In recent years, the rapidly growing attention on MXenes makes the material a rising star in the 2D materials family. Although most researchers' interests are still focused on the properties of bare ...MXenes, little attention has been paid to the surface chemistry of MXenes and MXene‐based nanocomposites. To this end, this Review offers a comprehensive discussion on surface modified MXene‐based nanocomposites for energy conversion and storage (ECS) applications. Based on the structure and reaction mechanism, the related synthesis methods toward MXenes are briefly summarized. After the discussion of existing surface modification techniques, the surface modified MXene‐based nanocomposites and their inherent chemical principles are presented. Finally, the application of these surface modified nanocomposites for supercapacitors (SCs), lithium/sodium–ion batteries (LIBs/SIBs), and electrocatalytic water splitting is discussed. The challenges and prospects of MXene‐based nanocomposites for future ECS applications are also presented.
Recently, MXenes have gained increasing attention in the field of energy conversion and storage (ECS). Meanwhile, the unique surface chemistry of MXenes endows them with great potential in the construction of 2D based nanocomposites. To this end, the present work offers a comprehensive summary of surface modified MXene‐based nanocomposites for ECS applications.
Herein, the authors present the development of novel 0D–2D nanohybrids consisting of a nickel‐based bimetal phosphorus trisulfide (Ni1−xFexPS3) nanomosaic that decorates on the surface of MXene ...nanosheets (denoted as NFPS@MXene). The nanohybrids are obtained through a facile self‐assemble process of transition metal layered double hydroxide (TMLDH) on MXene surface; followed by a low temperature in situ solid‐state reaction step. By tuning the Ni:Fe ratio, the as‐synthesized NFPS@MXene nanohybrids exhibit excellent activities when tested as electrocatalysts for overall water splitting. Particularly, with the initial Ni:Fe ratio of 7:3, the obtained Ni0.7Fe0.3PS3@MXene nanohybrid reveals low overpotential (282 mV) and Tafel slope (36.5 mV dec−1) for oxygen evolution reaction (OER) in 1 m KOH solution. Meanwhile, the Ni0.9Fe0.1PS3@MXene shows low overpotential (196 mV) for the hydrogen evolution reaction (HER) in 1 m KOH solution. When integrated for overall water splitting, the Ni0.7Fe0.3PS3@MXene || Ni0.9Fe0.1PS3@MXene couple shows a low onset potential of 1.42 V and needs only 1.65 V to reach a current density of 10 mA cm−2, which is better than the all noble metal IrO2 || Pt/C electrocatalyst (1.71 mV@10 mA cm−2). Given the chemical versatility of Ni1−xFexPS3 and the convenient self‐assemble process, the nanohybrids demonstrated in this work are promising for energy conversion applications.
Novel 0D–2D nanohybrids consisting of a nickel‐based bimetal phosphorus trisulfide (Ni1−xFexPS3) nanomosaic that decorates the surface of MXene nanosheets are obtained through a facile self‐assembly process. The Ni0.7Fe0.3PS3@MXene reveals low overpotential (282 mV) and Tafel slope (36.5 mV dec−1) for oxygen evolution reaction (OER) and the Ni0.7Fe0.3PS3@MXene || Ni0.9Fe0.1PS3@MXene couple shows good overall water splitting performance.
Mo‐Ni alloy‐based electrocatalysts are regarded as promising candidates for the hydrogen evolution reaction (HER), despite their vulnerable stability in alkaline solution that hampers further ...application. Herein, Mo2TiC2Tx MXene, is employed as a support for MoNi4 alloy nanocrystals (NCs) to fabricate a unique nanoflower‐like MoNi4–MXn electrocatalyst. A remarkably strong built‐in electric field is established at the interface of two components, which facilitates the electron transfer from Mo2TiC2Tx to MoNi4. Due to the accumulation of electrons at the MoNi4 sites, the adsorption of the catalytic intermediates and ionic species on MoNi4 is affected consequently. As a result, the MoNi4–MX10 nanohybrid exhibits the lowest overpotential, even lower than 10% Pt/C catalyst at the current density of 10 mA cm−2 in 1 m KOH solution (122.19 vs 129.07 mV, respectively). Furthermore, a lower Tafel slope of 55.88 mV dec−1 is reported as compared to that of the 10% Pt/C (65.64 mV dec−1). Additionally, the MoNi4–MX10 catalyst also displays extraordinary chemical stability in alkaline solution, with an activity loss of only 0.15% per hour over 300 h of operation. This reflects the great potential of using MXene‐based interfacial engineering for the synthesis of a highly efficient and stable electrocatalyst.
The strong built‐in electric field at the interface of the MoNi4–MXn heterostructure facilitates electron transfer and adsorption of intermedia species. Therefore, the nanohybrid shows the lowest overpotential of 122.19 mV at 10 mA cm−2 with Tafel slope of 55.88 mV dec−1 for hydrogen evolution reaction (HER), meanwhile exhibiting excellent stability over 300 h in 1 m KOH solution.
Sodium (Na) metal as an anode is one of the ultimate choices for the high‐energy rechargeable batteries in virtue of its intrinsic high theoretical capacity (1166 mAh g−1) and low redox potential ...(−2.71V vs standard hydrogen electrode (SHE)), as well as its low cost and broad sources. Nevertheless, the dendrite‐related hazards seriously block its practical application. Na dendrite formation mainly emanates from the uncontrolled Na deposition behavior. Therefore, it seems particularly important to employ appropriate strategies towards the homogeneous deposition of Na for the dendrite‐free metal anode. In this review, the challenge of regulating Na homogeneous deposition for dendrite‐free Na anodes is first discussed. Then, recent advances in the strategies of regulating the Na uniform deposition are summarized, including adjusting Na+ flux near the solid‐liquid interface and improving sodiophilicity on the biphase interface. Lastly, perspectives on further research and important factors toward the practical application of high‐energy‐density Na metal batteries are emphasized in detail.
The recent advances in the regulation of uniform Na deposition are summarized and discussed in detail from two aspects: regulating Na+ flux near the solid–liquid interface and improving sodiophilicity on the biphase interface, which can provide guidance for the realization of high‐performance Na metal batteries.
A typical polyanionic based material Na3V2(PO4)2O2F (Na3VPO2F) attracts much interest as a cathode for large‐scale sodium‐ion batteries in consideration of its stable structure and remarkable energy ...density. Nevertheless, the large coulombic attraction and repulsion suffered by the mobile Na+ from structural anions and surrounding Na+, respectively, result in a torpid reaction kinetics and inferior rate capability. Herein, Br−‐doped and Na+ vacancy preinstalled Na3−yVPO2−xBrxF is prepared to dilute the charges on and inside the Na+ transportation tunnel. In virtue of density functional theory analysis, Na3−yVPO2−xBrxF reveals a reduction in the bandgap and an increase in electronic conductivity. Meanwhile, the almost electrostatically shielded tunnel in Na3−yVPO2−xBrxF alleviates the coulombic hindrance imposed on Na+ during its (de)intercalation, which demonstrates a Na+ diffusivity about five times higher than that of Na3VPO2F. Consequently, the Na3−yVPO2−xBrxF cathode shows a superior rate capacity of 77.7 mAh g−1 under 50 C and great cycling property corresponding to a high capacity retention of 94.4% over 800 cycles at 10 C. The assembled Na3−yVPO2−xBrxF//hard‐carbon sodium‐ion full‐cell presents excellent specific energy/power (226 Wh kg−1@15424.2 W kg−1) as well as outstanding long‐term cyclic stability over 1000 cycles at 5 C.
Br‐doped and Na+‐vacancy‐preinstalled Na3V2(PO4)2O2F (Na3−yVPO2−xBrxF) is successfully prepared through a one‐step chemical vapor replacing (CVR) process. In virtue of density functional theory analysis, Na3−yVPO2−xBrxF reveals an increase in electronic conductivity with an almost electrostatically shielded tunnel for fast Na+ diffusion. Therefore, the Na3−yVPO2−xBrxF cathode shows superior Na+ storage capability in both half and full cells.
Ni‐rich layered cathodes with high energy densities reveal an enormous potential for lithium‐ion batteries (LIBs), however, their poor stability and reliability have inhibited their application. To ...ensure their stability over extensive cycles at high voltage, surface/interface modifications are necessary to minimize the adverse reactions at the cathode‐electrolyte interface (CEI), which is a critical factor impeding electrode performance. Therefore, this review provides a comprehensive discussion on the surface engineering of Ni‐rich cathode materials for enhancing their lithium storage property. Based on the structural characteristics of the Ni‐rich cathode, the major failure mechanisms of these structures during synthesis and operation are summarized. Then the existing surface modification techniques are discussed and compared. Recent breakthroughs in various surface coatings and modification strategies are categorized and their unique functionalities in structural protection and performance‐enhancing are elaborated. Finally, the challenges and outlook on the Ni‐rich cathode materials are also proposed.
Surface/interface modifications are an effective strategy to ensure the stability of Ni‐rich layered cathodes with high energy densities for lithium‐ion batteries (LIBs). This review summarized the major failure mechanisms of the Ni‐rich cathode, discussed the existing surface modification techniques, categorized the recent breakthroughs in various surface coatings and modification strategies, and elaborated their unique functionalities in structural protection and performance‐enhancing. Furthermore, we also proposed the challenges and outlook on the Ni‐rich cathode materials.
Manganese dioxide (MnO2) has been widely used in the field of energy storage due to its high specific capacitance, low cost, natural abundance, and being environmentally friendly. However, suffering ...from poor electrical conductivity and high dissolvability, the performance of MnO2 can no longer meet the needs of rapidly growing technological development, especially for the application as electrode material in metal‐ion batteries and supercapacitors. In this review, recent studies on the development of binary or multiple MnO2‐based composites with conductive components for energy storage are summarized. Firstly, general preparing methods for MnO2‐based composites are introduced. Subsequently, the binary and multiple MnO2‐based composites with carbon, conducting polymer, and other conductive materials are discussed respectively. The improvement in their performance is summarized as well. Finally, perspectives on the practical applications of MnO2‐based composites are presented.
The fabrication of binary or multi‐component MnO2‐based composites is summarized in this review, their applications in metal‐ion batteries and supercapacitors, as well as the effects on electrochemical performance, are discussed. The contribution of each component to the final performance is also illustrated.
Polyanionic transition metal polyphosphate (TMPO)‐type Na3V2(PO4)2O2F (NVPO2F) is promising as cathode for large‐scale sodium‐ion batteries (SIBs) on account of its considerable capacity and highly ...stable structure. However, the redox of transition metal and phase transitions along with the (de)intercalation of Na+ lead to its slow kinetics and inferior rate performance. Herein, chlorine (Cl) is applied as a heteropical dopant to obtain Cl‐doped NVPO2F (NVPO2−xClxF) cathode material for SIBs. Density functional theory investigation reveals that Cl doping tunes the localized electronic density and structure in NVPO2F lattice, causing the electron redistribution on vanadium center and dangling anions. Hence, the NVPO2−xClxF cathode exhibits a revised redox behavior of vanadium for Na+ extraction/insertion, increases Na+ diffusion rate, as well as lowers charge transfer resistance. A Na+ storage mechanism of reversible transformations between three phases and V4+/V5+ redox couple for NVPO2−xClxF cathode is verified. The NVPO2−xClxF cathode reveals a high rate capacity of ≈63 mAh g−1 at 30C and great cycle stability over 1000 cycles at 10C. More importantly, outstanding rate property (314 Wh kg−1 at 5850 W kg−1) and cycling capability are obtained for the NVPO2−xClxF//3DC@Se full cell. This study demonstrates a brand‐new strategy to prepare advanced cathode materials for superior SIBs.
Cl‐doped Na3V2(PO4)2O2F (NVPO2−xClxF) cathode material is prepared for the first time via a facile chemical vapor replacing process. The density functional theory investigations verify that the Cl doping tunes the electronic structure and causes the electron redistribution on vanadium center/dangling anions. Therefore, a revised redox behavior of vanadium and increased Na+ diffusivity are achieved, enabling superior rate property.
Na
V
(PO
)
O
F (NVPOF) is widely accepted as advanced cathode material for sodium-ion batteries with high application prospects ascribing to its considerable specific capacity and high working ...voltage. However, challenges in the full realization of its theoretical potential lie in the novel structural design to accelerate its Na
diffusivity. Herein, considering the important role of polyanion groups in constituting Na
diffusion tunnels, boron (B) is doped at the P-site to obtain Na
V
(P
B
O
)O
F (NVP
B
OF). As evidenced by density functional theory modeling, B-doping induces a dramatic decrease in the bandgap. Delocalization of electrons on the O anions in BO
tetrahedra is observed in NVP
B
OF, which dramatically lowers the electrostatic resistance experienced by Na
. As a result, the Na
diffusivity in the NVP
B
OF cathode has accelerated up to 11 times higher, which secures a high rate property (67.2 mAh g
at 60 C) and long cycle stability (95.9% capacity retention at 108.6 mAh g
at 10 C after 1000 cycles). The assembled NVP
B
OF//Se-C full cell demonstrates exceptional power/energy density (213.3 W kg
@ 426.4 Wh kg
and 17970 W kg
@ 119.8 Wh kg
) and outstanding capability to withstand long cycles (90.1% capacity retention after 1000 cycles at 105.3 mAh g
at 10 C).
In this work, Ti3Al1−xSixC2 (x=0, 0.2, 0.4, and 0.6) with Al/Si solid solution structure are synthesized, and the effects of Si on their oxidation behaviors at 1000 °C are evaluated. The addition of ...Si not only contributes to the formation of Ti5Si3 impurity but also affects the composition of the oxide scale. Particularly, the incorporation of Si in the TiO2 lattice is demonstrated, which alters the formation energy of the (110) plane in TiO2, thus leading to the preferential growth of Si‐doped TiO2 to dendritic congeries. Moreover, the Si addition is believed to affect mass transportation during the oxidation process, which accelerates the formation of a continuous Al2O3 layer in the oxide scale. With an optimized Si content, the oxidation of Ti3Al1−xSixC2 is restrained. However, with excess Si content, the continuity of the resulting Al2O3 layer is destroyed, thus the oxidation rate rises again.
The addition of Si alters the mass diffusion in the oxide scale of the Ti3Al1−xSixC2 at 1000 °C, which facilitates the diffusion of Ti, Al, as well as O atoms, thus impacting the structure of the oxide scale and its oxidation resistance.
PDF
