Highly selective thiocyanate electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) complex as neutral carrier

A novel selective thiocyanate PVC membrane electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) [Cu(II)₂–BBSTA] as neutral carrier is reported, which displays an anti-Hofmeister selectivity sequence in following order: SCN⁻ > ClO₄⁻ > I⁻ >Sal⁻ >SO₃²⁻ >NO₃⁻ > H₂PO₄⁻ > Cl⁻ >NO₂⁻ > SO₄²⁻. The electrode exhibits Nernstian potential linear range to thiocyanate from 1.0 × 10⁻¹ to 9.0 × 10⁻⁷ mol/l with a detection limit 7.0 × 10⁻⁷ mol/l and a slope of −57.0 mV/decade in pH 5.0 of phosphorate buffer solution at 25 °C. The response mechanism is discussed in view of the AC impedance technique and the UV spectroscopy technique. From comparison of potentiometric response characteristics between the binuclear metallic complex copper(II) [Cu(II)₂–BBSTA] and mononuclear copper(II) metallic complex [Cu(II)–BBSDA], an enhanced response towards thiocyanate from the electrode based on binuclear metallic complex copper (II) [Cu(II)₂–BBSTA] was observed. The electrode based on binuclear copper(II) compound was used to determine the thiocyanate content in waste water with satisfactory results.     

Effect of inorganic anions on the titanium dioxide-based photocatalytic oxidation of aqueous ammonia and nitrite

In this study, we investigated the effects of four inorganic anions (Cl⁻, SO₄²⁻, H₂PO₄⁻/HPO₄²⁻, and HCO₃⁻/CO₃²⁻) on titanium dioxide (TiO₂)-based photocatalytic oxidation of aqueous ammonia (NH₄⁺/NH₃) at pH ∼ 9 and ∼10 and nitrite (NO₂⁻) over the pH range of 4–11. The initial rates of NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation are dependent on both the pH and the anion species. Our results indicate that, except for CO₃²⁻, which decreased the homogeneous oxidation rate of NH₄⁺/NH₃ by UV-illuminated hydrogen peroxide, OH scavenging by anions and/or direct oxidation of NH₄⁺/NH₃ and NO₂⁻ by anion radicals did not affect rates of TiO₂ photocatalytic oxidation. While HPO₄²⁻ enhanced NH₄⁺/NH₃ photocatalytic oxidation at pH ∼ 9 and ∼10, H₂PO₄⁻/HPO₄²⁻ inhibited NO₂⁻ oxidation at low to neutral pH values. The presence of Cl⁻, SO₄²⁻, and HCO₃⁻ had no effect on NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation at pH ∼ 9 and ∼10, whereas CO₃²⁻ slowed NH₄⁺/NH₃ but not NO₂⁻ photocatalytic oxidation at pH ∼ 11. Photocatalytic oxidation of NH₄⁺/NH₃ to NO₂⁻ is the rate-limiting step in the complete oxidation of NH₄⁺/NH₃ to NO₃⁻ in the presence of common wastewater anions. Therefore, in photocatalytic oxidation treatment, we should choose conditions such as alkaline pH that will maximize the NH₄⁺/NH₃ oxidation rate.     

Radiotracer and analytical evidences proving the reduction of ClO4− ions at the cobalt/electrolyte solution interface

The occurrence of the reduction of ClO₄⁻ ions in the course of the dissolution (corrosion) of Co was indicated through the study of the adsorption of radio labelled (³⁶Cl) Cl⁻ ions. A detailed analytical study determining the Co²⁺ and Cl⁻ content of the solution phase furnished firm evidences that under suitable chosen experimental conditions the 4Co + ClO₄⁻ + 8H⁺=4Co²⁺ + Cl⁻ + 4H₂O reaction could be as important as the Co + 2H⁺=Co²⁺ + H₂ reaction considered in the literature as the only reaction path.     

Vibrational spectroscopic characterization of the phosphate mineral hureaulite – (Mn,Fe)5(PO4)2(HPO4)2·4(H2O)

This research was done on hureaulite samples from the Cigana claim, a lithium bearing pegmatite with triphylite and spodumene. The mine is located in Conselheiro Pena, east of Minas Gerais. Chemical analysis was carried out by Electron Microprobe analysis and indicated a manganese rich phase with partial substitution of iron. The calculated chemical formula of the studied sample is: (Mn_3.23, Fe_1.04, Ca_0.19, Mg_0.13)(PO₄)_2.7(HPO₄)_2.6(OH)_4.78. The Raman spectrum of hureaulite is dominated by an intense sharp band at 959 cm⁻¹ assigned to PO stretching vibrations of HPO₄²⁻ units. The Raman band at 989 cm⁻¹ is assigned to the PO₄³⁻ stretching vibration. Raman bands at 1007, 1024, 1047, and 1083 cm⁻¹ are attributed to both the HOP and PO antisymmetric stretching vibrations of HPO₄²⁻ and PO₄³⁻ units. A set of Raman bands at 531, 543, 564 and 582 cm⁻¹ are assigned to the ν₄ bending modes of the HPO₄²⁻ and PO₄³⁻ units. Raman bands observed at 414, and 455 cm⁻¹ are attributed to the ν₂ HPO₄²⁻ and PO₄³⁻ units. The intense A series of Raman and infrared bands in the OH stretching region are assigned to water stretching vibrations. Based upon the position of these bands hydrogen bond distances are calculated. Hydrogen bond distances are short indicating very strong hydrogen bonding in the hureaulite structure. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral hureaulite to be understood.     

Vibrational spectroscopic characterization of the phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO4)(OH)2·(H2O)

The phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO₄)(OH)₂·(H₂O) has been studied using a combination of electron probe analysis and vibrational spectroscopy. Eosphorite is the manganese rich mineral with lower iron content in comparison with the childrenite which has higher iron and lower manganese content. The determined formulae of the two studied minerals are: (Mn_0.72,Fe_0.13,Ca_0.01)(Al)_1.04(PO₄, OHPO₃)_1.07(OH_1.89,F_0.02)·0.94(H₂O) for SAA-090 and (Fe_0.49,Mn_0.35,Mg_0.06,Ca_0.04)(Al)_1.03(PO₄, OHPO₃)_1.05(OH)_1.90·0.95(H₂O) for SAA-072. Raman spectroscopy enabled the observation of bands at 970 cm⁻¹ and 1011 cm⁻¹ assigned to monohydrogen phosphate, phosphate and dihydrogen phosphate units. Differences are observed in the area of the peaks between the two eosphorite minerals. Raman bands at 562 cm⁻¹, 595 cm⁻¹, and 608 cm⁻¹ are assigned to the ν₄ bending modes of the PO₄, HPO₄ and H₂PO₄ units; Raman bands at 405 cm⁻¹, 427 cm⁻¹ and 466 cm⁻¹ are attributed to the ν₂ modes of these units. Raman bands of the hydroxyl and water stretching modes are observed. Vibrational spectroscopy enabled details of the molecular structure of the eosphorite mineral series to be determined.     

Synthesis,structure and NMR characterization of a new monomeric aluminophosphate [dl-Co(en)3]2[Al(HPO4)2(H1.5PO4)2(H2PO4)2](H3PO4)4 containing four different types of monophosphates

A new zero-dimensional (0D) aluminophosphate monomer [dl-Co(en)₃]₂[Al(HPO₄)₂(H_1.5PO₄)₂(H₂PO₄)₂](H₃PO₄)₄ (designated AlPO-CJ38) with Al/P ratio of 1/6 has been solvothermally prepared by using racemic cobalt complex dl-Co(en)₃Cl₃ as the template. The Al atom is octahedrally linked to six P atoms via bridging oxygen atoms, forming a unique [Al(HPO₄)₂(H_1.5PO₄)₂(H₂PO₄)₂]^6? monomer. Notably, there exists intramolecular symmetrical O?H?O bonds, which results in pseudo-4-rings stabilized by the strong H-bonding interactions. The structure is also featured by the existence of four different types of monophosphates that have been confirmed by ³¹P NMR and ¹H NMR spectra. The crystal data are as follows: AlPO-CJ38, [dl-Co(en)₃]₂[Al(HPO₄)₂(H_1.5PO₄)₂(H₂PO₄)₂](H₃PO₄)₄, M = 1476.33, monoclinic, C2/c (No. 15), a = 36.028(7) Å, b = 8.9877(18) Å, c = 16.006(3) Å, β = 100.68(3)°, U = 5093.2(18) Å³_, Z = 4, R₁ = 0.0509 (I > 2σ(I)) and wR₂ = 0.1074 (all data). CCDC number 689491.     

A Raman and infrared spectroscopic study of the phosphate mineral laueite

A laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn²⁺_0.85,Fe²⁺_0.10Mg_0.05)_∑1.00(Fe³⁺_1.90,Al_0.10)_∑2.00(PO₄)₂(OH)₂·8H₂O.The laueite structure is based on an infinite chains of vertex-linked oxygen octahedra, with Fe³⁺ occupying the octahedral centers, the chain oriented parallel to the c-axis and linked by PO₄ groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 980 and 1045 cm⁻¹ are assigned to the ν₁ PO₄³⁻ symmetric stretching mode. Intense Raman bands are observed at 525 and 551 cm⁻¹ with a shoulder at 542 cm⁻¹ are assigned to the ν₄ out of plane bending modes of the PO₄³⁻. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Intense Raman bands are observed at 3379 and 3478 cm⁻¹ and are attributed to the OH stretching vibrations of the hydroxyl units. Intense broad infrared bands are observed. Vibrational spectroscopy enables subtle details of the molecular structure of laueite to be determined.     

Syntheses,characterisation and solid state thermal studies of 1-(2-aminoethyl)piperidine (L), 1-(2-aminoethyl)pyrrolidine (L′) and 4-(2-aminoethyl)morpholine (L″) complexes of nickel(II): X-ray single crystal structure analyses of trans-[NiL2(CH3CN)2](ClO4)2, trans-[NiL2(NCS)2] and trans-[NiL″2(NCS)2]

Reactions of nickel(II) salts with substituted ethane-1,2-diamine where one of the amine nitrogens is a part of a flexible cyclic ring, e.g. 1-(2-aminoethyl)piperidine (L), 1-(2-aminoethyl)pyrrolidine (L′) and 4-(2-aminoethyl)morpholine (L″) produce a number of complexes of the type: (i) Ni(AA)₂X₂ (where X=CF₃CO₂ ⁻, SCN⁻ and NO₂ ⁻; AA represents L/L′/L″); (ii) Ni(AA)₂(CH₃CN)₂X₂ (X=ClO₄ ⁻ and NO₃ ⁻); (iii) Ni(AA)₂(H₂O)₂X₂ (X=CF₃SO₃ ⁻, Cl⁻, Br⁻ and I⁻); and (iv) Ni(AA)₂(H₂O)₄X₂ (X=0.5SO₄ ²⁻, 0.5SeO₄ ²⁻ and CF₃SO₃ ⁻). The complexes possess octahedral geometry. The major complexes upon desolvation retain trans-geometry, some of which are cis with respect to the counter-anion and a few of them are square planar. X-ray single crystal structure analyses of trans-[NiL₂(CH₃CN)₂](ClO₄)₂, trans-[NiL₂(NCS)₂] (violet) and trans-[NiL″₂(NCS)₂] (sky-blue) have been done. The violet and sky-blue thiocyanato species have blue and green coloured isomers, respectively, and these pairs of isomers are proposed to be conformational isomers. Solid state thermal investigation of the complexes has been carried out. The complexes show thermochromism due to deaquation–anation/deaquation reaction/change of conformation. Only [NiL₂](ClO₄)₂, [NiL′₂(CF₃CO₂)₂] and [NiL″₂(NO₂)₂] undergo thermally induced phase transition. The effect of flexible ring size on diamine has been discussed.     

Synthesis,characterization and batch assessment of groundwater fluoride removal capacity of trimetal Mg/Ce/Mn oxide-modified diatomaceous earth

In this study, trimetal Mg/Ce/Mn oxide-modified diatomaceous earth (DE) was synthesized at optimal conditions. Comparison of the SEM images and the results of EDX analyses of the raw and the modified DE confirmed the surface modification of the raw DE with the trimetal oxide. Groundwater fluoride removal capacity of the sorbent was evaluated by batch method at various defluoridation conditions. At a sorbent dosage of 0.6 g/100 mL (contact time: 60 min, mixing speed of 200 rpm and temperature: 297 K), the fluoride removal was >93% for solutions containing initial fluoride concentration of 10–60 mg/L. Sorbent’s optimum fluoride uptake capacity was 12.63 mg/g at the initial fluoride concentration of 100 mg/L. Fluoride removal was >91% for solutions with initial pH range of ∼4–11 (initial fluoride concentration: 9 mg/L, sorbent dosage: 0.6 g/100 mL). Appraisal of the effect of co-existing anions on fluoride removal showed that CO₃²⁻ would reduce the amount of fluoride removed from solution, while other anions such as PO₄³⁻, NO₃⁻ and SO₄²⁻ had no observable effect. K₂SO₄ solution was found to be most suitable for regeneration of spent Mg/Ce/Mn oxide-modified DE compared to Na₂CO₃ and NaOH. The mechanism of fluoride removal at pH > 5.45 (pHpzc = 5.45) occurred by exchange of hydroxyl groups on surface of sorbent with fluoride ions from solution. Sorption data fitted better to Langmuir isotherm and pseudo-second-order model. External diffusion was observed to be the sorption rate limiting factor.     

Thermodynamics of Cr2O3, FeCr2O4, ZnCr2O4, and CoCr2O4

High-temperature heat capacity measurements were obtained for Cr₂O₃, FeCr₂O₄, ZnCr₂O₄, and CoCr₂O₄ using a differential scanning calorimeter. These data were combined with previously available, overlapping heat capacity data at temperatures up to 400 K and fitted to 5-parameter Maier–Kelley C_p(T) equations. Expressions for molar entropy were then derived by suitable integration of the Maier–Kelley equations in combination with recent S^∘(298) evaluations. Finally, a database of high-temperature equilibrium measurements on the formation of these oxides was constructed and critically evaluated. Gibbs free energies of Cr₂O₃, FeCr₂O₄, and CoCr₂O₄ were referenced by averaging the most reliable results at reference temperatures of (1100, 1400, and 1373) K, respectively, while Gibbs free energies for ZnCr₂O₄ were referenced to the results of Jacob [K.T. Jacob, Thermochim. Acta 15 (1976) 79–87] at T = 1100 K. Thermodynamic extrapolations from the high-temperature reference points to T = 298.15 K by application of the heat capacity correlations gave Δ_fG^∘(298) = (−1049.96, −1339.40, −1428.35, and −1326.75) kJ · mol⁻¹ for Cr₂O₃, FeCr₂O₄, ZnCr₂O₄, and CoCr₂O₄, respectively.     

Hollow fiber supported liquid membrane: a novel technique for separation and recovery of plutonium from aqueous acidic wastes

Low plutonium content acidic waste is generated in nuclear chemical facilities. Study was initiated to develop hollow fiber supported liquid membrane (HFSLM) technique for quantitative separation and recovery of plutonium (Pu) from such wastes using tri-n-butyle phosphate (TBP) in dodecane as carrier. Hollow fiber test module was fabricated using 20 lumens of 33.91 cm² surface area and 9 cm length. After satisfactory testing of the hydrodynamic condition of the module, it was operated at a flow rate of 3 ml min⁻¹ on recycling mode with acidic waste solution containing Pu=8 mg dm⁻³, uranium=15 dm⁻³, gross β⁻=49.33 mCi dm⁻³, gross γ=15.73 mCi dm⁻³ and acidity 3 M HNO₃. In presence of various fission products, selective permeation of Pu(IV) through the bundle of hollow fiber test module was observed to be more than 90% into a stripping phase consisting 0.1 M NH₂OH·HCl in 0.3 M HNO₃. A model is presented to describe the transport mechanism and to evaluate the mass transfer coefficient. The radiation stability was also tested by exposing the membrane upto irradiation level of 1 M rad. Potentiality of the method for the selective separation of plutonium from acidic waste is, thus, clearly seen.     

Crystal structures of Th(OH)PO4, U(OH)PO4 and Th2O(PO4)2. Condensation mechanism of MIV(OH)PO4 (M = Th,U) into M2O(PO4)2

Three new crystal structures, isotypic with β-Zr₂O(PO₄)₂, have been resolved by the Rietveld method. All crystallize with an orthorhombic cell (S.G.: Cmca) with a = 7.1393(2) Å, b = 9.2641(2) Å, c = 12.5262(4) Å, V = 828.46(4) Å³ and Z = 8 for Th(OH)PO₄; a = 7.0100(2) Å, b = 9.1200(2) Å, c = 12.3665(3) Å, V = 790.60(4) Å³ and Z = 8 for U(OH)PO₄; a = 7.1691(3) Å, b = 9.2388(4) Å, c = 12.8204(7) Å, V = 849.15(7) Å³ and Z = 4 for Th₂O(PO₄)₂. By heating, the M(OH)PO₄ (M = Th, U) compounds condense topotactically into M₂O(PO₄)₂, with a change of the environment of the tetravalent cation that lowers from 8 to 7 oxygen atoms. The lower stability of Th₂O(PO₄)₂ compared to that of U₂O(PO₄)₂ seems to result from this unusual environment for tetravalent thorium.     

Redox behavior and transport properties of La0.5−2xCexSr0.5+xFeO3−δ and La0.5−2ySr0.5+2yFe1−yNbyO3−δ perovskites

The effects of doping the mixed-conducting (La,Sr)FeO_3−δ system with Ce and Nb have been examined for the solid-solution series, La_0.5−2xCe_xSr_0.5+xFeO_3−δ (x = 0–0.20) and La_0.5−2ySr_0.5+2yFe_1−yNb_yO_3−δ (y = 0.05–0.10). Mössbauer spectroscopy at 4.1 and 297 K showed that Ce⁴⁺ and Nb⁵⁺ incorporation suppresses delocalization of p-type electronic charge carriers, whilst oxygen nonstoichiometry of the Ce-containing materials increases. Similar behavior was observed for La_0.3Sr_0.7Fe_0.90Nb_0.10O_3−δ at 923–1223 K by coulometric titration and thermogravimetry. High-temperature transport properties were studied with Faradaic efficiency (FE), oxygen-permeation, thermopower and total-conductivity measurements in the oxygen partial pressure range 10⁻⁵–0.5 atm. The hole conductivity is lower for the Ce- and Nb-containing perovskites, primarily as a result of the lower Fe⁴⁺ concentration. Both dopants decrease oxide-ion conductivity but the effect of Nb-doping on ionic transport is moderate and ion-transference numbers are higher with respect to the Nb-free parent phase, 2.2 × 10⁻³ for La_0.3Sr_0.7Fe_0.9Nb_0.1O_3−δ cf. 1.3 × 10⁻³ for La_0.5Sr_0.5FeO_3−δ at 1223 K and atmospheric oxygen pressure. The average thermal expansion coefficients calculated from dilatometric data decrease on doping, varying in the range (19.0–21.2) × 10⁻⁶ K⁻¹ at 780–1080 K.     

Cathodic carboxylation of gold in thick {Au-CO2}n layers. A model for reversible electrochemical sequestration of CO2

Catalytic reduction of CO₂ (saturated in organic polar solvents, e.g. N,N-dimethylfomamide, containing Me₄NX or NaBF₄) was achieved at smooth gold electrodes and at glassy carbon electrodes galvanostatically capped with a thin layer of gold. Under these quite explicit conditions, very sharp reduction steps were observed near − 1.5 V vs. Ag/AgCl. With small cations listed above, an unexpected behavior was observed, a progressive electrode inhibition occurring upon several scans or after a fixed-potential electrolysis at E < − 1.7 V. This phenomenon could be attributed to the insertion of CO₂ into gold, leading to the formation of a thick iono-metallic multi-strata layer (less conducting than pure metal) that grows with the electrode charge. The formation of this new interface is due to the concur of three elements: transient CO₂ anion radical, the metal, and rather small-sized cations (M⁺ = Na⁺ or TMA⁺), the three possibly associated in a form {Au-CO₂⁻,M⁺} apparently very reactive with oxygen, moisture, and with some organic π-acceptors. Upon multi-scans up to − 2.2 V, the thickness of formed layer progressively increases reaching more than 10^− 7 to 10^− 6 mol cm^− 2. Such multi-layers undergo decomposition in the anodic domain at about + 1.7 V liberating CO₂ beforehand trapped in Au. Coulometric analyses demonstrated that insertion (cathodic) and release (anodic) steps are quite equivalent, which permits to consider this process as chemically reversible sequestration of carbon dioxide.     

A new intersecting tunnel structure in the AIMIII[PO3(OH)]2 series for AI = Ag,MIII = In: Analysis of structural relationships

A new indium hydroxyphosphate containing silver, AgIn[PO₃(OH)]₂, has been synthesized using hydrothermal method. It crystallizes in the P2₁/c space group with the cell parameters a = 6.6400(2) Å, b = 14.6269(6) Å, c = 6.6616(4) Å, β = 95.681(5)°, V = 643.82(6) Å³, Z = 4. Its three-dimensional framework, built up of corner-sharing PO₃(OH) tetrahedra and InO₆ octahedra, presents intersecting tunnels running along <111> and [100] directions, in which the Ag⁺ cations are located. The presence of hydroxyl groups has been confirmed from IR spectroscopy studies and hydrogen atoms were located from the single crystal X-ray diffraction study. The structural relationships with the other compounds of general formula A^IM^III[PO₃(OH)]₂ are analyzed.     

Synthesis and controlled release properties of β-naphthoxyacetic acid intercalated Mg–Al layered double hydroxides nanohybrids

Controlled release formulations have been proven to have potential in overcoming the drawbacks of conventional plant growth regulators. Novel controlled-release formulation of β-naphthoxyacetic acid (BNOA) intercalated MgAl-layered double hydroxides (LDHs) was prepared by co-precipitation method. The effects of temperature, pH value, and release medium on BNOA release were studied and the releasing mechanisms were discussed. The results of release show that the increase of temperature induces the increase of BNOA release extent. The release rate and accumulated release amount of BNOA are found to be dependent to the anion in the aqueous solution in the order of CO₃²⁻ > SO₄²⁻ > Cl⁻. Moreover, the pH is the key controlling factor for the BNOA release processes, and with strong acid medium, the release character of BNOA is different from those at pH 7 and 12, which accompanies with fast collapse of LDHs nanolayered structure. The nanohybrid of BNOA intercalated LDHs possessed good controlled release properties and the BNOA release character from the nanohybrid fitted pseudo-second-order model in neutral medium.     

Molecular spin ladders self-assembly from [Ni(dmit)2]− building blocks: Syntheses,structures and magnetic properties

Two ion-pair compounds, consisting of 1-(4′-R-benzyl)pyridinium ([RBzPy]⁺, R = NO₂ (1) and Br (2)) and [Ni(dmit)₂]⁻ (dmit²⁻ = 2-thioxo-1,3-dithion-4,5-dithiolato), have been synthesized and structurally characterized. The anions of [Ni(dmit)₂]⁻ stack into dimers, which further construct into two-leg ladder through terminal S⋯S interactions in 1, lateral S⋯S interactions in 2. The weak H-bonding interactions of C–H⋯S were observed in 2, while only weak van de Waals interactions between anion and cations in 1. The magnetic susceptibilities measured in 2–300 K indicate AFM exchange interaction domination both two compounds. A peculiar magnetic transition at ∼100 K was observed in 1. An AFM ordering below ∼11 K was found in 2, and the best fit to magnetic susceptibility above 45 K in this compound, using a dimer model with s = 1/2, give rise to Δ/k_B = 36.1 K, zJ = −0.91 K, C = 3.2 × 10⁻³ emu K mol⁻¹ and χ₀ = −4.0 × 10⁻⁶ emu mol⁻¹ with g of 2.0 fixed.     

Electrochemical cycling of Mg in Mg[TFSI]2/tetraglyme electrolytes

The electrochemical reversibility of magnesium was observed in an electrolyte consisting of 0.5 M Mg[TFSI]₂ in tetraglyme in the presence of a small amount of Mg[BH₄]₂. The cyclic efficiency of the cathodic/anodic process was found to increase initially with [BH₄]⁻ then plateau at about 75% beyond 6 mM in these experiments. This concentration is in the region of that indicated by Karl Fischer analysis of the electrolyte as required of [BH₄]⁻ as a dehydrating agent. Cyclic voltammetry showed the reduction onset potential at approximately − 0.35 V vs. Mg and subsequent oxidation around 0 V vs. Mg. Stable cyclic efficiency of approximately 75% over 500 cycles is demonstrated on a platinum substrate. Mg cycling on magnesium, copper and aluminium substrates all show stable cycling over 500 cycles with cyclic efficiency > 73%.     

Enhanced supercapacitive behaviors of birnessite

The birnessite type manganese dioxide electrode was prepared by the electrochemical stimulation as we recently described. It showed 190 F g⁻¹ in a Na₂SO₄ aqueous solution between −0.1 and 0.9 V versus Ag/AgCl at 1 A g⁻¹. The specific capacitance of birnessite was decreased by the manganese dissolution when the reduction and oxidation were repeated. By adding small amounts of Na₂HPO₄ or NaHCO₃ into the electrolyte, the capacitance increased to 200–230 F g⁻¹ and the manganese dissolution was successfully suppressed. Thanks to the additives, the birnessite demonstrated the much improved cycleability over >1800 cycles.