Fabrication of Cobaltous Sulfide Nanoparticle-Modified 3D MXene/Carbon Foam Hybrid Aerogels for All-Solid-State Supercapacitors

Progress and Perspective in harnessing MXene-carbon-based composites (0-3D): Synthesis, performance, and applications

MXene is recognized as a promising catalyst for versatile applications due to its abundant metal sites, physicochemical properties, and structural formation. This comprehensive review offers an in-depth analysis of the incorporation of carbon into MXene, resulting in the formation of MXene-carbon-based composites (MCCs). Pristine MXene exhibits numerous outstanding characteristics, such as its atomically thin 2D structure, hydrophilic surface nature, metallic electrical conductivity, and substantial specific surface area. The introduction of carbon guides the assembly of MCCs through electrostatic self-assembly, pairing positively charged carbon with negatively charged MXene. These interactions result in increased interlayer spacing, reduced ion/electron transport distances, and enhanced surface hydrophilicity. Subsequent sections delve into the synthesis methods for MCCs, focusing on MXene integrated with various carbon structures, including 0D, 1D, 2D, and 3D carbon. Comprehensive discussions explore the distinctive properties of MCCs and the unique advantages they offer in each application domain, emphasizing the contributions and advancements they bring to specific fields. Furthermore, this comprehensive review addresses the challenges encountered by MCCs across different applications. Through these analyses, the review promotes a deeper understanding of exceptional characteristics and potential applications of MCCs. Insights derived from this review can serve as guidance for future research and development efforts, promoting the widespread utilization of MCCs across a broad spectrum of disciplines and spurring future innovations.

Amorphous MoS3-modified porous Co4S3-embedded N,S co-doped carbon polyhedron as new high-capacity and high-rate anode materials for sodium-ion half/full cells

In this study, amorphous MoS3-modified porous Co4S3-embedded N,S co-doped carbon polyhedron (Co4S3@NSC/MoS3) was rationally prepared via a multi-step method. One-dimensional linear-like MoS3 with a high specific capacity of 894 mAh g-1 and abundant active sites compensated for the low capacity of Co4S3, thus enhancing the sodium ion storage capacity of the entire electrode. Moreover, three-dimensional N,S co-doped carbon networks (NSC) significantly inhibited large volumetric fluctuations in Co4S3 and MoS3, thereby sustaining the structural stability and enhancing the electron transfer efficiency. As a new anode material for sodium-ion half batteries, the constructed Co4S3@NSC/MoS3 with rapid Na+ diffusion and charge transfer kinetics demonstrated better sodium storage properties than Co4S3@NSC. At a rate of 0.5 A g-1 over 100 cycles, the reversible specific capacity of Co4S3@NSC/MoS3 reached 594 mAh g-1. Even when cycled at a rate of 2 A g-1 for 600 cycles, the charge capacity was stable at 435 mAh g-1. The rate performance of Co4S3@NSC/MoS3 was also found to be remarkable; when the rate increased to 10 A g-1, the average capacity was retained at 382 mAh g-1. Apart from half cells, reduced graphene oxide (rGO)-modified Na3V2(PO4)3 composite (Na3V2(PO4)3@rGO) was used as the cathode material to match with Co4S3@NSC/MoS3. The assembled full batteries were analyzed and their electrochemical properties were discussed. They also exhibited outstanding rate capability and high-rate long-life cyclic property. Even at 1 A g-1 over 500 cycles, the discharge capacity was stably maintained at 246 mAh g-1. The outstanding sodium storage properties of Co4S3@NSC/MoS3 mainly depended on the cooperative effects of MoS3 and Co4S3@NSC, indicating the potential application of Co4S3@NSC/MoS3 in energy storage fields.

MnOx-decorated MOF-derived nickel-cobalt bimetallic phosphide nanosheet arrays for overall water splitting

Exploring non-noble metal dual-functional electrocatalysts with high activity and stability for water splitting is highly desirable. In this study, using zeolitic imidazolate framework-L (ZIF-L) nanoarrays as the precursor, manganese oxide-decorated porous nickel-cobalt phosphide nanosheet arrays have been prepared on nickel foam (denoted as MnOx/NiCoP/NF) through cation etching, phosphorization and electrodeposition, which are utilized as an efficient dual-functional electrocatalyst for overall water splitting. The hierarchical porous nanosheet arrays provide abundant active sites for the electrochemical process, while the MnOx modification induces strong interfacial interaction, benefiting charge transfer. Thus, the MnOx/NiCoP/NF exhibits excellent electrocatalytic activity toward the hydrogen evolution reaction (HER, overpotential of 93 mV at 10 mA cm-2), oxygen evolution reaction (OER, overpotential of 240 mV at 10 mA cm-2) and overall water splitting (cell voltage of 1.59 V at 10 mA cm-2). Furthermore, it shows superior stability during continuous overall water splitting for 200 h. This work provides a simple and effective approach for developing efficient non-noble metal dual-functional catalysts for overall water splitting.

Improved supercapacitors and water splitting performances of Anderson-type manganese(III)-polyoxomolybdate through assembly with Zn-MOF in a host-guest structure

Enhancing performance through the combination of polyoxometalates (POMs) clusters with metal-organic frameworks (MOFs) that contain various transition metals is a challenging task. In this study, we synthesized a polyoxometalate-based metal-organic framework (POMOF) named HRBNU-5 using a solvothermal method. HRBNU-5 is composed of Zn[N(C4H9)4][MnMo6O18{(OCH2)3CNH2}2]@Zn3(C9H3O6)2·6C3H7NO, which includes two components: Zn[N(C4H9)4][MnMo6O18{(OCH2)3CNH2}2]·3C3H7NO ({Zn[MnMo6]}) and Zn3(C9H3O6)2·3C3H7NO (Zn-BTC). Structural characterization confirmed the host-guest structure, with Zn-BTC encapsulating {Zn[MnMo6]}. In a three-electrode system, HRBNU-5 exhibited a specific capacitance of 851.3 F g-1 at a current density of 1 A/g and retained high stability (97.2 %) after 5000 cycles. Additionally, HRBNU-5 performed well in aqueous-symmetric/asymmetric supercapacitors (SSC/ASC) in terms of energy density and power density in a double-electrode system. Moreover, it demonstrated excellent catalytic performance in a 1.0 M KOH solution, with low overpotentials and Tafel slopes for hydrogen and oxygen evolution reactions: 177.1 mV (η10 HER), 126.9 mV dec-1 and 370.3 mV (η50 OER), 36.3 mV dec-1, respectively, surpassing its precursors and most reported studies. HRBNU-5's positive performance is attributed to its host-guest structure, high electron-transfer conductivity, and porous structure that enhances efficient mass transport. This work inspires the design of Anderson-type POMOF electrode materials with multiple active sites and a well-defined structure.

Unleashing the Potential of MXene-Based Flexible Materials for High-Performance Energy Storage Devices

Since the initial discovery of Ti3 C2 a decade ago, there has been a significant surge of interest in 2D MXenes and MXene-based composites. This can be attributed to the remarkable intrinsic properties exhibited by MXenes, including metallic conductivity, abundant functional groups, unique layered microstructure, and the ability to control interlayer spacing. These properties contribute to the exceptional electrical and mechanical performance of MXenes, rendering them highly suitable for implementation as candidate materials in flexible and wearable energy storage devices. Recently, a substantial number of novel research has been dedicated to exploring MXene-based flexible materials with diverse functionalities and specifically designed structures, aiming to enhance the efficiency of energy storage systems. In this review, a comprehensive overview of the synthesis and fabrication strategies employed in the development of these diverse MXene-based materials is provided. Furthermore, an in-depth analysis of the energy storage applications exhibited by these innovative flexible materials, encompassing supercapacitors, Li-ion batteries, Li-S batteries, and other potential avenues, is conducted. In addition to presenting the current state of the field, the challenges encountered in the implementation of MXene-based flexible materials are also highlighted and insights are provided into future research directions and prospects.

A self-sacrificing template strategy: In-situ construction of bimetallic MOF-derived self-supported CuCoSe nanosheet arrays for high-performance supercapacitors

Transition metal selenides (TMSs) are viewed as a prospective high-capacity electrode material for asymmetric supercapacitors (ASCs). However, the inability to expose sufficient active sites due to the limitation of the area involved in the electrochemical reaction severely limits their inherent supercapacitive properties. Herein, a self-sacrificing template strategy is developed to prepare self-supported CuCoSe (CuCoSe@rGO-NF) nanosheet arrays by in situ construction of copper-cobalt bimetallic organic framework (CuCo-MOF) on rGO-modified nickel foam (rGO-NF) and rational design of Se2- exchange process. Nanosheet arrays with high specific surface area are considered to be ideal platforms for accelerating electrolyte penetration and exposing rich electrochemical active sites. As a result, the CuCoSe@rGO-NF electrode delivers a high specific capacitance of 1521.6 F/g at 1 A/g, good rate performance and an excellent capacitance retention of 99.5% after 6000 cycles. The assembled ASC device has a high energy density of 19.8 Wh kg-1 at 750 W kg-1 and an ideal capacitance retention of 86.2% after 6000 cycles. This proposed strategy offers a viable strategy for designing and constructing electrode materials with superior energy storage performance.

Fabrication, Performance, and Potential Applications of MXene Composite Aerogels

Aerogel, known as one of the remarkable materials in the 21st century, possesses exceptional characteristics such as high specific surface area, porosity, and elasticity, making it suitable for a diverse range of applications. In recent years, MXene-based aerogels and MXene composite aerogels as functional materials have solved some limitations of traditional aerogels, such as improving the electrical conductivity of biomass and silicon aerogels, further improving the energy storage capacity of carbon aerogels, enhancing polymer-based aerogels, etc. Consequently, extensive research efforts have been dedicated to investigating MXene-based aerogels, positioning them at the forefront of material science studies. This paper provides a comprehensive review of recent advancements in the preparation, properties, and applications of MXene-based composite aerogels. The primary construction strategies employed (including direct synthesis from MXene dispersions and incorporation of MXene within existing substrates) for fabricating MXene-based aerogels are summarized. Furthermore, the desirable properties (including their applications in electrochemistry, electromagnetic shielding, sensing, and adsorption) of MXene composite aerogels are highlighted. This paper delves into a detailed discussion on the fundamental properties of composite aerogel systems, elucidating the intricate structure-property relationships. Finally, an outlook is provided on the opportunities and challenges for the mass production and functional applications of MXene composite aerogels in the field of material engineering.

Design and synthesis of novel pomegranate-like TiN@MXene microspheres as efficient sulfur hosts for advanced lithium sulfur batteries†

Lithium–sulfur (Li–S) batteries have the characteristics of low cost, environmental protection, and high theoretical energy density, and have broad application prospects in the new generation of electronic products. However, there are some problems that seriously hinder the Li–S batteries from going from the laboratory to the factory, such as poor stability caused by the large volume expansion of sulfur during charging and discharging, sluggish kinetics of the electrochemical reaction resulting from the low conductivity of the active materials, and loss of active materials arising from the dissolution and diffusion of the intermediate product lithium polysulfides (LiPSs). In this paper, the two-dimensional layered material MXene and TiN are firstly combined by spray drying method to prepare pomegranate-like TiN@MXene microspheres with both adsorption capacity and catalytic effect on LiPSs conversion. The interconnected skeleton composed of MXene not only solves the problem of easy stacking of MXene sheets but also ensures the uniform distribution of sulfur. Without affecting the excellent characteristics of MXene itself, the overall conductivity of the composite electrode material is improved. The TiN hollow nanospheres are coated with MXene layers to form a shell, catalyzing the adsorption of LiPSs and accelerating the transformation of high-order LiPSs to Li₂S₂/Li₂S. As a result, the TiN@MXene cathode delivers a high initial discharge capacity of 1436 mA h g⁻¹ at 0.1C, excellent rate performance of 636 mA h g⁻¹ up to 3C, and an ultralong lifespan over 1000 cycles with a small capacity decay of 0.048% per cycle at the current density of 1.0C.

A novel pomegranate-like TiN@MXene microsphere was constructed by a facile spray drying method and synergistically enhanced the conversion of polysulfides in Li–S batteries.

Hollow CoS2 anchored on hierarchically porous carbon derived from Pien Tze Huang for high-performance supercapacitors

The development of electrode materials with a high specific capacitance, power density, and long-term stability is essential and remains a challenge for developing supercapacitors. Cobalt sulfides (CoS₂) are considered one of the most promising and widely studied electrode materials for supercapacitors. Herein, CoS₂ and hierarchical porous carbon derived from Pien Tze Huang waste are assembled into a cobalt sulfide/carbon (CoS₂/PZH) matrix composite using a one-step hydrothermal method to resolve the challenges of supercapacitors. The resulting CoS₂/PZH composite material exhibits a hierarchical porous structure with hollow CoS₂ embedded in a PZH framework. The uniform dispersion of the hierarchical porous structure CoS₂/PZH is achieved due to the PZH framework, while the uniform decoration of the porous PZH with the hollow CoS₂ prevents the PZH from stacking easily. Moreover, the excellent synergistic effect of the hierarchical porous and hollow structure of CoS₂/PZH can shorten the electron/ion diffusion channels, expose additional active sites, and provide stable structures for subsequent reactions. As a result, the CoS₂/PZH composite material displays a high initial specific capacity of 447.5 F g^-1 at 0.5 A g^-1, a high energy density of 22.38 W h kg^-1, and long-term cycling stability (a retention rate of 92.3% over 10 000 cycles at 5 A g^-1).

Three-Dimensional MXenes for Supercapacitors: A Review

Supercapacitors have the characteristics of high power density and long cycle life, but the low energy density limits their further development. The 2D transitional metal carbides/nitrides (MXenes) show great application prospects in the field of supercapacitors due to their superior volumetric capacitance, metallic-like conductivity, tunable surface terminations, and structural advantages. However, like other 2D materials, MXenes suffer from the inevitable problem of nanosheet restacking and aggregation, which reduces the overall active surface sites and blocks the accessibility of the electrolyte ions. The transformation of 2D MXene nanosheets into 3D architectures is proven effective to overcome the restacking problem. The review briefly summarizes the preparation strategies of 3D MXene materials, including template-assisted method, framework-assisted method, chemical assembly method, foaming method, and other methods with the discussion centered on the performances of 3D MXenes in supercapacitors. Finally, an outlook on the current progress and opportunities is given to highlight the increasing popularity of 3D MXenes in supercapacitors.

Two-dimensional material-based functional aerogels for treating hazards in the environment: synthesis, functional tailoring, applications, and sustainability analysis

Environmental pollution is a global problem that endangers human health and ecological balance. As a new type of functional material, two-dimensional material (2DM)-based aerogel is one of the most promising candidates for pollutant detection and environmental remediation. The porous, network-like, interconnected three-dimensional (3D) structure of 2DM-based aerogels can not only preserve the characteristics of the original 2DMs, but also bring many distinct physical and chemical properties to offer abundant active sites for adsorbing and combining pollutants, thereby facilitating highly efficient monitoring and treatment of hazardous pollutants. In this review, the synthesis methods of 2DM aerogels and their broad environmental applications, including various sensors, adsorbents, and photocatalysts for the detection and treatment of pollutants, are summarized and discussed. In addition, the sustainability of 2DM aerogels compared to other water purification materials, such as activated carbon, 2DMs, and other aerogels are analyzed by the Sustainability Footprint method. According to the characteristics of different 2DMs, special focuses and perspectives are given on the adsorption properties of graphene, MXene, and boron nitride aerogels, as well as the sensing and photocatalytic properties of transition metal dichalcogenide/oxide and carbon nitride aerogels. This comprehensive work introduces the synthesis, modification, and functional tailoring strategies of different 2DM aerogels, as well as their unique characteristics of adsorption, photocatalysis, and recovery, which will be useful for the readers in various fields of materials science, nanotechnology, environmental science, bioanalysis, and others.

Recent Progress on Two-Dimensional Carbon Materials for Emerging Post-Lithium (Na+, K+, Zn2+) Hybrid Supercapacitors

The hybrid ion capacitor (HIC) is a hybrid electrochemical energy storage device that combines the intercalation mechanism of a lithium-ion battery anode with the double-layer mechanism of the cathode. Thus, an HIC combines the high energy density of batteries and the high power density of supercapacitors, thus bridging the gap between batteries and supercapacitors. Two-dimensional (2D) carbon materials (graphite, graphene, carbon nanosheets) are promising candidates for hybrid capacitors owing to their unique physical and chemical properties, including their enormous specific surface areas, abundance of active sites (surface and functional groups), and large interlayer spacing. So far, there has been no review focusing on the 2D carbon-based materials for the emerging post-lithium hybrid capacitors. This concept review considers the role of 2D carbon in hybrid capacitors and the recent progress in the application of 2D carbon materials for post-Li (Na+, K+, Zn2+) hybrid capacitors. Moreover, their challenges and trends in their future development are discussed.