Multidimensional correlation analysis between charcoal structure and microbial colonization toward functional biochar design Daisuke Kimura, Yuya Sato, Hiroaki Horiyama, Hirokazu Nosato, Kazuki Imasato, Yoshitomo Kikuchi, Naoyuki Matsumoto Journal of Environmental Chemical Engineering, 2026 Biochar, produced through the thermal conversion of unused biomass, is increasingly recognized as a key technology for achieving carbon neutrality and advancing the circular economy by stabilizing carbon in solid form. Beyond carbon sequestration, recent research has emphasized its potential as a functional material that supports microbial communities. However, the multifactorial structural determinants of microbial colonization remain poorly understood, primarily due to the multidimensional nature of biochar structures, limiting the rational design of functional biochar. In this study, we conducted a comprehensive analysis of diverse charcoal materials to systematically clarify multidimensional relationships between structural features and microbial colonization patterns. Physical and chemical descriptors spanning pore structure, elemental composition, and surface functional groups were obtained from multiple analytical techniques and organized through category-wise dimensionality reduction, while microbial colonization patterns were classified through community-based clustering analysis. The integrated analysis revealed that microbial colonization patterns could be distinguished only by specific combinations of structural features, rather than by individual descriptors alone. In particular, the enrichment of the beneficial microorganism Candidatus Accumulibacter was associated with combined effects of surface chemical characteristics, bulk composition, and pore-related features, rather than with total phosphorus content alone. These results demonstrate that microbial colonization on charcoal materials is governed by multifactorial structural conditions acting in concert. By establishing a data-driven framework that links multidimensional structural information with microbial responses, this study provides practical guidance for future database construction and AI-assisted functional biochar design, supporting the high-value utilization of biomass resources and sustainable environmental technologies. • Multidimensional charcoal structures governed microbial colonization patterns. • Colonization was distinguished only by combinations of physicochemical features. • Preferential colonization of beneficial microbes required combined structures. • A data-driven framework guiding functional biochar design was demonstrated.
Achieving high thermoelectric performance of triple half-Heusler compositions enabled by high-throughput screening Kazuki Imasato, Haruhiko Morito, Hidetoshi Miyazaki, Fumikazu Hosono, Philipp Sauerschnig, Masanobu Miyata, Takao Ishida, Atsushi Yamamoto, Yukari Katsura, Michihiro Ohta Journal of Materials Chemistry A, 2025 The high-throughput experimental exploration of 90 DHH/THH compositions was conducted. MgV 2 Co 3 Sb 3 showed a zT of over 0.7 at 900 K, indicating the effectiveness of the high-throughput experiment to explore new compositions for functional materials.
Simultaneously Enhanced Thermoelectric and Mechanical Properties in Mg3(Sb,Bi)2by MXene Compositing for Automotive Waste Heat Recovery Philipp Sauerschnig, Masaki Naruke, Kazuki Imasato, Atsushi Yamamoto, Takao Ishida, Michihiro Ohta Chemistry of Materials, 2025 In this work, high-efficiency, lightweight, and robust Mg3(Sb,Bi)2-based thermoelectric materials were developed for a series hybrid electric vehicle powered by synthetic fuels (e-fuels) with a lean-burn spark-ignition (SI) internal-combustion engine to reduce greenhouse gas emissions. Our model simulation has demonstrated that the lean-burn process dramatically lowers the waste heat temperature to ∼450 K. By compositing Mg3(Sb,Bi)2-based materials with electrically conductive layered MXeneTi3C2Tx, we successfully enhanced the n-type thermoelectric figure of merit zT in the 300–500 K range as well as its room-temperature compressive strength. Scanning transmission electron microscopy images revealed MXene located at the grain boundaries of Mg3.2SbBi0.99Te0.01, preventing grain growth. The reduced grain size decreased the lattice thermal conductivity, while simultaneously improving the compressive strength. The MXene compositing also improved the chemical homogeneity, decreasing the electrical resistivity. A zT ∼ 1.2 at 473 K was obtained for n-type Mg3.2SbBi0.99Te0.01 + 1.0 wt% MXene. Simulations of the power generation characteristics of thermoelectric modules based on n-type Mg3.2SbBi0.99Te0.01 + 1.0 wt% MXene (with bismuth telluride p-type legs) showed a maximum conversion efficiency ηmax ∼7.9% for 473 K on the hot side and 293 K on the cold side. Using this module for waste heat recovery on the exhaust pipe of the automotive lean-burn SI internal-combustion engines, thermal efficiency under steady-state conditions could be improved by 0.7% and fuel efficiency under WLTC (Worldwide Harmonized Light Vehicles Test Cycle) conditions by 1.4% according to the simulation.
Oxidation Process and Addition of Zn and Te Lead to the Enhancement of Thermoelectric Figure of Merit in p-Type Bi2Te3 Kazuki Imasato, Shinichi Fujimoto, Yu Ikuta, Masanobu Miyata, Noriyuki Saitoh, Noriko Yoshizawa, Atsushi Yamamoto, Takao Ishida, Mikio Koyano, Michihiro Ohta ACS Applied Materials and Interfaces, 2025 To date, Bi2Te3-based systems are the most promising thermoelectric materials near room temperature for Peltier cooling and energy harvesting. Further improvement of the thermoelectric figure of merit zT is required to broaden the application of Bi2Te3-based thermoelectrics. In this study, we investigated the critical role of oxidation in the thermoelectric performance of p-type Bi0.45Sb1.55Te3 and proposed a way to improve the performance. Impurity oxides inevitably formed during the fabrication processes of constituent elements, leading to lowered mobility. To solve this problem, an oxygen getter element, Zn, was added to capture the oxygen from the Bi0.45Sb1.55Te3 matrix to increase the mobility. Moreover, the formed byproduct ZnO effectively scattered heat-carrying phonons simultaneously. The control of the oxidation process and the addition of Zn and Te led to a 30% enhancement in the zT of Bi0.45Sb1.55Te3 with the decoupling of improved electronic properties and reduced lattice thermal conductivity.
Giant Topological Hall Effect and Colossal Magnetoresistance in Heusler Ferromagnet near Room Temperature Premakumar Yanda, Leila Noohinejad, Ning Mao, Nikolai Peshcherenko, Kazuki Imasato, Abhay K. Srivastava, Yicheng Guan, Bimalesh Giri, Avdhesh Kumar Sharma, Kaustuv Manna, Stuart S. P. Parkin, Yang Zhang, Chandra Shekhar, Claudia Felser Advanced Materials, 2025 Colossal magnetoresistance (CMR) is an exotic phenomenon that allows for the efficient magnetic control of electrical resistivity and has attracted significant attention in condensed matter due to its potential for memory and spintronic applications. Heusler alloys are the subject of considerable interest in this context due to the electronic properties that result from the nontrivial band topology. Here, the observation of CMR near room temperature is reported in the shape memory Heusler alloy Ni2Mn1.4In0.6, which is attributed to the combined effects of magnetic field‐induced martensite twin variant reorientation (MFIR) and magnetic field‐induced structural phase transformation (MFIPT). This compound undergoes a structural phase transition from a cubic (austenite‐L21) ferromagnetic (FM) to a monoclinic (martensite) antiferromagnetic (AFM), which leads to an effective increase in the size of the Fermi surface and consequently in CMR. Additionally, it exhibits significant anomalous Hall conductivity in both antiferromagnetic and ferromagnetic phases. Furthermore, it demonstrates a giant topological Hall resistivity (THR) ≈6 µΩ.cm in the vicinity of martensite transition due to the enhanced spin chirality resulting from the formation of magnetic domains with Bloch‐type domain walls. The findings contribute to the understanding of the magnetotransport of Ni‐Mn‐In Heusler alloys, which are prospective candidates for room‐temperature spintronic applications.
Effects of the Fe/Ni ratio in double half-Heusler composition HfFe1–xNixSb Kazuki Imasato, Philipp Sauerschnig, Masanobu Miyata, Takao Ishida, Atsushi Yamamoto, Michihiro Ohta Journal of Materials Chemistry C, 2024 The adjustment of the Fe/Ni ratio in the double half-Heusler composition HfFexNi1−xSb leads to a p-type to n-type transition. The thermoelectric figures of merit zT = 0.36 and 0.22 at 950 K for n- and p-type, respectively, were demonstrated.
Integrating thermoelectric devices in pyrolysis reactors for biochar and electricity co-production Soumei Baba, Kazuki Imasato, Atsushi Yamamoto, Takao Ishida, Michihiro Ohta Energy Conversion and Management X, 2024 • Developed a novel approach to utilize Mizunara biomass for co-producing biochar and electricity. • Demonstrated the integration of thermoelectric devices with pyrolysis reactors to recover waste heat. • Achieved significant enhancements in CO 2 capture and storage using biochar derived from Japanese oak. • Proposed a sustainable solution to Japan’s forestry residue problem, advancing carbon–neutral goals. This study proposed an innovative approach to integrating thermoelectric devices with small-scale pyrolysis reactors by using Mizunara (Japanese oak) as the feedstock for biochar production. The primary objective of the study was to enhance the energy efficiency and carbon sequestration potential of the biochar production process by converting waste heat into electricity through thermoelectric devices. Comprehensive steady-state thermal balance analysis revealed that although covering the entire reactor surface with thermoelectric devices can result in excessive heat loss and reduced biochar yield, strategically limiting the installation area allows efficient power generation without considerably compromising biochar production. This balance between electricity generation and biochar yield is critical for optimizing the system’s efficiency. Historically, small-scale waste-heat power generation has been underdeveloped, but our studies have demonstrated that incorporating naturally cooled thermoelectric devices allows the generation of kilowatt-hour (kWh)-scale electricity from waste heat, which would otherwise be discarded. Furthermore, the analysis revealed that with optimized conditions, the CO 2 equivalent values of the sequestered carbon can be substantially increased, providing a viable solution for long-term carbon storage. The results highlight the potential of this integrated approach to improve the energy efficiency of biochar production and provide a solution for waste-heat management. Moreover, we assessed the implementation effects by assigning reasonable values for the thermoelectric device performance and provide a robust framework for biomass utilization, waste-heat recovery, and CO 2 sequestration.
Achieving Compatible p/n-Type Half-Heusler Compositions in Valence Balanced/Unbalanced Mg1-xVxNiSb Kazuki Imasato, Hidetoshi Miyazaki, Philipp Sauerschnig, Kishor Kumar Johari, Takao Ishida, Atsushi Yamamoto, Michihiro Ohta ACS Applied Materials and Interfaces, 2024 In thermoelectric and other inorganic materials research, the significance of half-Heusler (HH) compositions following the 18-electron rule has drawn interest in developing and exploiting the potential of intermetallic compounds. For the fabrication of thermoelectric modules, in addition to high-performance materials, having both p- and n-type materials with compatible thermal expansion coefficients is a prerequisite for module development. In this work, the p-type to n-type transition of valence balanced/unbalanced HH composition of Mg1-xVxNiSb was demonstrated by changing the Mg:V chemical ratio. The Seebeck coefficient and power factor of Ti-doped Mg0.57V0.33Ti0.1NiSb are -130 μV K-1 and 0.4 mW m-1 K-2 at 400 K, respectively. In addition, the reduced lattice thermal conductivity (κL < 2.5 W m-1 K-1 at 300 K) of n-type compositions was reported to be much smaller than κL of conventional HH materials. As high thermal conductivity has long been an issue for HH materials, the synthesis of p- and n-type Mg1-xVxNiSb compositions with low lattice thermal conductivity is a promising strategy for producing high-performance HH compounds. Achieving both p- and n-type materials from similar parent composition enabled us to fabricate a thermoelectric module with maximum output power Pmax ∼ 63 mW with a temperature difference of 390 K. This finding supports the benefit of exploring the huge compositional space of valence balanced/unbalanced quaternary HH compositions for further development of thermoelectric devices.
Sulfide Thermoelectrics: Materials and Modules Thermoelectric Micro Nano Generators Fundamental Physics Materials and Measurements, 2024
Thermoelectric Properties of Novel Semimetals: A Case Study of YbMnSb2 Yu Pan, Feng‐Ren Fan, Xiaochen Hong, Bin He, Congcong Le, Walter Schnelle, Yangkun He, Kazuki Imasato, Horst Borrmann, Christian Hess, Bernd Büchner, Yan Sun, Chenguang Fu, G. Jeffrey Snyder, Claudia Felser Advanced Materials, 2021
Heat capacity of Mg3Sb2, Mg3Bi2, and their alloys at high temperature Matthias T. Agne, Kazuki Imasato, Shashwat Anand, Kathleen Lee, Sabah K. Bux, Alex Zevalkink, Alexander J.E. Rettie, Duck Young Chung, Mercouri G. Kanatzidis, G. Jeffrey Snyder Materials Today Physics, 2018
