Shougo Higashi

Water is crucial in space missions, and developing lightweight, high-performing catalysts for water recycling is essential. Extensive research on nanosized and even single-atom catalysts supported on oxides has been conducted for this purpose. However, the oxide supports usually constitute over 90% of the total mass, so the catalysts are heavy. Here, we fabricated a light, fibrous RuO2 nanostructured textile consisting solely of RuO2 nanoparticles (NPs), which did not require an oxide support, and evaluated it in the Sabatier reaction for water recycling. Remarkably, this support-free catalyst textile displayed an unprecedented catalytic mass activity (~60 mmolCH4 h-1 gcat-1 at 160 °C), which was approximately 20 times higher than that of a previously reported Ru/TiO2 catalyst, and the highest TOF (0.021 s-1 at 160 °C). Although well-known catalyst degradation was observed during prolonged testing, the performance of the textile remained exceptional even after 46 hours of continuous operation. A detailed surface analysis unveiled phenomena such as RuO2 reduction, nanoparticle growth, surface smoothing, and Ru loss during the reaction, contributing to degradation. We expect that addressing these intrinsic and thermodynamically driven phenomena will improve activity and durability.

Electrodes with a maximal active site density are critical for high‐performance high‐temperature electrochemical cells (HTECs). One widely employed approach involves the use of porous nanostructures with a high surface‐to‐volume ratio. However, their active site densities inevitably decrease owing to particle aggregation induced at high temperatures, necessitating further development of electrode processing techniques. Taking Pt/yttria‐stabilized zirconia (YSZ) interface as a model system, a Pt nanostructured textile akin to the cantaloupe‐rind pattern with high mechanical integrity is fabricated. Application of an AC voltage to this textile electrode at an elevated temperature reduces the Pt particle size from submicron to 10–80 nm forming a nanocomposite with YSZ, accompanied by a 40‐fold increase in current density under high‐temperature water electrolysis conditions. Furthermore, the AC voltage application to a partially aggregated electrode restores its nano‐blended structure associated with the recovery of its activity. This technique is effective in counteracting particle aggregation on demand, providing an alternative approach to achieve high performance and extended lifetimes in HTECs.

This paper provides a comprehensive review of quantum spin sensing with a focus on the nitrogen vacancy (NV) center in diamond. Beginning with the discovery of optically detected magnetic resonance in NV centers, we trace the evolution of this technology and its integration with complementary metal-oxide-semiconductor technology, marking a significant advancement in measurement science. The unique optical and spin properties of NV centers, operational at room temperature and under ambient conditions, have broadened their application spectrum, notably in magnetometry for nanoscale magnetic field detection. This work describes the transition from isolated NV centers to dense ensembles, highlighting the challenges and advancements in microfabrication and nanofabrication that have facilitated the integration of these centers with photonic structures and electronic devices. The efficient readout of NV spin states and the challenges in miniaturization are addressed, showcasing the development of compact, portable quantum sensors. We also discuss the potential impact of these sensors in various domains, including vehicle sensor systems and biomedical applications, underscoring the significance of environmental influences on magnetometric readings.

Solar steam generation is an attractive method to produce clean water, and high steam generation rates have been achieved using nanostructured light absorbers. However, since it usually takes minutes to reach the temperature for steady-state steam generation under solar illumination, a material that responds quickly to intermittent sunlight is strongly desired. Here, we report an unprecedented heating rate in an ultralight freestanding textile consisting of interconnected Ag and Cu₂O nanoparticles. The textile demonstrated high solar absorption with low reflectance and transmittance, which were rationalized using our multiphysics simulations. A commercial polystyrene foam wrapped with this broadband light-absorbing textile showed the fastest response to sunlight together with a good steam generation rate compared to reported inorganic nanostructured steam generators. Furthermore, the textile exhibited antibacterial property, which might lower the risk of the vapor-induced transfer of bacteria during long-term intermittent use and the cost of subsequent water sanitization.

We report a method for fabricating a support-free catalytic textile consisting solely of nanoclusters. With IrO₂ textile, among the highest OER activity for IrO₂ was achieved, attributed to the presence of a large number of undercoordinated Ir atoms.

Electrospinning is a widely used production method for nanoscale fine polymer fiber fabrics. An ultrafine fiber made of polymers such as polyvinylpyrrolidone (PVP) polyacrylic acid (PAA) has immense potential for applications in air filters, batteries, and biosensors. However, producing fabrics with long uniformly distributed ultrafine fibers of a mean diameter below ~ 200 nm is still a challenge, because such elongated-ultrafine fibers tend to break into beads before they reach the collector. Here, we exploits the thixotropy of the solution given by the addition of 2,2,6,6-tetramethylpiperidin-1-oxyl-oxidized cellulose nanofibers to recover the solution viscosity for stabilizing the electrostatically elongated nanofibers, whereby the solution is smooth in the syringe needle owing to the shear force but regain its original viscosity after being freed from electrostatic force. Using this method, we successfully fabricated a non-woven ultrafine-long nanofiber made of PVP and PAA with a mean diameter as low as ~ 90 nm with a negligible number of beads.

Platinum nanocatalysts play critical roles in CO oxidation, an important catalytic conversion process. As the catalyst size decreases, the influence of the support material on catalysis increases which can alter the chemical states of Pt atoms in contact with the support. Herein, we demonstrate that under-coordinated Pt atoms at the edges of the first cluster layer are rendered cationic by direct contact with the Al₂O₃ support, which affects the overall CO oxidation activity. The ratio of neutral to cationic Pt atoms in the Pt nanocluster is strongly correlated with the CO oxidation activity, but no correlation exists with the total surface area of surface-exposed Pt atoms. The low oxygen affinity of cationic Pt atoms explains this counterintuitive result. Using this relationship and our modified bond-additivity method, which only requires the catalyst–support bond energy as input, we successfully predict the CO oxidation activities of various sized Pt clusters on TiO₂.

Ir nanoparticles are finely dispersed over whole particles of activated carbon (AC) via the gas phase adsorption of an organoiridium complex in the AC and subsequent heat treatment. Structural analysis of the supported Ir is performed in combination with X-ray absorption spectroscopy.