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Enhanced pseudocapacitive energy storage and thermal stability of Sn²⁺ ion-intercalated molybdenum titanium carbide (Mo₂TiC₂) MXene.

ABSTRACT: Electrochemical energy-storage (EES) devices are a major part of energy-storage systems for industrial and domestic applications. Herein, a two-dimensional (2D) transition metal carbide MXene, namely Mo₂TiC₂, was intercalated with Sn ions to study the structural, morphological, optical, and electrochemical energy-storage effects. The Sn²⁺-intercalated modified layered structure, prepared via a facile liquid-phase pre-intercalated cetyltrimethylammonium bromide (CTAB) method, showed a higher surface area of 30 m² g^-1, low band gap of 1.3 eV, and large interlayer spacing of 1.47 nm, as compared to the pristine Mo₂TiC₂. The Sn@Mo₂TiC₂ electrode showed a high specific capacitance of 670 F g^-1, representing a large diffusion control value compared to pure Mo₂TiC₂ (212 F g^-1) at a scan rate of 2 mV s^-1. The modified electrode also presented long-term cyclic performance, high-capacity retention and coulombic efficiency measured over 10 000 cycles. The Sn@Mo₂TiC₂ electrode showed much improved electrocatalytic efficiency, which may open up ways to employ double-transition 2D MXenes in energy-storage devices.

SUBMITTER: Ali I

PROVIDER: S-EPMC9641580 | biostudies-literature | 2022 Nov

REPOSITORIES: biostudies-literature

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Enhanced pseudocapacitive energy storage and thermal stability of Sn2+ ion-intercalated molybdenum titanium carbide (Mo2TiC2) MXene.

Ali Irfan I Haider Zulqarnain Z Rizwan Syed S

RSC advances 20221108 49

Electrochemical energy-storage (EES) devices are a major part of energy-storage systems for industrial and domestic applications. Herein, a two-dimensional (2D) transition metal carbide MXene, namely Mo2TiC2, was intercalated with Sn ions to study the structural, morphological, optical, and electrochemical energy-storage effects. The Sn2+-intercalated modified layered structure, prepared via a facile liquid-phase pre-intercalated cetyltrimethylammonium bro ...[more]

PMID: 36380943

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Project description:Transformations of oxygenates (CO2, CO, H2O, etc.) via Mo2C-based catalysts are facilitated by the high oxophilicity of the material; however, this can lead to the formation of oxycarbides and complicate the identification of the (most) active catalyst state and active sites. In this context, the two-dimensional (2D) MXene molybdenum carbide Mo2CTx (Tx are passivating surface groups) contains only surface Mo sites and is therefore a highly suitable model catalyst for structure-activity studies. Here, we report that the catalytic activity of Mo2CTx in Fischer-Tropsch (FT) synthesis increases with a decreasing coverage of surface passivating groups (mostly O*). The in situ removal of Tx species and its consequence on CO conversion is highlighted by the observation of a very pronounced activation of Mo2CTx (pretreated in H2 at 400 °C) under FT conditions. This activation process is ascribed to the in situ reductive defunctionalization of Tx groups reaching a catalyst state that is close to 2D-Mo2C (i.e., a material containing no passivating surface groups). Under steady-state FT conditions, 2D-Mo2C yields higher hydrocarbons (C5+ alkanes) with 55% selectivity. Alkanes up to the kerosine range form, with value of α = 0.87, which is ca. twice higher than the α value reported for 3D-Mo2C catalysts. The steady-state productivity of 2D-Mo2C to C5+ hydrocarbons is ca. 2 orders of magnitude higher relative to a reference β-Μo2C catalyst that shows no in situ activation under identical FT conditions. The passivating Tx groups of Mo2CTx can be reductively defunctionalized also by using a higher H2 pretreatment temperature of 500 °C. Yet, this approach leads to a removal of carbidic carbon (as methane), resulting in a 2D-Mo2C1-x catalyst that converts CO to CH4 with 61% selectivity in preference to C5+ hydrocarbons that are formed with only 2% selectivity. Density functional theory (DFT) results attribute the observed selectivity of 2D-Mo2C to C5+ alkanes to a higher energy barrier for the hydrogenation of surface alkyl species relative to the energy barriers for C-C coupling. The removal of O* is the rate-determining step in the FT reaction over 2D-Mo2C, and O* is favorably removed in the form of CO2 relative to H2O, consistent with the observation of a high CO2 selectivity (ca. 50%). The absence of other carbon oxygenates is explained by the energetic favoring of the direct over the hydrogen-assisted dissociative adsorption of CO.

Dataset Information

Enhanced pseudocapacitive energy storage and thermal stability of Sn²⁺ ion-intercalated molybdenum titanium carbide (Mo₂TiC₂) MXene.

Publications

Enhanced pseudocapacitive energy storage and thermal stability of Sn<sup>2+</sup> ion-intercalated molybdenum titanium carbide (Mo<sub>2</sub>TiC<sub>2</sub>) MXene.

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