Open-circuit-potentials of gas/electrode/YSZ boundary versus molten carbonate reference electrode at medium temperatures: II. Potential response of Au, Pt and Ni-cermet electrodes in CH4 + O2 and H2 + O2 gas mixtures

Values of open-circuit-potentials (OCP) have been determined for pairs of electrodes: Au and Pt, Ni-Ce_0.8Sm_0.2O_1.9 cermet and Au, Pt and Sm_0.5Sr_0.5CoO₃ composite at the YSZ electrolyte, in the uniform atmospheres of xCH₄ + yO₂ + (1 − x − y)Ar gas mixtures with variable x and y coefficients, at 600 °C. The determined dependencies of OCP values on the initial gas mixture compositions have been compared with the respective dependencies calculated for equilibrium or quasi-equilibrium compositions of these gas mixtures. The OCP values for the pair of Pt and Au electrodes have been measured also in the xH₂ + yO₂ + (1 − x − y)Ar uniform gas mixtures but no distinct difference of the OCP values has been observed in this atmosphere. For some pairs of electrodes investigated in xCH₄ + yO₂ + (1 − x − y)Ar atmospheres the measured OCP values have shown differences up to ca 0.9-1.0 V. These differences were stable within large range of compositions of this gas mixture. Within this gas composition range one of the electrodes conserves the potential of oxygen electrode determined by oxygen partial pressure in the initial gas mixture and is insensitive to reaction occurring in the gas phase. These results are discussed on the basis of equilibria or some quasi-equilibria, that establish in the C-H-O gas mixture and the solid carbon deposition is considered. For a given pair of dissimilar electrodes, their selective sensibility to the electrochemical process of oxygen electrode has been confirmed. Within large range of gas mixture concentrations, in the Pt-Au electrode pair Au has shown behavior of the oxygen electrode, whereas the OCP values of the Pt electrode are within the range of hydrogen electrode, also at gas compositions corresponding to the solid carbon stability. With this pair the OCP differences of ca. 600 mV have been obtained. Among three electrodes studied the cermet Ni-Ce_0.8Sm_0.2O_1.9 electrode shows the best electrocatalytic properties resulting in the OCP values following exactly the respective equilibrium dependence. In the pair Ni-Ce_0.8Sm_0.2O_1.9 and Au a stable potential difference of ca. 900 mV have been established. Unexpectedly, Pt electrode in the pair with the Sm_0.5Sr_0.5CoO₃ composite electrode plays role of the oxygen electrode quite insensitive to other components of the equilibrated initial gas mixture. This surprising fact seems indicate that in conditions of the experiments performed the electrocatalytic behavior of the electrode depends not only of the material of this electrode but also on the properties of the second electrode in the given pairs of electrodes.     

Dependencies of the open-circuit voltage of Au|YSZ|Pt single-chamber fuel cell on the composition of the uniform CH4 + O2 gas mixture with solid carbon deposition

Single-chamber solid oxide fuel cell is a device where two electrodes of different materials contacting a solid oxide ionic conductor, may generate a considerable potential difference and electrical power, when supplied by a common fuel + oxidant gas mixture. The Au|YSZ|Pt system in the CH₄ + O₂ gas mixture is one of the simplest examples of such a cell. In this article the open-circuit voltage (OCV) of this cell, supplied with the gas mixture xO₂ + aCH₄ + (1 − x − a)Ar (where a = 0.01, 0.1 or 0.5), is investigated. On the basis of the obtained results, as well as those for the xCH₄ + (1 − x)(0.2O₂ + 0.8Ar) (0 ≤ x ≤ 1) gas mixture, reported in our previous work [Electrochim. Acta, 50 (2005) 2771], we postulate that the OCV of the above system arises as a result of electrode modification resulting from solid carbon deposition in the cell. After oxidation of the carbon deposit, the system, once treated by the gas mixture enabling the formation of the carbon phase, shows more and more tendency to generate the OCV. The open-circuit potential of the Au electrode depends only on the O₂ concentration in the initial gas mixture, whereas in the case of the Pt electrode it becomes dependent on chemical equilibria determining the O₂ content in the converted gas mixture. Our results reveal that the OCV achieves a reproducible limiting value of ∼650 mV, which is lower by ∼400 mV than the calculated equilibrium value.     

Electrochemical decomposition of CO2 and CO gases using porous yttria-stabilized zirconia cell

Electrochemical decomposition of CO₂ and CO gases using a porous cell of Ru-8 mol% yttria-stabilized zirconia (YSZ) anode/porous YSZ electrolyte/Ni–YSZ cathode system at 400–800 °C was studied by analyzing the flow rate and composition of outlet gas, current density, and phases and elementary distribution of the electrodes and electrolyte. A part of CO₂ gas supplied at 50 ml/min was decomposed to solid carbon and O₂ gas through the cell at the electric field strengths of 0.9–1.0 V/cm. The outlet gas at a flow rate of 3 ml/min included 61–63% CO₂ and 37–39% O₂ at 700–800 °C and the outlet gas at a flow rate of 50 ml/min included 73–96% (average 85%) CO₂ and 4–27% (average 15%) O₂ at 800 °C. On the other hand, the supplied CO gas was also decomposed to solid carbon, O₂ and CO₂ gases at 800 °C. The fraction of outlet gas at a flow rate of 50 ml/min during the CO decomposition at 800 °C for 5 h was 11–36% CO, 59–81% O₂ and 2–9% CO₂. The detailed decomposition mechanisms of CO₂ and CO gases are discussed. Both Ni metal in the cathode and porous YSZ grains under the DC electric field have the ability to decompose CO gas into solid carbon and O²⁻ ions or O₂ gas.     

Electrochemical reforming of CH4−CO2 mixed gas using porous Gd-doped ceria electrolyte with Cu electrode

This paper reports on the composition and flow rate of outlet gas and current density during the reforming of CH₄ with CO₂ using three different electrochemical cells: cell A, with Ni−GDC (Gd-doped ceria: Ce_0.8Gd_0.2O_1.9) cathode/porous GDC electrolyte/Cu−GDC anode, cell B, with Cu−GDC cathode/ porous GDC electrolyte/Cu−GDC anode and cell C, with Ru−GDC cathode/ porous GDC electrolyte/ Cu−GDC anode. In the cathode, CO₂ reacts with supplied electrons to form CO fuel and O²⁻ ions (CO₂+2e⁻→CO+O²⁻). Too low affinity of Cu cathode to CO₂ in cell B reduced the reactivity of the CO₂ with electrons. The CO fuel, O²⁻ ions and CH₄ gas were transported to the anode through the porous GDC mixed conductor of O²⁻ ions and electrons. In the anode, CH₄ reacts with O²⁻ ions to produce CO and H₂ fuels (CH₄+O²⁻→2 H₂+CO+2e⁻). The reforming efficiency at 700−800 °C was lowest in cell B and highest in cell A. The Cu anode in cells A and C worked well to oxidize CH₄ with O²⁻ ions (2Cu+O²⁻→Cu₂O+2e⁻, Cu₂O+CH₄→2Cu+CO+2H₂). However, a blockage of the outlet gas occurred in all the cells at 700−800 °C. The gas flow is inhibited due to a reduction in pore size in the cermet cathode, as well as sintering and grain growth of Cu metal in the anode during the reforming.     

Effects of temperature and composition on the laminar burning velocity of CH4 + H2 + O2 + N2 flames

This work summarises available measurements of laminar burning velocities in CH₄ + H₂ + O₂ + N₂ flames at atmospheric pressure performed using a heat flux method. Hydrogen content in the fuel was varied from 0% to 40%, amount of oxygen in the oxidiser was varied from 20.9% down to 16%, and initial temperature of the mixtures was varied from 298 to 418 K. These mixtures could be formed when enrichment by hydrogen is combined with flue gas recirculation. An empirical correlation for the laminar burning velocity covering a complete range of these measurements is derived and compared with experiments and other correlations from the literature.     

Characterization of electrode/electrolyte interface using in situ X-ray reflectometry and LiNi0.8Co0.2O2 epitaxial film electrode synthesized by pulsed laser deposition method

An in situ experimental technique was developed for detecting structure changes at the electrode/electrolyte interface of lithium cell using synchrotron X-ray reflectometry and two-dimensional model electrodes with a restricted lattice plane. The electrode was constructed with an epitaxial film of LiNi_0.8Co_0.2O₂ synthesized by the pulsed laser deposition method. The orientation of the epitaxial film depends on the substrate plane; the 2D layer of LiNi_0.8Co_0.2O₂ is parallel to the SrTiO₃ (1 1 1) substrate ((0 0 3)_{LiCo0.2Ni0.8O2}//(1 1 1)SrTiO₃), while the 2D layer is perpendicular to the SrTiO₃ (1 1 0) substrate ((1 1 0)_{LiCo0.2Ni0.8O2}//(1 1 0)SrTiO₃). These films provided an ideal reaction field suitable for detecting structure changes at the electrode/electrolyte interface during the electrochemical reaction. The X-ray reflectometry indicated a formation of a thin-film layer at the LiNi_0.8Co_0.2O₂ (1 1 0)/electrolyte interface during the first charge-discharge cycle, while the LiNi_0.8Co_0.2O₂ (0 0 3) surface showed an increase in the surface roughness without forming the surface thin-film layer. The reaction mechanism at the electrode/electrolyte interface is discussed based on our new experimental technique for lithium batteries.     

Comparisons of graphite and spinel Li1.33Ti1.67O4 as anode materials for rechargeable lithium-ion batteries

The aim of this work was to compare the electrochemical behaviors and safety performance of graphite and the lithium titanate spinel Li_1.33Ti_1.67O₄ with half-cells versus Li metal. Their electrochemical properties in 1 M LiPF₆/EC + DEC (1:1 w/w) or 1 M LiPF₆/PC + DEC (1:1 w/w) at room and elevated temperatures (30 and 60 °C) have been studied using galvanostatic cycling. At 30 °C graphite has higher reversible capacity than Li_1.33Ti_1.67O₄ when using the LiPF₆/EC + DEC as electrolyte. At 60 °C graphite declines in cell capacity yet Li_1.33Ti_1.67O₄ remains almost unchanged. In a propylene carbonate (PC) containing electrolyte, graphite electrode exfoliates and loses its mechanical integrity while Li_1.33Ti_1.67O₄ electrode is very stable. An accelerating rate calorimeter (ARC) and microcalorimeter have been used to compare the thermal stability of lithiated lithium titanate spinel and graphite. Results show that Li_1.33Ti_1.67O₄ may be used as an alternative anode material offering good battery performance and higher safety.     

Investigation on electrochemical reduction process of Nb2O5 powder in molten CaCl2 with metallic cavity electrode

The direct electrochemical reduction process of Nb₂O₅ powder was investigated by cyclic voltammetry and constant potential electrolysis with a novel metallic cavity electrode in molten calcium chloride at 850 °C. The products of both constant potential and constant voltage electrolysis were characterized by XRD, SEM and EDX. CaNb₂O₆ was formed upon addition of solid Nb₂O₅ into molten CaCl₂ when CaO was present. During the electrolysis solid Nb₂O₅ was reduced to various niobium oxides of lower oxidation states, including some composite oxides, and then was converted completely to metallic niobium near −0.35 V (vs. Ag/AgCl), which was more positive than the reduction potential of Ca²⁺. Constant potential electrolysis was applied at the potentials near the reduction current peaks derived from the cyclic voltammetry curves, and cell voltages were monitored. The voltage was near 2.4 V when the oxide was metallized at −0.35 V (vs. Ag/AgCl). Nb₂O₅ pellet could be used to prepared metallic niobium at cell voltage 2.4 V in a larger electrolysis bath filled with calcium chloride at 850 °C. The experiment results further demonstrated the direct electrochemical reduction mechanism of Nb₂O₅ powder in a molten system.     

Preparation, electrochemical behavior and performance of gallium hexacyanoferrate as electrocatalyst of H2O2

The gallium hexacyanoferrate (GaHCF) was synthesized chemically and characterized by FTIR technique. Its electrochemical behavior was carefully investigated by fabricating a GaHCF modified carbon paste electrode in various supporting electrolyte. The experimental results showed that in KNO₃, K₂SO₄, KCl and other supporting electrolyte, GaHCF yielded one pair of ill-defined redox waves with a formal potential of 0.9 V (versus SCE). In 0.050 mol L⁻¹ phosphate buffer solution (PBS, pH 6.8), however, GaHCF yielded one pair of well-defined redox peaks with a formal potential of 0.222 V. Furthermore, this modified electrode exhibited a high electrocatalytic activity toward the reduction of H₂O₂ in pH 6.8 PBS, with over-potential dramatically lower than that of on the bare carbon paste electrode. Amperometry was used for the determination of H₂O₂, under the optimal conditions, a linear dependence of the catalytic current versus H₂O₂ concentration was obtained in the range of 4.9 × 10⁻⁶ to 4.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1 × 10⁻⁶ mol L⁻¹ when the signal-to-noise ratio was 3, and a sensitivity of 27.9 μA mM⁻¹ (correlation coefficient of 0.997). Chronoamperometry was used to conveniently determine the diffusion coefficient of H₂O₂ in the solution.     

Polarization properties of La0.6Sr0.4Co0.2Fe0.8O3-based double layer-type oxygen electrodes for reversible SOFCs

We have developed double layer-type (catalyst layer/current collecting layer) oxygen electrodes (DLE) for reversible SOFCs. As the catalyst layer (cathode for SOFC and anode for steam electrolysis) interfaced with a samaria-doped ceria [(CeO₂)_0.8(SmO_1.5)_0.2, SDC] interlayer/YSZ solid electrolyte, mixed conducting La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) and SDC particles were employed. The current collecting porous LSCF layer was formed on the catalyst layer. By controlling the SDC content, as well as the thickness and porosity of the catalyst layer, the gas diffusion rate and the conduction networks for electrons and oxide ions were optimized, resulting in a marked reduction of the overpotential. The LSCF + SDC/LSCF DLE exhibited higher performance than single-layer electrodes of LSCF + SDC or LSCF; the IR-free anode potential vs. an air reference electrode was 0.12 V (corresponding to an overpotential of 0.08 V) at 0.5 A cm⁻² and 900 °C under an atmosphere of O₂ (1 atm).     

An investigation of the causes of the difference in coal particle ignition temperature between combustion in air and in O2/CO2

The ignition temperatures of a Loy Yang brown coal and a Datong bituminous coal were investigated in a wire-mesh reactor where the secondary reactions of the evolved volatiles were minimised. An increase in the average particle ignition temperature of 21 °C was observed for the brown coal when air (21% O₂ + 79% N₂) was replaced with a mixture of 21% O₂ + 79% CO₂. Combustion was also carried out in the mixtures of 21% O₂ + 79% argon and 21%O₂ + 79% helium in order to determine the effects of heat transfer on the observed particle ignition temperature. It is concluded that the thermal conductivity of gas atmosphere surrounding the particles greatly influences the observed particle ignition temperature while the effects of the heat capacity of the gas atmosphere was very minor under our experimental conditions. The structure of char and the reactions involving the char (char-O₂ and char-CO₂) can greatly affect the observed particle ignition temperature. In particular, the char-CO₂ reactions were largely responsible for the observed difference in particle ignition temperature in air and in 21% O₂ + 79% CO₂. Alkali and alkaline earth metallic (AAEM) species in the brown coal also significantly affect the observed particle ignition temperature.     

Alkali carbonate-coated graphite electrode for lithium-ion batteries

Charge and discharge behavior of a graphite electrode for rechargeable lithium-ion batteries was successfully improved by pretreatment of graphite powders with A₂CO₃ (A = Li, Na, and K) aqueous solutions. In the process of the pretreatment, graphite powders were simply dispersed in the aqueous solutions, and then filtered and dried to modify the surface of graphite powder with solid alkali carbonate. With the optimum concentration of each carbonate, 1 wt.% Li₂CO₃, 5 wt.% Na₂CO₃, and 1 wt.% K₂CO₃, the irreversible reaction at the initial cycle was suppressed by the pretreatment which was capable of modifying the solid electrolyte interphase formed on the graphite electrode surface. Furthermore, the rate capability was improved by the surface modification, that is, the reversible discharge capacities at 175 mA g⁻¹ increased with adequate capacity retention in a 1 mol dm⁻³ LiClO₄ ethylene carbonate:diethyl carbonate electrolyte solution because of the kinetics enhancement of lithium-ion transfer at the interface.     

Ar, O2, CHF3, and SF6 plasma treatments of screen-printed carbon nanotube films for electrode applications

This paper investigates the consequence of the material property and the plasma gas chemistry (herein referred to the plasma gas-feeding species and methods) on the electrode performance in plasma treatments of screen-printed carbon nanotube (CNT) films. Four plasma gases (Ar, O₂, SF₆, and CHF₃) and three gas-feeding methods were examined. The surface morphology, microstructure, and composition of 11 sample groups have been carefully characterized. Tests of the CNT film electrode subjected to gas discharge and field emission show that surface morphology modification is the most influential factor in respect of lowering the onset voltages. In detail, O₂/Ar (O₂ followed by Ar) and Ar + CHF₃ + SF₆ (mixed three gases) treatments are the best choices for ionization and field emission applications, respectively. The relevant results are even better than that of the samples of aligned CNT films prepared by chemical vapor deposition. The underlying mechanisms are modeled by two opposing processes (etching and coating), which phenomenally produce three competing effects, i.e., CNT protruding, bundle forming, and neo-nanostructure forming. The results and the correct behavior of our model suggest that the plasma gas chemistry is the most fundamental factor in the process of plasma treatments of CNT films.     

Synthesis optimization of Li1 + x[Mn0.45Co0.40Ni0.15]O2 with different spherical sizes via co-precipitation

Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂ spherical cathode materials with different sizes (about 2 and 5 μm) were fabricated by calcining uniform spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃ with lithium hydroxide at high temperature. The precursor of spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃, was obtained via co-precipitation method at room temperature, which was significantly dependent on synthetic conditions, such as the reaction temperature, the concentration of NH₄HCO₃, and stirring speed, etc. The optimized condition resulted in [Mn_0.45Co_0.40Ni_0.15]CO₃, of which the particle size distribution was uniform and the particle shape was spherical. The final products, Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂, had a well-ordered layered structure and uniform homogeneity. Raman spectroscopy analysis showed the Raman-active species E_g and A_1g modes were observed at 488, 473 cm^− 1 and 597, 590 cm^− 1, respectively, for the obtained spherical cathode materials.     

<Emphasis Type="Italic">In situ</Emphasis> microobservation of the cathode in molten carbonate fuel cells

In molten carbonate fuel cells (MCFC), the wettability of the electrode and the electrolyte distribution are very important factors influencing the active reaction area. We have observed the molten carbonate behaviour directly on the cathode (porous NiO) and the electrolyte plate (LiAlO₂) under various gas conditions and at controlled potentials using an environmental scanning electron microscope (ESEM) equipped with a hot stage. We estimated the liquid electrolyte distribution in the cathode and measured the contact angles on NiO and LiAlO₂ in the electrolyte. Moreover, the electrolyte movement in the reaction CO₂ + O₂ + 2e^– = CO₃ ^2– was observed on the surface of the porous NiO in a CO₂/O₂ atmosphere. The reaction CO₃ ^2– + 2e^– = CO + 2 O^2– of the gas generation was observed in a H₂O atmosphere. The active reaction points on the electrode are the areas where the electrolyte film is thin.     

Effect of CeO2 addition on densification and microstructure of Al2O3-YSZ composites

Alumina (Al₂O₃) and alumina-yttria stabilized zirconia (YSZ) composites containing 3 and 5 mass% ceria (CeO₂) were prepared by spark plasma sintering (SPS) at temperatures of 1350-1400 °C for 300 s under a pressure of 40 MPa. Densification, microstructure and mechanical properties of the Al₂O₃ based composites were investigated. Fully dense composites with a relative density of approximately 99% were obtained. The grain growth of alumina was inhibited significantly by the addition of 10 vol% zirconia, and formation of elongated CeAl₁₁O₁₈ grains was observed in the ceria containing composites sintered at 1400 °C. Al₂O₃-YSZ composites without CeO₂ had higher hardness than monolithic Al₂O₃ sintered body and the hardness of Al₂O₃-YSZ composites decreased from 20.3 GPa to 18.5 GPa when the content of ZrO₂ increased from 10 to 30 vol%. The fracture toughness of Al₂O₃ increased from 2.8 MPa m^1/2 to 5.6 MPa m^1/2 with the addition of 10 vol% YSZ, and further addition resulted in higher fracture toughness values. The highest value of fracture toughness, 6.2 MPa m^1/2, was achieved with the addition of 30 vol% YSZ.     

Effects of the surface treatment of the Al2O3 filler on the lithium electrode/solid polymer electrolyte interface properties

The lithium deposition-dissolution process in solid polymer electrolytes containing Al₂O₃ filler treated under different conditions has been investigated comparing with the ionic conduction behavior of the electrolyte. The composite electrolytes were prepared from poly(ethylene oxide) (PEO), LiBF₄ and α-Al₂O₃ filler by using a dry process, where the surface of α-Al₂O₃ was beforehand modified by a wet process. The exchange current densities, i₀, of the lithium electrode process in P(EO)₂₀LiBF₄ with and without Al₂O₃ filler were determined by a micro-polarization method. The temperature dependence of i₀ provided similar values for activation energy, ca. 25 and 70 kJ mol⁻¹ in both temperature regions above and below 60 °C, respectively. The effect of the surface treatment of the filler on the lithium electrode process gave a different tendency from that on the ionic conductivity. The Al₂O₃ surface treated by alkali solution enhanced the electrode process to the largest extent among the fillers used here, while it led to rather poor cycling stability in voltammetry. The enhanced reaction rate at the lithium electrode/solid polymer electrolyte interface has probably resulted in the improved ion dissociation by the surface groups of the Al₂O₃ filler.     

Iron-enriched natural zeolite modified carbon paste electrode for H2O2 detection

This work demonstrates that iron-enriched natural zeolitic volcanic tuff (Paglisa deposit, Cluj county, Transilvania, Romania) resulting from a previous use as adsorbent in wastewater treatment can be recycled into effective electrode modifier applied to the electrocatalytic detection of hydrogen peroxide. After physico-chemical characterization of tuff samples using various techniques such as chemical analysis, X-ray diffraction, scanning electron microscopy, infrared spectroscopy, BET analysis and X-ray photoelectron spectroscopy, the electrochemical response of the iron-enriched zeolites was studied on the basis of solid carbon paste electrodes modified with these samples. The results indicate that iron centers in the zeolite are electroactive and that they act as electrocatalysts in the voltammetric and amperometric detection of H₂O₂. Best performance was achieved in phosphate buffer at pH 7, showing a sensitivity of 0.57 mA M⁻¹ cm⁻², a detection limit down to 60 μM, and a linear domain up to 100 mM H₂O₂.     

Extension of a compressible lattice model to CO2 + cosolvent + polymer systems

We have recently proposed a compressible lattice model for CO₂ + polymer systems in which CO₂ forms complexes with one or more functional groups in the polymer. Furthermore, we have shown that this model is able to simultaneously correlate phase equilibria, sorption behavior, and glass transition temperatures in such systems. In the present work, we extend the model to ternary CO₂ + cosolvent + polymer systems and demonstrate that cloud point behavior in CO₂ + dimethyl ether + poly (?-caprolactone), CO₂ + dimethyl ether + poly (isopropyl acrylate), and CO₂ + dimethyl ether + poly (isodecyl acrylate) systems can be predicted using parameters obtained from binary data. Our results also suggest that dimethyl ether may form weak complexes with poly (?-caprolactone), poly (isopropyl acrylate), and poly (isodecyl acrylate).     

Preparation of micro-dot electrodes of LiCoO2 and Li4Ti5O12 for lithium micro-batteries

Fabrications of micro-dot electrodes of LiCoO₂ and Li₄Ti₅O₁₂ on Au substrates were demonstrated using a sol-gel process combined with a micro-injection technology. A typical size of prepared dots was about 100 μm in diameter, and the dot population on the substrate was 2400 dots cm⁻². The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were characterized with scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and cyclic voltammetry. The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were evaluated in an organic electrolyte as cathode and anode for lithium micro-battery, respectively. The LiCoO₂ micro-dot electrode exhibited reversible electrochemical behavior in a potential range from 3.8 to 4.2 V versus Li/Li⁺, and the Li₄Ti₅O₁₂ micro-dot electrode showed sharp redox peaks at 1.5 V.