Li(4−x)/3Ti(5−2x)/3CrxO4 (0 ≤ x ≤ 0.9) spinels: New negatives for lithium batteries

Members of the spinel solid solution between Li_4/3Ti_5/3O₄ and LiCrTiO₄, i.e., Li_(4−x)/3Ti_(5−2x)/3Cr_xO₄ (0 ≤ x ≤ 0.9), have been investigated as possible negative electrodes for future lithium-ion batteries. Electrochemical behaviour have been studied over the potential range 1–3.5 V vs Li⁺/Li. Results are promising with anodic capacities between 129 and 163 mA h/g with a flat operating voltage at about 1.5 V, which is attributed to the pair Ti⁴⁺/Ti³⁺. The inclusion of Cr³⁺ in the spinel structure enhances the specific capacity. In-situ X-ray diffraction experiments confirm that the reaction proceeds in a topotactic manner.     

Solar biosupercapacitor

Here we report on an entirely new kind of bioelectronic device – a solar biosupercapacitor, which is built from a dual-feature photobioanode combined with a double-function enzymatic cathode. The self-charging biodevice, based on transparent nanostructured indium tin oxide electrodes modified with biological catalysts, i.e. thylakoid membranes and bilirubin oxidase, is able to capacitively store electricity produced by direct conversion of radiant energy into electric energy. When self-charged during 10 min, using ambient light only, the biosupercapacitor provided a maximum of 6 mW m^− 2 at 0.20 V.     

Electrochemical generation of solvated electrons from nanostructured carbon

Voltammograms for electrodes fabricated of nanostructured carbon of various morphology (nanotube paper, columnar and filament structures) in hexamethylphosphoric triamide (HMPA) solution have been obtained and analysed. Intensive dark-blue coloration near cathode surface at potentials as low as E ∼ −1.2 V (s.c.e.) has been observed. An ESR (electron spin resonance) spectrum of this frozen dark-blue solution was recorded. This spectrum coincides with one of free electrons. Experimental proofs of the existence of electron emission into electrolytic solutions at moderate cathodic potentials are present for all electrodes. This effect is established to be connected with the presence of atomically sharp areas on the electrode surfaces.     

Nanoporous carbon electrode from waste coffee beans for high performance supercapacitors

Activated carbon was produced from waste coffee grounds by treatment with ZnCl₂. Supercapacitor electrodes prepared from this coffee grounds carbon exhibited energy densities up to 20 Wh kg⁻¹ in 1 M H₂SO₄, and excellent stability at high charge–discharge rates. In a two-electrode cell a specific capacitance as high as 368 F g⁻¹ was observed, with rectangular cyclic voltammetry curves and stable performance over 10,000 cycles at a cell potential of 1.2 V and current load of 5 A g⁻¹. The good electrochemical performance of the coffee grounds carbon was attributed to a well developed porosity, with a distribution of micropores and mesopores 2–4 nm wide, and the presence of electrochemically active quinone oxygen groups and nitrogen functional groups. This work highlights the potential to utilize waste biomass to produce electrode materials for cost-effective energy storage systems.     

Ordered mesoporous silicon carbide-derived carbon for high-power supercapacitors

Micro/mesoporous carbon was prepared by chlorination of ordered mesoporous silicon carbide derived from magnesio-thermal reduction of templated carbon-silica precursors. These materials were then used as active materials for electrochemical capacitors and characterized in 1.5 M NEt₄BF₄/AN. The electrodes showed outstanding rate capability (90% of capacity retention at 1 V/s and time constant of 1 s) with high specific areal capacitance (0.5 F/cm² of electrode), that makes such hierarchical porous carbons promising for high power and energy density supercapacitors.     

Selective oxidation of ethanol to acetic acid in highly efficient polymer electrolyte membrane-direct ethanol fuel cells

The selective conversion of ethanol into potassium acetate with concomitant production of electrical energy has been achieved in both passive and active direct fuel cells containing platinum-free electrodes and an anion-exchange polymer membrane. The power densities supplied by the passive systems at r.t. can be as high as 55 mW cm^?2, while the active systems can deliver up to 170 mW cm^?2 at 80 °C. Such high values have never been reported for direct ethanol fuel cells with whatsoever electrocatalyst in either alkaline or acidic media.     

VO2 nano-sheet negative electrodes for lithium-ion batteries

Vanadium dioxide (VO₂) nano-sheets were directly synthesized via a continuous hydrothermal process and were investigated as electrodes in a wide potential range of 0.05–3 V vs. Li/Li⁺. The nano-sheets showed excellent capacity retention, with a specific capacity of 350 mAh g^− 1 at an applied current of 0.1 A g^− 1 and 95 mAh g^− 1 at 10 A g^− 1. Further electrochemical testing suggested that a significant proportion of the charge storage in the cells was due to pseudocapacitive processes.     

Development of MEMS-based direct methanol fuel cell with high power density using nanoimprint technology

Performance of MEMS-based DMFC is low, because graphite-based porous electrodes show poor compatibility with MEMS technology. Nanoimprint technology was adopted in this paper to prepare fine pattern on proton exchange membrane (PEM) in MEMS-based DMFC as a promising alternative to the graphite-based porous electrodes. Micro-convex with the diameter of about 600 nm and the height of 50–70 nm was prepared on Nafion^® 117 membrane by the nanoimprint at 130 °C using silicon mold. Thick Pt film (20 nm) was deposited as catalyst directly on the nanoimprinted Nafion^® 117 membrane. Then the Pt-coated PEM was sandwiched with micro-channeled silicon plates to form a micro-DMFC. With passively feeding of 1 M methanol solution and air at room temperature, the as-prepared cell had the open circuit voltage (OCV) of 0.74 V and the maximum power density of 0.20 mW/cm². The measured OCV was higher than those (0.1–0.3 V) of the state-of-the-art MEMS-based DMFC with planar electrode and pure Pt catalyst.     

Au-coated carbon cathodes for improved oxygen reduction and evolution kinetics in aprotic Li–O2 batteries

Metal-oxygen systems are an attractive option to enhance the specific energy of secondary batteries. However, their power is limited by the oxygen electrode. In this communication we address the issue of the sluggish kinetics of the oxygen cathode in the aprotic Li–O₂ batteries. The electrochemical performances of newly designed carbon electrodes coated with 50 Å thick Au layer are evaluated and compared with those of unmodified electrodes. Despite the low noble metal content (~ 2 wt.%), the Li–O₂ batteries built with the abovementioned Au-coated cathodes show considerably enhanced kinetics as demonstrated by the higher onset potentials for the oxygen reduction reaction (~ 2.6 V at a current rate of 1000 mA g^− 1), together with reduced oxygen evolution potentials.     

Direct determination of arsenate based on its electrocatalytic reduction at the poly(aniline-co-o-aminophenol) electrode

It was found that the copolymer poly(aniline-co-o-aminophenol) (PANOA) can strongly catalyze the reduction of arsenate in a NaCl solution, which was proved by cyclic voltammetry and the determination of activation energy. On the basis of the electrocatalytic reduction of arsenate, the PANOA copolymer was used as a probe to determine directly arsenate. The electrocatalytic activity of the PANOA electrode toward As(V) reduction strongly depended on the pH and the applied potential. Under the optimal conditions, the PANOA electrode can be used to determine directly As(V) concentration in a wide linear range (n = 19) of 0.949 and 495 μM with a correlation coefficient of 0.995 and a limit of detection of 0.495 μM. The sensitivity of the electrode was 0.192 μA μM^?1 cm^?2. The PANOA electrode had the good storage stability and a less negative operation potential of ?0.15 V (vs. SCE).     

Anomalous capacity and cycling stability of xLi2MnO3 · (1 − x)LiMO2 electrodes (M = Mn,Ni, Co) in lithium batteries at 50 °C

Transition metal oxides with composite xLi₂MnO₃ ·  (1 − x)LiMO₂ rocksalt structures (M = Mn, Ni, Co) are of interest as a new generation of cathode materials for high energy density lithium-ion batteries. After electrochemical activation to 4.6 or 4.8 V (vs. Li⁰) at 50 °C, xLi₂MnO₃ · (1 − x)LiMn_0.33Ni_0.33Co_0.33O₂ (x = 0.5, 0.7) electrodes deliver initial discharge capacities (>300 mAh/g) at a low current rate (0.05 mA/cm²) that exceed the theoretical values for lithiation back to the rocksalt stoichiometry (240–260 mAh/g), at least during the early charge/discharge cycles of the cells. Attention is drawn to previous reports of similar, but unaccounted and unexplained anomalous behavior of these types of electrode materials. Possible reasons for this anomalous capacity are suggested. Indications are that electrodes in which M = Mn, Ni and Co do not cycle with the same stability at 50 °C as those without cobalt.     

Sodium vanadium nitridophosphate Na3V(PO3)3N as a high-voltage positive electrode material for Na-ion and Li-ion batteries

We report the preparation and electrochemical properties of Na₃V(PO₃)₃N made by ammonolysis. Na₃V(PO₃)₃N is reversibly oxidized to Na₂V(PO₃)₃N at high voltage (4.0 V vs. Na⁺/Na⁰ and 4.1 V vs. Li⁺/Li⁰) with an unusually small difference in the insertion/extraction voltage between both alkali metal reference electrodes. In both cases, the voltage hysteresis is extremely small (~ 0.035 V vs. sodium and ~ 0.065 V vs. lithium), which suggests facile migration of alkali cations within the structure. Further oxidation to NaV(PO₃)₃N is predicted to occur beyond the voltage stability window of the electrolytes.     

A novel method for preparing PEMFC electrodes by the ultrasonic and sonoelectrochemical techniques

Novel ultrasonic and sonoelectrochemical methods for preparing Proton Exchange Membrane Fuel Cell (PEMFC) electrodes are described. Platinum loaded on Nafion-bonded carbon anodes in Membrane Electrode Assemblies (MEAs) were prepared in K₂PtCl₄ aqueous solutions by galvanostatic pulse electrodeposition in the absence and presence of power ultrasound (20 kHz). It was found that PEMFC electrodes prepared sonoelectrochemically showed better performance compared to those prepared by (i) galvanostatic pulse method only (i.e. silent conditions) and (ii) conventional method. Maximum power densities of 98.5 mW cm^?2 were found for anodes prepared sonoelectrochemically compared with 91.5 mW cm^?2 (by galvanostatic pulse method alone) and 86 mW cm^?2 (by conventional method).     

An enzymatic glucose/O2 biofuel cell: Preparation,characterization and performance in serum

This study demonstrates a new kind of single-walled carbon nanotubes (SWNT)-based compartment-less glucose/O₂ biofuel cell (BFC) with glucose dehydrogenase (GDH) and bilirubin oxidase (BOD) as the anodic and cathodic biocatalysts, respectively, and with poly(brilliant creysl blue) (BCB) adsorbed onto SWNT nanocomposite as the electrocatalyst for the oxidation of NADH. The prepared GDH-polyBCB-SWNT bioanode exhibits an excellent electrocatalytic activity toward the oxidation of glucose biofuel; in 0.10 M phosphate buffer containing 20 mM NAD⁺ and 100 mM glucose, the oxidation of glucose commences at −0.25 V and the current reaches its maximum of 310 μA/cm² at −0.05 V vs. Ag/AgCl. At the BOD-SWNT biocathode, a high potential output is achieved for the reduction of O₂ due to the direct electron transfer property of BOD at the SWNTs. In 0.10 M phosphate buffer, the electrocatalytic reduction of O₂ is observed at a high potential of 0.53 V vs. Ag/AgCl with an electrocatalytic current plateau of ca. 28 μA/cm² at 0.45 V under ambient air and ca. 102 μA/cm² under O₂-saturated atmosphere. In 0.10 M phosphate buffer containing 10 mM NAD⁺ and 40 mM glucose under O₂-saturated atmosphere, the power density of the assembled SWNT-based glucose/O₂ BFC reaches 53.9 μW/cm² at 0.50 V. The performance and the stability of the glucose/O₂ BFC are also evaluated in serum. This study could offer a new route to the development of new kinds of enzymatic BFCs with a high performance and provide useful information on future studies on the enzymatic BFCs as in vivo power sources.     

Novel concept of pseudocapacitor using stabilized lithium metal powder and non-lithiated metal oxide electrodes in organic electrolyte

A concept of using two non-prelithiated metal oxides (e.g., MnO₂, V₂O₅, and FeO_x) in both positive and negative electrodes in organic Li-ion electrolytes has been proposed and tested to improve the energy density of pseudocapacitors. To take the advantages of this concept, additional lithium source is essential to provide lithium ions during the charge–discharge cycles. The stabilized lithium metal powder (SLMP^?) developed by FMC Corp., provides such an essential Li⁺ source. Here we report the first result of the symmetric pseudocapacitor using two non-prelithiated metal oxide (i.e., manganese oxide/carbon nanotube (MnO₂/CNT)) electrodes, with added SLMP in one of them. The capacitor using the SLMP added MnO₂/CNT (positive) and pure MnO₂/CNT (negative) electrode in 1.2 M LiPF₆-EC:EMC electrolyte shows supercapacitive behaviors in 3.0 V voltage range. The addition of SLMP opens new opportunities of using the non-lithiated metal oxide electrodes in pseudocapacitors and hybrid electrochemical capacitors (ECs), which has not been possible before.     

Li2SO4-polyacrylamide polymer electrolytes for 2.0 V solid symmetric supercapacitors

A neutral polymer electrolyte comprised of lithium sulfate (Li₂SO₄) and polyacrylamide (PAM) was developed. The Li₂SO₄-PAM electrolyte film shows an ionic conductivity up to 10 mS cm^− 1 in 45%RH conditions. Solid double layer capacitors were demonstrated using CNT-graphite electrodes and Li₂SO₄-PAM solid electrolytes. The voltage window of the solid cell was about 2.0 V, identical to that of a Li₂SO₄ liquid cell used as baseline. The demonstrated voltage window is significantly larger than that reported for proton- or hydroxyl-conducting electrolytes, suggesting that the Li₂SO₄-PAM electrolyte is a promising system for high energy density supercapacitors. The solid device also demonstrated excellent rate capability (up to 5 V s^− 1) and good cycle life (beyond 10,000 charge/discharge cycles).     

Titanium vanadium nitride electrode for micro-supercapacitors

Here we report on the synthesis of binary transition metal nitride electrodes based on titanium vanadium nitride (TiVN) thin films. These films were deposited by a method compatible with micro-electronic processes which consists of DC co-sputtering of vanadium (V) and titanium (Ti) targets. TiVN films with different Ti/V ratio were deposited. A dependence of the capacitance and the cycling stability with the Ti/V atomic ratio in the films was established. While V rich sample exhibits a Faradic behavior that limits its cycling ability despite a high areal and volumetric capacity, the addition of Ti in the film drastically improves the cycling ability with virtually no fade in capacitance after 10,000 cycles. Furthermore, a 1.1 Ti/V ratio leads to an areal capacitance up to 15 mF·cm^− 2 in 1 M KOH electrolyte solution. Such electrodes shed light on the use of binary transition metal nitrides as candidate electrodes for micro-supercapacitor.     

An easy compartment-less biofuel cell construction based on the physical co-inclusion of enzyme and mediator redox within pressed graphite discs

We report on the easy and fast immobilization of glucose oxidase (GOD) and laccase by mechanical compression with graphite particles to form disc electrodes. The electrical wiring of GOD and laccase was efficiently carried out by their co-inclusion with ferrocene (Fc) and 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) respectively. A glucose/air compartment-less biofuel cell was constructed based on the association of GOD-ferrocene-graphite disc and laccase-ABTS – graphite disc electrodes as bioanode and biocathode respectively. Such biofuel cell yielded a power density of 23 μW cm^?2 at 0.33 V as well as an open-circuit voltage and a short-circuit current of 0.63 V and 166 μA, respectively.     

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.     

Modeling of the quaternary NaCl + KCl + CH3OH + H2O mixed electrolyte system: Binary and ternary mixing (ion + ion) and (ion + nonelectrolyte) interaction parameters

The purpose of this work is modeling of the quaternary system of mixed NaCl + KCl electrolyte in mixed CH₃OH + H₂O solvent, with different alcohol mass fractions by using particularly, the Pitzer (P) and Pitzer–Esteso (PE) equations and based on potentiometric measurement technique. The experimental data are obtained by different molal salt ratio r (r = m_NaCl/m_KCl = 100, 150, 200 and 250) in mixed solvent with different alcohol mass fractions x (x = 0.10, 0.20, 0.30, 0.40, and 0.50) in water. A galvanic cell is employed for collecting the potentiometric data by combining a Na⁺ glass membrane and Ag/AgCl electrodes and using different series of electrolyte solutions, at defined constant ionic strengths, with the molality ranging from 0.0005 up to 3.5 mol · kg⁻¹, at T = 298.15 ± 0.05 K of experiments. Comparison of the models shows that the modified Pitzer equation by Esteso (PE) present a better fit of the experimental data.