Graphene Quantum Dots Pinned on Nanosheets-Assembled NiCo-LDH Hollow Micro-Tunnels: Toward High-Performance Pouch-Type Supercapacitor via the Regulated Electron Localization

Aerophobic P-MoS2 on MOF-Derived Co,N-Codoped Carbon Nanosheets with Accelerated H2 Bubble Release Dynamics for Efficient Alkaline Water Splitting at 1000 mA cm-2

Rapid bubble release at high current densities results in the detachment of catalysts and performance degradation, posing a persistent challenge in actual alkaline water electrolysis (AWE). Here, hierarchical nanosheet structures (CoNC@P-MoS2) are constructed, with P-doped MoS2 on the surface of Co,N-codoped carbon. It exhibits low hydrogen evolution reaction overpotentials of 30 and 354 mV at 10 and 1000 mA cm-2 in 1 M KOH, respectively, with a small Tafel slope of 36 mV dec-1. The constructed CoNC@P-MoS2||NiFe-DLH cell requires only 1.44 and 1.92 V to achieve overall water splitting at 10 and 1000 mA cm-2, which outperforms the traditional catalysts like Pt/C||IrO2. The introduction of P stabilizes surface hydroxyl (OH*) and increases the proton penetration depth, thereby greatly enhancing its intrinsic activity. It also makes the surface aerophobic by introducing more microfeatures, which greatly improves the geometric activity by increasing the bubble release rate (∼5.8 times). Low energy consumption of 3.92 kW h Nm-3 was achieved with an energy efficiency close to 80%. Bubble growth kinetics analysis reveals that the time and growth factors for CoNC@P-MoS2 are increased to 0.54 and 11.79 from 0.45 and 6.09 for CoNC, respectively, which highlights its fast bubble reaction dynamics. The results suggest the feasibility of CoNC@P-MoS2 as a potential high-performance catalyst in commercial AWE.

Confined Space Dual-Type Quantum Dots for High-Rate Electrochemical Energy Storage

Owing to the quantum size effect and high redox activity, quantum dots (QDs) play very essential roles toward electrochemical energy storage. However, it is very difficult to obtain different types and uniformly dispersed high-active QDs in a stable conductive microenvironment, because QDs prepared by traditional methods are mostly dissolved in solution or loaded on the surface of other semiconductors. Herein, dual-type semiconductor QDs (Co9S8 and CdS) are skillfully constructed within the interlayer of ultrathin-layered double hydroxides. In particular, the expandable interlayer provides a very suitable confined space for the growth and uniform dispersion of QDs, where Co9S8 originates from in situ transformation of cobalt atoms in laminate and CdS is generated from interlayer pre-embedding Cd2+. Meanwhile, XAFS and GGA+U calculations are employed to explore and prove the mechanism of QDs formation and energy storage characteristics as compared to surface loading QDs. Significantly, the hybrid supercapacitors achieve a high energy density of 329.2 µWh cm-2, capacitance retention of 99.1%, and coulomb efficiency of 96.9% after 22 000 cycles, which is superior to the reported QDs-based supercapacitors. These findings provide unique insights for designing and developing stable, ordered, and highly active QDs.

In Situ Construction of NiCoMn-LDH Derived from Zeolitic Imidazolate Framework on Eggshell-Like Carbon Skeleton for High-Performance Flexible Supercapacitors

Active compounds based on LDH (ternary layered double hydroxide) are considered the perfect supercapacitor electrode materials on account of their superior electrochemical qualities and distinct structural characteristics, and flexible supercapacitors are an ideal option as an energy source for wearable electronics. However, the prevalent aggregation effect of LDH materials results in significantly compromised actual specific capacitance, which limits its broad practical applications. In this research, a 3D eggshell-like interconnected porous carbon (IPC) framework with confinement and isolation capability is designed and synthesized by using glucose as the carbon source to disperse the LDH active material and enhance the conductivity of the composite material. Second, by constructing NiCoMn-LDH nanocage structure based on ZIF-67 (zeolitic imidazolate framework-67) at the nanometer scale the obtained IPC/NiCoMn-LDH electrode material can expose more active sites, which allows to achieve excellent specific capacitance (2236 F g-1/ 310.6 mAh g-1 at 1 A g-1), good rate as well as the desired cycle stability (85.9% of the initial capacitance upon 5000 cycles test). The constructed IPC/NiCoMn-LDH//IPC ASC (asymmetric supercapacitor) exhibits superior capacitive property (135 F g-1/60.1 mAh g-1 at 0.5 A g-1) as well as desired energy density (40 Wh kg-1 at 800 W kg-1).

Regulating the Oxygen Vacancy and Electronic Structure of NiCo Layered Double Hydroxides by Molybdenum Doping for High-Power Hybrid Supercapacitors

Amelioration of nickel-cobalt layered double hydroxides (NiCo-LDH) with a high specific theoretical capacitance is of great desire for high-power supercapacitors. Herein, a molybdenum (Mo) doping strategy is proposed to improve the charge-storage performance of NiCo-LDH nanosheets growing on carbon cloth (CC) via a rapid microwave process. The regulation of the electronic structure and oxygen vacancy of the LDH is consolidated by the density functional theory (DFT) calculation, which demonstrates that Mo doping narrows the band gap, reduces the formation energy of hydroxyl vacancies, and promotes ionic and charge transfer as well as electrolyte adsorption on the electrode surface. The optimal Mo-doped NiCo-LDH electrode (MoNiCo-LDH-0.05/CC) has an amazing specific capacity of 471.1 mA h g-1 at 1 A g-1 , and excellent capacity retention of 84.8% at 32 A g-1 , far superior to NiCo-LDH/CC (258.3 mA h g-1 and 76.4%). The constructed hybrid supercapacitor delivers an energy density of 103.3 W h kg-1 at a power density of 750 W kg-1 and retains the cycle retention of 85.2% after 5000 cycles. Two assembled devices in series can drive thirty LED lamps, revealing a potential application prospect of the rationally synthesized MoNiCo-LDH/CC as an energy-storage electrode material.

Cobalt coordinated carbon quantum dots boosting the performance of NiCo-LDH for energy storage

Transition metal layered double hydroxides have extremely high specific capacitances but suffer from poor rate performance and cycling stability due to their low conductivity and structural stability. In this study, cobalt-coordinated carbon quantum dots (CoCQDs) were designed and synthesized to enhance the energy storage performance of nickel-cobalt layered double hydroxides (NiCo-LDH). Nickel and cobalt ions were co-electrodeposited with the CoCQDs to form a NiCo-LDH based composite electrode (denoted as CoC@LDH). Since the CoCQDs participated in the formation of the NiCo-LDH, the carbon quantum dots could be strongly bonded to the NiCo-LDH nanosheets through coordination interactions. Thus, the conductivity as well as the structure stability of the NiCo-LDH was effectively improved, which greatly boosted the cycle stability and rate performance of the NiCo-LDH. Several CoCQDs with different Co contents (nCoCQDs, n = 0.5, 1.0, 2.0) were fabricated and their effects on the performance of the resultant electrodes nCoC@LDH were investigated. The 1.0CoC@LDH electrode exhibited an impressive specific capacitance of 1867 F g-1 at 1 A-g-1, along with a significantly enhanced capacitance retention of 84.6 % after 6000 cycles at 5 A g-1 (benchmark 49.5 %). This ingenious design provides a new avenue for fabricating pseudo-capacitive materials with unprecedented high performance.

Hierarchical Hollow Carbon Particles with Encapsulation of Carbon Nanotubes for High Performance Supercapacitors

A novel and sustainable carbon-based material, referred to as hollow porous carbon particles encapsulating multi-wall carbon nanotubes (MWCNTs) (CNTs@HPC), is synthesized for use in supercapacitors. The synthesis process involves utilizing LTA zeolite as a rigid template and dopamine hydrochloride (DA) as the carbon source, along with catalytic decomposition of methane (CDM) to simultaneously produce MWCNTs and COx -free H2 . The findings reveal a distinctive hierarchical porous structure, comprising macropores, mesopores, and micropores, resulting in a total specific surface area (SSA) of 913 m2  g-1 . The optimal CNTs@HPC demonstrates a specific capacitance of 306 F g-1 at a current density of 1 A g-1 . Moreover, this material demonstrates an electric double-layer capacitor (EDLC) that surpasses conventional capabilities by exhibiting additional pseudocapacitance characteristics. These properties are attributed to redox reactions facilitated by the increased charge density resulting from the attraction of ions to nickel oxides, which is made possible by the material's enhanced hydrophilicity. The heightened hydrophilicity can be attributed to the presence of residual silicon-aluminum elements in CNTs@HPC, a direct outcome of the unique synthesis approach involving nickel phyllosilicate in CDM. As a result of this synthesis strategy, the material possesses excellent conductivity, enabling rapid transportation of electrolyte ions and delivering outstanding capacitive performance.

Constructing Hierarchical Porous MoO2 @Mo2 N@C Composite via a Confined Pyrolysis Synthetic Strategy Towards Lithium-Ion Battery Anodes

Molybdenum dioxide (MoO2 ) demonstrates a big potential toward lithium-ion storage due to its high theoretical capacity. The sluggish reaction kinetics and large volume change during cycling process, however, unavoidably lead to inferior electrochemical performance, thus failing to satisfy the requirements of practical applications. Herein, we developed a molybdenum-based oxyacid salt confined pyrolysis strategy to achieve a novel hierarchical porous MoO2 @Mo2 N@C composite. A two-step successive annealing process was proposed to obtain a hybrid phase of MoO2 and Mo2 N, which was used to further improve the electrochemical performance of MoO2 -based anode. We demonstrate that the well-dispersed MoO2 nanoparticles can ensure ample active sites exposure to the electrolyte, while conductive Mo2 N quantum dots afford pseudo-capacitive response, which conduces to the migration of ions and electrons. Additionally, the interior voids could provide buffer spaces to surmount the effect of volume change, thereby avoiding the fracture of MoO2 nanoparticles. Benefiting from the aforesaid synergies, the as-obtained MoO2 @Mo2 N@C electrode demonstrates a striking initial discharge capacity (1760.0 mAh g-1 at 0.1 A g-1 ) and decent long-term cycling stability (652.5 mAh g-1 at 1.0 A g-1 ). This work provides a new way for the construction of advanced anode materials for lithium-ion batteries.

GQD@NiFe-LDH Nanosheets for Photocatalytic Activity towards Textile Dye Degradation via Lattice Contraction

The functionalized NiFe-LDH with photosensitized GQDs were synthesized through the hydrothermal route by differing the amount of GQDs solution and studied its efficacy towards the mineralization of textile dyes under visible light. The synthesized samples were characterized by XRD, FESEM, HRTEM, DRUV-Vis, RAMAN, XPS, and BET. The combined effect of the hexagonal carbon lattice in GQD and open layered porous structure of NiFe-LDH nanosheets results in the contraction of the lattice. Different reactive and conventional dyes were taken as representative dyes to evaluate the activity of the as-synthesized photocatalysts. The enhanced electron absorption/donor effect between GQDs and NiFe-LDH, and the growth of oxygen-bridged Ni/Fe-C moieties enable the composite to exhibit better photocatalytic activity. Both photocatalytic activity and characterization results confirmed that the GQD@NiFe-LDH nanocomposite heterostructure synthesized at 160 °C by taking 10 mL of GQDs aqueous solution named GNFLDH10 has a higher degree of crystallinity and has the best photocatalytic efficiency compared to other reported visible light catalysts. Specifically, the above optimized GQD@NiFe-LDH photocatalyst is capable of photo-mineralizing 50 ppm of Reactive Green in 20 min, Reactive Red in 20 min, and Congo Red in 25 min respectively following a direct Z-scheme mechanism with substantial reusability.

Anchored growth of highly dispersed LDHs nanosheets on expanded graphite for fluoride adsorption properties and mechanism

In this study, a new composite with layered double hydroxides (LDHs) anchored grown on expanded graphite (EG) interlayers was prepared by vacuum-assisted intercalation and hydrothermal method. Both sides of EG were completely covered by highly dispersed LDHs nanosheets and formed a sandwich-like structure. The unique structure made expanded graphite/layered double hydroxides (EG/LDHs) composites which had excellent F^- adsorption performance. The adsorption performance of F^- on EG/LDHs was evaluated, and the results indicated that the adsorption process was consistent with the pseudo-second-order kinetic model and the Langmuir model. Pseudo-second-order kinetic model indicated that the adsorption sites were the main factor in the adsorption process. Moreover, the maximum adsorption capacity (Q_m) reached 63.21 mg·g^-1 at 30 min at room temperature, which was better than most of the same type of adsorbents. The highly dispersed of LDHs anchored growth on EG overcame the disadvantage of aggregation, which exposed more adsorption sites and improved the removal efficiency of F^-. In addition, the effects of pH, anion interference, different water quality, and regeneration tests on the EG/LDHs composites were also analyzed, showing that the composites have good stability.

Crystalline phase transformation of Co-MOF derivatives on ordered mesoporous carbons for high-performance supercapacitor applications

Preparation and phase transformation of Co-based metal–organic frameworks derivatives.

A high-performance asymmetric supercapacitor device based on CoO@CoAl-LDH hierarchical 3D nanobouquet arrays

3D core–shell CoO@CoAl-LDH nanobouquet arrays on Ni foam are promising active electrode materials for pseudocapacitors.

Facile Access to Fabricate Carbon Dots and Perspective of Large-Scale Applications

Carbon dots (CDs), fluorescent carbon nanoparticles with particle sizes < 10 nm, are constantly being developed for potential large-scale applications. Recently, methods allow CD synthesis to be carried out on large-scale preparation in a controlled fashion are potentially important for multiple disciplines, including bottom-up strategy, top-down method. In this review, the recent progresses in the research of the methods for large-scale production of CDs and their functionalization are summarized. Especially, the methods of CD synthesis, such as large-scale preparation, hydrothermal/solvothermal, microwave-assisted, magnetic hyperthermia microfluidic and other methods, along with functionalization of CDs, are summarized in detail. By promising applications of CDs, there are three aspects have been already reported, such as enhancing mechanical properties, flame retardancy, and energy storage. Also, future development of CDs is prospected.