Redox Reaction Mechanism Research Articles

Low-temperature and high-voltage Zn-based liquid metal batteries based on multiple redox mechanism

Liquid metal battery (LMB) has raised extensive interest in the field of large-scale energy storage applications. The Zn-based LMB composed of inexpensive Zn and low-temperature electrolyte have proven to be feasible and promising. However, the low voltage plateau and coulombic efficiency still limit their practical application. Here we demonstrate a simple design Zn-based LMB, which consists of Zn5Sn5 alloy as negative electrode, Bi as positive electrode and ZnCl2–LiCl–KCl molten salt with lower zinc chloride content as electrolyte. The battery can stably operate at a low temperature of 375 °C and exhibit a flat and high voltage plateau of 0.8–0.9 V. A high coulombic efficiency of over 96% can be achieved by optimizing the composition of electrolyte. Sn is added to yield a liquid negative electrode, and then the problem of Zn dendrites can be avoided. In addition to Zn, both Sn and Bi participate in the redox reaction, which contributes to a multiple redox reaction mechanism. The Zn-based liquid metal batteries with low temperature and high voltage will be a prospective choice for large-scale energy storage.

Redox Mechanisms in Li and Mg Batteries Containing Poly(phenanthrene quinone)/Graphene Cathodes using Operando ATR-IR Spectroscopy.

The redox reaction mechanism of a poly(phenanthrene quinone)/graphene composite (PFQ/rGO) was investigated using operando attenuated total reflection infrared (ATR‐IR) spectroscopy during cycling of Li and Mg batteries. The reference phenanthrene quinone and the Li and Mg salts of the hydroquinone monomers were synthesized and their IR spectra were measured. Additionally, IR spectra were calculated using DFT. A comparison of all three spectra allowed us to accurately assign the C=O and C−O− vibration bands and confirm the redox mechanism of the quinone/Li salt of hydroquinone, with radical anion formation as the intermediate product. PFQ/rGO also showed exceptional performance in an Mg battery: A potential of 1.8 V versus Mg/Mg2+, maximum capacity of 186 mAh g−1 (335 Wh kg−1 of cathode material), and high capacity retention with only 8 % drop/100 cycles. Operando ATR‐IR spectroscopy was performed in a Mg/organic system, revealing an analogous redox mechanism to a Li/organic cell.

Photometric determination of rhenium in mixed hydrochloric-nitric acidic solutions formed upon processing of molibdenite concentrate

The results of spectrophotometric study of the system Re (VII) – HNO 3 – HCl – mercaptoacetic acid – Sn (II) are used to develop a sensitive and selective method of photocolorimetric determination of rhenium in acid nitrate-sulfate solutions formed upon decomposition of molybdenite concentrates with nitric acid and also to reveal trends in complexation of aliovalent rhenium with organic sulfur ligands. Ammonium perrhenate (AR-0) was purified on a Purolite C-100 cation exchanger. Solutions of mercaptoacetic (thioglycolic) acid were prepared from chemically pure Apolda chemical (Germany). Light absorption spectra were recorded on EPS-3T (Hitachi, Japan) and Specord M-40 (Carl Zeiss Jena, Germany) spectrophotometers; the optical density of the solutions was recorded on a KFK-2 (Russia) photocolorimeter. Optimal conditions for the formation of a colored complex compound with mercaptoacetic acid in a mixed hydrochloric-nitric acid solution were determined along with the composition and stability of the complex. The mechanism of redox reactions that occur during complexation is proposed. A technique for monitoring the rhenium content in the products of hydrometallurgical processing of molybdenite concentrates is developed. The procedure provides rhenium determination in the presence of accompanying elements (Mo, Cu, Fe, Ni, etc.) and oxidizing agents (>120 g/liter The developed procedure includes preliminary separation of molybdenum and other interfering impurities by selective sorption of ions on a strongly basic anionite (ChFO) followed by their desorption with a 5 M HNO 3 solution and subsequent photocolorimetric determination of rhenium in the eluate in the form of an orange-yellow (λ max = 460 nm) mixes-ligand complex of Re (III) of assumed composition [Re(L) 3 NOCl]–, where L — is mercaptoacetic acid anion. The developed method of rhenium determination was used in analysis of effluents of washing sulfuric acid taken from the sulfuric acid workshop of the copper smelting plant of Almalyk MMC JSC (Uzbekistan).

Nitrogen-doped carbon quantum dots as a “turn off-on” fluorescence sensor based on the redox reaction mechanism for the sensitive detection of dopamine and alpha lipoic acid

A simple and reliable fluorescence sensing strategy, which depends on the strong fluorescence emission of nitrogen-doped carbon quantum dots (N-CQDs) and efficient catalytic oxidation of tyrosinase (Tyr), was demonstrated for the sensitive detection of dopamine (DA) and alpha lipoic acid (ALA). Under optimized conditions, the fluorescence intensity of N-CQDs was easily quenched by dopamine oxidation product dopaquinone with the addition of Tyr. When ALA was introduced into the sensing system, ALA could inhibit and reduce the oxidation process of DA, resulting in the fluorescence recovery of N-CQDs. This sensing platform showed a sensitive relationship to the DA and ALA concentrations within certain ranges of 0.05–15 and 0.5−55 μM, and low detection limits of 0.035 and 0.39 μM, respectively. Given the above mechanisms, the proposed biosensor was utilized for the detection of DA and ALA in real samples with satisfactory results. Moreover, we successfully measured ALA through spectrometry, which is expected to provide valuable information in medical and disease diagnosis.

Peri/Epicellular Thiol Oxidoreductases as Mediators of Extracellular Redox Signaling.

Significance: Supracellular redox networks regulating cell-extracellular matrix (ECM) and organ system architecture merge with structural and functional (catalytic or allosteric) properties of disulfide bonds. This review addresses emerging evidence that exported thiol oxidoreductases (TORs), such as thioredoxin, protein disulfide isomerases (PDIs), quiescin sulfhydryl oxidases (QSOX)1, and peroxiredoxins, composing a peri/epicellular (pec)TOR pool, mediate relevant signaling. pecTOR functions depend mainly on kinetic and spatial regulation of thiol-disulfide exchange reactions governed by redox potentials, which are modulated by exported intracellular low-molecular-weight thiols, together conferring signal specificity. Recent Advances: pecTOR redox-modulates several targets including integrins, ECM proteins, surface molecules, and plasma components, although clear-cut documentation of direct effects is lacking in many cases. TOR catalytic pathways, displaying common patterns, culminate in substrate thiol reduction, oxidation, or isomerization. Peroxiredoxins act as redox/peroxide sensors, contrary to PDIs, which are likely substrate-targeted redox modulators. Emerging evidence suggests important pecTOR roles in patho(physio)logical processes, including blood coagulation, vascular remodeling, mechanosensing, endothelial function, immune responses, and inflammation. Critical Issues: Effects of pecPDIs supporting thrombosis/platelet activation have been well documented and reached the clinical arena. Roles of pecPDIA1 in vascular remodeling/mechanosensing are also emerging. Extracellular thioredoxin and pecPDIs redox-regulate immunoinflammation. Routes of TOR externalization remain elusive and appear to involve Golgi-independent routes. pecTORs are particularly accessible drug targets. Future Directions: Further understanding mechanisms of thiol redox reactions and developing assays for assessing pecTOR redox activities remain important research avenues. Also, addressing pecTORs as disease markers and achieving more efficient/specific drugs for pecTOR modulation are major perspectives for diagnostic/therapeutic improvements.

MnO2 encapsulated electrospun TiO2 nanofibers as electrodes for asymmetric supercapacitors

We report a facile technique to fabricate manganese dioxide (MnO2) encapsulated titanium dioxide (TiO2) nanofiber heterostructure for its use as an electrode material in aqueous electrolyte based asymmetric supercapacitor (SC). MnO2 coated TiO2 nanofibers, prepared by electrospinning and post-hydrothermal process exhibited superior electrochemical properties in aqueous Na2SO4 electrolyte. The MnO2 shell with average thickness of approximately 10 nm contributed to the high electrochemical performance for charge storage by redox reaction and intercalation mechanisms, while the anatase phase TiO2 core provided an easy pathway for electronic transport with additional electrochemical stability over thousands of charge–discharge cycles. An asymmetric SC designed from the MnO2–TiO2 nanofiber electrode and single walled carbon nanotubes electrode showed high operating voltage window (2.2 V) with maximum gravimetric capacitance of 111.5 F g−1.

Dissociative electron transfer of copper(ii) complexes of glycyl(glycyl/alanyl)tryptophan in vacuo: IRMPD action spectroscopy provides evidence of transition from zwitterionic to non-zwitterionic peptide structures.

We report herein the first detailed study of the mechanism of redox reactions occurring during the gas-phase dissociative electron transfer of prototypical ternary [CuII(dien)M]˙2+ complexes (M, peptide). The two final products are (i) the oxidized non-zwitterionic π-centered [M]˙+ species with both the charge and spin densities delocalized over the indole ring of the tryptophan residue and with a C-terminal COOH group intact, and (ii) the complementary ion [CuI(dien)]+. Infrared multiple photon dissociation (IRMPD) action spectroscopy and low-energy collision-induced dissociation (CID) experiments, in conjunction with density functional theory (DFT) calculations, revealed the structural details of the mass-isolated precursor and product cations. Our experimental and theoretical results indicate that the doubly positively charged precursor [CuII(dien)M]˙2+ features electrostatic coordination through the anionic carboxylate end of the zwitterionic M moiety. An additional interaction exists between the indole ring of the tryptophan residue and one of the primary amino groups of the dien ligand; the DFT calculations provided the structures of the precursor ion, intermediates, and products, and enabled us to keep track of the locations of the charge and unpaired electron. The dissociative one-electron transfer reaction is initiated by a gradual transition of the M tripeptide from the zwitterionic form in [CuII(dien)M]˙2+ to the non-zwitterionic M intermediate, through a cascade of conformational changes and proton transfers. In the next step, the highest energy intermediate is formed; here, the copper center is 5-coordinate with coordination from both the carboxylic acid group and the indole ring. A subsequent switch back to 4-coordination to an intermediate IM1, where attachment to GGW occurs through the indole ring only, creates the structure that ultimately undergoes dissociation.

Reinventing the mechanism of high-performance Bi anode in aqueous K+ rechargeable batteries

Abstract Increasing attention has been paid to rechargeable aqueous batteries due to their high safety and low cost. However, they remain in their infancy because of the limited choice of available anode materials with high specific capacity and satisfying cycling performance. Bi metal with layered structure can act as an ideal anode material with high capacity; however, the energy storage mechanism has not well elucidated. Herein, we demonstrate that Bi metal enables affording ultra-high specific capacity (254.3 mAh g−1), superior rate capability and a capacity retention of 88.8% after 1600 cycles. Different from the previously-reported redox reaction mechanisms of Bi electrode, efficient (de)alloying of K+ is responsible for its excellent performance. An excellent aqueous Bi battery is fabricated by matching Bi anode with Co(OH)2 cathode in KOH (1 M) electrolyte. Its outstanding performance is quite adequate and competitive for electrochemical energy storage devices.

Green synthesis of CoWO4 powders using agar-agar from red seaweed (Rhodophyta): Structure, magnetic properties and battery-like behavior

This work reports a proteic sol-gel green method that uses agar-agar from red seaweed (Rhodophyta) for synthesizing cobalt tungstate (CoWO4) powders for battery-like electrodes. For comparison, CoWO4 is also prepared by a similar proteic chemical route that uses flavorless gelatin. The as-prepared powders were calcined at 800 °C for 2 h and further characterized by XRD (with Rietveld refinement), SEM/EDS, FTIR/Raman/UV–Vis–NIR spectroscopies, VSM, and various electrochemical techniques for assessing the battery-like behavior in alkaline media (3 M KOH). The results indicate that samples produced by gelatin show average particle size of 150 nm and crystallite size of 68 nm, against 284 nm (particle) and 84 nm (crystallite) for agar-agar processed materials. Magnetic assessment at 300 K showed a paramagnetic behavior for both samples. The analysis of these curves showed an effective magnetic moment per cobalt atom of 4.908 μB and 4.926 μB for samples prepared using gelatin and agar-agar, respectively. The performance of CoWO4 as battery-like electrodes is ascribed due to a surface faradaic redox reaction mechanism related to reversible valence state between Co2+ and Co3+. Discharging curves indicate no substantial difference of electrochemical performance, with maximum specific capacity of 77 C g−1 at a specific current of 1 A g−1. The long-term stability of electrodes is confirmed by a capacity retention of around 98% over 1000 charge-discharge cycles at 1 A g−1.

A theoretical study of the reverse water‐gas shift reaction on Ni(111) and Ni(311) surfaces

AbstractThis paper presents a systematic comparison study of the surface redox reaction mechanism for reverse water‐gas shift (RWGS) over Ni(111) and Ni(311) surfaces. Specifically, the most stable surface intermediates and the reaction kinetics involved in the direct CO2 activation and water formation steps are computed with density functional theory calculations and compared for the two different Ni surfaces. The results show that CO2, CO, O, H, OH, and H2O species adsorb stronger on Ni(311) than on Ni(111). Compared to Ni(111), the overall barriers for direct CO2 activation and water formation on Ni(311) are lower by 23 and 17 kJ/mol, respectively. These observations indicate that the RWGS reaction through the surface redox mechanism should be preferred on Ni(311).

First-principles study on structural and electronic properties of Prussian blue cathode material for sodium-ion battery

Prussian blue, Fe[Fe(CN)6] currently attracts a huge attention as a promising material in the application of large-scale energy storage because of its cost-effective and environmental friendly material. Besides, open framework structure and stability are the main causes for PB performance. In this study, effects of sodium cation insertion/deinsertion toward the structural and electronic properties were analyzed. The use of Hubbard U method successfully delivered a good approximation on electronic properties of the transition-metal ions in PB. The calculated band gap of 1.84 eV was in good agreement with theoretical and experimental results. Upon the insertion of the sodium cation, volume of the cathode material expanded between 2% and 4% showing that this cathode material has good cycle retention. From partial density of states, Fe 3d dominated the conduction and valence band. Furthermore, the redox reaction mechanism of Prussian blue can also be depicted. The voltage obtained from energy calculation for the first and second insertion of cation was 3.32 and 3.42 V, respectively.

Metal–Organic Frameworks‐Derived Tunnel Structured Co3(PO4)2@C as Cathode for New Generation High‐Performance Al‐Ion Batteries

AbstractDespite great progress in aluminum ion batteries (AIBs), the commercialization and performance improvement of AIBs‐based carbon cathodes is greatly impeded by sluggish intercalation/extraction and redox kinetics due to large‐sized AlCl4− anions. Phosphates with tunnel channels and much larger d‐spacing than the radius of Al3+ could be an alternative candidate as a cathode for potential high‐performance AIBs. Herein, elaborately designed porous tunnel structured Co3(PO4)2@C composites derived from ZIF‐67 as AIBs cathodes are demonstrated, showing increased active sites, high ionic mobility, and high Al3+ ion diffusion coefficient, leading to remarkably enhanced discharge–charge redox reaction kinetics. Furthermore, the carbon shell and porous structure performs as armor to alleviate volume change and maintain the structure integrity of the cathodes. As expected, the rationally constructed Co3(PO4)2@C composite exhibits a superior capacity of 111 mA h g−1 at a high current density of 6 A g−1 and 151 mA h g−1 at 2 A g−1 after 500 cycles with capacity decay of 0.02% per cycle. This innovative strategy could be a big step forward for long‐term cycle stable AIBs and reveals significant insights into the redox reaction mechanism for high‐performance AIBs based on Al3+ rather than large‐sized AlCl4−.

Simultaneous Cationic and Anionic Redox Reactions Mechanism Enabling High‐Rate Long‐Life Aqueous Zinc‐Ion Battery

AbstractRechargeable aqueous zinc‐ion batteries hold great promise for potential applications in large‐scale energy storage, but the reversible insertion of bivalent Zn2+ and fast reaction kinetics remain elusive goals. Hence, a highly reversible Zn/VNx Oy battery is developed, which combines the insertion/extraction reaction and pseudo‐capacitance‐liked surface redox reaction mechanism. The energy storage is induced by a simultaneous reversible cationic (V3+ ↔ V2+) and anionic (N3− ↔ N2−) redox reaction, which are mainly responsible for the high reversibility and no structural degradation of VNxOy. As expected, a superior rate capability of 200 mA h g−1 at 30 A g−1 and high cycling stability up to 2000 cycles are achieved. This finding opens new opportunities for the design of high‐performance cathodes with fast Zn2+ reaction kinetics for advanced aqueous zinc‐ion batteries.

Molecular recognition: Evidence of the redox role of ferrocenyl-imine derivatives in the presence of copper (II) ions

The design and development of new selective and sensitive chemosensors for metal ions is an area of intense research activity due to their important roles in medicine, living systems, and the environment. In this work, novel ferrocenyl derivatives functionalized with a crown ether linked via an olefin-imine spacer have been designed as versatile molecular recognizers for a series of metal ions (Na+, Ca+2, Cu2+, and Cd2+). By using UV-vis titrations, these systems showed a high affinity for Cu2+ among other metal ions, nevertheless, with unexpected optical behavior. With Spectroelectrochemical studies and electrochemical titrations we revealed that redox reactions between the ferrocenyl and the imine moieties of the spacer and the copper ions took place. These experimental results prove a redox reaction mechanism between both ferrocenyl and imine moieties in the presence of Cu2+. Therefore, this work puts a notice about the redox reaction that takes place between copper (II) and ferrocenyl-imine derivatives, and this information should be considered when designing metal ion chemosensors based on ferrocenyl and imine units, because this redox interaction would become a possible competition reaction.

Colorimetric sensing towards spermine based on supramolecular pillar[5]arene reduced and stabilized gold nanoparticles.

We develop a novel and fast colorimetric sensing platform for spermine (Sp) by using macrocyclic host hydroxyl pillar[5]arene (P5) molecule reduced and stabilized Au nanoparticles via the supramolecular host-guest recognition interaction between P5 and Sp. The P5-modified Au nanoparticles (P5-Au) are easily obtained by redox reaction between hydroxyl groups in P5 and Au3+ in HAuCl4, where hydroxyl groups are oxidized to carboxyl groups and Au3+ is reduced to Au0+ under alkali catalysis at room temperature without NaBH4 or other reducing agent. A uniform diameter of about 5.0 nm and wine red color P5-Au nanoparticles can be synthesized by this green and rapid method. The mechanism of redox reaction between P5 and HAuCl4 is studied by the XPS and 13C NMR, and the P5-Au is characterized by the TEM, XRD and XPS.

Multi-Site Redox Activities in Chemically Complex Sodium Layered Oxide Cathode Materials

Sodium layered oxide cathode materials with high specific capacity, energy density, and long cycle life have been the bottleneck for the widespread market implementation of sodium-ion batteries. Even though sodium layered oxide materials share many similarities with their Li-ion counterpart, there are many dissimilarities between the two which can be utilized to design high performance sodium layered oxide cathode materials. Sodium layered oxide materials can incorporate almost all of the first row transition metals in the transition metal oxide layer. Herein, we have synthesized a sodium layered oxide material with five transition metals to demonstrate such concept. The material is synthesized following a simple co-precipitation method and is a mixture of P2 and P3 type crystal structures (P2/P3=1). The material has good electrochemical performance with excellent stability on long term cycling. It delivers a specific capacity in the range of 95 mAh/g at C/10 with no capacity fading after 100 cycles, 72 mAh/g at 1C with 95% capacity retention after 500 cycles, and 55 mAh/g at 5C with 85% capacity retention after 1000 cycles. We further demonstrate the surprisingly good performance of the material at low temperatures. For example, the material delivers a 60 mAh/g capacity at 1C and 0°C with no capacity fading after 100 cycles. We further studied the structural evolution and redox reaction mechanism of the cathode material at different states of charge. The reversibility of the Na (de)insertion is evident from the reversibility of the XRD pattern upon cycling. Hard XAS study has revealed that most transition metals contribute to some degree towards the redox reaction of the cathode material, with most energy derived from the redox of Ni2+ and Co3+. This study has demonstrated that selecting the ideal transition metal hosts and building up the compositional complexity can be a path towards further improving sodium cathode materials.

Reaction schemes of barium ferrite in biomass chemical looping gasification for hydrogen-enriched syngas generation via an outer-inner looping redox reaction mechanism

Abstract The objective of this study was to build an efficient outer-inner looping redox reaction mechanism called steam recycled biomass chemical looping gasification (SR-BCLG) for H2 production by using BaFe2O4 as an oxygen carrier (OC). The X-ray diffraction (XRD) results showed the phase changes of BaFe2O4 in the SR-BCLG process can be oxidized to its initial state stimulated by steam. In addition, the impacts on the temperature, water injection rate (steam/biomass ratio) and OC loading were investigated. The maximum H2 production of 28.5 mol/kg· biomass was achieved in the 60 min of gasification with a BaFe2O4 load amount of 10 wt%, which is an increase in H2 production of 109.6% compared with the no-OC biomass gasification process under the optimal conditions. Durative high production of H2-enriched syngas was obtained during the cyclic stability tests, indicating the significant redox durability and high H2-generation properties of BaFe2O4. The XRD, scanning electron microscopy (SEM), and thermo-gravimetric analyzer (TG) characterizations revealed the high stability of BaFe2O4, which can be ascribed to the existence of Ba2+. The bimetal functional BaFe2O4 allows for an innovative method of outer-inner looping redox reactions for continuous H2-enriched syngas generation in the SR-BCLG process.

Rational Design of Efficient Amine Reductant Initiators for Amine-Peroxide Redox Polymerization.

Amine-peroxide redox polymerization (APRP) has been highly prevalent in industrial and medical applications since the 1950s, yet the initiation mechanism of this radical polymerization process is poorly understood so that innovations in the field are largely empirically driven and incremental. Through a combination of computational prediction and experimental analysis, we elucidate the mechanism of this important redox reaction between amines and benzoyl peroxide for the ambient production of initiating radicals. Our calculations show that APRP proceeds through SN2 attack by the amine on the peroxide but that homolysis of the resulting intermediate is the rate-determining step. We demonstrate a correlation between the computationally predicted initiating rate and the experimentally measured polymerization rate with an R2 = 0.80. The new mechanistic understanding was then applied to computationally predict amine reductant initiators with faster initiating kinetics. This led to our discovery of N-(4-methoxyphenyl)pyrrolidine (MPP) as amine reductant, which we confirmed significantly outperforms current state-of-the-art tertiary aromatic amines by ∼20-fold, making it the most efficient amine-peroxide redox initiator to date. The application of amines with superior kinetics such as MPP in APRP could greatly accelerate existing industrial processes, facilitate new industrial manufacturing methods, and improve biocompatibility in biomedical applications conducted with reduced initiator concentrations yet higher overall efficiency.

Mechanistic studies on reversible conversion reaction in Li2MnO3-carbon nanotube composite anode

Li2MnO3 is a popular cathode material in lithium-ion batteries, however in this study Li2MnO3-carbon nanotube composite is utilized as an anode material and its electrochemical reaction mechanism is systematically studied by using electrochemical, synchrotron radiation-based X-ray diffraction and absorption techniques along with the density functional calculations. This material demonstrates a significantly high initial reversible capacity of 1006.4 mAh g−1. Electrochemical characterization suggests that this unique anode material operates by a conversion reaction, involving the formation of Li2O and Mn metal. Diffraction patterns are measured at different state of charge and Pawley fitting of these patterns reveal that during lithiation Li2MnO3 initially converts into Mn3O4 and at the end of discharge, Li2O and Mn phases are formed. During delithiation, Li2MnO3 is not reversibly formed, instead [Li0.5Mn0.5]O-type phase appears after a complete electrochemical cycle. X-ray absorption spectroscopy and density functional calculations are used to confirm the validity of the electrochemical redox reaction mechanism derived from the electrochemical and diffraction measurements.

Optimization of coagulation-flocculation treatment of wastewater containing Zn(II) and Cr(VI)

In this study, polymeric ferric sulfate (PFS) was employed as a coagulant to treat the wastewater containing Zn(II) and Cr(VI). Based on the mechanism of redox reaction, Cr(VI) was firstly transferred to Cr(III) with the help of (NH4)2Fe(SO4)2) (FAS) as the reductant. Afterwards, the influence of variable factors including FAS dosage, PFS dosage, pH value and settling time on the coagulation-flocculation treatment of the two heavy metals was estimated. The results show that the optimum removal efficiency of Zn(II) was obtained at a PFS dosage of 100 mg/L, pH 7-8 and settling time of 30 minutes. Meanwhile, the removal efficiency of Cr(VI) reached the highest value when the FAS dosage was 1.2 times of theoretical requirement, with the PFS dosage of 20 mg/L, pH 7-8 and settling time of about 30 minutes.