Metal Reduction Potentials Research Articles

Cu-Doped V-Based MOF Derivative VO2@Cu-VMOF as a Cathodic Catalyst for Electro-Fenton Degradation of Antibiotics.

In this study, the VO2@5%Cu-VMOF/graphite felt (GF) is prepared as an electro-Fenton cathode via hydrothermal process and low-temperature carbonization for efficient antibiotics degradation. The VO2@5%Cu-VMOF/GF cathode exhibit great ciprofloxacin (CIP) degradation performance over the pH range of 2.1-7.2, and CIP removal reached 98.1% within 60min at a pH of 3.4, with corresponding total organic carbon (TOC) removal of 68.7%. The cathode also showed desired catalytic performance toward various antibiotics decomposition. The great catalytic activity of the VO2@5%Cu-VMOF/GF cathode is attributed to lattice strain induced by Cu doping, and the elimination of the overpotential difference between the optimal oxygen reduction potential (OP ORR) and optimal metal reduction potential (OP MRR). Density Function Theory (DFT) calculations showed that Cu doping facilitated electrons accumulation around V atoms, and thus increased the content of low-valence metals in the cathode material. Four possible degradation pathways for CIP are proposed and intermediate toxicity is evaluated. This work advances the design and application of MOF derivatives as electro-Fenton cathodic materials for emerging contaminants degradation.

Antibiotic Indexing and Heavy Metal Reduction Potential of Four Multi-metal Tolerant Bacterial Strains in Real-Time Sanitary Landfill Leachate Matrix.

Sanitary leachate from urban landfills is known to be contaminated with multi-metals and residual antibiotics. Current research edges on exploring the multi-metal and antibiotic sensitivity profile of four indigenous strains, "Brevibacillus spp. Leclercia spp. Pseudescherichia spp., and Brucella spp." isolated from the leachate of a sanitary landfill in a tropical region. Indigenous isolates were observed to be antibiotic-resistant and have high tolerance against eight of the ten tested metals except Cu & Co. It was observed that interaction with multi-metals in laboratory conditions significantly altered the cell morphology of bacterial strains, as depicted by Scanning Electron Microscope. Metal adsorption onto the microbial surface was deciphered through Electron Dispersive Spectrometer analysis and elemental mapping. Application of isolated strains into real-time leachate matrix exhibits a complete reduction of Ag and Zn and for other tested metals. Their response to these toxicants may facilitate their application in bioremediation-based treatment technologies for urban landfill leachate.

Screening of Metal Reduction Potential for Thermochemical Hydrogen Storage

The screening of all non-radioactive metals without lanthanides for thermochemical hydrogen storage was performed based on physical chemistry calculations. The thermodynamic data were collected from the NIST (National Institute of Standards and Technology) public data repository, which was followed by calculations regarding the change in enthalpy, entropy, Gibbs free energy and equilibrium reaction temperature. The results were critically evaluated based on thermodynamic parameters, viable metals were identified, and their hydrogen storage densities and energy–enthalpy ratios were evaluated. The elements viable for controlled thermochemical hydrogen storage via the reversible reduction and oxidation of metal oxides and metals are manganese (Mn), iron (Fe), molybdenum (Mo) and tungsten (W). Manganese has the largest theoretical potential for hydrogen storage with reversible reduction and oxidation of metal oxides and metals. The second candidate is iron, while the other two (Mo and W) have much lower potential. More research efforts should be dedicated to experimental testing of the identified metals (Mn, Fe, Mo and W) and their different oxides for thermochemical hydrogen storage capabilities both on laboratory and pilot scales. Ferromanganese alloy(s) might also prove itself as an efficient and affordable thermochemical hydrogen storage material. Our theoretical investigation expanded the knowledge on thermochemical hydrogen storage and is accompanied with a brief literature review revealing the lack of experimental studies, especially on oxidation of metals with water vapor occurring during the hydrogen release phase of the cycle. Consequently, accurate modelling of transport, kinetics and other phenomena during hydrogen storage and release is scarce.

Atomic Ordering Engineering of Precious Metal Alloys in Liquid Phase Synthesis.

Atomic ordering of noble metal alloys is an effective strategy for improving catalytic performance, yet the low-temperature synthesis of ordered alloys still faces significant challenges. The low-temperature liquid phase method has enormous potential for the synthesis of alloys; however, the atomic ordering mechanism of this process has not been thoroughly studied. Herein, we investigate the mechanism of the influence of metal precursors, reducing agents, solvents, and mixing modes of reactant regulating strategies on precious metal alloy ordering using this method. These regulating strategies are designed to change the coordination structure of metal complexes, affect the reduction potential of metals, and thus change the reduction order of metals and their arrangement in the alloy products. Notably, the reduction potential differences between metal complexes can be used to predict the ordering of the synthetic products (Pd-Cu, Pd-Cd, Pd-Sn, Pd-Pb, and Pt-Sn). This work provides an excellent platform for investigating atomic arrangement engineering.

Galvanic replacement-induced preparation of bloom-like Pt23Ni77 for methanol coupled efficient hydrogen production.

Galvanic replacement reaction (GRR) leverages the difference in metal reduction potentials to regulate the structure of nanomaterials. The crucial aspect of constructing highly active catalysts lies in the precise manipulation of both the oxidative dissolution of sacrificial template metals and reductive deposition of alternate metals. Herein, we investigated the morphological transformation of metal Ni as a sacrificial template in the presence of different amounts of H2PtCl6 solution and the Pt4+ substitution of Ni to achieve the redistribution of elements on the catalyst surface, which provides superior performance in both the methanol oxidation reaction (MOR) and hydrogen evolution reaction (HER). The uniform distribution of Pt on a three-dimensional transition metal Ni substrate allows for the complete exposure of the noble metal to the catalyst surface. This distribution increases the reaction area, facilitating easy access for reactants and promoting electron transfer. Meanwhile, Pt (1.39 Å) has a larger atomic radius compared to Ni (1.24 Å), and the substitution reaction in the transition metal phase induces strong compressive strain, which effectively regulates the electronic structure of Ni.

Correlating Metal Redox Potentials to Co(III)K(I) Catalyst Performances in Carbon Dioxide and Propene Oxide Ring Opening Copolymerization

AbstractCarbon dioxide copolymerization is a front‐runner CO2 utilization strategy but its viability depends on improving the catalysis. So far, catalyst structure‐performance correlations have not been straightforward, limiting the ability to predict how to improve both catalytic activity and selectivity. Here, a simple measure of a catalyst ground‐state parameter, metal reduction potential, directly correlates with both polymerization activity and selectivity. It is applied to compare performances of 6 new heterodinuclear Co(III)K(I) catalysts for propene oxide (PO)/CO2 ring opening copolymerization (ROCOP) producing poly(propene carbonate) (PPC). The best catalyst shows an excellent turnover frequency of 389 h−1 and high PPC selectivity of >99 % (50 °C, 20 bar, 0.025 mol% catalyst). As demonstration of its utility, neither DFT calculations nor ligand Hammett parameter analyses are viable predictors. It is proposed that the cobalt redox potential informs upon the active site electron density with a more electron rich cobalt centre showing better performances. The method may be widely applicable and is recommended to guide future catalyst discovery for other (co)polymerizations and carbon dioxide utilizations.

Correlating Metal Redox Potentials to Co(III)K(I) Catalyst Performances in Carbon Dioxide and Propene Oxide Ring Opening Copolymerization.

Carbon dioxide copolymerization is a front-runner CO2 utilization strategy but its viability depends on improving the catalysis. So far, catalyst structure-performance correlations have not been straightforward, limiting the ability to predict how to improve both catalytic activity and selectivity. Here, a simple measure of a catalyst ground-state parameter, metal reduction potential, directly correlates with both polymerization activity and selectivity. It is applied to compare performances of 6 new heterodinuclear Co(III)K(I) catalysts for propene oxide (PO)/CO2 ring opening copolymerization (ROCOP) producing poly(propene carbonate) (PPC). The best catalyst shows an excellent turnover frequency of 389 h-1 and high PPC selectivity of >99 % (50 °C, 20 bar, 0.025 mol% catalyst). As demonstration of its utility, neither DFT calculations nor ligand Hammett parameter analyses are viable predictors. It is proposed that the cobalt redox potential informs upon the active site electron density with a more electron rich cobalt centre showing better performances. The method may be widely applicable and is recommended to guide future catalyst discovery for other (co)polymerizations and carbon dioxide utilizations.

Refractory Metal Speciation and Electrochemistry in Novel Deep Eutectic Solvents: Progress Towards Electrodeposition

Deep eutectic solvents offer a broad landscape of benign, inexpensive electrodeposition solvents with tunable electrochemical properties. However, the combinatorial nature of binary deep eutectics makes the number of possible solvents very large, and thus solvent-specific fundamental electrochemical properties of even common solvated metal species, much less refractory metals, are severely underpopulated in the body of literature. Additionally, fundamental questions remain unanswered about the effect of electroplating additives on the speciation of solvated metal complexes in these inherently multicomponent solvents, and the ensuing connection between complex speciation and metal reduction potentials. Here we discuss previously undescribed fundamental electrochemical properties of solvated Niobium in various novel, predominantly choline chloride based, deep eutectic solvents, with and without additives, and the resulting implications for the pursuit of refractory metal electrodeposition.

Synthesis of Intermetallic Pt-Based Catalysts by Lithium Naphthalenide-Driven Reduction for Selective Hydrogenation of Cinnamaldehyde.

Intermetallic nanoparticles (NPs) with a well-defined atom binding environment and a long-range ordering structure can be used as ideal models to understand their physical and catalytic properties. In this work, several kinds of nanostructured and carbon nanotube (CNT)-supported Pt-based intermetallic compounds (IMCs) have been synthesized by one-step lithium naphthalenide-driven reduction at room temperature without the use of surfactants in light of the reduction potential of metals. In the chemoselective hydrogenation of cinnamaldehyde, the second metal in Pt-M IMCs significantly creates a suitable reaction environment through construction of a good geometric and electronic structure. The Pt3Sn/CNT catalyst presents highly efficient and good chemoselective hydrogenation of cinnamaldehyde to cinnamyl alcohol. This can be attributed to the fact that the incorporated Sn atoms effectively dilute large Pt ensembles and increase the electron density of Pt. The in situ-formed SnOx interfaces as Lewis acid sites facilitate the coordination of C═O bonds, enhancing the selectivity to cinnamyl alcohol. In addition, the SnOx interface as the joint between Pt3Sn IMCs NPs and CNTs significantly improves the stability of the catalyst in the reaction environment.

How Transition Metals Enable Electron Transfer through the SEI: Part II. Redox-Cycling Mechanism Model and Experiment

At high operating voltages, metals like Mn, Ni, and Co dissolve from Li-ion cathodes, deposit at the anode, and interfere with the performance of the solid-electrolyte interphase (SEI) to cause constant Li loss. The mechanism by which these metals disrupt SEI processes at the anode remains poorly understood. Experiments from Part I of this work demonstrate that Mn, Ni, and Co all affect the electronic properties of the SEI much more than the morphology, and that Mn is the most aggressively disruptive of the three metals. In this work we determine how a proposed electrocatalytic mechanism can explain why Mn contamination is uniquely detrimental to SEI passivation. We develop a microkinetic model of the redox cycling mechanism and apply it to experiments from Part I. The results show that the thermodynamic metal reduction potential does not explain why Mn is the most active of the three metals. Instead, kinetic differences between the three metals are more likely to govern their reactivity in the SEI. Our results emphasize the importance of local coordination environment and proximity to the anode within the SEI for controlling electron transfer and resulting capacity fade.

Novel Approach for the Electrosynthesis of Copper Nanoparticles

In recent decades, nanoparticles have become a prominent research topic due to their increased catalytic activity, which is attributed to their high surface areas. Although typical synthesis methods yield highly ordered monodispersed particles, they often require harsh synthesis conditions, such as high pressure or temperatures, and the use of high-purity reagents. Moreover, these syntheses are conducted on a microliter basis and are not easily scaled-up.1 Electrochemistry offers an alternative approach for the synthesis of nanoparticles under mild conditions, since most metal reduction potentials occur at less than 2 V. One of the earliest attempts at the electrosynthesis of nanoparticles was conducted by Reetz et al.2 In their work, a palladium sheet was stripped and then reduced ions at a platinum sheet to form nanoparticles. However, these nanoparticles were not monodispersed, and therefore not ideal for catalysis. In the present work, copper nanoparticles have been synthesized in bulk via oxidation of a copper wire into a 99.7:2.3 nitromethane-water solution in the presence of an acid. A copper wire was stripped into solution and monitored via chronocoulometry. Once oxidized, copper ions were stabilized with polyethylene glycol and diffused to the cathode where they underwent electrochemical reduction with the aid of a sonic probe, which dispersed uniform-sized nanoparticles into solution. The size of these nanospheres can be controlled to range from approximately 2 nm to 250 nm due to different amounts of surfactant and copper in solution. In addition, other nanoparticle shapes, namely nanospheres and nanocubes, were obtained when the acid was changed from perchloric acid to hydrochloric acid. These changes in composition of the electrolyte allow for control over the shape and size of nanoparticles. This new method for electrosynthesis of nanoparticles allows for their shape and size control, which can be useful for large-scale, industrial purposes. References Gawande, M.B., Goswami, A., Felpin, F., Asefa, T., Huang, X., Silva, R., Zou, X., Zboril, R., Varma, R. S., Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis. Rev. 2016, 116, 3722–3811.Reetz, M.T. , Helbig W., Size-Selective Synthesis of Nanostructured Transition Metal Clusters. Am. Chem. Soc. 1994, 116, 7401–7402.

Characterisation of lithium-ion battery anodes fabricated via in-situ Cu6Sn5 growth on a copper current collector

Li-ion batteries (LIBs) are favoured in many applications due to their high energy density and good cyclic performance. However, some safety concerns remain with respect to the risk of fires and explosions with LIBs. Carbon-based anode materials in LIBs operate close to the Li metal reduction potential, therefore Li dendrites can grow during voltage fluctuations, causing short circuits which may lead to fires. The Cu6Sn5 anodes has the lithiation potential at about 0.4 V vs Li/Li+ and therefore less prone to Li metal plating. A new manufacturing method involving direct in-situ formation of Cu6Sn5 on a Cu current collector via melt-solid contact is proposed. This method combines the active material production and the anode fabrication into a single process. Lithiation and delithiation mechanisms of the anode produced are studied by in-situ synchrotron X-ray powder diffraction (XRPD) and ex-situ high voltage transmission electron microscope (HV-TEM). The in-situ XRPD study shows a reversible two-step reaction during cycling, and also reveals the differences in the reaction mechanisms at higher charge/discharge rates than those in published data.

Assessing the bioaugmentation potentials of individual isolates from landfill on metal-polluted soil

Heavy metals from leachate are persistent pollutants in soil, especially when landfills lack liners and basic structural system that prevents overflow of leachate beyond restricted areas. It is not ideal to rely only on physical and chemical options for the reclamation/restoration of such contaminated soil. Therefore, it is imperative to adopt bioremediation through the enhancement of microbial potentials. The present study investigated the use of individual isolates for the remediation of soil contaminated by leachate-metals. This is a way to understand the discrete potentials of the gram-positive bacteria species. Environmental isolates taken from contaminated soil were used to remedy soil characterized with various concentrations of metals (Al, Cd, Cr, Fe, Ni, Pb and Zn). Treatments A, B, and C amended with Bacillus sp., Lysinibacillus sp., and Rhodococcus sp., respectively, demonstrated better metal reduction potentials than the control experiment (Treatment D; zero microbial amendment) that depended solely on natural attenuation. With the exception of Ni, the degree of reduction of other metals was less than 50% for all treatments. This study suggests that such result reflects the potential ability of the microbes to metabolize selectively in the presence of metal pollution. However, it is difficult for the individual microbes to attain higher metal reduction efficiency (above 50%) except when blended in the appropriate formulation.

Effects of pH Value in the Electrolyte on the Properties of Cu2ZnSnS4 Thin Film Fabricated by Single Step Co-Electrodeposition

CZTS thin films have been prepared from the electrolyte with different pH values by co-electrodeposition. The effects of bath pH value on the cyclic voltammetry, structure, morphology, composition and optical properties of CZTS thin films have been investigated in details. Cyclic voltammetry measurements reveal that pH value impacts the reduction potential of metals and the composition in precursors. The analyses of XRD and Raman spectroscopy suggest that the CZTS films have better crystallinity and less secondary phases when the bath pH is about 5.0. The chemical composition and morphological studies indicate the formation of compact and homogenous CZTS thin films with stoichiometric composition at a pH value of 5.0. And its bandgap energy is around 1.49 eV.

Electrical resistivity and magnetic properties of electrodeposited nanocrystalline CoFe thin films

Nanocrystalline CoFe thin films were electrodeposited from baths containing sodium citrate as complexing agent. Cyclic voltammogrames of CoFe baths showed that addition of sodium citrate to the electrolytes shifted reduction potential of metals toward more negative values. X-ray diffraction patterns of CoFe thin films deposited at different current densities illustrated a transition from FCC(Co) phase to FCC(Co) + BCC(Fe) phases with increasing applied current density. Estimation of average grain size (D) of CoFe thin films by Scherrer’s equation showed all coatings had nanocrystalline structures. The accuracy of results obtained by Scherrer’s equation was confirmed by transmutation electron microscope images. Study of magnetic properties by vibrating sample magnetometer indicated that reduction in grain size of CoFe films resulted in noticeable decrease in coercivity, according to “D6” law. Moreover, decreasing grain size in CoFe thin films led to reduction in resistivity which could be attributed to scattering of conduction electrons, according to “Scattering Hypotheses”. However, average grain size of nanocrystalline CoFe films had no effect on the saturation magnetization which is mostly controlled by chemical composition. The results showed that increasing iron content in the deposited CoFe films from 17 to 31 at.% caused enhancement of saturation magnetization.

Role of Tartaric and Malic Acids in Wine Oxidation

Tartaric acid determines the reduction potential of the Fe(III)/Fe(II) redox couple. Therefore, it is proposed that it determines the ability of Fe to catalyze wine oxidation. The importance of tartaric acid was demonstrated by comparing the aerial oxidation of 4-methylcatechol (4-MeC) in model wine made up with tartaric and acetic acids at pH 3.6. Acetic acid, as a weaker Fe(III) ligand, should raise the reduction potential of the Fe couple. 4-MeC was oxidized in both systems, but the mechanisms were found to differ. Fe(II) readily reduced oxygen in tartrate model wine, but Fe(III) alone failed to oxidize the catechol, requiring sulfite assistance. In acetate model wine the reverse was found to operate. These observations should have broad application to model systems designed to study the oxidative process in foods and other beverages. Consideration should be given to the reduction potential of metal couples by the inclusion of appropriate ligands.

Soft Magnetic Properties and Electrochemical Behavior of Nanocrystalline CoFeCu Thin Films Electrodeposited from Citrate-Added Baths

CoFeCu thin films were electrodeposited from baths with natural pH (instead of pH∼2.8 used in conventional baths) and containing different sodium citrate dosages. ChemEQL V.3.0 software was employed to study speciation diagrams of citrate-added CoFeCu bath with natural pH. At low sodium citrate dosage, Co++, Fe++, and Cu++ species were dominant in CoFeCu bath with natural pH (around 5.2). However, as dosage of sodium citrate in the bath increased, the concentration of complexed species (especially Co(C6H5O7)−, Fe(C6H5O7)−, and Cu(OHC6H5O7)2−) significantly raised. Cyclic voltammetry (CV) studies showed that the formation of complexed species in the bath shifted reduction potential of metals towards more negative potentials. Moreover, in order to deposit cobalt and iron simultaneously with copper, it was necessary to increase the reverse potential (E λ ) value gradually with sodium citrate dosage, otherwise, only copper would have deposited from citrate-added CoFeCu bath. Scanning electron micrographs illustrated that using natural pH (about 5.2) remarkably decreased the number of microvoids in the deposited films compared with the film deposited from conventional baths with pH level of 2.8. EDS, XRD, and VSM were also used for characterization of the deposited films. All deposited films exhibited nanocrystalline structures, and increasing sodium citrate into the baths led to reduction in grain sizes (D) and coercivity (H c) of the CoFeCu thin films. Plotting log(H c) versus log(D 6) demonstrated that films coercivity followed the “D 6 law”. There were only two phase structures (FCC (Co) or BCC (Fe)) observed in the X-ray diffraction patterns of the films. In addition, films with double-phase structures (FCC+BCC) showed finer grain sizes and therefore exhibited lower coercivity in comparison with single-phase (FCC or BCC) films. CoFeCu thin films deposited at higher dosages of sodium citrate (>20 g/L) were poor in diamagnetic copper and consequently showed higher saturation magnetizations.

Electrodeposition of nickel, cobalt, and iron on polypyrrole films

Ni, Co, and Fe, which are metals with relatively low redox potentials, have been electrodeposited on a polypyrrole surface. The conductivity of polypyrrole depends on its oxidation state: the reduced state of the polymer film (at negative potentials) is poorly conducting, whereas the partially oxidized state shows high electronic conductivity (at positive potentials). The redox potentials of the deposited metals are located within the potential range of the low-conductivity state of polypyrrole. The metal layer is deposited under two-step potentiostatic conditions. First, the polymer is oxidized. Next, the metal reduction potential is applied. At this potential, the polymer maintains its high conductivity for a short time, allowing metal deposition to occur on the polymer surface. The amount of metal deposited on the polypyrrole depends on the thickness of the polymeric layer and the concentration of metal ions in solution. Nickel and cobalt form dendritic structures, whereas the iron film is more uniform.

Effect of sodium citrate as complexing on electrochemical behavior and speciation diagrams of CoFeNiCu baths

In this study, the effects of addition of sodium citrate dosages and different pH levels on the electrochemical behavior of CoFeNiCu alloy baths (electrolytes containing metal ions) were investigated. Stability (Pourbiax) diagrams and also speciation diagrams of cobalt, iron, nickel and copper, in conventional and citrate-added CoFeNiCu bath, were calculated by ChemEQL V.3.0 software. Stability diagrams showed that addition of 20 g L−1 sodium citrate to the bath increased the pH of formed detrimental metal hydroxides (especially Fe(OH)3 from pH 3.4 to pH ~ 6.9) through forming stable complexed species that were more stable than metal hydroxides at low pH levels ( ~ 7.5 or sodium citrate dosage > ~ 30 g L−1), Fe(C6H5O7)− (at pH > ~ 5.5 or sodium citrate dosage > ~ 25 g L−1), Ni(C6H5O7)− (at pH > ~ 6 or sodium citrate dosage > ~ 30 g L−1), and Cu(OHC6H5O7)2− ( at pH > ~ 8 or sodium citrate dosage > ~ 20 g L−1) became significant. The effects of sodium citrate and reverse potential (E λ) on cyclic voltammetry curves were also studied. The addition of sodium citrate in the bath shifted the reduction potential of metals towards more negative potentials. Moreover, in order to deposit cobalt, iron, and nickel simultaneously with copper, it was necessary to increase E λ value gradually with sodium citrate dosage; otherwise, only copper would have deposited from citrate-added CoFeNiCu bath. The study of speciation diagrams showed that reduction of metals from CoFeNiCu bath with natural pH (no acid or base is added to adjust pH and it was ~ 5.2) and containing 20 g L−1 of sodium citrate mainly occurred directly from complexed species.

Mapping Irreversible Electrochemical Processes on the Nanoscale: Ionic Phenomena in Li Ion Conductive Glass Ceramics

A scanning probe microscopy approach for mapping local irreversible electrochemical processes based on detection of bias-induced frequency shifts of cantilevers in contact with the electrochemically active surface is demonstrated. Using Li ion conductive glass ceramic as a model, we demonstrate near unity transference numbers for ionic transport and establish detection limits for current-based and strain-based detection. The tip-induced electrochemical process is shown to be a first-order transformation and nucleation potential is close to the Li-metal reduction potential. Spatial variability of the nucleation bias is explored and linked to the local phase composition. These studies both provide insight into nanoscale ionic phenomena in practical Li-ion electrolyte and also open pathways for probing irreversible electrochemical, bias-induced, and thermal transformations in nanoscale systems.