The problem of dendrite growth remains unresolved in secondary zinc batteries. In order to improve the cycle life of zinc-secondary batteries, we developed an organic/inorganic composite separator that exhibits an inhibitory effect on short circuits caused by zinc dendrite growth. This separator is designed to have a sufficient ionic conductivity as well as suppression properties for preventing a short circuit. To obtain these performances, inorganic particles and hydrophobic particles are utilized which provide no extra space and no extra electrolyte for dendrite growth. Additionally, this material exhibits a good ionic conductivity. It was also confirmed that the separator we developed provided the carbon-zinc hybrid capacitor with a long life. It was also found that the carbon-zinc hybrid capacitor systems are preferable for evaluating the cyclability of separators used for zinc secondary batteries because the system has a good reproducibility. Consequently, the cycle life using the organic/inorganic composite separator was more than 10 times longer than that of conventional microporous membranes.

A novel interdigitated flow field design for polymer electrolyte electrolysis cells (proton exchange membrane water electrolysis cells) composed of oxygen exhaust channels apart from liquid water feed channels has been developed for ground and space applications because the design is advantageous in terms of oxygen/water separation without buoyancy, and dispenses with water circulators for bubble removal in a cell and external separators by natural or centrifugal buoyancy. Finite element modeling of water transport in the polymer electrolyte (proton exchange) membrane in a cell with the interdigitated flow fields is conducted. Current-voltage (I–V) measurement of the cell is also performed for comparison with numerical modeling. Deviation of the experimental I–V characteristics from those of the numerical model indicates a possible water transport path in the in-plane direction of hydrophobic microporous layers (MPLs) coated on gas diffusion layers installed between the anode catalyst layers (CLs) and oxygen flow channels in the cell. Analysis of the deviation associated with the limitation of water transport also suggests fractional bubble coverage of produced oxygen gas at the CLs. The hydrophobic MPL acts to separate oxygen gas and pressurized liquid water due to the capillary pressure, while it determines the limitation of water transport to the CLs with the oxygen bubble coverage.

Conversion efficiency of a dye-sensitized solar cell (DSC) using poly(3,4-ethylenedioxythiophene) (PEDOT)-coated transparent conducting substrate as a counter electrode was shown to be 7.88 %, which is slightly higher compared to a DSC using classical platinum sputtered counter electrode (7.65 %). From electrochemical impedance analysis, the PEDOT based cell was found to show lower charge-transfer resistance assigned to the I⁻/I₃⁻ redox reaction as a mediator on the counter electrode compared to the platinum based cell. More quantitatively, electron transfer rate constant (k⁰) for the I⁻/I₃⁻ redox reaction on the counter electrode was remarkably estimated by voltammetric kinetic analysis. The k⁰ obtained for the PEDOT electrode (3.47 × 10⁻³ cm s⁻¹) was larger than that for the platinum electrode (2.76 × 10⁻³ cm s⁻¹) of the approximately same electrode thickness and surface roughness. This research revealed the higher conversion efficiency of the PEDOT based cell is essentially attributed to the faster mediator reaction (reduction of I₃⁻) on the counter electrode in its cell.

The distribution of relaxation time (DRT) is increasingly investigated as a novel analytical method for electrochemical impedance spectroscopy. However, this method has not yet been generalized, as it cannot be applied to a spectrum influenced by an isolated capacitator and a resistor connected in parallel with an inductor. To generalize the DRT analysis, we propose a novel principal relation and actual calculation methods using an iterative elastic net regularization algorithm. The elastic net regularization was implemented using the Levenberg–Marquardt method. The proposed algorithm aids in analyzing the DRT for spectra that cannot be solved using conventional methods. We compared the DRT results in different regularization methods obtained from the proposed program with those obtained from other open-source programs. Additionally, the realistic problems of the DRT analysis are discussed considering the calculated results and their theoretical basis. Different DRT curves can be obtained depending on the particular program and regularization methods, even when the spectrum is the same. Moreover, overconfidence in the electrochemical DRT method can be avoided with a clear understanding of DRT basics.

K₂NiF₄-type oxides are expected to be potential lithium-ion conductors because they have a structure similar to that of perovskites, which provide a reasonably flexible framework for accommodating defects such as charge carriers within the lattice. However, the K₂NiF₄-type structure as a framework for lithium conductors is scarcely reported. This article presents the preparation of Sr(La_1−xLi_3x)ScO₄ with a K₂NiF₄ structure by a solid-state reaction at a high pressure of 2 GPa, and elucidates its lithium-ion-conducting properties. Sr(La_1−xLi_3x)ScO₄ forms solid solutions in the x range of 0.05–0.20. Its orthorhombic lattice expands with lithium doping, indicating the incorporation of lithium ions as interstitial species in the structure. The highly doped samples exhibit high ionic conductivities (e.g., 4.66 × 10⁻⁶ S cm⁻¹ at 250 °C for x = 0.15 and 4.29 × 10⁻² S cm⁻¹ at 375 °C for x = 0.2) with an activation energy of ∼100 kJ mol⁻¹. The samples show an abnormal increase in the ionic conductivity at ∼300 °C, possibly due to the increase in the orthorhombicity of Sr(La_1−xLi_3x)ScO₄. As the electronic conductivities of the developed oxide materials are a few orders of magnitude lower than their total conductivities, they can be used as solid electrolytes in all-solid-state lithium batteries. The study reveals that K₂NiF₄-type oxides are attractive candidates for developing novel lithium-ion conductors.

Oxide-type all-solid-state batteries are expected to be the next-generation batteries owing to their safety performance. Similarly, Li₂S and Si are also attracting attention as next-generation active materials owing to their high theoretical energy density. However, battery performances and manufacturing methods are associated with many challenges. Thus, this study focuses on an effective method for manufacturing Li₂S positive and Si negative composite electrodes for oxide-type all-solid-state Li₂S–Si batteries. These composite electrodes are prepared via a one-step mechanical milling process using Li₂S or Si as the active materials, carbon with a high specific surface area, and raw materials of oxide glass electrolyte. A solid electrolyte (SE), as well as composites of the active materials, SE, and carbon, are simultaneously generated via this process. Thereafter, the all-solid-state Li₂S–Si full battery cell comprising Li₂S positive and Si negative composite electrodes, respectively, as prepared via the cold press technology, exhibits a relatively high energy density of 283 Wh kg⁻¹ (sum of the masses of the positive and negative composite electrodes) and an area capacity of 4.0 mAh cm⁻² at 0.064 mA cm⁻² and 25 °C.

A “heat- and mass-balance analysis” for a direct-methanol fuel cell (DMFC) system, accounting for actual experimental data and the heat- and mass transfer of the DMFC, is proposed to facilitate the usage of general spreadsheet software. The spreadsheet software enables the use of various functions on the data and visualizes the data using graphs. In addition, this application has a light computational load and is thus easy to implement in system control. The output of the analysis is the transfer of material and heat within the DMFC, as well as the heat balance and electrical efficiency of the DMFC. The analysis was verified using experimental data of the DMFC system, and the results of the verification indicated that the analysis could predict heat balance and system efficiency with accuracies of approximately 3.7 and 2.5 %, respectively. Further, the analysis was used to investigate the effect of stack temperature on the electrical efficiency of the system, and the results showed that the optimum stack temperature at a system power of 130 W was 60 °C and the electrical efficiency at that temperature was 21.8 % HHV.

A lithium-rich layered structure in lithium-ion batteries (LIBs) has attracted much attention due to its high capacity of over 250 mAh g⁻¹ after activation. This could satisfy the requirements of next-generation energy-storage devices. However, a spinel-like impurity phase that forms from the pristine layered structure during cycling is considered to be harmful to the structure stability and Li⁺ mobility, resulting in undesired electrochemical performance. In this study, nanorod-like Li_1.2Ni_0.2Mn_0.6O₂ with a three-dimensional architecture was synthesized by evaporative-crystallization with as-prepared nano-MnO₂ as a hard template. The structure stability and Li⁺ mobility of the nanorod-like Li_1.2Ni_0.2Mn_0.6O₂ was improved by the addition of an appropriate molar ratios of (La, Zr) co-dopants. This combination exhibited outstanding capacity retention of 80.9 % with a stable discharge capacity of 102 mAh g⁻¹ after 300 cycles under a high current density of 1000 mA g⁻¹ (corresponding to 5 C). This study suggests that the use of a multi-prong strategy that combines morphology control and co-doping should be an effective method for improving the high-rate performance of Li-rich materials.

Magnesium and magnesium alloys are light-weighting candidates as the structure materials. The microstructure and corrosion behavior of Mg–4Al–xEr–0.3Mn (x = 2, 4, 6 all in wt%) alloys were studied. The results showed that the morphology, size and distribution of Mg₁₇Al₁₂ phase were gradually improved with the increasing of Er content, and a large number of Al₂Er were observed. The Al₂Er inhibited the hydrogen evolution reaction and promoted the growth of passivation film. Er oxides or hydroxides were found on the surface of the passivation film, and the charge transfer resistance of the film was 4447 Ω cm², while the film resistance was 5852 Ω cm², which reduced the electron transfer efficiency and improved the density and stability of the passivation film, thus greatly improving the corrosion resistance. As Er content reaches 6 wt%, the corrosion rate decreases by nearly 45 %.

Spherical LiNi_0.5Mn_1.5O₄ particles co-doped with lanthanum (La) and sulfur (S) were synthesized by a facile co-precipitation assisted solid-state annealing method with stable oxysulfide La₂O₂S (x = 0, 0.3, 0.5, 0.7, 1.0, and 1.2 at%) as a dopant. The prepared composite materials exhibited a slight shrinkage of lattice parameters without any impurity phase under x ≤ 0.7 at%, and the Ni/Mn disordered arrangement in the spinel lattice increased with an increase in the ratio of dopants, as confirmed by X-ray diffraction and Raman spectroscopy. X-ray photoelectron spectroscopy and electrochemical measurements also clearly indicated that the residual Mn³⁺ in the cubic lattice could be effectively eliminated with the use of La₂O₂S dopants. The composite materials showed outstanding rate and cycling performance compared with those of the pristine material. Specifically, the material doped with 0.5 at% La₂O₂S showed a high reversible capacity of 115.9 mAh g⁻¹ at 10 C, and a remarkable cycling performance of 109.2 mAh g⁻¹ even after 200 cycles. All of these extraordinary performances were attributed to the synergistic effects of La and S in the spinel structure, which induce a suitable pathway for lithium ion and a robust architecture during the electrochemical assessment.

Impact of hydrogen peroxide on carbon corrosion is investigated by immersion tests of catalyst-deposited highly oriented pyrolytic graphite (HOPG) samples to an aqueous solution of 1.0 mol dm⁻³ KOH + 5 mmol dm⁻³ H₂O₂. The surfaces of the HOPG samples are observed with field-emission scanning electron microscopy and X-ray photoelectron spectroscopy. HOPG without catalyst shows almost no morphological change while the distribution of C-O and C=O functional groups increases. In contrast, Pt-loaded HOPG exhibits the formation of scars and COO functional groups, which shows a relatively severe carbon corrosion reaction resulting in CO₃²⁻ formation. Since the Pt-loaded HOPG after the immersion test to 0.5 mol dm⁻³ H₂SO₄ + 5 mmol dm⁻³ H₂O₂ shows much smaller scars, it can be concluded that hydrogen peroxide corrodes Pt-loaded carbon more severely in the alkaline electrolyte solution than the acid electrolyte solution. Ag-loaded HOPG also shows the scars, while the sizes of scars are much smaller than those on the Pt-loaded HOPG. In contrast, MnO_x and CoO_x-loaded HOPGs exhibit no scar and minor oxygen-containing functional groups than the HOPG without catalyst, whereas MnO_x and CoO_x-loaded HOPGs shows larger scars than Pt and Ag-loaded HOPGs after electrochemical carbon corrosion test.

The evaluation of the powder catalyst activity is essential for the development of high-performance electrocatalysts for water electrolysis. However, the gas generated therein interferes with the accurate measurement by covering the catalyst surface. In this study, we have developed a new evaluation method for a powder oxide electrocatalyst using an alkaline electrolyte. This measurement and analysis method can obtain the intrinsic catalyst activity with no influence from the generation of bubbles. To establish this method, the electrolyzer for evaluation adopts the interdigit flow field for the forced-flow method, and the two methods, namely time zero analysis and flow rate infinitization analysis, were demonstrated by the extrapolation of the measurement data. As a result, the combination of forced-flow method and time-zero analysis is the best evaluation method for the determination of kinetic current at time zero as the equivalent of the no-generation gas condition.