Two-electron Transfer Reaction Research Articles

Red Shift in the Absorption Spectrum of Phototropin LOV1 upon the Formation of a Semiquinone Radical: Reconstructing the Orbital Architecture.

Flavin mononucleotide (FMN) is a ubiquitous blue-light pigment due to its ability to drive one- and two-electron transfer reactions. In both light-oxygen-voltage (LOV) domains of phototropin from the green algae Chlamydomonas reinhardtii, FMN is noncovalently bound. In the LOV1 cysteine-to-serine mutant (C57S), light-induced electron transfer from a nearby tryptophan occurs, and a transient spin-correlated radical pair (SCRP) is formed. Within this photocycle, nuclear hyperpolarization is created by the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect. In a side reaction, a stable protonated semiquinone radical (FMNH·) forms undergoing a significant bathochromic shift of the first electronic transition from 445 to 591 nm. The incorporation of phototropin LOV1-C57S into an amorphous trehalose matrix, stabilizing the radical, allows for application of various magnetic resonance experiments at ambient temperatures, which are combined with quantum-chemical calculations. As a result, the bathochromic shift of the first absorption band is explained by lifting the degeneracy of the molecular orbital energy levels for electrons with alpha and beta spins in FMNH· due to the additional electron.

Electrochemical detection of the neurotransmitter glutamate and the effect of the psychotropic drug riluzole on its oxidation response.

Glutamate is the main excitatory neurotransmitter in the brain and plays a leading role in degenerative diseases, such as motor neuron diseases. Riluzole is a glutamate regulator and a therapeutic drug for motor neuron diseases. In this work, the interaction between glutamate and riluzole was studied using cyclic voltammetry and square-wave voltammetry at a glassy carbon electrode (GCE). It was shown that glutamate underwent a two-electron transfer reaction on the GCE surface, and the electrochemical detection limits of glutamate and riluzole were 483μmol/L and 11.47μmol/L, respectively. The results confirm that riluzole can promote the redox reaction of glutamate. This work highlights the significance of electrochemical technology in the sensing detection of the interaction between glutamate and related psychotropic drugs.

Development of Inverse-Opal-Structured Charge-Deficient Co9S8@nitrogen-Doped-Carbon to Catalytically Enable High Energy and High Power for the Two-Electron Transfer I+/I- Electrode.

The iodine (I) electrode involving two-electron transfer chemistry by converting between I+ and I-, has the potential to deliver theoretically doubled capacity and higher working voltage platforms, thus achieving higher energy density. However, owing to the slow kinetics of the cascade two-electron transfer reactions, the system suffers from large overpotentials and low power density, especially at high working currents and low temperatures. Here, an inverse-opal-structured cobalt sulfide@nitrogen-doped-carbon (Co9S8@NC) catalyst with unique charge-deficient states is developed to promote the reaction kinetics of the I-/I+ electrode. The charge-deficient Co9S8@NC catalyst not only enables strong physicochemical adsorption with the iodine species but also significantly reduces the activation energy and interfacial charge transfer resistance of the cascade I+/I0/I- conversion reaction. Consequently, the prototypical Zn‖I+/I0/I- battery equipped with the Co9S8@NC catalyst can deliver a high energy density of 554 Wh kg-1 and a stable cycle life of 5000 cycles at 30°C. Moreover, at a subzero temperature of -30 °C, the battery can exhibit enhanced kinetics and a high power density of 1514 W kg-1, high energy density of 485 Wh kg-1.

Mechanistic complexities of sulfite oxidase: An enzyme with multiple domains, subunits, and cofactors

Sulfite oxidase (SO) deficiency, an inherited disease that causes severe neonatal neurological problems and early death, arises from defects in the biosynthesis of the molybdenum cofactor (Moco) (general sulfite oxidase deficiency) or from inborn errors in the SUOX gene for SO (isolated sulfite oxidase deficiency, ISOD). The X-ray structure of the highly homologous homonuclear dimeric chicken sulfite oxidase (cSO) provides a template for locating ISOD mutation sites in human sulfite oxidase (hSO). Catalysis occurs within an individual subunit of hSO, but mutations that disrupt the hSO dimer are pathological. The catalytic cycle of SO involves five metal oxidation states (MoVI, MoV, MoIV, FeIII, FeII), two intramolecular electron transfer (IET) steps, and couples a two-electron oxygen atom transfer reaction at the Mo center with two one-electron transfers from the integral b-type heme to exogenous cytochrome c, the physiological oxidant. Several ISOD examples are analyzed using steady-state, stopped-flow, and laser flash photolysis kinetics and physical measurements of recombinant variants of hSO and native cSO. In the structure of cSO, Mo…Fe = 32 Å, much too long for efficient IET through the protein. Interdomain motion that brings the Mo and heme centers closer together to facilitate IET is supported indirectly by decreasing the length of the interdomain tether, by changes in the charges of surface residues of the Mo and heme domains, as well as by preliminary molecular dynamics calculations. However, direct dynamic measurements of interdomain motion are in their infancy.

Thin Zinc Oxide Layer Passivating Bismuth Vanadate for Selective Photoelectrochemical Water Oxidation to Hydrogen Peroxide.

Selective photoelectrochemical (PEC) water oxidation to hydrogen peroxide is an underexplored option as opposed to the mainstream oxygen reduction reaction. Albeit interesting, selective H2 O2 production via oxidative pathway is plagued by the noncontrollable two-electron transfer reaction and the overoxidation of the thus-formed H2 O2 to O2 . Here, ZnO passivator-coated BiVO4 photoanode is reported for selective PEC H2 O2 production. Both the H2 O2 selectivity and production rate increase in the range of 1.0-2.0V versus RHE under simulated sunlight irradiation. The photoelectrochemical impedance spectra and open-circuit potentials suggest a flattened band bending and positively shifted quasi-Fermi level of BiVO4 upon ZnO coating, facilitating H2 O2 generation and suppressing the competitive reaction of O2 evolution. The ZnO overlayer also inhibits H2 O2 decomposition, accelerates charge extraction from BiVO4 , and serves as a hole reservoir under photoexcitation. This work offers insights into surface states and the role of the coating layer in manipulating two/four-electron transfer for selective H2 O2 synthesis from PEC water oxidation.

Polysulfide cluster formation, surface reaction, and role of fluorinated additive on solid electrolyte interphase formation at sodium-metal anode for sodium-sulfur batteries.

Room-temperature sodium-sulfur batteries are promising next-generation energy storage alternatives for electric vehicles and large-scale applications. However, they still suffer from critical issues such as polysulfide shuttling, which inhibit them from commercialization. In this work, using first-principles methods, we investigated the cluster formation of soluble Na2S8 molecules, the reductive decomposition of ethylene carbonate (EC) and propylene carbonate (PC), and the role of fluoroethylene carbonate (FEC) additive in the solid electrolyte interphase formation on the Na anode. The clustering of Na2S8 in an EC solvent is found to be more favorable than in a PC solvent. In the presence of an electron-rich Na (001) surface, EC decomposition undergoes a two-electron transfer reaction with a barrier of 0.19eV for a ring-opening process, whereas PC decomposition is difficult on the same surface. Although the reaction kinetics of an FEC ring opening in the EC and PC solvents are quite similar, the reaction mechanisms of the open FEC are found to be different in each solvent, although both lead to the production of NaF on the surface. The thick NaF layers reduce the extent of charge transfer to Na2S8 at the anode/electrolyte interface, thus decelerating the Na2S8 decomposition reaction. Our results provide an atomistic insight into the interfacial phenomena between the Na-metal anode surface and electrolyte media.

Roles of Ferredoxin-NADP+ Oxidoreductase and Flavodoxin in NAD(P)H-Dependent Electron Transfer Systems.

Distinct isoforms of FAD-containing ferredoxin-NADP+ oxidoreductase (FNR) and ferredoxin (Fd) are involved in photosynthetic and non-photosynthetic electron transfer systems. The FNR (FAD)-Fd [2Fe-2S] redox pair complex switches between one- and two-electron transfer reactions in steps involving FAD semiquinone intermediates. In cyanobacteria and some algae, one-electron carrier Fd serves as a substitute for low-potential FMN-containing flavodoxin (Fld) during growth under low-iron conditions. This complex evolves into the covalent FNR (FAD)-Fld (FMN) pair, which participates in a wide variety of NAD(P)H-dependent metabolic pathways as an electron donor, including bacterial sulfite reductase, cytochrome P450 BM3, plant or mammalian cytochrome P450 reductase and nitric oxide synthase isoforms. These electron transfer systems share the conserved Ser-Glu/Asp pair in the active site of the FAD module. In addition to physiological electron acceptors, the NAD(P)H-dependent diflavin reductase family catalyzes a one-electron reduction of artificial electron acceptors such as quinone-containing anticancer drugs. Conversely, NAD(P)H: quinone oxidoreductase (NQO1), which shares a Fld-like active site, functions as a typical two-electron transfer antioxidant enzyme, and the NQO1 and UDP-glucuronosyltransfease/sulfotransferase pairs function as an antioxidant detoxification system. In this review, the roles of the plant FNR-Fd and FNR-Fld complex pairs were compared to those of the diflavin reductase (FAD-FMN) family. In the final section, evolutionary aspects of NAD(P)H-dependent multi-domain electron transfer systems are discussed.

Enhanced catalytic activity of copper nanoparticles electrochemically Co-deposited with cadmium towards the electroreduction of nitrate

• Size of polyhedral Cu nanoparticles (NPs) shrank once Cd was introduced. • Size shrink was accompanied with evident activity promotion to nitrate reduction. • Mismatch between the two metal lattices might cause the size shrink. • Rate determining step for CuNPs and CuCdNPs was probably different. • Size or synergistic (CuCd bimetal) effect needs to be further studied. Polyhedral copper nanoparticles (CuNPs) were potentiostatically electrodeposited upon stainless-steel from a hydrophobic protic amide-type ionic liquid (IL), i.e. protonated-betaine bis((trifluoromethyl)sulfonyl)amide ([Hbet][TFSA]) containing CuO as the precursor. The surface morphologies and electrocatalytic activities of the CuNPs towards nitrate reduction were significantly altered after the co-deposition of cadmium (Cd). The variation of morphology and activity was caused by the significant shrinkage of the particle size as a result of the Cd co-deposition and the synergistic effect of Cu and Cd bimetal. In the galvanostatic electrolysis of nitrate, CuNPs showed a much higher reductive overpotential in comparison with CuCdNPs. It might be caused by a kinetic hindrance for the CuNPs in the rate-determining step of nitrate reduction ( i.e. formation of nitrite ion NO 2 − ). CuCdNPs, however, exhibited the robust and stable activity in which the rate-determining step was determined as a two-electron transfer reaction in accordance with the Tafel slope.

Bromine–Graphite Intercalation Enabled Two-Electron Transfer for a Bromine-Based Flow Battery

Br2/Br− is a promising redox couple in flow batteries because of its high potential, solubility, and low cost. However, the reaction between Br− and Br2 only involves a single-electron transfer process, which limits its energy density. Herein, a novel two-electron transfer reaction based on Br−/Br+ was studied and realized through Br+ intercalation into graphite to form a bromine–graphite intercalation compound (Br–GIC). Compared with the pristine Br−/Br2 redox pair, the redox potential of Br intercalation/deintercalation in graphite is 0.5 V higher, which has the potential to substantially increase the energy density. Different from Br2/Br− in the electrolyte, the diffusion rate of Br intercalation in graphite decreases with increasing charge state because of the decreasing intercalation sites in graphite, and the integrity of the graphite structure is important for the intercalation reaction. As a result, the battery can continuously run for more than 300 cycles with a Coulombic efficiency exceeding 97% and an energy efficiency of approximately 80% at 30 mA/cm2, and the energy density increases by 65% compared with Br−/Br2. Combined with double-electron transfer and a highly reversible electrochemical process, the Br intercalation redox couple demonstrates very promising prospects for stationary energy storage.

Unraveling the rate-limiting step of two-electron transfer electrochemical reduction of carbon dioxide

Electrochemical reduction of CO2 (CO2ER) has received significant attention due to its potential to sustainably produce valuable fuels and chemicals. However, the reaction mechanism is still not well understood. One vital debate is whether the rate-limiting step (RLS) is dominated by the availability of protons, the conversion of water molecules, or the adsorption of CO2. This paper describes insights into the RLS by investigating pH dependency and kinetic isotope effect with respect to the rate expression of CO2ER. Focusing on electrocatalysts geared towards two-electron transfer reactions, we find the generation rates of CO and formate to be invariant with either pH or deuteration of the electrolyte over Au, Ag, Sn, and In. We elucidate the RLS of two-electron transfer CO2ER to be the adsorption of CO2 onto the surface of electrocatalysts. We expect this finding to provide guidance for improving CO2ER activity through the enhancement of the CO2 adsorption processes by strategies such as surface modification of catalysts as well as careful control of pressure and interfacial electric field within reactors.

Efficient degradation of aqueous organic contaminants in manganese(II)/peroxymonosulfate system assisted by pyridine organic ligands

Although manganese(II) is known to have no role in peroxymonosulfate (PMS) activation, through a series of sulfamethoxazole (SMX) oxidation experiments, we found that the addition of pyridine organic ligands can improve the catalytic activity and accelerate SMX oxidation. For the organic ligands to be effective: the stability constant of the Mn(III) complex should be higher than that of the Mn(II) complex. A positive correlation was observed between the SMX oxidation rate and Mn(II) concentration, and the maximum PMS utilization efficiency was achieved. Many shreds of evidence verified that neither •SO4− nor •OH was associated with SMX oxidation. The enhanced effect of phenanthroline on the Mn(II)/PMS system was attributed to the highly oxidative intermediate manganese species (Mn(V)), originating from the two-electron transfer reaction of complexed Mn(III) and PMS. Notably, the main oxidizing species did not change (η-(PMSO2) ∼ 100%) regardless of the initial PMSO concentration or pH value. Additionally, the analysis of SMX degradation products revealed that the oxygen transfer oxidation pathway was dominant in the Mn(II)/phenanthroline/PMS system, while the N radical coupling pathway also contributed significantly to SMX oxidation. This work offers new insights into the formation of high-valent manganese species and provides a potential strategy for applying low-concentration Mn(II) to wastewater treatment.

Eco-Friendly Extraction of Lead from Galena by In Situ Electrochemical Reduction in ChCl-EG Deep Eutectic Solvent

One-step electrochemical extraction of metallic lead from solid galena in choline chloride-ethylene glycol deep eutectic solvent (ChCl-EG DES) was studied for the first time. Cyclic voltammetry on a Pt powder microcavity electrode shows that solid galena can be directly reduced to metallic lead by a one-step, two-electron transfer reaction at a potential of −0.47 V (vs Ag). The constant voltage electrolysis using galena powders as cathode in the range of 5 h to 30 h reaction time and 3.0 V to 3.8 V cell voltage further proves that metallic lead can be obtained at the cathode. With the extension of reaction time, the morphology of lead powders transforms from interconnected wax to irregular rod-like and needle particles. As the cell voltage is elevated, the microstructure of metallic lead changes from irregular flake and rod to nano-needle particles. The direct electrolysis process of solid galena is analyzed, and a schematic diagram is also exhibited. It is pointed out that the close contact between galena powders and current collector is the key to facilitate the in situ reduction. These findings put forward a green and convenient route for direct extraction of metals from sulphide ores at near room temperature.

Bromide–acetate co-mediated high-power density rechargeable aqueous zinc–manganese dioxide batteries

A new bromide-acetate co-mediated multicomponent metal-ion aqueous electrolyte was for the first time developed to achieve a high specific capacity two-electron transfer reaction between Mn2+ and MnO2 with extremely fast reaction kinetics.

Fabrication and Electrochemical Evaluation of Organic Secondary Battery Capable of Charging and Discharging in Neutral Solution

There are attractive attentions on organic secondary batteries as new energy storage devices, in which organic compounds as electrode active materials supported on a porous carbon. Dilute sulfuric acid and organic solvents were used as electrolytes1,2). On the other hand, an organic electrolyte has a risk of ignition, and an acidic electrolyte is low safety when leaked.In this study, we newly fabricated an organic secondary battery that can be charged and discharged with a non-flammable, non-poisonous neutral aqueous solution, and evaluated its electrochemical performance.4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl-benzoate (TEMPO-benzoate) was used as the cathode active material, and 9,10-anthraquinone (AQ) was used as the anode active material. Both active materials are hydrophobic and expected to overcome the problem of elution of the active material into the electrolyte.Firstly, carbon cloth was immersed in a slurry of acetylene black and polyvinylidene fluoride (PVdF) ultrasonically dispersed in N-methyl-2-pyrrolidone (NMP) and dried at 60 ° C for 48 hours. Next, each active material solution was dropped, dried under reduced pressure for 4 hours to adsorb each active material, and a porous carbon electrode was produced. For single electrode evaluation, cyclic voltammetry was performed at a scanning speed of 10 mV s-1. The as-fabricated electrodes were used as the working electrode, a platinum mesh was used as the counter electrode, a saturated KCl/Ag/AgCl electrode (SSE) was used as the reference electrode, and a 1 mol/dm3 KCl aqueous solution was used as the electrolyte. An organic secondary battery was fabricated using the as-fabricated electrode, and electrochemical evaluation was performed by a charge and discharge test using a reference electrode. A cellophane was used for the separator.Figure 1 (A) shows the reaction mechanism of the active materials of both electrodes used in this study. Figure 1 (B) and (C) show the cyclic voltammograms of AQ and TEMPO-benzoate. It was found that AQ showed an anodic peak near -0.65 V vs. SSE and a cathodic peak near -0.8 V vs. SSE (Fig. 1(B)). The anodic current and cathodic current is related to the two-electron transfer reaction between quinone and hydroquinone shown on the left side of Fig.1 (A). TEMPO-benzoate showed an anodic peak near 0.85 V vs. SSE and a cathodic peak near 0.65 V vs. SSE (Fig. 1(C)) due to the one-electron transfer reaction between the NO radical and the NO cation on TEMPO-benzoate shown on the right side of Fig. 1 (A). The peak appeared near 1.1 V vs. SSE in Fig. 1 (C) is considered to be due to chlorine gas generation on the electrode surface by chloride ions in the electrolyte.Figure1 (D) shows the results of a charge and discharge test performed by applying a constant current of 820 mA to an organic secondary battery. The cut-off voltage were 2 V and 0.4 V, respectively. A large irreversible capacity appeared during the first charge. The potentials of the two electrodes during charging and discharging using the reference electrode suggested that reduction of dissolved oxygen in the negative electrode and oxygen in the porous carbon pores and side reactions were caused. On the other hand, it was confirmed that charge and discharge was performed stably repeatedly after the first discharge. We also tried to improve cycling characteristics by suppressing irreversible capacity by performing thorough degassing of porous carbon and degassing of electrolyte, and assembling cells in an inert gas atmosphere. References 1) T. Tomai et al., Scientific reports, 4, 3591 (2014).2) B. Huskinson et al., Nature, 505, 195-198 (2014). Acknowledgments This work was partially supported by JST-ASTEP Grant Number JPMJTS1513, JSPS Grant Number 17H02162 and Private University Research Branding Project (2017-2019) from Ministry of Education, Culture, Sports, Science and Technology, and Tokyo University of Science Grant for President's Research Promotion． Figure 1

Dipotassium terephthalate as promising potassium storing anode with DFT calculations

We report combined experimental and theoretical studies of dipotassium terephthalate as anode material for K-ion battery application. Both pristine and carbon nanotube-containing dipotassium terephthalate materials are synthesized using an ultrafast microwave-assisted method. We found that carbon nanotube (CNT)-containing dipotassium terephthalate composite electrode delivers an initial reversible capacity of 247 mAh/g with 78% capacity retention, whereas pristine K2Tp deliveries an initial reversible capacity of 212 mAh/g with 53% capacity retention at the end of 100 cycles, at a current density of 50 mA/g. The density functional theory-based calculations have shown superior stability of dipotassium terephthalate lattice against the intercalation of potassium atoms. The quantum calculations are also employed to unravel the specifics of intercalation energetics of potassium ions into dipotassium terephthalate lattice. The intercalation and de-intercalation potentials of K-ions are obtained using cyclic voltammetry and compared with theoretical calculations under the assumption of a two-electron transfer reaction. The results of this study lay the ground for understanding the electrochemical processes involved in the operation of an organic anode in K-ion batteries, and thereby can facilitate the design of optimal organic molecular crystal-based electrode materials for battery applications.

Dendrite-Free Sn Anode with High Reversibility for Aqueous Batteries Enabled by “Water-in-Salt” Electrolyte

Metallic tin (Sn) has always been considered as an anode candidate for nonaqueous lithium-ion batteries (LIBs). Nevertheless, there were hardly any attempts to use Sn as an anode material in aqueous batteries. Although Sn possesses relatively high specific capacity (451.54 mAh/g, two-electron transfer reaction), mild electrode potential (−0.1375 V vs the standard hydrogen electrode, Sn2+ + 2e– = Sn), high hydrogen overpotential, and environmental friendliness, it also suffers from bad reversibility and low Coulombic efficiency (CE) in common aqueous electrolytes. In this work, a dendrite-free Sn anode with highly improved reversibility in an aqueous electrolyte was realized using a type of “water-in-salt” electrolyte (1 m Sn(OTf)2 + 20 m LiTFSI). The results of Fourier transform infrared (FTIR) spectra and density functional theory (DFT) calculations have verified the significant impact of highly concentrated LiTFSI salt on Sn2+ hydrolysis, which is the key factor in improving the reversibility of the Sn anode and suppressing the dendrite formation. A Sn/LiFePO4 cell applying this electrolyte was acquired with a discharge plateau at around 0.6 V. In the cyclability test, the Sn anode exhibited a stable discharge capacity of more than 107 mAh/g with a Coulombic efficiency (CE) of 95% for 35 cycles (0.2C rate).

Manganese carbonate as active material in potassium carbonate electrolyte

In this work, we explore the possibility of using MnCO3 as active material for alkaline rechargeable batteries. K2CO3 solution is chosen as electrolyte because the solubility of MnCO3 in K2CO3 electrolyte keeps lower than that in KOH electrolyte of the same pH values, which may promote the cyclability of MnCO3. XRD and XPS measurements reveal a two-electron transfer reaction during cycling, corresponding to the conversion of MnCO3/MnO2. Further investigations demonstrate the MnCO3 electrode can be cycled 50 cycles without obvious capacity decay and the coulombic efficiency keeps over 95.0% after the 8th cycle. The present study provides a new perspective in searching new electrode materials and electrolyte systems for alkaline rechargeable batteries.

A Molecular Mechanics Model for Flavins.

Flavin containing molecules form a group of important cofactors that assist a wide range of enzymatic reactions. Flavins use the redox-active isoalloxazine system, which is capable of one- and two-electron transfer reactions and can exist in several protonation states. In this work, molecular mechanics force field parameters compatible with the CHARMM36 all-atom additive force field were derived for biologically important flavins, including riboflavin, flavin mononucleotide, and flavin adenine dinucleotide. The model was developed for important protonation and redox states of the isoalloxazine group. The partial charges were derived using the CHARMM force field parametrization strategy, where quantum mechanics water-solute interactions are used to target optimization. In addition to monohydrate energies and geometries, electrostatic potential around the compound was used to provide additional restraints during the charge optimization. Taking into account the importance of flavin-containing molecules special attention was given to the quality of bonded terms. All bonded terms, including stiff terms and torsion angle parameters, were parametrized using exhaustive potential energy surface scans. In particular, the model reproduces well the butterfly motion of isoalloxazine in the oxidized and reduced forms as predicted by quantum mechanics in gas phase. The model quality is illustrated by simulations of four flavoproteins. Overall, the presented molecular mechanics model will be of utility to model flavin cofactors in different redox states. © 2019 Wiley Periodicals, Inc.

Concerted Two-Electron Reduction of Ubiquinone in Respiratory Complex I.

Respiratory complex I catalyzes two-electron/two-proton reduction of a ubiquinone (Q) substrate bound at its Q-binding pocket; upon reduction, ubiquinole carries electrons further down the electron transport chain. The mechanism of this two-electron transfer reaction is poorly understood. Here we consider a hypothetical scheme in which two electrons transfer together with two protons in a concerted fashion. On one side, a coupled electron/proton transfer occurs from the reduced N2 FeS cluster and protonated His38 residue, respectively, while on the other side a hydrogen atom transfer occurs from the neutral Tyr87 residue, generating a tyrosyl radical. A method to evaluate the coupling matrix element that corresponds to a concerted tunneling of two electrons was developed. Overall, our calculations indicate that the concerted reaction is feasible, in which case a transient tyrosyl radical is formed during the catalytic cycle of the enzyme.

Cathodic process of aluminum deposition in NaF-AlF3-Al2O3 melts with low cryolite ratio

In the present study, theoretical analysis and electrolysis testing in the laboratory scale demonstrated the potential of Al metal production by electrolysis in a NaF-AlF3-Al2O3 melt with a cryolite ratio (CR; molar ratio of NaF/AlF3) of 1.3. Subsequently, the electrochemical processes of Al deposition on a tungsten cathode in this melt at 860 °C were comprehensively evaluated by cyclic voltammetry, potentiodynamic cathodic polarization, square wave voltammetry, chronopotentiometry, and potentiostatic electrolysis. The results revealed Al deposition on the tungsten cathode, first as an Al4W alloy at approximately − 0.14 V (vs W), and then as liquid metallic Al-containing a co-deposition of metallic Na at − 0.94 V (vs W). The reduction of Al4W alloy and the deposition of metallic Al were both diffusion-controlled and quasi-reversible. The diffusion coefficient of the Al(Ш) ions was calculated to be 1.77 × 10−8 cm2 s−1. The square wave voltammetry curves indicated that the process of AlF4− ion reduction involved both a three-electron transfer reaction resulting in Al deposition (AlF4− → Al), and a two-electron transfer reaction resulting in the formation of monovalent aluminum ions AlF2− (AlF4− → AlF2−). The chronopotentiometry results revealed that the critical cathodic current for Al deposition was approximately 150 mA. X-ray diffraction (XRD) measurements and scanning electron microscope (SEM) observations confirmed that Al4W alloy and metallic Al existed on the electrode surface after potentiostatic electrolysis.