Nickel hydroxide is well known as a positive active material in nickel-cadmium and nickel-metal hydride batteries; its redox potential is close to that of the oxygen evolution reaction (OER), and it is known that the OER occurs simultaneously with a charging reaction when a battery is nearly fully charged. For this reason, nickel hydroxide electrodes are incorporated into designs where the oxygen generated at a positive electrode is absorbed by a negative electrode. However, when zinc is used as the negative active material, a dense separator is required to suppress zinc dendrites, making it difficult to design such an oxygen absorption system. In this study, we focused on nickel-based layered double hydroxide (LDH), instead of nickel hydroxide, to develop a cathode with low oxygen generation. We found that a Ni-Co LDH can be used as a positive electrode and can be charged with almost no oxygen generation up to the fully charged state. The expression capacity depended on the Ni content in the host layer, and a maximum of approximately 280 mAh g⁻¹ was obtained. The output performance of the LDH electrode was comparable to that of the nickel hydroxide electrode, but the input performance was found to be significantly greater. These results suggest that nickel-based LDH can be used as a cathode active material in aqueous zinc anode batteries instead of nickel hydroxide.

Garnet-like oxide lithium ionic conductor Li₇La₃Zr₂O₁₂ (LLZO) exhibits relatively high ionic conductivity and electrochemical stability against lithium metals, attracting much attention as a solid electrolyte for all-solid-state lithium metal batteries. However, for practical use, the improvement in the ionic conductivity of the grain boundaries and sinterability of LLZO is necessary. Nano-sized fumed Al₂O₃ prepared by the vapor phase with various specific surface areas as a sintering aid has been applied to the garnet-type lithium ionic conductor, Li_6.25Ga_0.25La₃Zr₂O₁₂ (LGLZ) and Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZT). The addition effect of fumed Al₂O₃ on lattice parameters, particle morphology, sinterability, and ionic conductivity has been investigated. The sinterability has improved by the addition of nano-sized fumed Al₂O₃ with a high specific surface area, and ionic conductivity does not exhibit a significant change for LGLZ. The addition of fumed Al₂O₃ with a specific surface of 130 m² g⁻¹ has lowered the sintering temperature of LLZT by 200 °C, which indicates nano-sized Al₂O₃ is quite useful as a sintering aid for garnet-type solid electrolytes.

A series of organic thin-film solar cells using electrodeposited polythiophene films were fabricated and characterized. The cells consisted of an indium-tin oxide transparent electrode/electrodeposited poly(3,4-ethylenedioxythiophene) doped with different anions as a hole transport layer/electrodeposited poly(2,2′-bithiophene) film as a photoexciting p-type semiconductor layer/[6,6]-phenyl-C₆₁-butyric acid methyl ester as an n-type semiconductor layer/aluminum as a top electrode, were fabricated. Obtained solar cells were characterized and photoelectric properties were evaluated. These organic thin-film solar cells generated photovoltages and photocurrents. The photovoltaic property was varied depending on the structure of dopant anions, which seems to be correlated with the surface morphology of each poly(3,4-ethylenedioxythiophene)-dopant anion.

A coating consisting of titanium nitride (TiN) microparticles and styrene butadiene rubber (SBR) was developed as a surface treatment for titanium (Ti) anode bipolar plates used in proton exchange membrane (PEM) water electrolysis, in place of conventional precious metal coatings. The TiN/SBR coating significantly reduced the interfacial contact resistance between the Ti bipolar plate and the porous transport layer (PTL), resulting in initial high-frequency resistance (HFR) comparable to that of Au plating. The performance and durability of the Ti bipolar plate with the TiN/SBR coating were investigated by cyclic voltammetry for 1800 cycles. A single cell using the TiN/SBR-coated Ti bipolar plate exhibited clearly improved iV performance compared with a cell using bare Ti bipolar plate. Surface analysis after durability testing revealed that the SBR layer underwent local degradation, particularly in areas not covered by TiN particles, leading to exposure and partial oxidation of the Ti substrate. In contrast, TiN particles largely remained on the surface and contributed to maintaining low interfacial contact resistance. The extent of TiN oxidation appeared minimal compared with that of bare Ti, suggesting that TiN/SBR coatings offer a promising non-precious metal coating for bipolar plates in PEM water electrolysis.

Streaming potential is the potential difference established between the inlet and outlet of a narrow channel while pumping a low-concentration electrolyte and is used in various applications, such as power generation devices, zeta potential analyzers, and electrochemical reactions. However, the effects of cell parameters, such as the geometry and resistance of channels with porous fillers, on streaming potential generation have not been clarified. Herein, the effects of the shape of a channel filled with a porous phenolic resin monolith material on streaming potential and current generation behavior were comprehensively investigated. Additionally, the energy conversion efficiency of streaming potential generation using a cell based on this channel was elucidated.

Designing positive electrode materials for Li-ion and Na-ion batteries without using expensive metals is of critical importance for sustainable energy storage systems. One of the most promising candidates, P3-type layered sodium manganese oxide (P3-Na_xMnO₂) can be obtained via solid-state reaction. While there is no report on P3-Li_xMnO₂ synthesis and electrochemistry because of its instability, lithium ion exchange of Na in P3-Na_xMnO₂ is a plausible strategy to test its Li₊ insertion/extraction. In this study, we investigate the electrochemical activity of P3-Na_xMnO₂ electrodes in both Li and Na cells. We found a high capacity of ca. 200 mAh/g is achieved in both cells, and P3-Na_xMnO₂ electrodes undergo spontaneous Na/Li ion exchange in the Li⁺-containing electrolyte, which can thereafter be reversibly cycled. To improve electrochemical performance, we demonstrated two approaches: partial Ti or other metal substitution for Mn in P3-Na_xMnO₂ and using a highly concentrated electrolyte of 5.5 mol dm⁻³ Li(N(SO₂F)₂) dimethyl carbonate solution. Particularly, the highly concentrated Li-electrolyte provides a significant enhancement on the cycle stability in the Li cell, demonstrating no apparent capacity loss up to 100 cycles.

Antimony-based sulfide solid electrolytes exhibit high conductivity for alkaline cations. In this study, we synthesized K₃SbS₄ potassium-ion conductors using the mechanochemical method for the nominal compositions with x mol% excess K₂S (x = 0, 5, 10, and 15) to compensate for the chemical impurities in the K₂S reagent. The mechanochemically prepared samples showed X-ray diffraction patterns similar to β-K₃SbS₄ in all the compositions. Raman bands attributed to the SbS₄³⁻ unit were observed in all the samples. The ionic conductivities at 25 °C showed a positive correlation with increasing x, reaching a maximum ionic conductivity of 3.6 × 10⁻⁶ S cm⁻¹ at 10 mol% excess K₂S. Subsequent heat-treatment further enhanced the ionic conductivity, achieving 1.2 × 10⁻⁵ S cm⁻¹ at 25 °C. This improvement is attributed to the nominal composition being close to that of K₃SbS₄ by adjusting the excess amount of K₂S and the increased crystallinity of β-K₃SbS₄.