Author: Omar, Ahmad × DDC: 620 ×

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Directly Anodized Sulfur-Doped TiO2 Nanotubes as Improved Anodes for Li-ion Batteries
    (Basel : MDPI, 2020) Sabaghi, Davood; Madian, Mahmoud; Omar, Ahmad; Oswald, Steffen; Uhlemann, Margitta; Maghrebi, Morteza; Baniadam, Majid; Mikhailova, Daria
    TiO2 represents one of the promising anode materials for lithium ion batteries due to its high thermal and chemical stability, relatively high theoretical specific capacity and low cost. However, the electrochemical performance, particularly for mesoporous TiO2, is limited and must be further developed. Elemental doping is a viable route to enhance rate capability and discharge capacity of TiO2 anodes in Li-ion batteries. Usually, elemental doping requires elevated temperatures, which represents a challenge, particularly for sulfur as a dopant. In this work, S-doped TiO2 nanotubes were successfully synthesized in situ during the electrochemical anodization of a titanium substrate at room temperature. The electrochemical anodization bath represented an ethylene glycol-based solution containing NH4F along with Na2S2O5 as the sulfur source. The S-doped TiO2 anodes demonstrated a higher areal discharge capacity of 95 µAh·cm−2 at a current rate of 100 µA·cm−2 after 100 cycles, as compared to the pure TiO2 nanotubes (60 µAh·cm−2). S-TiO2 also exhibited a significantly improved rate capability up to 2500 µA·cm−2 as compared to undoped TiO2. The improved electrochemical performance, as compared to pure TiO2 nanotubes, is attributed to a lower impedance in S-doped TiO2 nanotubes (STNTs). Thus, the direct S-doping during the anodization process is a promising and cost-effective route towards improved TiO2 anodes for Li-ion batteries.
  • Thumbnail Image
    Item
    Comparative Study of Onion-like Carbons Prepared from Different Synthesis Routes towards Li-Ion Capacitor Application
    (Basel : MDPI, 2022) Permana, Antonius Dimas Chandra; Ding, Ling; Gonzalez-Martinez, Ignacio Guillermo; Hantusch, Martin; Nielsch, Kornelius; Mikhailova, Daria; Omar, Ahmad
    Li-ion capacitors (LIC) have emerged as a promising hybrid energy storage system in response to increasing energy demands. However, to achieve excellent LIC performance at high rates, along with cycling stability, an alternative anode to graphite is needed. Porous high-surface-area carbons, such as onion-like carbons (OLCs), have been recently found to hold high potential as high-rate-capable LIC anodes. However, a systematic understanding of their synthesis route and morphology is lacking. In this study, OLCs prepared from self-made metal organic frameworks (MOFs) Fe-BTC and Fe-MIL100 by a simple pyrolysis method were compared to OLCs obtained via high-temperature annealing of nanodiamonds. The LICs with OLCs produced from Fe-BTC achieved a maximum energy density of 243 Wh kg−1 and a power density of 20,149 W kg−1. Furthermore, excellent capacitance retention of 78% after 10,000 cycles was demonstrated. LICs with MOF-derived OLCs surpassed the energy and power density of LICs with nanodiamond-derived OLCs. We determined the impact of the MOF precursor structure and morphology on the resulting OLC properties, as well as on the electrochemical performance. Thus, MOF-derived OLCs offer significant potential toward high-performance anode material for LICs, enabling control over structure and morphology, as well as easy scalability for industrial implementation.
  • Thumbnail Image
    Item
    Freestanding MXene‐based macroforms for electrochemical energy storage applications
    (Hoboken, NJ : Wiley, 2023) Lu, Qiongqiong; Liu, Congcong; Zhao, Yirong; Pan, Wengao; Xie, Kun; Yue, Pengfei; Zhang, Guoshang; Omar, Ahmad; Liu, Lixiang; Yu, Minghao; Mikhailova, Daria
    Freestanding MXene-based macroforms have gained significant attention as versatile components in electrochemical energy storage applications owing to their interconnected conductive network, strong mechanical strength, and customizable surface chemistries derived from MXene nanosheets. This comprehensive review article encompasses key aspects related to the synthesis of MXene nanosheets, strategies for structure design and surface medication, surface modification, and the diverse fabrication methods employed to create freestanding MXene-based macroform architectures. The review also delves into the recent advancements in utilizing freestanding MXene macroforms for electrochemical energy storage applications, offering a detailed discussion on the significant progress achieved thus far. Notably, the correlation between the macroform's structural attributes and its performance characteristics is thoroughly explored, shedding light on the critical factors influencing efficiency and durability. Despite the remarkable development, the review also highlights the existing challenges and presents future perspectives for freestanding MXene-based macroforms in the realms of high-performance energy storage devices. By addressing these challenges and leveraging emerging opportunities, the potential of freestanding MXene-based macroforms can be harnessed to enable groundbreaking advancements in the field of energy storage.