Search

Two-dimensional (2D) nanomaterials are some of the most promising bifunctional electrocatalysts that can simultaneously catalyze the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). They have attracted extensive attention owing to their decent electrocatalytic performance and cost advantages. In this review, we first provide an overview of 2D bifunctional electrocatalyst categories including layered double hydroxides, graphitic carbon nitride, metal–organic frameworks, transition metal dichalcogenides, and transition metal carbon/nitrogen compounds, and discuss their structures and synthesis methods, presenting detailed discussion on how the special 2D systems are synthesized and characterized experimentally, which complement a comprehensive understanding of the characteristics of 2D bifunctional electrocatalysts. Moreover, we focus on the recent development of 2D nano-catalysts with both HER and OER activity in the field of overall water splitting and summarize some typical strategies for enhancing the bifunctional activities, including doping, nanocomposite construction, interface formation, defect engineering and morphology modulation. The structure–activity relationships are also discussed with the aim of providing guidance in designing novel 2D bifunctional electrocatalysts. Finally, we explore some of the challenges and perspectives that remain in this rapidly growing field. We believe that the systematic and comprehensive contents of this review will stimulate wider research and attention. [ABSTRACT FROM AUTHOR]

Bismuth (Bi) is a promising alloy-type material for potassium-ion batteries (KIBs). However, its large volume variation during the cycling process remains a great challenge to its practical application. Here, a one-step approach was developed to synthesize a novel Bi-based composite structure comprising Bi nanorod networks confined in a N, S co-doped carbon matrix (Bi∈NS–C). As an anode, the Bi∈NS–C structure successfully integrated the merits of the micro-sized N, S co-doped carbon matrix, which functioned concurrently as a conductive framework and a robust buffer for large volume variation, and the network structure of Bi nanorods which enhanced the reaction kinetics and accommodated the large strain originating from the alloying/dealloying process. As a result, the Bi∈NS–C electrodes exhibited an excellent overall performance, i.e., high rate capabilities of 338 mA h g−1 and 289 mA h g−1 at current densities of 0.5 and 6 A g−1, respectively, and outstanding long-term cycling stability with 91% capacity retention at 5 A g−1 after 1000 cycles. Furthermore, a full KIB with hexacyanoferrate as the cathode and Bi∈NSC as the anode was assembled, which was demonstrated to be able to deliver a decent energy density of 295 W h kg−1 and superior cycling stability with 83% capacity retention after 800 cycles. [ABSTRACT FROM AUTHOR]

Engineering microwave absorption materials with absorption in multiple bands and strong absorption performance in the C-band remains challenging to date. Herein, coaxial stacking VS2 nanosheets (CSVNs) were customized via a facile one-step hydrothermal route for the first time and their microwave absorption (MA) properties were systematically investigated. The complex permittivity and conductivity of CSVNs could be tuned by regulating the hydrothermal reduction temperature. When the reaction temperature was 190 °C, the VS2 nanosheets exhibited unique dual-band absorption characteristics in the C-band and Ku-band. A minimum reflection loss value of −57 dB and an average absorption intensity exceeding 15 dB in both the C (4–8 GHz) and Ku (12–18 GHz) bands were obtained. For the optimized CSVNs, the qualified bandwidth with reflection loss less than −10 dB reached up to 7 GHz, which almost covered the whole measured range of the C- and Ku-bands. Notably, this desirable microwave absorption performance, which probably results from the good conductivity of the 1T-phase CSVNs in the 2H phase, the well-matched impedance and the multiple reflections induced by their distinctive stacking structure, demonstrates that CSVNs are potential outstanding absorbers. More importantly, this study provides an effective strategy to tune the microwave performance of CSVNs by tailoring their structures. [ABSTRACT FROM AUTHOR]

The electrocatalytic nitrogen reduction reaction (e-NRR), an eco-friendly and economical approach to convert nitrogen to ammonia under mild conditions, has received widespread attention in recent years. Defect engineering has been illustrated to be an effective strategy to improve the catalytic activity and selectivity of electrocatalysts via changing the electronic states as well as creating additional active sites for reduction reactions. Thus far, various approaches have been adopted to tune the physical and chemical properties of catalyst materials by means of inducing defects of different types and varying their concentrations or locations in host materials. In this review, the mechanisms and design principles of defective electrocatalysts for the NRR are introduced, and the refined synthesis and characterization techniques of defect engineering are systematically summarized. Based on the recent advances in defect engineering of electrocatalysts for the NRR, the roles of various defect states, such as vacancies and the amorphous phase, in the catalytic enhancement mechanism are comprehensively discussed. Finally, perspectives on the challenges and opportunities in developing new cost-effective and high-efficiency NRR catalysts for practical applications are outlined. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable zinc ion batteries with advantages of low cost and high level of safety have been considered as a promising candidate for large-scale energy storage. In this work, a freestanding, binder-free cathode comprising hierarchical VS2 in the 1T phase grown directly on a stainless steel mesh (VS2@SS) was developed for aqueous zinc ion batteries. The battery exhibited an excellent Zn ion storage capacity of 198 mA h g−1 and stable cycling performance (above 80% capacity retention over 2000 cycles at 2 A g−1). The detailed structural and chemical composition analyses revealed the phase evolution of VS2 and the reversible Zn ion insertion/extraction mechanism during the charge/discharge process. Notably, with an increased mass loading of VS2 over the commercial level (∼11 mg cm−2), a long-term cycling stability with 90% capacity retention after 600 cycles (only 0.017% loss per cycle) could be achieved, which suggests that the electrodes are promising for practical applications. Furthermore, flexible solid-state Zn ion batteries were demonstrated by using the VS2@SS electrodes, and reliable electrochemical performance could be observed even after 200 cycles. [ABSTRACT FROM AUTHOR]

Three-dimensional Co3O4–Co4N porous nanosheet network (PNSN) heterostructures were controllably prepared on hydrophilic carbon cloth (HCC) through in situ plasma nitridation of cobalt hydroxide, and the Co4N grains were observed to grow epitaxially on Co3O4 with an orientation relationship of Co3O4 (331)//Co4N (111). To achieve effective loading of active materials, we demonstrated a simpler and more eco-friendly approach to ameliorate the hydrophilicity of carbon cloth through hydrogen plasma treatment. The Co3O4–Co4N PNSNs/HCC obtained under optimized conditions showed high catalytic activity and excellent stability for the hydrogen evolution reaction (HER) under basic conditions, e.g., a low overpotential of 90 mV at 10 mA cm−2 and a low Tafel slope of 57.8 mV dec−1. It was revealed that the electron transfer from Co3O4 to Co4N enabled the nanohybrid to have a synergistic effect in terms of the desorption of Had and the release of OH− during the HER, leading to an enhanced intrinsic activity. Moreover, a large number of active sites and a fast charge transport capability of the hybrid system also played beneficial roles in achieving an outstanding HER performance. The in situ plasma nitridation technique provides an alternative approach for developing new nitride-hybridized catalysts based on earth-abundant materials for electrolytic hydrogen production. [ABSTRACT FROM AUTHOR]

Although some progress has been made in flexible supercapacitors (SCs), their high energy density, mechanical robustness, and device-level editability and programmability are still highly desirable for the development of advanced portable and miniaturized electronics, especially considering the fact that these flexible devices are likely to experience some mechanical impact and potential damage. Herein, we demonstrate the fabrication of hybrid electrodes containing self-assembled 2D metal–organic framework (MOF)/reduced graphene oxide (rGO) papers, which not only efficiently alleviate the self-restacking of rGO and the MOF but also maintain high electrical conductivity (0.32 Ω cm), excellent flexibility and mechanical properties with a Young's modulus of 34.4 GPa and a tensile strength of 89.9 MPa. In addition, a one-for-two strategy is introduced to construct two types of porous electrodes for flexible asymmetric SCs via a one MOF-derived synthesis route with simply changing metal ion precursors. As a consequence, the flexible asymmetric SCs possess a high volumetric energy density of 1.87 mW h cm−3 and an outstanding volumetric power density of 250 mW cm−3. More importantly, the all-solid-state asymmetric SCs exhibit high editability and bending-tolerance properties and perform very well under various severe service conditions, such as being seriously cut, bent, and heavily loaded. Particularly, the operations of micro-SCs with artistically designed patterns are demonstrated. Being high-strength, easily programmable and connectable in series and in parallel, the editable supercapacitor is promising for developing stylish energy storage devices to power various portable, miniaturized, and wearable devices. [ABSTRACT FROM AUTHOR]

Construction of high-energy density asymmetric supercapacitors is often hindered by unsatisfactory matching between the anode and cathode. Thus, it is crucial to develop composite anodes with high specific capacitance to match that of cathodes. In this work, a novel anode material with well-dispersed Fe2O3 decorated on vertically aligned carbon nanotubes has been synthesized by a facile two-step method, consisting of supercritical carbon dioxide (SCCO2) assisted impregnation and subsequent thermal annealing. Due to the advantageous nanostructure, the Fe2O3/VACNT composites exhibit a large specific capacitance of 248 F g−1 at 8 A g−1 in 2 M KOH between −1.2 and 0 V versus SCE. An asymmetric supercapacitor operating at 1.8 V is assembled using the Fe2O3/VACNTs as the anode and the NiO/VACNTs as the cathode in a 2 M KOH aqueous electrolyte. The NiO/VACNTs//Fe2O3/VACNT asymmetric supercapacitor achieves an extremely high energy density of 137.3 W h kg−1 at a power density of 2.1 kW kg−1, and still retains 102.2 W h kg−1 at the high power density of 39.3 kW kg−1. Moreover, it also shows an outstanding cycling stability with ∼89.2% capacitance retention after 5000 cycles. The facile and effective synthesis method, as well as the superior electrochemical performance of the Fe2O3/VACNT composites, pave a way for promising applications in high-performance energy storage. [ABSTRACT FROM AUTHOR]

A new probe (RosN3), which displayed excellent selectivity to H2S in mixed aqueous media, was synthesized. This method employed the H2S-mediated reduction of azides to amines, resulting in fluorescence quenching. The probe exhibited high H2S selectivity over other common anions and biothiols. The detection limit was measured to be 0.25 μM. Furthermore, the live cell imaging results demonstrated its potential for practical application in biological systems. [ABSTRACT FROM AUTHOR]

In order to enhance and tune the electrocaloric effect (ECE) and ferroelectric responses, nanocomposites containing ferroelectric copolymer poly(vinylidene fluoride trifluoroethylene) and two-dimensional (2D) graphitic-C 3 N 4 (g-C 3 N 4 ) are synthesized. The effects of g-C 3 N 4 on the ferroelectric-to-paraelectric phase transition of the copolymer are investigated by the differential scanning calorimetry (DSC), P-E hysteresis loop and dielectric spectrum measurements. The results indicate that the addition of 2D g-C 3 N 4 in the ferroelectric copolymer is an effective approach in enhancing its dielectric and ferroelectric properties. Furthermore, the nanocomposites show the maximum absolute value of negative electrocaloric effect (ECE) of 5.4 K at 322 K under an electric field of 0.45 MV cm -1 , which is much better than that of pristine copolymer. The negative ECE of the nanocomposites can be well explained by the Kauzmann theory. The low cost and enhanced negative ferroelectric properties of P(VDF-TrFE) make them more feasible over ceramics materials such as lead zirconate titanate (PZT) based ferroelectrics for applications in electrocaloric refrigeration., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Effective separation and rapid transfer of photogenerated electron-hole pairs are key features of photocatalytic materials with high catalytic activity, which could be achieved in co-catalysts. It is reported that the two-dimensional (2D) MoS 2 is a promising co-catalyst due to its unique semi-conductive properties and graphene-like layered structure. However, the application of MoS 2 as a co-catalyst is limited by its poor electrical conductivity. On the other hand, it is worth noting that TiO 2 possesses reactive crystal facets, which is one of the dominant mechanisms for the separation of photogenerated electron-hole pairs. In this work, we prepared MoS 2 /RGO hybrids as co-catalysts which were doped to TiO 2 with highly reactive {001} planes via the hydrothermal method. It was found that the {001}-TiO 2 /MoS 2 /RGO photocatalysts with 7 wt% MoS 2 /RGO co-catalyst show the highest photodegradation activity for the degradation of Rh B under visible light irradiation ( λ > 400 nm), which could result from the synergy of the effective separation of electron-hole pairs by the {001} facets in TiO 2 and the rapid transfer of electron-hole pairs in MoS 2 /RGO. The results show that the {001}-TiO 2 /MoS 2 /RGO hybrid is a low-cost and stable photocatalyst for the effective degradation of Rh B under visible light., Competing Interests: There is no conflict in the statement., (This journal is © The Royal Society of Chemistry.)

The potential toxicity and irreversibility of radionuclide Cs place severe pressure on the natural environment, which has become one of the most forefront pollution problems in nuclear energy utilization. To solve this problem, novel self-assembled membranes consisting of two-dimensional (2D) metal-organic frameworks (MOFs) and graphene oxide (GO) were prepared by a facile filtration method, which can efficiently absorb Cs + from aqueous solutions. The batch experimental results showed that the sorption of Cs + on the GO/Co-MOF composite membrane was strongly dependent on the addition mass and the membrane compositions. Thus, the dominant interaction mechanism was interface or surface complexation and electrostatic interaction. The maximum sorption efficiency of Cs + on GO/Co-MOF was 88.4% with 8 mg addition mass at pH = 7.0 and 299 K. Detailed FT-IR and XPS analyses suggested that the efficient synergistic effects in the unique architectures of GO/Co-MOF play an important role in the high sorption capacity of Cs + . The facile preparation method and the highly-efficient Cs + removal behaviour of GO/Co-MOF make the novel membrane a promising candidate for the elimination of radionuclide contamination., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Two-dimensional (2D) MoS 2 /graphene nanosheet (MoS 2 /GN) hybrids have been demonstrated to be promising microwave absorption (MA) materials due to their unique chemical and physical properties as well as rich impedance matching. However, the reported strategies for preparing MoS 2 /GN hybrids have limited their application potential due to the complex, high-cost and inefficient preparation processes. On the other hand, it is of note that the main source of graphene is based on converting insulating graphene oxides (GO) back to conductive reduced graphene oxides (RGO). Thus, the MA performance of obtained MoS 2 /RGO nanohybrids is greatly affected by the conversion process of GO. In this work, we prepared the MoS 2 /GN hybrids by a facile hydrothermal method with directly introducing highly pure and electroconductive GNs. It is found that the highest reflection loss value of the sample-wax containing 40% MoS 2 /GN is -57.31 dB at a thickness of 2.58 mm, and the bandwidth of RL values less than -10 dB can reach up to 12.28 GHz (from 5.72 to 18 GHz) when an appropriate absorber thickness between 1.5 and 4 mm is chosen. The excellent MA performances emanate from effective conjugation of MoS 2 with GN (Mo-C bond between the interfaces), which provides the dielectric loss caused by multi-relaxation, conductance, and polarization. Taking into account the facile synthesis route and their excellent MA performance, the MoS 2 /GNs hybrid nanosheets and those composite materials with similar isomorphic hetero-structures are very promising for a wide range of MA applications., Competing Interests: There is no conflict in the statement., (This journal is © The Royal Society of Chemistry.)