwent spontaneous disproportionation into borophene and . It is also shown that oxidizing borophene inside the flakes is thermodynamically unfavorable over forming at the edges. All findings can be rationalized by oxygen’s preference of two-fold coordination which is incompatible with higher in-plane coordination numbers preferred by boron. These results agree well with recent experiments and pave the way to better understand the process of oxidation of borophene and other two-dimensional materials.

The Long-Term Stability of KO2 in K-O2 Batteries.

The rechargeable K-O2 battery is recognized as a promising energy storage solution owing to its large energy density, low overpotential, and high coulombic efficiency based on the single-electron redox chemistry of potassium superoxide. However, the reactivity and long-term stability of potassium superoxide remains ambiguous in K-O2 batteries. Parasitic reactions are explored and the use of ion chromatography to quantify trace amounts of side products is demonstrated. Both quantitative titrations and differential electrochemical mass spectrometry confirm the highly reversible single-electron transfer process, with 98 % capacity attributed to the formation and decomposition of KO2 . In contrast to the Na-O2 counterparts, remarkable shelf-life is demonstrated for K-O2 batteries owing to the thermodynamic and kinetic stability of KO2 , which prevents the spontaneous disproportionation to peroxide. This work sheds light on the reversible electrochemical process of K+ +e- +O2 ↔KO2 .

The Long‐Term Stability of KO2 in K‐O2 Batteries

AbstractThe rechargeable K‐O2 battery is recognized as a promising energy storage solution owing to its large energy density, low overpotential, and high coulombic efficiency based on the single‐electron redox chemistry of potassium superoxide. However, the reactivity and long‐term stability of potassium superoxide remains ambiguous in K‐O2 batteries. Parasitic reactions are explored and the use of ion chromatography to quantify trace amounts of side products is demonstrated. Both quantitative titrations and differential electrochemical mass spectrometry confirm the highly reversible single‐electron transfer process, with 98 % capacity attributed to the formation and decomposition of KO2. In contrast to the Na‐O2 counterparts, remarkable shelf‐life is demonstrated for K‐O2 batteries owing to the thermodynamic and kinetic stability of KO2, which prevents the spontaneous disproportionation to peroxide. This work sheds light on the reversible electrochemical process of K++e−+O2↔KO2.

Triphos–Fe dinitrogen and dinitrogen–hydride complexes: relevance to catalytic N2reductions

The two electron reduction of iron complexes [(PRP2Cy)Fe(Cl)2] (R = Ph or tBu) 2a-b afforded complexes [(PRP2Cy)Fe(N2)2] 4a-b. Protonation of 4a at the metal center and subsequent reduction to Fe(i)-H species lead to complex [(PPhP2Cy)Fe(N2)(H)2] 6avia a spontaneous disproportionation reaction. Complex 4a behaves as one of the most efficient monometallic Fe-catalysts reported to date for N2-to-N(SiMe3)3 functionalization under atmospheric pressure.

Spontaneous disproportionation of lithium biphenyl in solution: a combined experimental and theoretical study

Spontaneous disproportionation of lithium biphenyl radical anion into a lithium biphenyl dianion plus neutral biphenyl, according to 2LiBiph ⇄ Li2Biph + Biph, has been evidenced experimentally by UV-vis spectroscopy and backed up theoretically using TDDFT methods.

Visible-Light-Promoted AuI to AuIII Oxidation in Triazol-5-ylidene Complexes.

Reaction of triazolium precursors [MIC(CH2 )n - H+ ]I- (n=1-3) with potassium hexamethyldisilazane (KHMDS) and AuCl(SMe2 ) generates the gold(I) complexes of the type MIC(CH2 )n ⋅AuI. Visible light exposure of the latter complexes promotes a spontaneous disproportionation process rendering gold(III) complexes of the type [{MIC(CH2 )n }2 ⋅AuI2 ]+ I- . Both the AuI and AuIII complex series were tested in the catalytic hydrohydrazination of terminal alkynes using hydrazine as nitrogen source.

Developing Pathways to the Synthesis of Low‐Valence Molybdenum Methoxides: Preparation, Characterization, and Redox Chemistry of Dimeric and Tetrameric Molybdenum Alkoxide Clusters

AbstractThe rare Mo=Mo double‐bonded dimeric alkoxide complex [Mo2Cl4(OCH3)4(CH3OH)2] (1) was prepared by the simple methanolysis reaction of [MoCl4(CH3CN)2]. It was shown that the dissolution of 1 in thf results in the formation of the [Mo2O2Cl4(OCH3)2(thf)2] (2) and [Mo2Cl4(OCH3)4(thf)2] (3) dimers. A novel tetranuclear 10e molybdenum cluster [Mo4Cl4O2(OCH3)6(CH3OH)4] (4) was synthesized by the spontaneous disproportionation of 1 in methanol. An alternative pathway to 4 based on the redox reaction of Mo3+ and Mo5+ compounds {in the form of [MoCl3(thf)3] and [Mo2Cl4(OCH3)6] (5), respectively} was proposed and realized. The redox behavior of 4 was investigated by means of cyclic voltammetry. It was demonstrated that 4 may undergo a reversible two‐electron reduction process, which implies the retention of the {Mo4} core, whereas the oxidation is irreversible, proceeding apparently with the destruction of the tetranuclear cluster core.

Unravelling the role of Li2S2 in lithium–sulfur batteries: A first principles study of its energetic and electronic properties

It is widely believed that Li2S2 is one of the intermediate products of lithium–sulfur (Li–S) batteries. However, contradicting proposals regarding the role and even the existence of Li2S2 in Li–S batteries persist. To address this, we have carried out first principles calculations of the energetic and electronic properties of Li2S2 based on the most promising structures found through an evolutionary algorithmic study. Our proposed Li2S2 structure(s) give a discharge voltage of 2.11 V for 2Li+ + 2e− + Li2S2 → 2Li2S, which matches the lower plateau of the experimental discharge profile of Li–S cells. Our results also show that Li2S2 is subject to spontaneous disproportionation. Together these results indicate that Li2S2 plays a key intermediate non-equilibrium role in the discharge of Li–S batteries.

Synthesis and Characterization of an f-Block Terminal Parent Imido [U═NH] Complex: A Masked Uranium(IV) Nitride

Deprotonation of [U(TrenTIPS)(NH2)] (1) [TrenTIPS = N(CH2CH2NSiPri3)3] with organoalkali metal reagents MR (M = Li, R = But; M = Na–Cs, R = CH2C6H5) afforded the imido-bridged dimers [{U(TrenTIPS)(μ-N[H]M)}2] [M = Li–Cs (2a–e)]. Treatment of 2c (M = K) with 2 equiv of 15-crown-5 ether (15C5) afforded the uranium terminal parent imido complex [U(TrenTIPS)(NH)][K(15C5)2] (3c), which can also be viewed as a masked uranium(IV) nitride. The uranium–imido linkage was found to be essentially linear, and theoretical calculations suggested σ2π4 polarized U–N multiple bonding. Attempts to oxidize 3c to afford the neutral uranium terminal parent imido complex [U(TrenTIPS)(NH)] (4) resulted in spontaneous disproportionation to give 1 and the uranium–nitride complex [U(TrenTIPS)(N)] (5); this reaction is a new way to prepare the terminal uranium–nitride linkage and was calculated to be exothermic by −3.25 kcal mol–1.

Studies on galactose oxidase active site model complexes: effects of ring substituents on Cu(II)-phenoxyl radical formation

Copper(II) complexes of new N 3O- and N 2O 2-donor tripodal ligands bearing one or two o-substituted phenol moieties have been synthesized as models for the galactose oxidase active site. The complexes of 2-[ N-(1-methyl-2′-imidazolylmethyl)- N-(6″-methyl-2″-pyridylmethyl)-aminomethyl)]-4-methyl-6-methylthiophenol (MeSL), [Cu(MeSL)Cl], and N-(6-methyl-2-pyridylmethyl)- N, N-bis(2′-hydroxy-3′,5′-di- tert-butylbenzyl)amine (t-buL2mepy), [Cu(t-buL2mepy)(H 2O)], have been revealed by X-ray structural analysis to have a square-pyramidal structure with one and two phenolate oxygens in the basal plane, respectively. [Cu(MeSL)Cl] was converted into a Cu(II)- o-methylthiophenoxyl radical species by electrochemical or Ce(IV) oxidation. An o-methoxyphenoxyl radical in a similar complex was considerably more stable than the 2,4-di( tert-butyl)phenoxyl radical. While t-buL2mepy reacted with Cu(ClO 4) 2 to give [Cu(t-buL2mepy)(H 2O)] without disproportionation, an N2O2-donor ligand containing an o-methoxyphenol, a 2,4-di( tert-butyl)phenol, and an N-methylimidazole moiety gave a phenoxyl radical complex exhibiting the characteristic absorption peak at 478 nm as a reddish powder by the reaction with Cu(ClO 4) 2 as a result of spontaneous disproportionation. It exhibited a quasi-reversible redox wave at E 1/2=0.34 V (vs. Ag/AgCl) in CH 3CN, which is lower than the potentials of the copper complexes of various N 3O-donor ligands, and oxidized ethanol to acetaldehyde with a low turnover number.

Brown pigments produced by Yarrowia lipolytica result from extracellular accumulation of homogentisic acid.

Yarrowia lipolytica produces brown extracellular pigments that correlate with tyrosine catabolism. During tyrosine depletion, the yeast accumulated homogentisic acid, p-hydroxyphenylethanol, and p-hydroxyphenylacetic acid in the medium. Homogentisic acid accumulated under all aeration conditions tested, but its concentration decreased as aeration decreased. With moderate aeration, equimolar concentrations of alcohol and p-hydroxyphenylacetic acid (1:1) were detected, but with lower aeration the alcohol concentration was twice that of the acid (2:1). p-Hydroxyphenylethanol and p-hydroxyphenylacetic acid may result from the spontaneous disproportionation of the corresponding aldehyde, p-hydroxyphenylacetaldehyde. The catabolic pathway of tyrosine in Y. lipolytica involves the formation of p-hydroxyphenylacetaldehyde, which is oxidized to p-hydroxyphenylacetic acid and then further oxidized to homogentisic acid. Brown pigments are produced when homogentisic acid accumulates in the medium. This acid can spontaneously oxidize and polymerize, leading to the formation of pyomelanins. Mn(2+) accelerated and intensified the oxidative polymerization of homogentisic acid, and lactic acid enhanced the stimulating role of Mn(2+). Alkaline conditions also accelerated pigment formation. The proposed tyrosine catabolism pathway appears to be unique for yeast, and this is the first report of a yeast producing pigments involving homogentisic acid.