In sulfuric acid (H₂SO₄) aqueous solutions containing manganese (Mn) and titanium (Ti) ions, which were developed to be used for the positive electrolyte in redox flow (RF) batteries, the addition of tellurium (Te) or antimony (Sb) has been found very effective in suppressing the MnO₂ precipitation in the charging process from Mn²⁺ to Mn³⁺. To investigate its mechanism, x-ray absorption near edge structure (XANES) measurements were carried out for cations in the solution samples at various state of charges (SOCs). In the case of the Te-added solutions, the change rate of Mn ion valence over the SOC was found to very low at the SOCs lower than 30 %. It was also indicated that the valence change of Te ions from Te⁴⁺ to Te⁶⁺ proceeded at the SOCs below 30 %. On the other hand, no significant change was observed in the valence of Ti at any SOCs. Similar trends were confirmed in the Sb-added solution samples. In conclusion, the supplied charges were considered to be used to increase not only the valence of Mn ions but also that of Te or Sb ions, which resulted in the suppression of the MnO₂ precipitation.

To better understand the Na⁺ storage mechanism of general carbon materials, the suitable choice of study model is really pivotal. Carbon black (CB) attracts us to consider that it is a suitable model to study the Na⁺ storage mechanism because CB is an extremely popular industry product, and a lot of organic groups exist on its surface. After detailed electrochemical evaluations, it is surprisingly observed that the CB shows the tremendous Na⁺ storage capacity. For instance, Na⁺ storage capacity is 103.3 mAh g⁻¹, after the discharge-charge process was performed 10000 cycles at 5.0 A g⁻¹. Additionally, the CB still shows the storage capacity at 90 mAh g⁻¹, during 10000 cycles at 10.0 A g⁻¹. The storage mechanism was studied from two aspects which are structural conversions and surface effect. After performing the XRD, XPS, BET measurements and DFT and GITT calculations, it is aware of that the synergistic effect of capacitive effect brought by the –C=O of ester groups on the CB surface and structural conversions of CB contribute to the Na⁺ storage capacity. Our analysis results about storage mechanism of CB are capable to provide a beneficial reference for unfolding the carbon materials having storage capacity for Na⁺.

Despite the high energy densities offered by secondary batteries with metallic lithium (Li) anodes, their commercialization is hindered by the problem of dendritic growth of metallic lithium at the anode. Therefore, we aim to address this problem by evaluating the morphology of the deposited lithium, which is affected by the surface film produced by various side reactions in the system. Considering the wide potential windows of quaternary ammonium ionic liquids, we study precipitation morphologies using these ionic liquids as electrolytes. In this study, we examine the side reactions of Li electrodeposition using impedance spectroscopy and transmission electron microscopy. Samples were prepared and observed by gradually decreasing the potential from 2.8 V, the open circuit potential. As a result, it was confirmed that surface films were formed at about 1.5 V (vs. Li reference electrode), even when ionic liquids with a wide potential window were used, although the direct cause of the surface film formation is not known. Importantly, the vertex frequency of the semi-circular arc derived from the surface film in the impedance measurement was 500 Hz, which is faster than the time constant of the semi-circular arc due to the dissolution and precipitation reaction of Li.

The photographic development of AgBr microcrystals yields the formation of silver nanofilaments (pAgNF). Subsequent treatment of pAgNF with a gold(I)-thiourea complex solution results in a hollow nanostructure composed of gold and silver (hAuAgNS). The formation mechanism of the hollow structure is believed to be a galvanic reaction. In this study, we investigated the formation process using a macroscopic electrochemical model cell, where the anodic and cathodic half-reactions are spatially separated, enabling independent control of the conditions in each half-cell. The model cell experiments consistently corroborate the two-step mechanism for hollow structure formation: 1) direct galvanic replacement of silver by gold on the pAgNF surface, giving the gold-covered exterior on pAgNF, and 2) galvanic deposition of gold on the pre-deposited gold surface, accompanied by the dissolution of silver from the gold-uncovered sites (galvanic pitting). The transition of pAgNF to hAuAgNS was further traced through chemical analysis and electron micrographic observation, with discussion and interpretation of the results of the model cell experiments.

A dense NiO-Fe₂O₃ (NiFe) pellet has been developed as a potential anode-support for thin-film solid oxide fuel cells (SOFCs). However, preparation of dense NiFe is very challenging. Hole-formed NiFe pellets or porous NiFe pellets are frequently formed, which cannot be used as a support (substrate) for thin-film SOFCs. Therefore, this hole-formed NiFe support is simply wasted. In this report, we attempt to re-qualify this NiFe support to be a valuable substrate, which can be used for fabricating thin-film SOFCs. By deposition of smaller NiFe particles to cover the hole-formed NiFe support, the surface of this NiFe pellet is modified. Large holes on the surface disappear. The newly formed NiFe support can be used for fabricating a single cell with La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ as thin-film electrolyte operated at intermediate temperature. Maximum power density generated from this cell is 0.45, 0.86 and 1.28 W cm⁻² at 873, 923 and 973 K, respectively.

Saliva-based biosensors are emerging as viable tools for non-invasive, painless, and easily administered household medical diagnostics. Despite their potential, the complexity of saliva, containing various non-target molecules and contaminants, presents significant challenges due to nonspecific interactions with biosensors. This study utilizes surface-charge modulated graphene field-effect transistors (SCM-GFETs) for the detection of C-reactive protein (CRP) in artificial saliva, using portable measurement apparatus. Our findings indicate that SCM-GFETs exhibit nonspecific responses to saliva components. To address this issue, a two-step preprocessing method is implemented: diluting the saliva in phosphate-buffered saline at a 1 : 10⁴ ratio and subsequent membrane filtration. This process significantly reduced nonspecific interactions, enabling CRP detection in saliva samples. These advancements hold promise for enhancing graphene field-effect transistor technology in point-of-care diagnostic devices.

Electrochemical impedance spectroscopy (EIS) of lithium insertion electrodes is a powerful technique to facilitate the further development of lithium-ion batteries (LIBs) because it provides useful information on electrochemical reactions. However, EIS methodology using a three-electrode cell is yet to be established owing to the difficulty in designing the reference electrode configuration. Therefore, a symmetric-cell method has been proposed to measure the EIS of a single electrode in a two-electrode cell, and it has been actively applied to EIS measurements in recent years. EIS measurements using symmetric cells have resulted in several new discoveries and deepened our understanding of the EIS behavior of lithium insertion electrodes. In this review, we outline the progress of EIS measurements using the symmetric-cell method for lithium insertion electrodes. First, we explain the principle, fabrication method, and EIS analysis of symmetric cells. Subsequently, an equivalent-circuit model representing lithium insertion electrodes is proposed based on the EIS measurement results. Furthermore, the factors affecting the various resistances comprising the equivalent circuit, such as charge transfer, contact, and ionic transport resistances, are discussed, including the dependence of the resistances on the electrode thickness, porosity, and measurement temperature on the resistances. Finally, applications of the EIS of a single electrode obtained using symmetric cells are described, including the prediction of the EIS of LIB and acquisition of the EIS of a single electrode from that of full cells.

A thin-film battery composed of a LiFePO₄ cathode/Li₃PO₄ electrolyte/Li anode was fabricated on a Pt/Ti/Si (PTS) substrate via RF magnetron sputtering. The amorphous Li₃PO₄ film was densely stacked on a 60 nm-thick LiFePO₄ film, which provided a suitable reaction field for understanding the electrochemical properties of LiFePO₄ at the interface with the solid electrolyte. The LiFePO₄ cathode film exhibited highly reversible lithium desertion/insertion at the interface at room temperature and 60 °C, without any side reactions. An irreversible oxidation reaction occurred during the initial charging process at 100 °C, leading to an increase in the charge-transfer resistance of the LiFePO₄/Li₃PO₄ interface with no significant decrease in the lithium desertion/insertion capacity of LiFePO₄. This result suggests the formation of a resistive interphase via the decomposition of Li₃PO₄ at 100 °C. A severe decrease in capacity is observed at 125 °C, which indicates the LiFePO₄-side interface contributed to the side reactions. The film battery exhibits a severe decrease in capacity at 125 °C.