JSPS KAKENHI Research Articles

Intra-patient spatial comparison of non-metastatic and metastatic lymph nodes reveals the reduction of CD169+ macrophages by metastatic breast cancers

Breast cancer cells suppress the host immune system to efficiently invade the lymph nodes; however, the underlying mechanism remains incompletely understood. Here, we aimed to comprehensively characterise the effects of breast cancers on immune cells in the lymph nodes. We collected non-metastatic and metastatic lymph node samples from 6 patients with breast cancer with lymph node metastasis. We performed bulk transcriptomics, spatial transcriptomics, and imaging mass cytometry to analyse the obtained lymph nodes. Furthermore, we conducted histological analyses against a larger patient cohort (474 slices from 58 patients). The comparison between paired lymph nodes with and without metastasis from the same patients demonstrated that the number of CD169+ lymph node sinus macrophages, an initiator of anti-cancer immunity, was reduced in metastatic lymph nodes (36.7±21.1 vs 7.3±7.0cells/mm2, p=0.0087), whereas the numbers of other major immune cell types were unaltered. We also detected that the infiltration of CD169+ macrophages into metastasised cancer tissues differed by section location within tumours, suggesting that CD169+ macrophages were gradually decreased after anti-cancer reactions. Furthermore, CD169+ macrophage elimination was prevalent in major breast cancer subtypes and correlated with breast cancer staging (p=0.022). We concluded that lymph nodes with breast cancer metastases have fewer CD169+ macrophages, which may be detrimental to the activity of anti-cancer immunity. JSPS KAKENHI (16H06279, 20H03451, 20H04842, 22H04925, 19K16770, and 21K15530, 24K02236), JSPS Fellows (JP22KJ1822), AMED (JP21ck0106698), JST FOREST (JPMJFR2062), Caravel, Co., Ltd, Japan Foundation for Applied Enzymology, and Sumitomo Pharma Co., Ltd. under SKIPS.

Tetra-Peg Gels with Highly Concentrated Sulfolane-Based Electrolytes Exhibiting High Li-Ion Transference Numbers

To achieve high safety of lithium-ion batteries (LIBs), non-flammable electrolytes and prevention of liquid electrolytes are desirable. Sulfolane (SL) is a thermally stable and non-flammable solvent, and can dissolve high concentration Li salts. Recently, highly concentrated electrolytes (HCEs) containing Li salts over 3 mol dm−3 have attracted much attention for their attractive properties such as high thermal stability and wide electrochemical windows. We previously reported that SL-based HCEs exhibit Liion hopping conduction mechanism.1,2 In SL-based HCEs, a unique solvation structure is formed in which different Li+ ions are cross-linked by the SL and anions. In the cross-linked structure, Li+ ions dynamically exchange the ligands (SL and anion) and diffuse/migrate faster than SL solvent and anion, leading to high transference numbers of Li+ ion (>0.5). The high transference number of Li+ is effective in suppressing the concentration polarization during high-rate charging and discharging of a LIB.Gelation of the HCEs can prevent the leakage of liquids and further improve the safety of LIBs. In the case of polymer gel electrolytes, liquid electrolytes are incorporated in the polymer network. Ionic conductivity of a gel electrolyte is generally lower than that of its parent liquid electrolyte. However, to prepare self-standing and mechanically robust gel electrolytes high polymer concentrations (typically over 20 wt%) are required. To achieve both high ionic conductivity and mechanical toughness of a gel electrolyte, the use of tetra-arm poly(ethylene glycol) (TPEG) has been proposed.3 TPEG gels obtained by the end-coupling reaction of two symmetrical TPEGs with different terminals exhibit excellent mechanical properties.4 TPEG forms a homogeneous polymer network, allowing the resulting gels to uniformly disperse external stresses. Consequently, TPEG gels possess excellent mechanical toughness even at low polymer concentrations (<10 wt%). In this work, we prepared self-standing TPEG gel membranes containing a high concentration LiN(SO2CF3)2/SL electrolyte.5 The mechanical, ion transport, and electrochemical properties of the gels were characterized. TPEG gels exhibited high transference numbers of Li+. The low polymer concentration and homogeneous polymer network in the gel electrolyte were useful in achieving both mechanical reliability and high Li+ transport ability. Li/LiCoO2 cell with a TPEG gel electrolyte membrane could discharge at a current density of 2.9 mA cm−2 despite the low ionic conductivity (0.26 mS cm−1) of the gel electrolyte. Acknowledgements : This study was partially supported by the JSPS KAKENHI (Grant No. JP19H05813, JP22H00340, and JP23K17370). References K. Dokko, et al, J. Phys. Chem. B, 2018, 122, 10736–10745.A. Nakanishi, et al., J. Phys. Chem. C, 2019, 123, 14229–14238.K. Fujii, et al., Soft Matter, 2012, 8, 1756–1759T. Sakai, et al., Macromolecules, 2008, 41, 5379–5384.N. Tasaki, et al., Phys. Chem. Chem. Phys., 2023, 25, 17793–17797

(Invited) Role of Oxidant Gas for Atomic Layer Deposition of HfxZr1−XO2 Thin Films on Ferroelectricity of Metal-Ferroelectric-Metal Capacitors

Since the first report of ferroelectricity in HfxZr1−xO2 (HZO) in 2011 [1], a lot of attention has been devoted for future non-volatile memory device applications due to its scalability (< 10 nm), low thermal budget (< 400°C) and matured atomic layer deposition (ALD) technique [2]. The thermal ALD process using H2O or O3 is generally employed for the fabrication of ferroelectric HZO thin films. On the other hand, the effect of the plasma-enhanced ALD process using O2 plasma gas on the crystallinity and ferroelectricity has not been systematically clarified. In this paper, we report the importance of ALD oxidant gases for HZO films using H2O or O2 plasma on the ferroelectricity of metal–ferroelectric–metal (MFM) capacitors.MFM capacitors with the H2O- and O2 plasma-based HZO films were fabricated as follows. A 10-nm-thick HZO films were deposited on a TiN bottom-electrode (BE-TiN) by ALD at 300°C using H2O or O2 plasma as oxidant gases and (Hf/Zr)[N(C2H5)CH3]4 (Hf:Zr = 1:1) cocktail precursor. The Hf/Zr ratios in both types of HZO films were estimated to be 0.4/0.6 using X-ray photoelectron spectroscopy (XPS). Next, a post-deposition annealing (PDA) process was carried out at 400 °C for 1 min under a N2 atmosphere. Finally, a TiN top-electrode was deposited by DC sputtering.First, the crystallinity and remanent polarization (2P r = P r + − P r −) of the H2O- and O2 plasma-based HZO films were investigated. Nanocrystals with ferroelectric orthorhombic (O), tetragonal (T), cubic (C) phases partially existed in the O2 plasma-based film after the ALD process, while an amorphous structure dominantly existed in the H2O-based film, analyzed by the grazing-incidence X-ray diffraction analysis and cross-sectional transmission electron microscopy images [3]. This could be because of a strong oxidation power and high energy ion/electron bombardment of O2 plasma. After the PDA process, the O phase was formed more in the O2 plasma-based HZO film than the H2O-based film. Therefore, the nanocrystal grains in the as-grown O2 plasma-based HZO film could play an important role as nuclei for the crystallization and formation of O phase [3,4]. From the polarization–electric field hysteresis curves, the PDA-treated O2 plasma-based capacitor exhibited 2P r of 20 µC/cm2, which was 1.5 times higher than that (13 µC/cm2) of the H2O-based capacitor. Thus, these results indicate that the crystallization and O phase formation of HZO films were promoted by using O2 plasma gas as an ALD oxidant, resulted in a higher 2P r.Next, endurance properties of these MFM capacitors were evaluated. In the wake-up state, both capacitors showed almost the same increase rate (~8%) of switching polarization (P sw). In the fatigued state, on the other hand, the O2 plasma-based capacitor exhibited less P sw degradation (~33%) after 106 cycles, whereas the P sw of H2O-based capacitor decreased by ~47%. To clarify these different fatigue properties, the TiOxNy interface reaction layer (IRL) formation at the HZO/BE-TiN interface was analyzed using synchrotron hard X-ray photoelectron spectroscopy (HAXPES). For the HAXPES Ti 2p spectra, the Ti-O peak intensity for the O2 plasma-based capacitor was larger than that of the H2O-based capacitor [5]. Therefore, an oxygen-rich TiON-IRL could be formed at the HZO/BE-TiN interface during ALD process due to the stronger oxidizing power of O2 plasma. Additional oxygen vacancies (VO) were reported to formed in HfO2-based films during field cycling due to the interface reaction between the HfO2-based film and TiN electrode. Moreover, one of the origins of the P sw degradation was thought to be domain pinning caused by VO [6]. Therefore, an oxygen-rich TiON-IRL for the MFM capacitor with the O2 plasma-based HZO film could prevent the interface reaction and formation of additional VO in HZO films, led to superior fatigue properties.In summary, the MFM capacitor with the O2 plasma-based HZO film showed superior 2Pr and fatigue resistance compared to those of the H2O-based one. Based on these experimental results, it is important to consider the selection of an ALD oxidant for fabrication of HZO-based MFM capacitors.This work was partly supported by JSPS KAKENHI (Nos. JP21J01667, JP20H02189, and JP18J22998) and MEXT Leading Initiative for Excellent Young Researchers (No. JPMXS0320220213). The HAXPES measurements were performed under approval of the NIMS Synchrotron X-ray Station (2020A4602 and 2020A4651).[1] J. Müller et al., Appl. Phys. Lett. 99, 112901 (2011).[2] J.-H. Kim et al., ACS Appl. Electron. Mater. 5, 4726 (2023).[3] T. Onaya et al., APL Mater. 10, 051110 (2022).[4] T. Onaya et al., Microelectron. Eng. 215, 111013 (2019).[5] T. Onaya et al., Solid State Electron. 210, 108801 (2023).[6] M. Pešić et al., Adv. Funct. Mater. 26, 4601 (2016).

(Digital Presentation) Cooperative Quantum Dynamics of Excitons in Colloidal Quantum Dots for Novel Optoelectronic Applications

Colloidal semiconductor quantum dots (QDs) are excellent materials for combining photonics and nanoscience. They have been extensively studied to understand the photophysics of quantum confined excitons and to develop efficient optoelectronic devices such as QD solar cells and light-emitting diodes. The photophysical processes of QD devices are governed by a large number of QDs constructing the devices. Therefore, cooperative quantum dynamics of QDs, i.e., synchronous responses of QD ensembles, have a great potential for boosting optoelectronic device performances.Before the use of cooperative quantum dynamics in QD devices, the understanding of quantum dynamics of excitons, i.e., coherent properties of multiexcitons, is required to draw out quantum cooperativity from QD ensembles. In order to elucidate coherent dynamics of multiexcitons during resonant laser-pulse excitation, we performed a quantum interference spectroscopy of QD responses. We found that multiexcitons generate the high-frequency coherent oscillations with integer multiples of the exciton resonance frequency, which is called harmonic quantum coherence, and that the coherent responses govern the microscopic processes in the resonant multiphoton absorption [1-3]. Furthermore, it was demonstrated that the coherent responses were detectable as photocurrent signals in thin films of QD ensembles [4]. These developments build up an essential base of quantum cooperativities emerging in optoelectronics.Here, we report recent investigations of cooperative quantum dynamics in QDs. In optoelectronic devices, electronic couplings between QDs are expected to generate a new type of quantum cooperativities. To generate electronic coupling, we fabricated closely packed PbS QDs by using a ligand exchange method. We found that nonlinear photocurrent signals are strongly enhanced in the QD solids. The comparison analysis of different ligands clarified that the enhancement ratio increases monotonically with the decrease of the inter-QD distance [5]. This means that the signal enhancement originates from the electronic coupling and cooperative behavior of QDs. These findings show that the cooperative quantum dynamics provide a new route to advanced optoelectronic technology such as nonlinear amplifiers.Part of this work was supported by JSPS KAKENHI (JP19H05465, JP22H01990, and JP23K17877), JST PRESTO (JPMJPR23H3), and JST CREST (JPMJCR21B4).

Mechanochemical Synthesis of Sodium-Ion Conducting Chloride NaTaCl6

All-solid-state sodium batteries have been attracting attentions owing to their high energy density and safety. Solid electrolytes play a significant role in the electrochemical performances of all-solid-state batteries. Chloride-based solid electrolytes are particularly important for achieving high energy densities because of their high oxidation stability, ionic conductivity, and formability. Fewer sodium-ion conducting chlorides have been developed compared to lithium-ion conducting materials. It is necessary to discover the chlorides as the end-member of sodium-ion conductors. In this study, we report the development of a new NaTaCl6 chloride as an end-member sodium-ion conductor with high ionic conductivity. NaTaCl6 sample was mechanically prepared using a planetary ball mill apparatus. The X-ray diffraction patterns of the obtained sample displayed a broad pattern similar to the reported NaTaCl6 (ICSD#36519), suggesting that the sample contains both amorphous and crystalline phases. The reference intensity ratio method was used to investigate the weight ratios of the amorphous phases in the sample. The ratio was approximately 45 %. Transmission electron microscopy observations suggested that the sample consisted of the amorphous matrix and crystalline with the crystallite size of approximately 20 nm. The electrical conductivities of the pelletized samples were measured using two-terminal AC electrochemical impedance spectroscopy. The sample pellets were prepared by uniaxial pressing at 360 MPa without heat treatment. The pellet sample had the relative density of 85 % (powder density: 3.32 g cm–3, pellet density: 2.83 g cm–3). The sample shows σ 25ºC of 6.2×10–5 S cm–1, and the activation energy of 0.37 eV. To determine the NaTaCl6 onset oxidation voltage (OOV), linear sweep voltammetry measurement was carried out. The OOV of the sample at 60 ºC was 3.8 V vs. Na15Sn4. To demonstrate the high oxidation stability of NaTaCl6 in all-solid-state sodium batteries, it was used in a positive electrode by mixing Na3V2(PO4)3 as the active material and the buffer layer. The cell exhibited an initial reversible capacity of 96 mAh g–1 and stable cycling after 40 cycles with the capacity retention of 99.5 %. A 3.3 V all-solid-state sodium battery without oxide solid electrolytes was successfully operated. In this study, the NaTaCl6 electrolyte was developed with a high ionic conductivity and oxidation stability.Acknowledgement: This work was partly supported by JSPS KAKENHI (Grant Numbers: JP21H04701 and JP19H05816) and MEXT Program: Data Creation and Utilization-Type Material Research and Development Project Grant Number JPMXP1122712807.

(Invited) Synthesis and Application of 1D vdW Heterostructures Based on Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) with diverse optical and electronic properties (metallic or semiconducting) depending on chiral indices (n, m) have been the key nanomaterials in advanced applications [1,2]. Even though a mixture of metallic and semiconducting SWCNT can be used for bulk and film-form applications such as batteries and solar cells [3], the controlled growth of (n, m) or the sorting of (n, m) is essential for electronics applications such as field effect transistors (FET) [4]. On the other hand, the controlled modulation of properties can also be possible either by employing the inner space of the SWCNTs to encapsulate various materials or by externally wrapping the SWCNT template with additional atomic layers [5]. Here, I mainly discuss the latter case as a one-dimensional (1D) van der Waals (vdW) heterostructure based on SWCNT [6]. We have demonstrated the atomically precise one-dimensional (1D) van der Waals (vdW) heterostructure -- SWCNTs, boron nitride nanotubes (BNNTs), and molybdenum disulfide (MoS2) sequentially wrapped in radial direction -- by chemical vapor deposition in 2020 [6]. One of the obvious extensions of this work is the use of BNNT-SWCNT [7], which have superior semiconductor properties such as field effect transistors [8,9]. We have developed various characterization techniques for BNNT-SWCNT for the growth optimization and quality control of BNNT in various kinds of SWCNT [10-12]. Yet another extension is the various kinds of transition metal dichalcogenides (TMD) nanotubes. We have optimized CVD conditions for various metal dichalcogenides such as tungsten disulfide (WS2), niobium disulfide (NbS2), and molybdenum diselenide (MoSe2) so far in addition to the original MoS2. Here, we further broaden the concept of 1D vdW heterostructure by combining 2 transition metal species. By setting WS2 growth right after the MoS2 growth, we can observe the axial junction of the outermost tube, MoS2 - WS2. The junction is atomically smooth within a few nanometers. On the other hand, by setting the 2 transition metal species at the same CVD time, we can observe {WxMo(1-x)}S2 alloy nanotube. Both axial junction and alloy nanotubes are preferentially monolayers.Part of this work was supported by JSPS KAKENHI Grant Numbers JP23H00174, JP23H05443 and by JST, CREST Grant Number JPMJCR20B5, Japan.

(Invited) Quantitative Prediction of Exciton Dynamics

Thermally activated delayed fluorescence (TADF) is now an established way to convert inhelently dark triplet excitons into light through reverse intersystem crossing (RISC).1-4 To realize the RISC process, minimizing the energy gap (ΔE ST) between S1 and T1 is considered to be effective theoretically, and this has been realized experimentally. At the beginning of the research, RISC had been the rate-limiting process in TADF, although RISC was possible. In such situation, we have shown that acceleration of RISC has now become possible through a variety of methods.5-7 Although excellent TADF materials and highly efficient TADF-based organic light-emitting diodes (OLEDs) have been realized as described above, the fundamental understanding is still insufficient. In the presentation, we first show our recently-proposed method for quantitatively predicting rate constants of all electronic transitions relevant to light emission.8-10 The method proposed here has successfully predicted all rate constants quantitatively and therefore can predict TADF performance precisely. The method also allows quantitative predictions of dynamics (time evolution) of experimentally-obtained rate constants for radiative, non-radiative, intersystem crossing, and RISC as well as exciton population dynamics.11 Such an approach will contribute significantly to the fundamental science of exciton dynamics.We express sincere thanks to my group members. This work was supported by JSPS KAKENHI Grant Numbers JP20H05840 (Grant-in-Aid for Transformative Research Areas, “Dynamic Exciton”). Computation time and NMR measurements were supported by the international Joint Usage/Research Centre at the Institute for Chemical Research, Kyoto University, Japan. Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C., Highly efficient organic light-emitting diodes from delayed fluorescence. Nature 2012, 492, 234. Kaji, H., et al., Purely organic electroluminescent material realizing 100% conversion from electricity to light. Nat. Commun. 2015, 6, 8476. Yang, Z., et al., Recent advances in organic thermally activated delayed fluorescence materials. Chem. Soc. Rev. 2017, 46, 915. Wong, M. Y.; Zysman-Colman, E., Purely organic thermally activated delayed fluorescence materials for organic light-emitting diodes. Adv. Mater. 2017, 29, 1605444. Wada, Y.; Nakagawa, H.; Matsumoto, S.; Wakisaka, Y.; Kaji, H., Organic light emitters exhibiting very fast reverse intersystem crossing. Nat. Photon. 2020, 14, 643. Ren, Y.; Wada, Y.; Suzuki, K.; Kusakabe, Y.; Geldsetzer, J.; Kaji, H., Efficient blue thermally activated delayed fluorescence emitters showingvery fast reverse intersystem crossing. Appl. Phys. Express 2021, 14, 071003. Wada, Y.; Wakisaka, Y.; Kaji, H., Efficient direct reverse intersystem crossing between charge transfer‐type singlet and triplet states in a purely organic molecule. ChemPhysChem 2021, 22, 625. Shizu, K.; Kaji, H., Theoretical determination of rate constants from excited states: Application to benzophenone. J. Phys. Chem. A 2021, 125, 9000. Shizu, K.; Kaji, H., Comprehensive understanding of multiple resonance thermally activated delayed fluorescence through quantum chemistry calculations. Commun. Chem. 2022, 5. Shizu, K.; Ren, Y. X.; Kaji, H., Promoting reverse intersystem crossing in thermally activated delayed fluorescence via the heavy-atom effect. J. Phys. Chem. A 2023, 127, 439.Shizu, K.; Kaji, H., submitted.

Evaluation of Thermal Transport Characteristics of Three-Dimensional Self-Ordered Multilayered Silicon-Germanium Nanodots

1. Background and purpose Silicon-germanium (SiGe) alloys have much lower thermal conductivity than Si and Ge single crystals and are expected to be candidates for next-generation thermoelectric device materials of internet of things society. It is important to achieve both high carrier mobility and low thermal conductivity on the basis of the dimensionless figure of merit [1]. There are several studies on the thermoelectric properties of SiGe with low-dimensional structures such as superlattice and nanodots [2,3] to dramatically decrease thermal conductivity. However, the relationship between the nanoscale thermal properties and the phonon scattering mechanism of self-ordered multilayer SiGe nanodots with high uniformity grown by Stranski-Krastanov [4] mode is unclear. In this study, we demonstrated the thermal transport characteristics of the self-ordered multilayer SiGe nanodots. 2. Experiments Si/SiGe superlattice and nanodots samples were fabricated by reduced pressure chemical vapor deposition. We set to 20 cycles of Si0.65Ge0.35 / Si superlattice, the staggered Si0.65Ge0.35 nanodots (alternately stacked) and the dot-on-dot Si0.65Ge0.35 nanodots (vertically stacked) by changing growth temperature and precursors for Si spacer growth [4], as shown in Fig. 1. Thermal properties were evaluated by the Time Domain Thermoreflectance (TDTR) method. The strain states and Ge fraction were evaluated by Raman spectroscopy. The focal length and wavenumber resolution of the Raman spectrometer were 2,000 mm and 0.1 cm-1, respectively. The excitation light source was a green laser (wavelength: 532 nm). We obtained the Raman spectra of Si-Si, Si-Ge, and Ge-Ge vibrational modes derived from the SiGe regions. 3. Results and discussion Figure 2 shows the thermal conductivity for the SiGe region of the superlattice and nanodots (dot-on-dot and staggered structures) obtained by TDTR method. We found that the SiGe nanodots with the dot-on-dot structure have the highest thermal conductivity, while the SiGe nanodots with the staggered structure and SiGe superlattice have almost the same thermal conductivity. We consider that the heat flow easily penetrates from the top (surface) to the bottom (Si substrate interface) in the dot-on-dot structures. On the other hand, it is possible that the staggered SiGe nanodots can play a sufficient role as a phonon scatterer compared to the dot-on-dot structures since the superlattice structure and the staggered SiGe nanodots have almost the same thermal properties. In conclusion, we demonstrated the possibility of controlling phonon scattering by changing the arrangement of the self-ordered multilayer SiGe nanodots. Acknowledgement This work was supported by JSPS KAKENHI Grant Number 21K14201, Japan.

Analysis of the stimulative effect of arginine on translation initiation of protein synthesis in skeletal muscle

Introduction: Amino acids are not only important precursors for the synthesis of proteins, but also participate in the regulation of major metabolic pathways. Specific amino acids stimulate protein synthesis. Previous studies have shown that arginine (Arg) stimulates protein synthesis at the level of translation initiation through the activation of the mechanistic target of rapamycin complex 1 (mTORC1) in cell culture system; however, little is known about the effect of Arg on protein synthesis in vivo. Here, we evaluated whether Arg stimulates protein synthesis at the level of translation initiation and compared the effects of Arg on translation initiation with those of leucine (Leu), which is well-studied the detail of its stimulative mechanism, in mouse skeletal muscle. Methods: Eighteen hour-fasted mice were intraperitoneally injected with saline or 4.6 mmol/ kg/ body weight of Arg or Leu and subsequently sacrificed and excised gastrocnemius muscles at 1 h after injection. In addition, we used mouse-derived C2C12 myotubes treated with Arg to examine the mechanism by which Arg stimulates translation initiation in mouse skeletal muscle. The cells were preincubated with several kinds of inhibitors for appropriate time and then treated with Arg or Leu. Using homogenate of skeletal muscle and cell lysate, the phosphorylation states of eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6K1), key regulatory factors involved in the translation initiation were measured by immunoblotting as indicators of translation initiation activity. Results: Intraperitoneal injection of either Arg or Leu significantly increased S6K1 phosphorylation compared to the saline-injection, but the increase in 4E-BP1 phosphorylation was observed in Leu-injected mice not in Arg-injected mice. These results suggest that Arg can stimulate translation initiation in skeletal muscle of fasted mice. In C2C12 myotubes, as with Leu, Arg increased both 4E-BP1 and S6K phosphorylation, and these increases were abolished by the treatment of rapamycin, a mTORC1 inhibitor. These data indicate that Arg directly activates mTORC1 pathway as well as Leu. In addition, the treatment of a phosphoinositide 3-kinase (PI3K) inhibitor and a AKT inhibitor completely cancelled Arg-dependent 4E-BP1 and S6K1 phosphorylation; however, the inhibition of Leu-induced 4E-BP1 and S6K1 phosphorylation by these inhibitors were in partial. Furthermore, the inhibitor of the G protein‐coupled receptor family C, group 6, subtype A (GPRC6a), which has been shown to associate with regulation of PI3K/AKT pathway and mTORC1 activation, completely suppressed the increases of 4E-BP1 and S6K1 phosphorylation by Arg. Conclusion:Our data indicate that Arg has the ability to activate translation initiation in mouse skeletal muscle. In addition, the results of our experiments using skeletal muscle cells support the idea that Arg stimulates translation initiation via GPRC6a/PI3K/AKT/mTORC1 pathway in mouse skeletal muscle. Unlike the effects of Arg, it is likely that besides the PI3K/AKT pathway, Leu activates another signaling pathways upstream of mTORC1 to stimulate translation initiation in skeletal muscle. This research was funded by JSPS KAKENHI, grant number 18K05501. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

SERCA mediated thermogenesis during contraction-relaxation cycle in rat skeletal muscle in vivo

BACKGROUND: Across the lifespan, body temperature homeostasis is tightly regulated and impacts various physiological phenomena. In skeletal muscle, heat is produced via contraction-dependent (shivering) and independent (nonshivering) mechanisms, regulating the body temperature and muscle physiology including contractile properties. PURPOSE: In this study, we aimed to reveal the intracellular temperature dynamics in skeletal muscle in vivo during the contraction-relaxation cycle. Additionally, we tested the hypothesis that calcium ion (Ca2+) handling mediated by sarcoplasmic reticulum Ca2+ ATPase (SERCA) is involved in the thermogenesis process during contraction-relaxation cycle in skeletal muscle fibers. METHOD: The spinotrapezius muscle of anesthetized adult male Wistar rats (n = 18) was exteriorized and subjected to microinjection of fluorescent probe Cellular Thermoprobe for Fluorescence Ratio (49.3 μM) for intracellular temperature imaging in vivo. The fluorescence ratio (R: 580 nm / 515 nm) was measured in vivo during temperature increases induced by an external heater for thermoprobe calibration. R was also measured following Ca2+ injection (3.9 nL, 2.0 mM), and Ca2+ injection with SERCA inhibition by cyclopiazonic acid (CPA, 100 μM). RESULTS: The fluorescence ratio linearly increased with the increase of the muscle surface temperature from 25 °C to 40 °C (r2 = 0.97, P &lt; 0.01). The intracellular temperature in muscle was increased and sustained following the Ca2+ injection and this thermogenetic response was significantly suppressed with SERCA inhibition (Ca2+: 38.3 ± 1.4 °C vs Ca2++CPA: 28.3 ± 2.8 °C, P &lt; 0.01 at 1 min following injection). Importantly, elevated muscle temperature occurred predominantly in the muscle relaxation phase that followed the muscle shortening: That shortening occurred immediately and transiently after the Ca2+ injection. CONCLUSION: In this investigation, we demonstrated a novel technique for in vivo intracellular temperature imaging of skeletal muscle. Herein we demonstrate that substantial heat is generated concomitantly with SERCA mediated Ca2+ handling and muscle relaxation. This work was supported by JSPS KAKENHI Grant Numbers 20H04074, 19K22800. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A prospective observational study on hemodynamic risk in cerebral aneurysm growth

Introduction: Hemodynamic factors are thought to play a major role in the development, growth, and rupture of cerebral aneurysms, but the hemodynamics related to enlargement remain unclear. We prospectively enrolled patients with unruptured cerebral aneurysms and performed Computational Fluid Dynamics (CFD) analysis using 3D CT images to investigate differences in hemodynamic environments between aneurysms that grew and those that did not grow over a 3-year period. Methods: This prospective observational study was approved by the National Hospital Organization Central Ethics Review Board. Hemodynamic distributions were examined using ANSYS-CFX software. Patient-specific arterial geometries and inflow velocities were obtained from 3D-CTA and carotid ultrasound Doppler examinations. The distributions of hemodynamic metrics of 17 enlarged and 70 unenlarged aneurysms was compared. In addition, the distributions of hemodynamic metrics of the neck, body, and dome of the aneurysm was also examined in 9 enlarged and 41 non-enlarged cases. A multivariate logistic analysis was performed to investigate the influence of the six hemodynamic metrics, i.e., the time-averaged wall shear stress (TAWSS), time-averaged WSS gradient (TAWSSG), oscillatory shear index (OSI), gradient oscillatory number (GON), transverse WSS (transWSS), and normalized transWSS (NtransWSS) after adjustment forknown risk factors for aneurysm growth, i.e., age, sex, hypertension, smoking history, and aneurysm location, size, and history of subarachnoid hemorrhage. Results: Regarding the distributions of hemodynamic metrics throughout the aneurysm, NtransWSS was significantly higher in the cases with growth than in the cases without growth (odds ratio 2.09, 95% CI 1.02-4.29). the distributions of hemodynamic metrics at each cerebral aneurysm growth site showed that NtransWSS at the dome was significantly higher in the growth cases than in the non-enlargement cases (odds ratio 4.14, 95% CI 1.02-16.80). Conclusion: The data suggest that multidirectional disturbance of wall shear stress is involved in cerebral aneurysm growth, and the disturbance at the dome of the aneurysm may be particularly strongly related. This study was supported by a Grant-in-Aid from the Japanese National Hospital Organization Multi-Center Clinical Research, AMED under grant no. JP15gm0810006h0301 and a JSPS KAKENHI Grant, no. 15K10323. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The development of Japanese-English and English-Japanese parallel corpus, including search system and its utilisation

Parallel corpora play a central role in translation studies, contrastive linguistics, bilingual lexicography and language teaching/learning, facilitating the comparison of linguistic features across languages. But it is challenging to construct a parallel corpus and there are few of them. Also, they can quickly become outdated and unusable. Professor Yasunori Nishina, Faculty of Global Communication, Kobe Gakuin University, Japan, is an expert in applied translation, corpus linguistics and applied linguistics working to develop a website for searching Japanese-English and English-Japanese parallel corpora. He is revitalising an existing unusable, unsearchable corpus with assistance from Lago NLP. He has a keen focus on design as he wants to ensure diversity of genres and translation directions and, in a world first, is incorporating the ability to analyse parallel corpora. The tool that Nishina and Lago NLP are developing with support from the JSPS KAKENHI grant number 20K00692 (and 23K00599 from 2023) is called Parallel Link. Nishina will also collaborate with a researcher at the University of Oxford, UK, where experts who developed the Japanese corpus online search tool are based. The University has established a collaborative relationship with the National Institute for Japanese Language and Linguistics (NINJAL), which is the centre for Japanese language research, and has carried out joint projects of the Oxford NINJAL Corpus of Old Japanese (ONCOJ). Nishina has completed the development of version 1.20 of Parallel Link and intends to develop it to version 2.0 in the coming years.

Self-Repairing Ability of Hybrid Cobalt Hydroxide Nanosheets As Oxygen Evolution Catalysts in Alkaline Electrolytes

Introduction Water electrolysis is a key technology to produce H2 from renewable energy. Because proton exchange membrane water electrolyzers (PEMWE) require noble metals as catalysts, alkaline-type electrolyzers, such as alkaline water electrolyzers (AWE) and anion exchange membrane water electrolysis (AEMWE), have attracted much attention for the use of nonnoble-metal-based catalysts. One of the most important issues of AWE is the degradation of catalysts due to generation of reverse current upon shutdown and power fluctuation. Reverse current hardly generates in AEMWE in principle; however, it possibly generates if an electrolyte is supplied instead of pure water.We have previously reported the self-repairing anode catalysts for AWE [1, 2]. A hybrid cobalt hydroxide nanosheet (denoted as Co-ns, Figure 1a), a Brucite-type cobalt hydroxide modified with tripodal ligands (tris(hydroxymethyl)aminomethane), was dispersed in an alkaline electrolyte. Co-ns is deposited on the anode during the electrolysis at 800 mA/cm2 to form a catalyst layer. After the degradation of the catalyst by potential cycling, Co-ns is deposited to retain the catalytic activity. To develop catalysts with higher activity, durability, and repairing ability, the understanding of the electrochemical deposition of Co-ns is quite important. Here, we demonstrate the mechanism of the electrochemical deposition of Co-ns.ExperimentalCo-ns was synthesized according to our previous report [1]. The Co-ns was dispersed in 1 M KOH electrolyte at varied concentrations of Co-ns. Ni electrodes were used as both working and counter electrodes. Reversible hydrogen electrode (RHE) was used as a reference. Constant current electrolysis at 800 mA/cm2 was applied for 30 min, followed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to evaluate the oxygen evolution reaction (OER) activity and the amount of deposited Co. These processes ware repeated for several times to characterize the deposition behaviors. Similar experiments were performed, using Co(OH)2 or CoOOH instead of Co-ns.Results and DiscussionCo-ns was transformed into CoOOH by the decomposition of the tripodal ligand. The deposited amount of Co was evaluated by CV, in which the charge of the cathodic currents at 0.8–1.6 V vs. RHE (denoted as Q c) was proportional to the amount of Co measured by ICP-AES. Figure 1b shows the plots of Q c vs. duration of electrolysis. The amounts of deposited CoOOH depended on the concentration of Co-ns. The deposition rates (slope of the curves) gradually decreased along with the progress of the catalyst deposition. During the electrolysis, the electrode potential decreased because of the increased OER activity due to the catalyst deposition. Assuming that the deposition of CoOOH is a pseudo first-order reaction, its rate constant was calculated by dividing the deposition rate by the concentration of Co-ns. The rate constants are linearly correlated with the electrode potential (Figure 1c); thus, the deposition was confirmed to be an electrochemical process. The present results mean that the electrochemical deposition of CoOOH is accelerated when the electrode potential increases due to the degradation of catalysts. Therefore, the self-repairing process is automatically controlled by the condition of the electrode.The electrochemical deposition proceeds with Co(OH)2, whereas CoOOH hardly deposited at the same conditions, indicating that the oxidation of Co2+ to Co3+ is an essential step of the electrochemical deposition. The electrochemical deposition of Co(OH)2 was stopped after 60 min of electrolysis because of the autooxidation of Co(OH)2 by dissolving O2. It was shown that Co-ns is stable in an electrolyte saturated with O2 probably because the organic modification suppresses the autooxidation. Thus, it is shown that the organic modification of cobalt hydroxide is crucial to retain the self-repairing ability in an electrolyzer.ConclusionIn conclusion, the potential dependence of the rate constant and the essential step of electrochemical deposition of Co-ns were elucidated through systematic studies using Co-ns and related metal hydroxide catalysts. These findings lead to the design of self-repairing electrocatalysts with high activity, long lifetime, and high self-repairing ability using organic functionalization.Acknowledgement This work was supported by the JSPS KAKENHI (grant number 20H02821). Part of this study uses outcomes of the development of fundamental technology for the advancement of water electrolysis hydrogen production in the advancement of hydrogen technologies and utilization projects (grant number JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) in Japan.

Understanding the Effect of Mechanical Degradation on the Performance of Solid-State Batteries through Particle Simulations

All-solid-state batteries (ASSBs) have garnered significant interest as a promising alternative to conventional lithium-ion batteries, offering improved safety, higher energy density, longer lifespan, faster charging and wider operating temperature range. A key advantage of ASSBs is the use of solid electrolytes (SE), which eliminate the risks associated with flammable liquid electrolytes. However, the complex electrochemical behavior and multi-scale nature of ASSBs pose challenges in designing and optimizing their performance. This study employs Discrete Element Method (DEM) particle-based models to better understand degradation behavior of ASSBs by considering electrochemical reaction, mass and charge transfer, intercalation expansion and material deformationOur simulations were developed in MATLAB and were performed on a half-cell configuration comprising a SE-layer and an anode electrode. The anode electrode was composed of a particle mixture containing active material (AM) and SE. In our simulations, Si was employed as AM, which experiences substantial intercalation expansion during charge cycling 1. Our previously developed DEM model2,3 resolved elastic and plastic deformation of both AM and SE particles which become compressed due to the intercalation expansion. The simulation of intercalation was achieved by integrating the Newman electrochemical model,4 into the DEM mechanical model. Building on our earlier study5, where the Li concentration was resolved within each AM particle, this study is also accounting for the Li-ion potential within each SE particle. Interparticle conduction and diffusion were computed by determining the contact area of AM-AM and SE-SE contacts, which were affected by the compression of the electrode. The electrochemical reaction was calculated at the AM-SE interface using the Butler-Volmer equation, and in addition the influence of compressive stress on the reaction6 was included.Figure 1(a) depicts the Li concentration and Li-ion potential distribution within the half-cell during charging at different states of charge (SOC), while Figure 1(b) provides a 3D view of the distributions at a SOC of 50%. A considerable expansion of the Si anode is evident. The gradients of Li concentration and Li-ion potential signify significant mass and charge transfer resistance during the charging process. Comparing the distribution of the particles, the anode becomes more porous after the first cycle for the same value of SOC. This effect is attributed to the extensive expansion of the Si anode, leading to plastic compression of the SE layer, which becomes more compact after each cycle. The growing porosity diminishes the contact area between particles, ultimately resulting in the degradation of the half-cell's capacity. In addition to SE-layer compaction, this study aims to investigate several degradation mechanisms and their impact on the performance of ASSBs, including the development of shell voids resulting from AM-SE delamination, crack propagation through SE, and fragmentation of AM.The results of this study provide valuable insights into understanding the effect of mechanical degradation on the performance of ASSBs. By improving our understanding of these mechanisms, we can work towards enhancing the durability and lifespan of ASSBs, ultimately contributing to the development of next-generation energy storage systems. Acknowledgment This work was supported by JSPS KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices, Computational & Data Science” (Gp-A03, grant number 19H05815); and MEXT “Program for Promoting Researches on the Supercomputer Fugaku” (Fugaku battery & Fuel Cell Project), grant number JPMXP1020200301. References M. N. Obrovac and L. Christensen, Electrochem. Solid-State Lett., 7, A93 (2004).M. So, G. Inoue, R. Hirate, K. Nunoshita, S. Ishikawa, and Y. Tsuge, J. Electrochem. Soc., 168, 030538 (2021).M. So, G. Inoue, R. Hirate, K. Nunoshita, S. Ishikawa, and Y. Tsuge, Journal of Power Sources, 508, 230344 (2021).J. Newman and K. E. Thomas-Alyea, Electrochemical Systems, 3rd edition., p. 672, Wiley-Interscience, Hoboken, N.J, (2004).M. So, S. Yano, A. Permatasari, T. D. Pham, K. Park, and G. Inoue, Journal of Power Sources, 546, 231956 (2022).G. Bucci, T. Swamy, S. Bishop, B. W. Sheldon, Y.-M. Chiang, and W. C. Carter, J. Electrochem. Soc., 164, A645 (2017). Figure 1

Iridium Oxide Nanorods Supported on Sb-Doped SnO2 As Highly Active Oxygen Evolution Catalysts for PEM Water Electrolysis

With the increasing installation of renewable energy generation systems such as solar and wind power, efficient energy storage devices are required to overcome the problem of fluctuations in the availability of electric energy. In particular, the splitting of water by electrolysis to produce storable hydrogen and oxygen appears to be one of the most promising approaches for large-scale energy storage. Proton exchange membrane water electrolysis (PEMWE) has received a great deal of attention due to its ability to respond quickly to renewable energy fluctuations and to operate at high current densities. However, a key limitation of PEMWE is the high cost associated with the use of high loadings of noble metal Ir catalysts at the anode electrode, which is necessary due to the slow kinetics of the oxygen evolution reaction (OER). Therefore, reducing the Ir loading at the OER electrode is essential to realize large-scale applications of PEMWE. This requires the development of highly active OER catalysts to accelerate the reaction or reduce the overpotential. Herein, we report a remarkably active OER catalyst of Ir oxide with nanorod-like structure supported on antimony-doped tin oxide (Sb-SnO2), showing an order of magnitude increase in Ir mass-specific activity than a commercial IrOx catalyst at 1.5 V vs. RHE. We also investigated the temperature dependence of the OER activity, as a way to elucidate the mechanism of enhanced catalysis, from both experimental and theoretical perspectives.The Sb-SnO2 support material (Sb dopant content 4 at.%) with fused-aggregate network structure was prepared by flame pyrolysis method.1 The as-prepared support powder was annealed at 700 oC for 2 h in air using a rotary kiln furnace. Sb-SnO2 supported IrOx nanorods (NRs) catalyst was synthesized by a colloidal method.2 The obtained IrOx NRs/Sb-SnO2 powder was heat-treated at 350 °C in N2 atmosphere for 2 h and at 150 °C in 1% H2 (N2 balance) for 2 h. The Ir loading was determined to be 49.3 wt.% by inductively coupled plasma optical emission spectrometry (ICP-OES). The OER activity was evaluated in 0.1 M HClO4 at 25 to 80 oC using the rotating disk electrode (RDE) technique.2,3 From Figure 1a, it can be seen that the Sb-SnO2 support particles present an interconnected network structure, which is considered to be beneficial to enhance the electron conduction and gas diffusion in the electrocatalytic reaction. On the support, the majority of IrOx nanoparticles are shown to have coalesced, forming rodlike structures. Figure 1b shows OER polarization curves (iR-corrected and normalized to the Ir mass) of the IrOx NRs/Sb-SnO2 catalyst compared to commercial IrOx catalyst (TANAKA Precious Metals). It is clear that the IrOx NRs/Sb-SnO2 catalyst significantly outperforms the IrOx reference catalyst over the entire potential range, and the OER onset potential of the IrOx NRs/Sb-SnO2 catalyst is lower. At 1.5 V (Figure 1c), the IrOx NRs/Sb-SnO2 catalyst exhibits a mass activity (MA) of 0.40 A mg-1 Ir, which is about 10 times higher than that of the IrOx reference catalyst. This dramatically enhanced activity makes it possible to significantly reduce the Ir loading on the anode of PEMWE. Experimental observations and density functional theory (DFT) calculations suggest that the nanorod geometry and strong metal-support interactions may play an important role in lowering the energy barrier for the crucial first step of the OER, thereby enhancing the OER activity. Acknowledgement This work was partly supported by the JSPS KAKENHI (23H02059) and by the project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

(Invited) Physical Understanding of HfZrO2/Si FeFET Memory and Its AI Applications

Since the discovery of ferroelectricity in HfO2-based dielectric films in 2011 [1], FeFETs using HfO2-based ferroelectric films as gate dielectrics have attracted strong interest and have been intensively studied in the worldwide research community for various applications including memory, logic, and AI computing. In this paper, we present our recent activities on HfZrO2 (HZO)/Si FeFETs memory [2-6] and FeFET reservoir computing [7-9] for low-power memory and AI applications.HZO-based FeFETs are currently expected for a variety of applications such as embedded nonvolatile memory, cross-bar Commutation-in-Memory (CiM), and so on. However, the device operation has not been quantitatively understood yet. One of the fundamental questions in FeFETs is a mismatch between areal surface carrier concentration (Ns) in MOSFETs, ~1013 cm-2 at maximum, and typical polarization (P) values, ~10-20 mC/cm2. These polarization values correspond to Ns higher than 1014 cm-2 and induce an electric field across an interfacial layer (IL) of 30 MV/cm or higher, which could cause oxide breakdown. On the other hand, when a large amount of traps is included in an HZO film or an HZO/IL interface, sufficient P values can be obtained without too high Ns and the electric field [2, 4-6]. Thus, it is very important to experimentally characterize P, Ns, and trapped charge density, which were evaluated by P-V, quasi-static split C-V, and Hall measurements, respectively, [2, 3, 6] for 10-nm-thick HZO/Si n- and p-FeFETs with 0.7-nm-thick SiO2 IL. As a result, it has been found that a high trap density of around 1014 cm-2 is observed in n-FeFETs, while there is almost no hole trapping in p-FeFETs. This high electron trap density leads to the high electric field across the HZO film and resulting high P values in n-FeFETs, which is in contrast to p-FETs. Thus, the larger memory window in n-FeFETs than that in p-FeFET is attributed to the difference in P values with applying the positive and negative gate voltages.On the other hand, we have proposed and demonstrated reservoir computing, which is one of AI calculations using a recurrent neural network, by using HZO/Si FeFETs [7-9]. Reservoir computing has recently been attracting strong attention as a method to realize real-time learning of time-series data at the edge. Furthermore, when this reservoir is represented by hardware that has input-history-dependent and nonlinear dynamics (physical reservoir), we can expect significant improvement in the energy efficiency of AI calculations. In our FeFET reservoir, the time response of a drain current of Si FeFETs was utilized as the virtual nodes. We have experimentally demonstrated high classification accuracy in speech recognition by using this HZO/Si FeFET reservoir computing with parallel data processing [9]. The spoken digit recognition task, which is an example of speech recognition applications, was performed on a basis of multiple frequency channel (cochleagram) data, which were input to multiple FeFETs. The final inference was conducted by a majority vote of the multiple FeFET reservoirs. We introduced several approaches in the proposed FeFET reservoir computing system, such as optimization of the number of virtual nodes per time step, analog and digital input waveforms, the utilization of other currents than the drain current, and the combination of different frequency channels, in order to improve the classification accuracy. The choice of a combination of frequency channels was effective in improving recognition accuracy. Also, combining the time responses of the drain, source, and substrate currents was also important. These various methods additively improved the recognition accuracy. As a result, we have experimentally demonstrated a classification accuracy of 95.9 % in the task to classify the audio waveforms of ‘0’ to ‘9’ spoken digits.This work was supported by JST CREST (JPMJCR20C3) and JSPS KAKENHI (21H01359).

(Invited) Epitaxial Growth Technique for Si1−X Sn x Binary Alloy Thin Films

Silicon tin (Si1−x Sn x ) binary alloys are attractive materials for next-generation Si-based photonics and thermoelectronics. The energy band calculations predicted that the conduction band at the Γ point is more rapidly decreased than the others by the Sn substitution, and direct band gap semiconductors can be realized at more than sufficient Sn content [1], although they varied from 25 to 90% by the calculation methods. The corresponding wavelength range will be matched to the optical communication band, suggesting Si1−x Sn x can be applied to near-infrared light source and detector. Another interest is the dramatic reduction of the thermal conductivity by the Sn substitution owing to the mass-difference phonon scattering. Theoretically [2], the thermal conductivity of bulk Si (145 Wm−1K−1 [3]) can be decreased to ~5 Wm−1K−1 by the 10% Sn substitution; the lowest thermal conductivity (3 Wm−1K−1) is obtained at 50% Sn, which is the lowest value among bulk group-IV alloys. The low thermal conductivity achieves high thermoelectric performance and can help to ensure temperature differences within small thermoelectric generators (TEGs) integrated on Si chips, as is the case of Si nanowire TEGs [4].In contrast to the theoretical studies mentioned above, experimental studies are very limited compared with other group-IV alloys such as silicon germanium and germanium tin. Difficulties of the Si1−x Sn x synthesizing are the extremely low solid solubility of Sn in Si (0.1%), a tenth of that in Ge, and the large (∼20%) mismatch between the Si and α-Sn lattices. Nevertheless, some research groups, including us, showed some possibilities to achieve a high Sn content Si1−x Sn x thin films (x>10%) experimentally; reported the optical properties such as photoluminescence and photo-absorption. However, the technology for freely controlling Sn content is still in its infancy; the Si1−x Sn x ’s thermoelectric properties have not been clarified yet. We will discuss the recent progress on the growth techniques of Si1−x Sn x thin films using solid phase epitaxy/crystallization [5-7], molecular beam epitaxy [8,9], sputtering [10], and the potential in thin-film TEGs application. Acknowledgments This work was partly supported by JSPS KAKENHI (Nos. 19K21971, 20H05188, and 21H01366), PRESTO (No. JPMJPR15R2), and CREST (No. JPMJCR19Q5) from JST, the TEPCO Memorial Foundation, and the Naito Research Grant.

Effect of Pore Size on the Oxygen Evolution Reaction Activity of Hydrogel Electrodes Composed of Hybrid Cobalt Hydroxide Nanosheets

Introduction Alkaline water electrolysis (AWE) is a promising technology for large-scale production of hydrogen from renewable energy; however, the sluggish oxygen evolution reaction leads to a large overvoltage. Porous electrodes with a large specific surface area are useful to achieve high current densities in AWE, whereas mass transport in small pores often reduces the overall current density. We have reported that hydrogel electrodes, possessing a flexible framework composed of interconnected hybrid cobalt hydroxide nanosheets (Co-ns), exhibit enhanced mass transport at high current density.1 Hydrogel electrodes can be regarded as porous electrodes swollen by electrolytes. They are expected to repair cracked surfaces by recombination of microparticles and to optimize the framework structure suitable for mass transport. In this study, we demonstrate the relationship between the pore size of the hydrogel electrodes and the OER activity at high current density. Experiment Co-ns was synthesized by mixing aqueous solutions of 1.0 M tris(hydroxymethyl)aminomethane and 0.1 M CoCl2·6H2O, followed by heating at 90 °C.2 The heating time was varied as 1, 5 and 10 days in order to control the particle size.Electrochemical measurements were performed in a 1.0 M KOH, using a PFA three-electrode cell. Co-ns was dispersed in the electrolyte (200 ppm). Nickel plate, nickel coil, and reversible hydrogen electrode (RHE) were used as working, counter, and reference electrodes, respectively. Co-ns was deposited on the electrode by constant current electrolysis at 800 mA cm–2 for varied time (10 min–100 h). The OER activity was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy for iR correction. Result and Discussion TEM images of the synthesized Co-ns exhibited that the diameter (long axis) of Co-ns increased along with the heating time. Therefore, the samples were named as 1d_21, 5d_34 and 10d_42, based on the heating time (days) and average diameter (nm). The FESEM images of the hydrogels after drying showed that nanosheets were assembled into house-of-cards structures (Figure 1). The assembled structures of Co-ns with different diameters were analogous to each other.The charges of the cathodic peaks (Q c) at 0.8–1.5 V vs. RHE due to Co2+/3+ and Co3+/4+ in cyclic voltammograms were used as a measure of the amount of deposited Co-ns. The linear relationship between Q c and the thickness of catalyst layers exhibited that deposited Co-ns presented uniformly along the thickness of catalyst layers (Figure 2). The slope of this line corresponds to the porosity of the hydrogels. The porosity increased along with the diameter of Co-ns; therefore, the pore size is expected to depend on the diameter of Co-ns because of the analogy of the assembled structure.Polarization curves of representative hydrogels are shifted from the Tafel equation at high current densities, indicating the influence of mass transport (Figure 3). The OER current densities at 1.6 V vs. RHE (i geo-1.6 V) of relatively thin hydrogels were linearly correlated with their thicknesses (Figure 4), though they were saturated for hydrogels with larger thicknesses. In the thicker hydrogels, OER is limited by mass transport of generated O2 and OH– in pores. The order of the limiting current densities were 1d_21 < 5d_34 < 10d_42; thus, the influence of mass transport is lowered for hydrogels with larger pores.In conclusion, the size of Co-ns was used to control the porosity and pore size of hydrogel electrodes. Hydrogel electrodes with larger pore size exhibited better mass transport to achieve higher OER activity at high current density. These insights will contribute to designing an optimal hydrogel as an oxygen evolving electrode. Acknowledgement This work was supported partially by the JSPS KAKENHI from MEXT, Japan. References R. Nakajima, T. Taniguchi, Y. Sasaki, Y. Nishiki, A. Zaenal, T. Nakai, A. Kato, S. Mitsushima, and Y. Kuroda, Autumn Meeting of the Electrochemical Society of Japan, 1P15 (2022).Y. Kuroda, T. Koichi, K. Muramatsu, K. Yamaguchi, N. Mizuno, A. Shimojima, H. Wada, and K. Kuroda, Chem. Eur. J., 23 (2017) 5023. Figure 1

Anionic Effects on Li-Ion Activity and Intercalation Kinetics in Highly Concentrated Electrolytes

Certain highly concentrated electrolytes (HCEs) enhance the charge-transfer reaction rate at the electrode/electrolyte interface in Li-ion batteries. The solvation structure of Li+ in HCEs significantly affects the electrochemical interfacial reaction kinetics.1 However, the effects of different anions on these kinetics have not yet been fully understood. In this study, we investigated the effects of anionic species on the liquid structure and electrochemical reactions of HCEs composed of various Li salts and propylene carbonate (PC).2 Raman spectra revealed that both PC and anions were coordinated to Li+ ions in HCEs and that the concentration of uncoordinated (free) PC changed depending on the anionic species. Consequently, the activity of Li+ in the electrolyte changed depending on the anionic species. The use of Li salts with weakly Lewis basic anions increased the activity of Li+ and decreased the concentration of free PC in HCEs.The activity of Li+ in the electrolyte significantly affected the Li+ intercalation/deintercalation reaction rate of the LiCoO2 thin-film electrode. Electrochemical impedance spectroscopy revealed that the interfacial reaction rate of LiCoO2 was enhanced in the HCEs with anions having weaker Lewis basicity owing to the higher Li+ ion activity. In addition to the Li+ ion activity, the electrolyte viscosity also gives a significant effect on the charge-transfer kinetics at the electrode/electrolyte interface. The effects of salt concentration and anionic species on Li+ ion activity, electrolyte viscosity, and reaction kinetics in the HCEs will be discussed in detail. Acknowledgements : This study was partially supported by the JSPS KAKENHI (Grant No. JP19H05813, JP21H04697, and JP22H00340). References Y. Kondo et al., ACS Appl. Mater. Interfaces 2022, 14, 22706-22718.Y. Ugata et. al., J. Phys. Chem. C 2023, 127, 3977-3987.

Iron Phosphates as Highly Efficient Precatalysts for Oxygen Evolution Reaction and Their in Situ Electrochemical Conversion

Current energy issues have prompted demand for the innovations in constructing a clean and sustainable energy platforms. One of examples for energy carrier to actualize a zero carbon society is hydrogen, which is a promising carbon-free fuel with an excellent weight energy density. Hydrogen production through alkaline water electrolysis using renewable energy resources (light and wind)-derived electricity is an attractive ecofriendly and cost-effective technology because cheap nonprecious electrocatalysts can be employed in alkaline media. However, oxygen evolution reaction (OER) at the anode side in the water electrolysis is basically slow and prevents the widespread applications of water electrolysis. Thus, highly efficient and cheap electrocatalysts for OER are highly desirable.Iron (Fe)-based compounds have recently received much attention as OER electrocatalysts because Fe is a quite earth-abundant metallic element that is a very cheap and non-toxic. Therefore, Fe is a promising candidate as electrocatalyst for OER. Due to the insufficient OER activity on simple Fe oxides, previous studies have attempted to enhance the activity by incorporating Fe and other metallic elements.[1,2] Recently, we established a novel comprehensive structural descriptor for the OER on Fe-based simple and multimetal oxides;[3] i.e., shorter minimum Fe–O bond length in the crystalline structures led to higher OER activity regardless of elemental composition, Fe–O coordination number, and crystal category. Thus, this descriptor enabled us to quickly develop excellent OER catalyst, Ba0.65Ca0.35Fe12O19, comprising extremely short Fe–O bond lengths.[4] Furthermore, we found that post-spinel CaFe2O4 catalyzes OER via "multi-iron-site mechanism" involving a reaction intermediate with O–O direct formation on multiple Fe atoms, and CaFe2O4 consequently displayed outstanding OER activity despite the long Fe–O bond length.[5] However, we speculate that OER activity of Fe-based oxides cannot be further enhanced based on crystal structures, and it necessitates to employ another type of compounds.In this study, we report the OER performances of Fe-based phosphates in alkaline media. We selected three kinds of Fe-based phosphates with distinct crystal structures: trigonal FePO4, trigonal Fe3O3(PO4), and monoclinic Fe4(P2O7)3. The electrochemical measurements and post-characterizations identified the Fe-based phosphates as efficient precatalysts that can be electrochemically converted into highly active Fe-based compounds. Notably, the OER performances of the electrochemically converted Fe-based compounds overcame those of the above-mentioned most active Fe-based multimetal oxides and any previously reported crystalline OER electrocatalysts. Therefore, the Fe-based phosphates are promising candidates as OER precatalysts, which can be in situ converted into excellent OER electrocatalysts, and have further advantages of low price, environmental friendliness, and easy production.[6] The part of this paper is based on results obtained from a project, JPNP14021, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). This paper was funded in part by the JSPS KAKENHI Grant-in-Aid (18H01786), the JST PRESTO (JPMJPR15S3) and CREST (JPMJCR16P3) programs, the Tokuyama Science Foundation, and the “Creation of Life Innovative Materials for Interdisciplinary and International Researcher Development” program of the MEXT. The authors thank Dr. Takeshi Aihara in Tokyo Institute of Technology for fruitful discussions.