As a 2D material, Ti 3 C 2 (MXene) has been recently used as electrodes for electrochemical capacitors. Herein, a two-step procedure is used to obtain a highly opened layer structure for Ti 3 C 2 , which differs from the methods used in the literature for synthesizing exfoliated MXene. First, the mild NH 4 HF 2 etching agent is used to prepare the regular Ti 3 C 2 MXene. Second, KOH is added into the obtained solution for K + to intercalate the MXene. The K + intercalation is found to greatly increase the (002) crystal planar spacing of the Ti 3 C 2 from 10.8 to 12.4 Å. More importantly, this K + -intercalated MXene exhibits a highly opened layer structure, whereas the regular MXene only has a partially opened layer structure. Consequently, the former is expected to allow much more active sites exposed to liquid electrolyte, and also facilitates remarkably higher ion and electron transport efficiency. To investigate their electrochemical capacitance properties, the regular and K + -intercalated Ti 3 C 2 MXenes are used to fabricate binder-free electrodes on nickel foams by an electrophoretic deposition method. The K + -intercalated MXene-based electrode is found to have twice higher specific capacitance than the regular MXene. Furthermore, the K + -intercalated Ti 3 C 2 MXene-based electrode exhibits an excellent cyclic stability.
Ruiming Fang,Zhongqing Yang,Zukhra C. Kadirova,Ziqiang He,Ziqi Wang,Jingyu Ran,Li Zhang
The visible-light photocatalytic reduction of CO 2 becomes a vital breakthrough to alleviate the greenhouse effect and achieve carbon neutrality. In this paper, ultrathin g-C 3 N 4 nanosheets of 1.74 nm were constructed, and K + was successfully doped between layers. The yields of CO and CH 4 are 1.65 μmol·g −1 ·h −1 and 0.15 μmol·g −1 ·h −1 , which are 4.70 and 7.27 times higher than the original g-C 3 N 4 , respectively. The ultra-thin nano-lamellar structure shortens the carrier transmission distance, and the intercalation of K + not only promotes the electron transport between g-C 3 N 4 layers but also changes the original hybrid mode of the catalytic system, thus shortening the band gap and adjusting the energy band structure. In addition, the CO 2 adsorption center of the K + intercalated g-C 3 N 4 is transferred from the coordinated carbon atom to the center of the triazine unit, and the binding energy is obviously increased, which strengthens the CO 2 adsorption. Finally, through in-situ DRIFT characterization, it is speculated that the reaction enhancement mechanism is that the modified catalyst promotes the adsorption and activation of CO 2 , resulting in the production of more intermediates, especially more hydrocarbon intermediates, which is more conducive to the photocatalytic reduction of CO 2 .
S doping is an effective strategy to improve the potassium-ion storage performance of carbon-based materials. However, due to the large atomic radius of S and poor thermal stability, it is challenging to synthesize carbon materials with high sulfur content by solid-phase transformation. In this work, we designed a multi-cavity structure that can confine the molten S during heat treatment and make it fully react, then achieving high S doping (7.6 at. %). As we known, S doping can also effectively increase the active sites of carbon materials to obtain higher capacity. In addition, through different ex/in-situ characterizations and DFT calculations , we confirmed that the S atoms can effectively expand the interlayer spacing of carbon, which facilitates the intercalation/deintercalation reaction of K + , thereby significantly improving the rate performance. Therefore, benefiting from the effect of S-doping, the sample exhibits high reversible specific capacity (401.0 mAh g −1 at 0.1 A/g) and rate performance (167.2 mAh g −1 at 5 A/g). The as-assembled K + hybrid capacitor delivers both high energy density and power density (138.5 W h kg −1 and 7692.5 W kg −1 , respectively). This work provides a new approach to design S content carbon-based materials for high performance K + storage.
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