Researcher:
Varzeghani, Amir Rahimi

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Phd Student

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Amir Rahimi

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Varzeghani

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Varzeghani, Amir Rahimi

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2018 - 20202

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Researcher Of Publications: search.filters.isAuthorOfPublication.9c6859b8-8e36-4105-8736-1d986d96c991

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    Performance of high capacity Li-ion pouch cells over wide range of operating temperatures and discharge rates
    (Elsevier Science Sa, 2020) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Alipour, Mohammad; Esen, Ekin; Varzeghani, Amir Rahimi; Kızılel, Rıza; PhD Student; PhD Student; PhD Student; Researcher; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 114475
    Operating temperature of Lithium-ion batteries (LIBs) significantly affects their electrochemical-thermal performance, cycle life, and cost. This study presents the thermal and electrochemical performance of 20 Ah LiFePO4 cells for 8 current rates (0.2C-5C) at 8 operating temperatures (-20 degrees C to 50 degrees C). Results show that the effects of operating temperature and current rate on cell performance differ above 10 degrees C, between 10 degrees C and 0 degrees C, and at subzero temperatures. Based on the electrochemical impedance spectroscopy (EIS) measurements, significantly higher bulk and charge-transfer resistances in conjunction with the lower diffusion coefficients results in poor battery efficiency at subzero temperatures. Optimum operating condition is 50 degrees C at a rate of 0.2C, in terms of utilized power and capacity, while a considerable power loss and capacity decrease occur below 20 degrees C. Furthermore, increasing the current rate is detrimental above 0 degrees C, whereas it improves cell performance at -10 degrees C, in terms of cell capacity. Moreover, cell temperature reaches an undesirable value at 50 degrees C and 5C rate, thus a thermal management system is necessary for high capacity LiFePO4 cells at higher temperatures and/or at higher C-rates. Additionally, temperature differences on the surface of high capacity cells reach 10 degrees C below room temperature at high current rates which can lead to nonuniform material utilization, and consequently cell failures. Finally, the cycle life of 20 Ah LiFePO4 cells decreases dramatically as discharge current rate increases. (C) 2020 Elsevier B.V. All rights reserved.
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    Electrocatalytic reduction of CO2 to produce higher alcohols
    (Royal Soc Chemistry, 2018) N/A; N/A; N/A; Department of Chemistry; Munir, Shamsa; Varzeghani, Amir Rahimi; Kaya, Sarp; Researcher; PhD Student; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 116541
    Electrodeposited and thermally oxidized copper surfaces have been documented in recent years to produce simple alcohols. In this work, we endeavored to study the electrochemical reduction of CO2 at different electrodes prepared via the electrodeposition method, namely, Cu-Cu2O, Cu-Cu2O-ZnO, and Cu-ZnO. In addition, thermally oxidized Cu (Cu-TO) was also investigated. C1, C2, and C3 species were produced on Cu-Cu2O-ZnO, Cu-Cu2O, and Cu-ZnO. The highest faradaic efficiency (FE of 97.4%) of the liquid products (methanol, formate, n-propanol, acetone) was evidenced on Cu-ZnO. The formation of C3 species with high FE on the Cu-ZnO electrode is attributed to the fast C-C-C coupling at the Cu-Zn interface. on thermally oxidized Cu, the total FE of the liquid products (methanol, formate, ethanol, acetate, n-propanol) was found to be 58.51%, which is considerably closer to the already reported values for these electrodes. Moreover, the Cu-Cu2O-ZnO electrode revealed selectivity toward methanol production. Detailed morphological and elemental analyses of the electrode, performed using XPS, Raman spectroscopy, and FESEM, as well as activity measurements to obtain an insight into the mechanistic pathways, reveal that C-C coupling is favored on Cu-0 sites rather than Cu2O. Moreover, methanol formation seems to proceed via O coordination of CO2 to Cu-Cu2O surface having (100) facets, whereas C coordination is favored on Cu-TO with (111) exposed faces, resulting in Cu-0 sites. The localized formation of ZnO nanoflowers was observed on Cu-ZnO electrodes after the electrochemical reduction of CO2, which is attributed to the mechanistic pathway involving chemical steps, leading to the formation of C3 species.