Bioethanol and ethanol electro-oxidation by amorphous alloys with low amount of platinum

The ethanol and bioethanol electro-oxidation on amorphous Ni₅₉Nb₄₀Pt_0.6Ru_0.4, Ni₅₉Nb₄₀Pt_0.6Sn_0.4 and Ni₅₉Nb₄₀Pt_0.6Ru_0.2Sn_0.2 electro-catalysts was analyzed by electrochemical techniques such as Cyclic Voltammetry (CV) and chrono-amperometry. The different micro-particulated amorphous alloys were obtained by Mechanical Alloying (MA) during 40 h, being characterized by Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) to verify their amorphous nature. The minimum amount of platinum and the addition of co-catalysts were found to have a significant effect on catalytic response of anodic reaction. Although the tri-catalytic alloy provides smaller rate of poisoning (δ) than bi-catalytic alloys, the presence of tin does not improve the ethanol/bioethanol electro-oxidation reaction due to limit the distribution of platinum atoms by the ligand effect, avoiding alcohol adsorption. Concerning the reactivity towards bioethanol electro-oxidation, the current densities are considerably higher than ethanol one for all amorphous catalysts. The presence of small amount of acetaldehyde and formic acid in bioethanol, provides a synergic effect during electrooxidative process. On the other hand, the voltammograms for CO stripping clearly show that alloy with ruthenium possesses a better CO tolerance, decreasing the onset potential 20 and 16 mV with regard to Ni₅₉Nb₄₀Pt_0.6Sn_0.4 and Ni₅₉Nb₄₀Pt_0.6Ru_0.2Sn_0.2 alloys respectively.     

Acetic acid decarboxylation by amorphous alloys with low loading of platinum

The aim of this work focuses on studying the metallic amorphous alloys of composition Ni₅₉Nb₄₀Pt_1−xY_x (Y = Cu, Ru, x = 0.4% at.), obtained by mechanical alloying (MA), in the ethanol oxidation. The addition of copper or ruthenium as co-catalysts, modifies the electronic properties of platinum, demonstrating better performance in ethanol and CO electro-oxidation reactions. Ni₅₉Nb₄₀Pt_0.6Cu_0.4 alloy provides higher current densities towards ethanol electro-oxidation than Ni₅₉Nb₄₀Pt_0.6Ru_0.4 alloy but the possible formation of copper oxides limits its performance. The voltammograms for CO stripping clearly show that alloy with ruthenium possesses a better CO tolerance, decreasing the onset potential 109 mV with regard to Ni₅₉Nb₄₀Pt_0.6Cu_0.4 alloy. The presence of ruthenium is able to provide oxygenated adsorbed species coming from the cleavage of the water molecule, according to Langmmuir-Hinshelwood mechanism that it allows the CO oxidation to CO₂. The homolytic cleavage C-C bond is critical step in the ethanol electro-oxidation to CO₂. The formation of acetic acid (AA) as final product is known, limiting the electric efficiency in Direct Ethanol Fuel Cells (DEFCs). The oxidation process was investigated by in situ Fourier Transformed Infrared Reflectance (FTIR) spectroscopy. The experimental results showed that both amorphous alloys can oxidize AA to CO₂.     

Ethanol and CO electro-oxidation with amorphous alloys as electrodes

In recent years the interest in the use of ethanol as fuel in direct ethanol fuel cells (DEFCs) has increased. Ethanol is less toxic than methanol and the bigger size of the molecule reduces the permeability through the electrolytic membrane. But, the use of this fuel with platinum catalysts leads to the acetaldehyde and acetic acid formation as main reaction products, so the electrical efficiency decreases. Furthermore, platinum shows an important susceptibility to CO poisoning which is formed during the ethanol electro-oxidation.The aim of this work is the study of the electro-catalytic behaviour of ethanol and CO electro-oxidation reaction with amorphous alloys, obtained by mechanical alloying technique. Ni₅₉Nb₄₀Pt_0.6Pd_0.4, Ni₅₉Nb₄₀Pt_0.6Rh_0.4 and Ni₅₉Nb₄₀Pt_0.6Rh_0.2Ru_0.2 compositions were studied. The bi-catalytic alloys show a similar behaviour for the ethanol electro-oxidation. In comparison to these, the current density towards ethanol oxidation decreases with the presence of Ru, although the tri-catalytic electrode shows the best tolerance to CO, with a lower surface coverage compared to other studied.     

Hydrogen production from ethanol steam reforming over core–shell structured NixOy–, FexOy–, and CoxOy–Pd catalysts

The present work focused on the investigation of the hydrogen generation through the ethanol steam reforming over the core–shell structured Ni_xO_y–, Fe_xO_y–, and Co_xO_y–Pd loaded Zeolite Y catalysts. The transmission electron microscopy (TEM) image of Ni_xO_y–Pd represented a very clear core–shell structure, but the other two catalysts, Co_xO_y– and Fe_xO_y–Pd, were irregular and non-uniform. The catalytic performances differed according to the added core metal and the support. The core–shell structured Co_xO_y–Pd/Zeolite Y provided a significantly higher reforming reactivity compared to the other catalysts. The H₂ production was maximized to 98% over Co_xO_y–Pd(50.0 wt%)/Zeolite Y at the conditions of reaction temperature 600 °C, CH₃CH₂OH:H₂O = 1:3, and GHSV (gas hourly space velocity) 8400 h⁻¹. In the mechanism that was suggested in this work, the cobalt component played an important role in the partial oxidation and the CO activation for acetaldehyde and CO₂ respectively, and eventually, cobalt increased the hydrogen yield and suppressed the CO generation.     

Understanding the electrocatalytic activity of PtxSny in direct ethanol fuel cells

In the present work, the activity of Pt_xSn_y/C catalysts towards ethanol, acetaldehyde and acetic acid electrooxidation reactions is investigated for each one separately by means of cyclic voltammetry. To this purpose, a series of Pt_xSn_y/C catalysts with different atomic ratio (x:y = 2:1, 3:2, 1:1) and small particle size (∼3 nm) are fast synthesized by using the pulse microwave assisted polyol method. The catalysts are well dispersed over the carbon support based on the physicochemical characterization by means of XRD and TEM. Concerning the ethanol electrooxidation, it is found that the Sn addition strongly enhances Pt's electrocatalytic activity and the contributing effect of Sn depends on: (i) the Sn content and (ii) the operating temperature. More precisely, at lower temperatures, Sn-rich catalysts exhibit better ethanol electrooxidation performance while at higher temperatures Sn-poor catalysts give better performance. In the case of acetaldehyde electrooxidation, Pt₁Sn₁/C catalyst exhibits the highest activity at all the investigated temperatures; due to the role of Sn, which could effectively remove C₂ species and inhibit the poison formation by supplying oxygen-containing species. Finally, it is found that the Pt_xSn_y/C catalysts are almost inactive (little current was measured) towards the acetic acid electrooxidation. The above findings indicate that Sn cannot substantially promote the electrooxidation of acetic acid to C₁ species.     

Effect of Y substitution for Nb in Li5La3Nb2O12 on Li ion conductivity of garnet-type solid electrolytes

We report the effect of Y substitution for Nb on Li ion conductivity in the well-known garnet-type Li₅La₃Nb₂O₁₂. Garnet-type Li₅La₃Nb_2−xY_xO_12−δ (0 ≤ x ≤ 1) was prepared by ceramic method using the high purity metal oxides and salts. Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), ⁷Li nuclear magnetic resonance (Li NMR) and AC impedance spectroscopy were employed for characterization. PXRD showed formation of single-phase cubic garnet-like structure for x up to 0.25 and above x = 0.25 showed impurity in addition to the garnet-type phases. The cubic lattice constant increases with increasing Y content up to x = 0.25 in Li₅La₃Nb₂−_xY_xO12−δ and is consistent with expected ionic radius trend. ⁷Li MAS NMR showed single peak, which could be attributed to fast migration of ions between various sites in the garnet structure, close to chemical shift 0 ppm with respect to solid LiCl and which confirmed that Li ions are distributed at an average octahedral coordination in Li₅La₃Nb₂−_xY_xO₁₂−_δ. Y-doped compounds showed comparable electrical conductivity to that of the parent compound Li₅La₃Nb₂O₁₂. The x = 0.1 member of Li₅La₃Nb₂−_xY_xO₁₂−_δ showed total (bulk + grain-boundary) ionic conductivity of 1.44 × 10⁻⁵ Scm⁻¹ at 23 °C in air.     

A novel binary Pt3Tex/C nanocatalyst for ethanol electro-oxidation

The Pt₃Te_x/C nanocatalyst was prepared and its catalytic performance for ethanol oxidation was investigated for the first time. The Pt₃Te/C nanoparticles were characterized by an X-ray diffractometer (XRD), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy equipped with TEM (TEM-EDX). The Pt₃Te/C catalyst has a typical fcc structure of platinum alloys with the presence of Te. Its particle size is about 2.8 nm. Among the synthesized catalysts with different atomic ratios, the Pt₃Te/C catalyst has the highest anodic peak current density. The cyclic voltammograms (CV) show that the anodic peak current density for the Pt₃Te/C, commercial PtRu/C and Pt/C catalysts reaches 1002, 832 and 533 A g⁻¹, respectively. On the current–time curve, the anodic current on the Pt₃Te/C catalyst was higher than those for the catalysts reported. So, these findings show that the Pt₃Te/C catalyst has uniform nanoparticles and the best activity among the synthesized catalysts, and it is better than commercial PtRu/C and Pt/C catalysts for ethanol oxidation at room temperature.     

PtxSn/C electrocatalysts synthesized by improved microemulsion method and their catalytic activity for ethanol oxidation

The Pt_xSn/C (x = 1, 2, 2.5, 3, 4) anodic catalysts for direct ethanol fuel cell (DEFC) have been prepared by an improved microemulsion method. Ethylene glycol is used as cosurfactant, and metal precursors are dissolved in it beforehand to prevent the hydrolysis of metal precursors. The composition, particle size and structure of these catalysts are characterized by energy dispersive X-ray spectrum (EDX), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results show that the synthesized Pt₃Sn/C catalyst has part of Pt and Sn alloying. The average diameter is about 2.9 nm, and has a narrow size distribution and a good dispersivity. The electrochemical experiments indicate that the Pt₃Sn/C catalyst prepared in the neutral microemulsion has superior catalytic activity for ethanol oxidation. The Pt_xSn/C nanoparticle formation in the improved microemulsion is also discussed.     

Physical and electrochemical properties of spherical Li1+x(Ni1/3Co1/3Mn1/3)1−xO2 cathode materials

A (Ni_1/3Co_1/3Mn_1/3)CO₃ precursor with an uniform, spherical morphology was prepared by coprecipitation using a continuously stirred tank reactor method. The as-prepared spherical (Ni_1/3Co_1/3Mn_1/3)CO₃ precursor served to produce dense, spherical Li_1+x(Ni_1/3Co_1/3Mn_1/3)_1−xO₂ (0 ≤ x ≤ 0.15) cathode materials. These Li-rich cathodes were also prepared by a second synthesis route that involved the use of an M₃O₄ (M = Ni_1/3Co_1/3Mn_1/3) spinel compound, itself obtained from the carbonate (Ni_1/3Co_1/3Mn_1/3)CO₃ precursor. In both cases, the final Li_1+x(Ni_1/3Co_1/3Mn_1/3)_1−xO₂ products were highly uniform, having a narrow particle size distribution (10-μm average particle size) as a result of the homogeneity and spherical morphology of the starting mixed-metal carbonate precursor. The rate capability of the Li_1+x(Ni_1/3Co_1/3Mn_1/3)_1−xO₂ electrode materials, which was significantly improved with increased lithium content, was found to be better in the case of the denser materials made from the spinel precursor compound. This result suggests that spherical morphology, high density, and increased lithium content were key factors in enabling the high rate capabilities, and hence the power performances, of the Li-rich Li_1+x(Ni_1/3Co_1/3Mn_1/3)_1−xO₂ cathodes.     

The influence of compositional change of 0.3Li2MnO3·0.7LiMn1−xNiyCo0.1O2 (0.2 ≤ x ≤ 0.5, y = x − 0.1) cathode materials prepared by co-precipitation

Cathode materials prepared by a co-precipitation are 0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (0.2 ≤ x ≤ 0.4) cathode materials with a layered-spinel structure. In the voltage range of 2.0-4.6 V, the cathodes show more than one redox reaction peak during its cyclic voltammogram. The Li/0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (x = 0.3, y = 0.2) cell shows the initial discharge capacity of about 200 mAh g⁻¹. However, when x = 0.2 and y = 0.1, the cell exhibits a rapid decrease in discharge capacity and poor cycle life.     

Effect of CO2 on layered Li1+zNi1−x−yCoxMyO2 (M = Al,Mn) cathode materials for lithium ion batteries

We investigated the effect of CO₂ on layered Li_1+zNi_1−x−yCo_xM_yO₂ (M = Al, Mn) cathode materials for lithium ion batteries which were prepared by solid-state reactions. Li_1+zNi_(1−x)/2Co_xMn_(1−x)/2O₂ (Ni/Mn mole ratio = 1) singularly exhibited high storage stability. On the other hand, Li_1+zNi_0.80Co_0.15Al_0.05O₂ samples were very unstable due to CO₂ absorption. XPS and XRD measurements showed the reduction of Ni³⁺ to Ni²⁺ and the formation of Li₂CO₃ for Li_1+zNi_0.80Co_0.15Al_0.05O₂ samples after CO₂ exposure. SEM images also indicated that the surfaces of CO₂-treated samples were covered with passivation films, which may contain Li₂CO₃. The relationship between CO₂-exposure time and CO₃²⁻ content suggests that there are two steps in the carbonation reactions; the first step occurs with the excess Li components, Li₂O for example, and the second with LiNi_0.80Co_0.15Al_0.05O₂ itself. It is well consistent with the fact that the discharge capacity was not decreased and the capacity retention was improved until the excess lithium is consumed and then fast deterioration occurred.     

Trimetallic amorphous catalyst with low amount of platinum: Comparative study for ethanol,bioethanol and CO electrooxidation

The use of ethanol and bioethanol demonstrates the viability of alternative fuels to gasoline with optimum energy purposes. The development of suitable catalysts is fundamental to improve the electrical performance in Direct Alcohol Fuel Cells (DAFCs). For that reason, a series of amorphous Ni₅₉Nb₄₀Pt_0.6Y_0.2Z_0.2 (PtYZ) alloys adding three different transition metals (Y, Z = Cu, Ru and Sn) were manufactured by Mechanical Alloying (MA) method. The low amount of Pt and bifunctional-electronic role of cocatalysts was analyzed using electrochemical techniques such as Cyclic Voltammetry (CV), chronoamperometry and CO stripping experiments. Concerning to reactivity towards alcohol electrooxidations, alloys with Cu showed the best catalytic performance. However, its use is limited by Cu dissolution in acid media. The PtYZ catalysts showed higher CO tolerance, achieving smaller rates of poisoning (δ) for PtRuSn alloy. CO stripping reveals that CO oxidation on alloys with Ru takes place at lower electrode potentials. The experimental results showed better electric performance, but higher poisoning of the catalytic surface for bioethanol electrooxidation. Acetaldehyde and formic acid were found in bioethanol by HPLC, influencing the electrochemical response.     

Ethanol electro-oxidation on carbon-supported Pt,PtRu and Pt3Sn catalysts: A quantitative DEMS study

The electrocatalytic activity of commercial carbon supported PtRu/Vulcan and Pt₃Sn/Vulcan bimetallic catalysts (E-TEK, Inc.) for ethanol oxidation under well defined electrolyte transport conditions and their selectivity for complete oxidation were evaluated using cyclic voltammetry combined with on-line differential electrochemistry mass spectrometry (DEMS) measurements and compared to the activity/selectivity of standard Pt/Vulcan catalysts. The main reaction products CO₂, acetaldehyde and acetic acid were determined quantitatively, by appropriate calibration procedures, current efficiencies and product yields were calculated. Addition of Ru or Sn in binary Pt catalysts lowers the onset potential for ethanol electro-oxidation and leads to a subtle increase of the total activity of the Pt₃Sn/Vulcan catalyst. It does not improve, however, the selectivity for complete oxidation to CO₂, which is about 1% for all three catalysts under present reaction conditions—incomplete ethanol oxidation to acetaldehyde and acetic acid prevails on all three catalysts. The results demonstrate that the performance of the respective catalysts is limited by their ability for C–C bond breaking rather than by their activity for the oxidation of poisoning adsorbed intermediates such as CO_ad or CH_x,ad species.     

Preparation and electrochemical properties of Li[Ni1/3Co1/3Mn1−x/3Zrx/3]O2 cathode materials for Li-ion batteries

Layer-structured Zr doped Li[Ni_1/3Co_1/3Mn_1−x/3Zr_x/3]O₂ (0 ≤ x ≤ 0.05) were synthesized via slurry spray drying method. The powders were characterized by XRD, SEM and galvanostatic charge/discharge tests. The products remained single-phase within the range of 0 ≤ x ≤ 0.03. The charge and discharge cycling of the cells showed that Zr doping enhanced cycle life compared to the bare one, while did not cause the reduction of the discharge capacity of Li[Ni_1/3Co_1/3Mn_1/3]O₂. The unchanged peak shape in the differential capacity versus voltage curve suggested that the Zr had the effect to stabilize the structure during cycling. More interestingly, the rate capability was greatly improved. The sample with x = 0.01 presented a capacity of 160.2 mAh g⁻¹ at current density of 640 mA g⁻¹(4 C), corresponding to 92.4% of its capacity at 32 mA g⁻¹(0.2 C). The favorable performance of the doped sample could be attributed to its increased lattice parameter.     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

Production of metallic glassy bipolar plates for PEM fuel cells by hot pressing in the supercooled liquid state

A screening test was conducted to optimize the alloy composition in the Ni₆₀Nb_xCr_yMo_zP₁₆B₄ (x + y + z = 20 at%) alloy system in order to achieve a large supercooled liquid region, ΔT_x, and a low crystallization temperature, T_x. From this study, the Ni₆₀Nb₂Cr₁₆Mo₂P₁₆B₄ glassy alloy was found to be the optimal alloy. The static and potentiodynamic corrosion behaviors of this glassy alloy were measured. Polarization measurements showed that the current density of the non-polished glassy alloy sample was smaller than that of a SUS316L sample. By contrast, the current density of the surface-polished glassy sample was slightly larger than that of the SUS316L sample in the voltage range of 0.2–0.7 V. The interfacial contact resistance of the Ni₆₀Nb₂Cr₁₆Mo₂P₁₆B₄ glassy alloy was smaller than that of the SUS316L alloy and it decreased with increasing compaction force. A bipolar plate was successfully produced by hot pressing the glassy alloy sheet in a supercooled liquid state. The I–V characteristics of a single cell with the glassy bipolar plates were measured.     

Synthesis and characterization of quaternary PtRuIrSn/C electrocatalysts for direct ethanol fuel cells

To find a more durable anode with high performance for direct ethanol fuel cells (DEFCs), the present study investigates a series of quaternary electrocatalysts, Pt₃₀Ru₃₀Ir_40−xSn_x/C (wt.%), for the ethanol electro-oxidation reaction (EOR). The carbon-supported Pt₃₀Ru₃₀Ir_40−xSn_x/C electrocatalysts were prepared by a known impregnation-reduction (borohydride) method. The microstructure and chemical composition were determined by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The activity of the electrocatalysts for EOR was compared to commercial Pt₆₇Ru₃₃/C (HISPEC5000) using linear sweep voltammetry (LSV) based on similar Pt loading. The results of this study show that electrocatalyst composition with 10 and 20% Ir (wt.%) exhibit higher electrocatalytic activity than the commercial PtRu electrocatalyst. The single fuel cell testing at 90 °C comparing Pt₃₀Ru₃₀Ir_40−xSn_x/C to commercial Pt₆₇Ru₃₃/C and Pt₈₃Sn₁₇/C anodes showed an enhancement of Pt activity (normalized to Pt loading) in the following order: Pt₃₀Ru₃₀Ir₁₀Sn₃₀ > Pt₃₀Ru₃₀Sn₄₀ ≥ Pt₃₀Ru₃₀Ir₄₀ ≥ Pt₈₃Sn₁₇ > Pt₆₇Ru₃₃. After a long-term performance test, the activity changed to the following order: Pt₃₀Ru₃₀Ir₁₀Sn₃₀ > Pt₃₀Ru₃₀Ir₄₀ > Pt₃₀Ru₃₀Sn₄₀ > Pt₈₃Sn₁₇ > Pt₆₇Ru₃₃. Pt₃₀Ru₃₀Ir₁₀Sn₃₀/C exhibited both a higher performance with a specific power density of 29 mW mg_Pt⁻¹ without O₂ backpressure at the cathode and an excellent long-term stability in a DEFC operating at 90 °C.     

Minimization of the cation mixing in Li1+x(NMC)1−xO2 as cathode material

Li_1+x(Ni_1/3Mn_1/3Co_1/3)_1−xO₂ layered materials were synthesized by the co-precipitation method with different Li/M molar ratios (M = Ni + Mn + Co). Elemental titration evaluated by inductively coupled plasma spectrometry (ICP), structural properties studied by X-ray diffraction (XRD), Rietveld analysis of XRD data, scanning electron microscopy (SEM) and magnetic measurements carried out by superconducting quantum interference devices (SQUID) showed the well-defined α-NaFeO₂ structure with cationic distribution close to the nominal formula. The Li/Ni cation mixing on the 3b Wyckoff site of the interlayer space was consistent with the structural model [Li_1−yNi_y]_3b[Li_x+yNi_{(1−x)/3−y}Mn_(1−x)/3Co_(1−x)/3]_3aO₂ (x = 0.02, 0.04) and was very small. Both Rietveld refinements and magnetic measurements revealed a concentration of Ni²⁺-3b ions lower than 2%; moreover, for the optimized sample synthesized at Li/M = 1.10, only 1.43% of nickel ions were located into the Li sublattice. Electrochemical properties were investigated by galvanostatic charge-discharge cycling. Data obtained with Li_1+x(Ni_1/3Mn_1/3Co_1/3)_1−xO₂ reflected the high degree of sample optimization. An initial discharge capacity of 150 mAh g⁻¹ was delivered at 1 C-rate in the cut-off voltage of 3.0-4.3 V. More than 95% of its initial capacity was retained after 30 cycles at 1 C-rate. Finally, it is demonstrated that a cation mixing below 2% is considered as the threshold for which the electrochemical performance does not change for Li_1+x(Ni_1/3Mn_1/3Co_1/3)_1−xO₂.     

Synthesis and electrochemical properties of lithium non-stoichiometric Li1+x(Ni1/3Co1/3Mn1/3)O2+δ prepared by a spray drying method

Lithium non-stoichiometric Li[Li_x(Ni_1/3Co_1/3Mn_1/3)_1−x]O₂ materials (0 ≤ x ≤ 0.17) were synthesized using a spray drying method. The electrochemical properties and structural stabilities of the synthesized materials were investigated. The synthesized materials exhibited a hexagonal structure in all the x-value and the lattice parameters of the materials were gradually decreased with increasing x-value due to an increasing amount of Ni³⁺ ions for charge compensation. The capacity retention ability and rate capability of the stoichiometric Li(Ni_1/3Co_1/3Mn_1/3)O₂ material were improved by increasing x-value, the so-called overlithiation. We found that the overlithiated materials could keep more structural integrity than the stoichiometric one during electrochemical cyclings, which could be one of reasons for a better electrochemical properties of the overlithiated materials.     

Electrochemically synthesized large area network of CoxNiyAlz layered triple hydroxides nanosheets: A high performance supercapacitor

A network of Co_xNi_yAl_z layered triple hydroxides (LTHs) nanosheets was prepared by the potentiostatic deposition process at −1.0 V (vs. Ag/AgCl) onto stainless steel electrodes. X-ray diffraction patterns show that the Co_xNi_yAl_zLTHs belong to the hexagonal system with layered structure. Cyclic voltammetry and charge discharge measurements in the potential range of −0.1 to 0.5 V and 0.0–0.4 V, respectively, vs. Ag/AgCl in 1 M KOH electrolyte indicate that Co_xNi_yAl_zLTHs have excellent supercapacitive characteristics. The maximum specific capacitance of ∼1263 F g⁻¹ was obtained for Co_0.59Ni_0.21Al_0.20LTH. The impedance studies indicated highly conducting nature of the Co_xNi_yAl_zLTHs.