Browsing by Author "Li, M"

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    Copper diffusion rates and hopping pathways in superionic Cu 2Se: implications for thermoelectricity
    (SSRN, 2020-10-21) Nazrul Islam, SMK; Mayank, P; Ouyang, Y; Chen, J; Sagotra, AK; Li, M; Cortie, MB; Mole, RA; Cazorla, C; Yu, DH; Wang, XL; Robinson, RA; Cortie, DL
    The ultra-low thermal conductivity of Cu2Se is well established, but there is so far no consensus on the underlying mechanism. One proposal is that the fast-ionic diffusion of copper suppresses the acoustic phonons. The diffusion coefficients reported previously, however, differ by two orders of magnitude between the various studies and it remains unclear whether the diffusion is fast enough to impact the heat-bearing phonons. Here, a two-fold approach is used to accurately re-determine the diffusion rates. Ab-initio molecular dynamics simulations, incorporating landmark analysis techniques, were closely compared with experimental quasielastic/inelastic neutron spectroscopy. Reasonable agreement was found between these approaches, consistent with the experimental coefficient of 3.1 ± 1.3 10-5 cm2.s-1 and an activation barrier of 140 ± 60 meV. The hopping mechanism includes short 2 Å hops between tetragonal and interstitial octahedral sites. This process forms dynamic Frenkel defects, however, there is no indication of additional broadening in the density-of-states indicating the intrinsic anharmonic interactions dictate the phonon lifetimes. © Preprint article - 2023 Elsevier Inc.
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    Copper diffusion rates and hopping pathways in superionic Cu2Se
    (Elsevier, 2021-08-15) Nazrul Islam, SMK; Mayank, P; Ouyang, Y; Chen, J; Sagotra, AK; Li, M; Cortie, MB; Mole, RA; Cazorla, C; Yu, DH; Wang, XL; Robinson, RA; Cortie, DL
    The ultra-low thermal conductivity of Cu2Se is well established, but so far there is no consensus on the underlying mechanism. One proposal is that the fast-ionic diffusion of copper suppresses the acoustic phonons. The diffusion coefficients reported previously, however, differ by two orders of magnitude between the various studies and it remains unclear whether the diffusion is fast enough to impact the heat-bearing phonons. Here, a two-fold approach is used to accurately re-determine the diffusion rates. Ab-initio molecular dynamics simulations, incorporating landmark analysis techniques, were closely compared with experimental quasielastic/inelastic neutron scattering. Reasonable agreement was found between these approaches, consistent with a diffusion coefficient of 3.1 ± 1.3 x 10−5 cm2.s−1 at 675 K and an activation barrier of 140 ± 60 meV. The hopping mechanism includes short 2 Å hops between tetrahedral and interstitial octahedral sites. This process forms dynamic Frenkel defects. Despite the latter processes, there is no major loss of the phonon mode intensity in the superionic state, and there is no strong correlation between the phonon spectra and the increased diffusion rates. Instead, intrinsic anharmonic phonon interactions appear to dictate the thermal conductivity above and below the superionic transition, and there is only subtle mode broadening associated with the monoclinic-cubic structural transition point, with the phonon density-of-states remaining almost constant at higher temperatures. © 2021 Acta Materialia Inc.
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    In operando‐formed interface between silver and perovskite oxide for efficient electroreduction of carbon dioxide to carbon monoxide
    (Wiley, 2023-04) Wu, XH; Guo, Y; Gu, Y; Xie, F; Li, M; Hu, Z; Lin, HJ; Pao, CW; Huang, YC; Dong, CL; Peterson, VK; Ran, R; Zhou, W; Shao, ZP
    Electrochemical carbon dioxide (CO2) reduction (ECR) is a promising technology to produce valuable fuels and feedstocks from CO2. Despite large efforts to develop ECR catalysts, the investigation of the catalytic performance and electrochemical behavior of complex metal oxides, especially perovskite oxides, is rarely reported. Here, the inorganic perovskite oxide Ag‐doped (La0.8Sr0.2)0.95Ag0.05MnO3–δ (LSA0.05M) is reported as an efficient electrocatalyst for ECR to CO for the first time, which exhibits a Faradaic efficiency (FE) of 84.3%, a remarkable mass activity of 75 A g−1 (normalized to the mass of Ag), and stability of 130 h at a moderate overpotential of 0.79 V. The LSA0.05M catalyst experiences structure reconstruction during ECR, creating the in operando‐formed interface between the perovskite and the evolved Ag phase. The evolved Ag is uniformly distributed with a small particle size on the perovskite surface. Theoretical calculations indicate the reconstruction of LSA0.05M during ECR and reveal that the perovskite–Ag interface provides adsorption sites for CO2 and accelerates the desorption of the *CO intermediate to enhance ECR. This study presents a novel high‐performance perovskite catalyst for ECR and may inspire the future design of electrocatalysts via the in operando formation of metal–metal oxide interfaces. © 2022 The Authors. Carbon Energy published by Wenzhou University and John Wiley & Sons - Open Access CC BY 4.0
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    Topological insulator VxBi1.08-x Sn0.02Sb0.9Te2S as a promising n-type thermoelectric material
    (Elsevier, 2022-10) Chen, L; Zhao, WY; Li, M; Yang, G; Guo, L; Bake, A; Liu, P; Cortie, DL; Zheng, RK; Cheng, ZX; Wang, XL
    As one of the most important n-type thermoelectric (TE) materials, Bi2Te3 has been studied for decades, with efforts to enhance the thermoelectric performance based on element doping, band engineering, etc. In this study, we report a novel bulk-insulating topological material system as a replacement for n-type Bi2Te3 materials: V doped Bi1.08Sn0.02Sb0.9Te2S (V:BSSTS). The V:BSSTS is a bulk insulator with robust metallic topological surface states. Furthermore, the bulk band gap can be tuned by the doping level of V, which is verified by magnetotransport measurements. Large linear magnetoresistance is observed in all samples. Excellent thermoelectric performance is obtained in the V:BSSTS samples, e.g., the highest figure of merit ZT of ~ 0.8 is achieved in the 2% V doped sample (denoted as V0.02) at 530 K. The high thermoelectric performance of V:BSSTS can be attributed to two synergistic effects: (1) the low conductive secondary phases Sb2S3, and V2S3 are believed to be important scattering centers for phonons, leading to lower lattice thermal conductivity; and (2) the electrical conductivity is increased due to the high-mobility topological surface states at the boundaries. In addition, by replacing one third of costly tellurium with abundant, low-cost, and less-toxic sulfur element, the newly produced BSSTS material is inexpensive but still has comparable TE performance to the traditional Bi2Te3-based materials, which offers a cheaper plan for the electronics and thermoelectric industries. Our results demonstrate that topological materials with unique band structures can provide a new platform in the search for new high performance TE materials. © 2022 Elsevier B.V.