The cover art highlights the review article by Isao Shitanda et al., “Rheo-Impedance Spectroscopy: A Dual Readout of Structural Evolution in Electrochemical Materials and Soft Matter.”

This review introduces rheo-impedance as an approach that combines rheological measurements with electrical, electrochemical, or dielectric measurements to follow structural evolution in soft materials and complex fluids. Rheology probes flow and mechanical properties, whereas impedance and related measurements provide information on charge transport and interfacial processes. Their combination can distinguish structural states that may appear similar when examined by either method alone. The review surveys applications to conductive colloids, battery slurries, fuel-cell catalyst inks, gels and stimuli-responsive systems, and drying, curing, and sintering processes. It also discusses measurement configurations and cautions in interpreting coupled mechanical and electrical responses across different material systems.

The cover image visualizes this dual-readout concept. A rheometer-integrated electrical measurement system is placed at the center, surrounded by represen­tative particle assemblies, conductive networks, and polymer or gel structures. These elements illustrate the wide range of materials addressed by rheo-impedance and convey how complementary mechanical and electrical responses can reveal structural evolution, network formation and disruption, and changes in transport pathways.

In lithium–oxygen batteries (LOBs), the chemical stability of electrolyte solvents is a critical factor determining cell performance. While sulfonamides represent a promising class of solvents for LOB electrolytes, systematic investigations into the structure–stability relationship of their analogs remain limited. In particular, although reactions involving the α-hydrogen (i.e., hydrogen abstraction and/or deprotonation of the hydrogen atom α to the sulfonyl group) have been widely considered to be initiating steps of solvent decomposition in various electrolytes, their actual impact on solvent decomposition and subsequent battery performance remain unclear. In this study, we performed a comparative analysis to elucidate the structure–stability relationships of sulfonamides with the general structure R¹–SO₂–NCH₃(C₄H₉). Differential electrochemical mass spectrometry (DEMS) measurements revealed that the presence of α-hydrogens is not the dominant factor in solvent decomposition. Instead, the decomposition of the N-alkyl (butyl) chain plays a major role. These results suggest that longer alkyl chains lower the corresponding C–H bond dissociation energies through stabilization of the resulting alkyl radicals, thereby enhancing susceptibility to hydrogen abstraction by reactive oxygen species generated during the discharge/charge process. Our findings indicate that considering only the presence or absence of α-hydrogens is insufficient for designing chemically stable solvents. Rather, minimizing the number of C–H bonds susceptible to hydrogen abstraction is crucial for improving solvent stability.

The development of on-demand sterilization systems for highly resistant bacterial spores remains a critical challenge in the fields of food safety and healthcare. In this study, we developed a visible-light-driven photocatalytic system for the in situ generation of organic peroxides from aqueous ethanol solutions using palladium-loaded tungsten trioxide (Pd/WO₃). The loading of Pd nanoparticles (0.1 wt%) significantly enhanced the photocatalytic activity compared to that of bare WO₃, promoting the simultaneous production of hydrogen peroxide (H₂O₂) and organic acids (acetic and formic acids). This enhancement could be attributed to the improved charge carrier separation and the role of Pd in facilitating the reduction of oxygen to H₂O₂. The generated H₂O₂ and organic acids further reacted on the WO₃ surface to form organic peroxides, such as peracetic acid, via a two-step sequential process. Under optimized conditions (80 % v/v EtOH/H₂O), the Pd/WO₃ system achieved a 6-log reduction in Bacillus subtilis spores within 12 h of visible-light irradiation, whereas bare WO₃ required 16 h for the same effect. Our findings demonstrate that the Pd/WO₃ photocatalytic system provides a safe and efficient approach for the localized production of high-level disinfectants, offering a promising alternative to conventional corrosive chemical agents for inactivating resilient pathogens.

The origin of the semi-circles in Nyquist plots of lithium-ion battery composite electrodes obtained using a four-electrode cell was investigated using Li₄Ti₅O₁₂ (LTO) composite electrodes. No distinct semi-circle was observed for the LTO composite electrode, even though the electrolyte within pores was present. In contrast, semi-circles assigned to the impedance related to ionic transport resistance within the composite electrode were observed for the LTO/acetylene black (AB) composite electrode. These results indicate that the presence of the electrolyte within pores is insufficient for the appearance of the semi-circles and that a continuous electronic conduction phase must be formed on the solid side. Thus, the semi-circles are assigned to an apparent R//C response originating from the coupling between ionic transport resistance in the pores and the capacitance made observable by the continuous electronic conduction phase.

Rheo-impedance is the joint use of a rheological measurement and an electrical, electrochemical, or dielectric measurement to follow how a soft material or complex fluid reorganizes as it is processed or as it changes state. The two answer different questions about the same sample: rheology reports how the material flows and how stiff or elastic it is, while impedance, conductivity, and dielectric data report how well charge moves through it and what is happening at its interfaces. Because the mechanical and the electrical responses often depend on different parts of the microstructure, and need not change at the same moment, measuring both can separate states that look identical to either method alone. In this review, “rheo-impedance” is used as an organizing term rather than the name of a single standardized technique. The literature is grouped into three configurations—simultaneous, separate-but-linked, and correlation-based—and five material classes: carbon-black and conductive-colloid suspensions, lithium-ion battery slurries, polymer-electrolyte fuel-cell catalyst inks, gelation and stimuli-responsive systems, and drying, curing, and sintering. Four observations recur across these systems: the mechanical and electrical changes may be linked to the same process yet appear at different stages; a stiffer structure does not necessarily carry charge better; the structure present under flow is not always the one retained after processing; and both agreement and disagreement between the two responses can be informative. Throughout, we try to separate what has been shown experimentally from what is still system-dependent interpretation or future prospect. The main open problems are the ambiguity of equivalent-circuit interpretation, the limited transfer of descriptors between the flowing and the finished state, and the absence of standard geometries, frequency windows, and reporting conventions.