Abundant Edge Sites Research Articles

Carboxymethylcellulose Induced the Formation of Amorphous MnO2 Nanosheets With Abundant Oxygen Vacancies for Fast Ion Diffusion in Aqueous Zinc‐Ion Batteries

AbstractManganese dioxide with high theoretical capacity has drawn a great deal of attention for aqueous zinc‐ion batteries (ZIBs). Nevertheless, their sluggish diffusion kinetics, low electrical conductivity and limited active sites are still hindering the potential application in batteries. Herein, amorphous MnO2 nanosheets with abundant oxygen vacancies are facilely prepared by using carboxymethylcellulose sodium (CMC) as a capping agent. During the growth process, CMC can preferentially attach to the (003) facet of MnO2 to guide its crystal growth and morphology. The small nanosheets can expose abundant edge sites, along with the surface oxygen vacancies, to facilitate the insertion/extraction of H+ and Zn2+ in ZIBs. Moreover, the presence of CMC can stabilize the Mn3+ to inhibit the Jahn–Teller effect in the preparation process. As a result, CMC‐MnO2 based ZIB can provide a specific capacity of 324 mAh g−1 at 0.5 A g−1, and achieve 86.2% retention after a long cycle test of 1000 cycles. Furthermore, the energy storage mechanism may be attributed to the insertion/extraction of H+/Zn2+, dissolution/deposition of MnO2 and Zn4SO4(OH)6·nH2O, and irreversible transformation of vermiculite during long cycles. This work may open new perspectives for the development of MnO2‐based cathodes in ZIBs.

Construction of a novel Mott-Schottky heterostructure gas sensor g-C3N4/SnO2 with layered nanorods array for high-sensitivity acetone detection

Developing exhaled acetone sensors with high performance can be effectively applied to the medical diagnosis and the health monitoring. Herein, a two-dimensional (2D) layered graphitic carbon nitride (g-C3N4) with tunable electronic structure, abundant edge sites, and high stability is proposed, and it is further coupled with stannic oxide (SnO2) by one-step hydrothermal approach to construct a Mott-Schottky heterostructure with layered nanorods array. The exceptional response of the as-fabricated g-C3N4/SnO2 gas sensor to 50 ppm acetone at 100 °C is four times higher than that of the pristine SnO2 sensor. Additionally, the g-C3N4/SnO2 sensor’s remarkable selectivity, long-term stability against acetone gas, and detection limit of 250 ppb are exhibited. The unique hierarchical design and the Mott-Schottky heterostructure creation which validated by electrochemical study, may be in charge of the enhanced acetone sensing capabilities of g-C3N4/SnO2 gas sensor. This work will provide a concise and effective avenue to construct hierarchical composite with Mott-Schottky heterostructure for high-performance acetone gas sensor.

Ultrasmall Fe‐Nanoclusters‐Anchored Carbon Polyhedrons Interconnected with Carbon Nanotubes for High‐Performance Zinc‐Air Batteries

The catalytic activity of metal catalyst is closely related to its particle size. Yet, the size effect in electrocatalytic oxygen reduction reaction (ORR), an important reaction for metal‐air batteries and fuel cells, has not been clearly studied. Herein, a two‐step anchoring method is utilized to control the Fe catalyst in forms of nanoparticles (NPs), ultrasmall nanoclusters (NCTs), and isolated atoms as well as stabilized and dispersed by carbon polyhedrons interconnected with carbon nanotubes (CNTs). The uniformly distributed Fe NCTs displays superior ORR performance compared with Fe NPs, isolated Fe atoms, and commercial Pt/C. The brilliant ORR activity of Fe NCTs is a result of its unique electron structure and abundant edge and corner active sites. Due to the porous structure of carbon polyhedrons and high electron conductivity of CNTs, Fe NCTs also delivers an excellent discharge performance in zinc‐air battery with a peak power density of 213.3 mW cm−2 and long‐term stability. In these findings, a new strategy for the design of metal NCTs catalysts applied in various catalytic reactions is opened up.

Building 3D Crosslinked Graphene-MXene Nanoarchitectures Decorated with MoS2 Quantum Dots Enables Efficient Electrocatalytic Hydrogen Evolution.

Although MoS2 quantum dots with abundant edge sites have been regarded as promising eletrode materials for the hydrogen evolution reaction (HER), their electrocatalytic capacity still requires improvements in actual applications. Herein. we demonstrate a controllable and robust bottom-up approach to build 3D crosslinked graphene-Ti3C2Tx MXene frameworks decorated with MoS2 quantum dots (MQD/RGO-MX) via a convenient co-assembly process. The novel structural design gives the MQD/RGO-MX nanoarchitectures a series of superior textural attributes, including 3D interconnected networks, continuous meso- and macropores, well-dispersed quantum dots, ameliorative electronic configuration, and excellent electrical conductivity. Accordingly, the resulting hybrid nanoarchitectures express superior electrocatalytic properties in terms of a low onset potential of only 45 mV, a small Tafel slope of 61 mV dec-1 as well as a long service life towards the HER, which make it quite competitive against bare MoS2 quantum dots, MXene as well as binary MQD/RGO and MQD/MXene electrocatalysts.

Engineering Three-Dimensional Interconnected Pores with Plentiful Edge Sites via a Confined Space for Enhanced Oxygen Reduction.

N-Doped carbon sheets based on edge engineering provide more opportunities for improving oxygen reduction reaction (ORR) active sites. However, with regard to the correlation between porous structural configurations and performances, it remains underexplored. Herein, a silica-assisted localized etching method was employed to create two-dimensional mesoporous carbon materials with customizable pore structures, abundant edge sites, and nitrogen functionalities. The mesoporous carbon exhibited superior electrocatalytic performance for the ORR compared to that of a 20 wt % Pt/C catalyst, achieving a half-wave potential of 0.88 V versus RHE, situating them in the leading level of the reported carbon electrocatalysts. Experimental data suggest that the edge graphitic nitrogen sites played a crucial role in the ORR process. The three-dimensional interconnected pores provided a high density of active sites for the ORR and facilitated the efficient transport of electrons. These unique properties make the carbon sheets a promising candidate for highly efficient air cathodes in rechargeable Zn-air batteries.

Enriched edge sites of ultrathin Ni3S2/NiO nanomeshes promote surface reconstruction for robust electrochemical water splitting

Developing highly efficient nonnoble bifunctional electrocatalysts for both the H2 evolution reaction (HER) and O2 evolution reaction (OER) is essential but challenging for overall water splitting (OWS). Ni based catalysts are proved as promising candidates for water splitting, which usually undergo surface reconstruction by transforming into nickel oxyhydroxides as active sites. Although evidence suggests that the reconstruction originates from the exchange of surface lattice oxygen with the OH- in the electrolyte under electric field, modulating the reconstruction of Ni based catalysts remains a great challenge. Herein, we propose an edge sites enrichment strategy to promote the active phase evolution. The one-step synthesized ultrathin Ni3S2/NiO nanomeshes exhibited an ultrathin porous structure which contain abundant edge sites and Ni3S2/NiO in-plane interface sites. Owing to the unique structure, Ni3S2/NiO nanomeshes possessed an affinity feature to proton and OH-, resulting in a faster reconstruction from Ni3S2 to Ni(OH)2 than Ni3S2 bulk which subsequently converted into γ-NiOOH and a lower adsorption barrier for H*. Consequently, the Ni3S2/NiO nanomeshes exhibited outstanding OER activity (300 mV at 200 mA cm−2) and unexpected HER activity (73 mV at 10 mA cm−2) in 1.0 M KOH. Remarkably, the nanomeshes achieved an ultralow voltage of 1.41 V at 10 mA cm−2 with excellent stability for overall water splitting, which prevailed over most of the reported catalysts. Moreover, the nanomeshes performed a H2 yield of 900 µmol/h in a solar-assisted water splitting system with a H2 minimum sales price of $1.77/kg, much lower than that of the commercial catalyst ($7.18/kg). This work sets a new benchmark of monometallic bifunctional catalysts for industrial water splitting and provides new insights into the synthesis of 2D nanomeshes.

Diversity in Atomic Structures of Zeolite-Templated Carbons and the Consequences for Macroscopic Properties.

Zeolite-templated carbons (ZTCs) are a family of ordered microporous carbons with extralarge surface areas and micropore volumes, which are synthesized by carbon deposition within the confined spaces of zeolite micropores. There has been great controversy regarding the atomic structures of ZTCs, which encompass two extremes: (1) three-dimensionally connected curved open-blade-type carbon moieties and (2) ideal tubular structures (commonly referred to as "Schwarzites"). In this study, through a combination of experimental analyses and theoretical calculations, we demonstrate that the atomic structure of ZTCs is difficult to define as a single entity, and it widely varies depending on their synthesis conditions. Carbon deposition using a large organic precursor and low-temperature framework densification generates ZTCs predominantly composed of open-blade-type moieties, characterized by low surface curvature and abundant H-terminated edge sites. Meanwhile, synthesis using a small precursor with high-temperature densification produces ZTCs with an increased portion of closed-strut carbon moieties (or closed-fullerene-like nodes), exhibiting large surface curvature and diminished edge sites. The variations in the atomic structure of ZTCs result in significant differences in their macroscopic properties, such as N2/CO2 adsorption, oxidative stability, work function, and electrocatalytic properties, despite the presence of comparable pore structures. Therefore, ZTCs demonstrate the potential to synthesize ordered nanoporous carbons with tunable physicochemical properties.

Edge-rich reduced microcrystalline graphite oxide for Li-ion hybrid capacitors with ultrahigh volumetric energy density

Compact and high-performance carbon cathode materials are vital to improve the gravimetric and volumetric energy/power density of advanced energy storage devices such as lithium-ion hybrid capacitors (LIHCs). Graphite has a high mass density and the areal specific capacitance at the edge plane is far larger than that in the basal plane. Hence, increasing the proportion of edges can effectively improve the specific capacitance of the carbon material. However, it is challenging to expose more edges of graphite due to its high thermal and chemical stability. In this work, a compact cathode is prepared through a facile high-temperature ammonia treatment of microcrystalline graphite oxide (MGO). The obtained edge-rich reduced microcrystalline graphite oxide (ER-RMGO) demonstrates abundant edge sites, a high mass density of 1.48 g cm−3 and an extremely high areal specific capacitance of up to 319.3 μF cm−2. As a result, the fabricated Li-ion hybrid capacitor delivers an ultrahigh volumetric energy density of 392 Wh L−1 and power density of 9.49 W LkW L−1. This work sheds light on the great potential of microcrystalline graphite derived edge-rich carbon materials for compact capacitive energy storage.

Metallic 1T phase molybdenum disulfide cocatalyst with abundant edge and substrate active sites for enhanced photocatalytic hydrogen production activity of zinc indium sulfide nanoflowers

The formation of composites by loading co-catalysts on semiconductor photocatalysts to improve hydrogen (H2) evolution performance is a feasible strategy. Metallic 1T phase molybdenum disulfide (MoS2) as cocatalysts were decorated on zinc indium sulfide (ZnIn2S4) nanoflowers by a grinding method to construct 1T-MoS2@ZnIn2S4 composites. The H2 production rate of 1T-MoS2@ZnIn2S4 composites with optimum 7 wt% 1T-MoS2 loading achieves 15.6 mmol g−1 h−1, 5.5 times higher than ZnIn2S4 nanoflowers. The apparent quantum efficiency (AQY) increases from 3.1 % (ZnIn2S4 nanoflowers) to 13.0 % (1T-MoS2@ZnIn2S4 composites) under the wavelength light irradiation at λ = 370 nm. The loading of metallic 1T-MoS2 with abundant edge and substrate active sites on ZnIn2S4 can enhance visible light absorption, promote the transfer of electrons, and inhibit carrier recombination, thereby improving photocatalytic performance. This work offers inspiration for the design of composite photocatalysts with efficient photocatalytic capabilities.

Efficient and stable CO2 to formate conversion enabled by edge-site-enriched SnS2 nanoplates

Layered materials have been investigated in many different catalytic reactions due to their excellent functionalities. In particular, understanding the anisotropic properties of layered materials is important for the design of more efficient catalysts. Herein, SnS2 nanoflakes with abundant edge sites (E-SnS2) were synthesized and their catalytic properties towards the electrochemical CO2 reduction reaction (CO2RR) were studied. Combining experimental data and computational analysis, we found that the edge sites of SnS2 are more active for CO2 to formate conversion compared with the basal sites. Moreover, a CO2 reduction intermediates triggered activation mechanism at the edge sites is proposed, the formation of sulfur vacancies at the edges would generate more active sites for CO2RR. The as-synthesized E-SnS2 shows high selectivity, activity and robust stability for at least 12 h in a flow cell under a current density of − 200 mA·cm-2. This work may provide a new perspective on rational catalyst design for CO2RR.

Excellent performance of nitrogen-doped carbon nanofibers as electrocatalysts for water splitting reactions

Green hydrogen production by water electrolysis with the least possible energy waste requires the application of suitable electrocatalytic electrodes. In this work, highly active, free-standing electrodes were prepared by deposition of nitrogen-doped carbon nanofibers (N-CNFs) on oxidized carbon cloth. Different types of N-CNFs with variable structures, nitrogen dopant concentrations and defect contents were synthesized. Their electrocatalytic activities as hybrids with oxidized and raw carbon cloth electrodes were evaluated in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). We show that the N–CNF sample with the highest nitrogen doping in the series (6.7 at.%) and the predominance of well-ordered herringbone/bamboo-like structure with abundant edge sites, exhibited both the highest OER and HER activities (with overpotentials of 330 and 410 mV, respectively at j = ±10 mA cm−2) and excellent performance stability. The hybrid material provided abundant active sites on N-CNFs that show good adhesion to the hydrophilic carbon cloth.

Edge-Enriched Molybdenum Disulfide Ultrathin Nanosheets with a Widened Interlayer Spacing for Highly Efficient Gaseous Elemental Mercury Capture.

Transition metal sulfides have exhibited remarkable advantages in gaseous elemental mercury (Hg0) capture under high SO2 atmosphere, whereas the weak thermal stability significantly inhibits their practical application. Herein, a novel N,N-dimethylformamide (DMF) insertion strategy via crystal growth engineering was developed to successfully enhance the Hg0 capture ability of MoS2 at an elevated temperature for the first time. The DMF-inserted MoS2 possesses an edge-enriched structure and an expanded interlayer spacing (9.8 Å) and can maintain structural stability at a temperature as high as 272 °C. The saturated Hg0 adsorption capacities of the DMF-inserted MoS2 were measured to be 46.91 mg·g-1 at 80 °C and 27.40 mg·g-1 at 160 °C under high SO2 atmosphere. The inserted DMF molecules chemically bond with MoS2, which prevents possible structural collapse at a high temperature. The strong interaction of DMF with MoS2 nanosheets facilitates the growth of abundant defects and edge sites and enhances the formation of Mo5+/Mo6+ and S22- species, thereby improving the Hg0 capture activity at a wide temperature range. Particularly, Mo atoms on the (100) plane represent the strongest active sites for Hg0 oxidation and adsorption. The molecule insertion strategy developed in this work provides new insights into the engineering of advanced environmental materials.

Controllable and universal anisotropic vapor–solid growth of vertical 2D metal chalcogenide nanoflakes with enhanced photoelectric and electrocatalytic properties

Epitaxial growth and subsequent processing of 2D materials are mostly confined to xy plane parallel to the substrate. Introducing another degree of freedom, i.e., the vertical direction perpendicular to the base plane, is very intriguing, as the resulting vertically aligned 2D materials will intuitively have a high aspect ratio, anisotropic structure, and abundant edge sites, holding great promise in field emission, photoelectronics, piezoelectricity, clean energy catalysis, etc. However, the key factors governing the spatially anisotropic growth to selectively obtain vertically or horizontally aligned 2D nanoflakes remain elusive. Herein, we report a controllable and general strategy to vertically grow representative 2D metal chalcogenide materials, including but not limited to SnS, SnSe, Bi2Se3, MoO3, and MoS2 nanoflakes, via a rapid heating–cooling process on various optional substrates. The rapid heating–cooling process allows rapid desublimation and nucleation of highly-supersaturated precursor vapor, leading to ultrafast growth of vertically aligned nanoflakes with exposed side surfaces and edges. As an example, the vertically grown SnS nanoflakes exhibit anisotropic spectroscopic features, superior photoelectric properties and enhanced electrocatalytic performances for the nitrate reduction and CO2 reduction reactions. This work provides a feasible approach to controllably synthesize versatile vertically aligned 2D metal chalcogenide nanoflakes on various substrates, which can advance the mechanistic understanding of anisotropic growth and physicochemical properties of 2D materials towards photoelectric devices and clean energy conversion.

Interface engineering assisted Fe-Ni3S2/Ni2P heterostructure as a high-performance bifunctional electrocatalyst for OER and HER

Rational development and construction of electrochemical water splitting catalysts with excellent activity and super-durability utilizing earth-abundant elements are extremely desirable and imperative for energy crisis. Herein, a self-supported hierarchical Fe-doped nickel sulfide/nickel phosphide (nanoflower-linked nanosheet arrays grown vertically on nickel foam) heterostructure electrocatalyst was obtained via a successive structural transformation to realize high-efficiency alkaline OER and HER performance. Benefiting from the novel nanoflower-sheet crosslinked structure on NF, electronic coupling reconstruction and abundant edge sites, as-synthesized Fe-Ni3S2/Ni2P electrocatalyst exhibits remarkable electrocatalytic OER and HER activity in both low and high current density regions. Specifically, the Fe-Ni3S2/Ni2P electrode achieved low overpotentials of 172, 277 and 357 mV at current densities of 10, 50 and 100 mA·cm−2 for OER, respectively. A series of experimental results confirmed that the surface reconfiguration behavior of Fe-Ni3S2/Ni2P heterostructure led to the formation of amorphous M-OH bond system, which was answerable to the prominent OER catalyst properties. This work confirms the potential of designing robust bifunctional electrocatalysts for alkaline water electrocatalysis by carefully combining doping engineering as well as interfacial effects.

Unlocking the Ultrahigh‐Current‐Density Hydrogen Evolution on 2H‐MoS2 via Simultaneous Structural Control across Seven Orders of Magnitude

AbstractMembers of transition metal dichalcogenides, particularly molybdenum disulfide, have been recognized as promising efficient and durable earth‐abundant catalysts for the hydrogen evolution reaction (HER). Despite the recent significant progress, the HER performance of MoS2 is still far from satisfactory, especially at high current densities. Here, a simultaneous multilevel structural control strategy is reported to cooperatively boost hydrogen evolution on 2H‐MoS2, unlocking its potential for practical hydrogen evolution at ampere‐level current densities. By confining the epitaxial growth of few‐layered, curved MoS2 nanosheets within a tubular mesoporous graphitic framework, one can achieve deliberate structural control of MoS2 across seven orders of magnitude on the length scale. The resulting MoS2@C supertubes, benefiting from their unique structural features across atomic‐to‐microscopic scales, are characterized by abundant edge sites and sulfur vacancies, facilitated charge and mass transport, and rapid gas bubble removal. As a consequence, such MoS2@C supertubes exhibit exceptional high‐current‐density HER activity surpassing previously reported 2H‐MoS2 catalysts and even commercial Pt/C catalysts. This work demonstrates the validity of multilevel structural engineering of 2H‐MoS2 by confinement growth, opening a viable route of developing low‐cost catalysts toward practical hydrogen evolution.

Engineering edge sites based on NiS2/MoS2/CNTs heterojunction catalyst for overall water splitting

Boosting the hydrogen and oxygen evolution reaction (HER/OER) on MoS2-based catalysts is a challenging scientific issue due to the activity of MoS2 is significantly rely on the edge site which is limited in regular structure. Herein, a highly dispersed edge site-rich NiS2/MoS2/CNTs heterojunction catalyst is successfully developed via facile etching the nanoflower-like NiS2/MoS2 spheres on carbon nanotubes (CNTs). Through expanding the lattice spacing of 2H-MoS2, generating abundant Mo-S edge sites (i.e. generating a large number of unsaturated S atoms) together with enhancing the dispersity of NiS2/MoS2 nanosheets, the etching posttreatment significantly regulates the electronic and geometric structure of NiS2/MoS2/CNTs. Further combining the extremely intimate electronic interaction between MoS2/NiS2 heterogeneous interfaces, the optimal NiS2/MoS2/CNTs presents a preeminent alkali water splitting performance with overpotentials of 149 for HER and 315 mV for OER at 10 mA cm−2, which are 29 and 35 mV lower than the catalyst before etch treatment (NiS2/MoS2/CNTs-p), respectively. Moreover, the electrolyzer assembled with NiS2/MoS2/CNTs drives a voltage of 1.73 V at 10 mA cm−2 and a continuous stable operation of 50 h toward overall water splitting.

Magnetoelectric synergy strategy for superior iron disulfide anode

The magnetic FeS2/C@VS2 heterostructure with abundant edge sites and dangling sites was designed to achieve highly reversible sodium storage.

Unraveling the efficiency of heteroatom-doped graphene quantum dots incorporated MOF-derived bimetallic layered double hydroxide towards oxygen evolution reaction

Addressing energy and environmental issues, developing highly efficient, durable, and earth-abundant, electrocatalysts are crucial in oxygen evolution reaction (OER) for energy conversion and storage. Extensive research about the metal-organic framework (MOF) derived layered double hydroxides (LDH) and carbon-based electrocatalysts have been devoted, despite the exceptional performance in OER, yet the limited exposed active sites remain a challenge. Therefore, we reported a novel heteroatom-doped graphene quantum dots (GQDs) incorporated into MOF-derived NiFe-LDH. Taking advantage of abundant active and edge sites of GQDs and modifying the surface chemistry by chemical doping with foreign atoms, the designed heteroatom-doped GQDs/MOF-derived LDH exhibited superior catalytic performance low overpotential of 251 mV at a current density of 100 mA cm −2 in alkaline media. Our result confirmed the synergistic effect between the doped heteroatom and the uttermost exposure of heteroatom-doped GQDs/MOF-derived LDH's active sites on its surface, providing swift reactant's transportation and adequate contact for improving the OER performance. • A novel hybrid heteroatom-doped GQDs/MOF-derived LDH electrocatalyst has been developed. • The relationship between single and dual-doped GQDs in OER activity has been explored and optimized. • Synergistic effect of N and B dopants within GQDs significantly improves the OER performance. • B,N-GQDs/MOF-derived NiFe LDH exhibits superior electrocatalytic OER performance (η 100 = 251 mV).

Enhanced photocatalytic hydrogen evolution by piezoelectric effects based on MoSe2/Se-decorated CdS nanowire edge-on heterostructure

The build-in electric field by the construction of heterojunction is one of the most promising strategies to suppress the recombination of photogenerated carriers. Here, we reported a piezo-photocatalytic system composed of Se-decorated CdS nanowires and few-layered edge-on MoSe2 nanosheets for efficient H2 generation by two-pot hydrothermal synthesis. The few-layered MoSe2 exposed abundant edge sites for hydrogen evolution reaction (HER). The activity of 20-MoSe2/CdS0.95Se0.05 (20-MS/CSS, with 20 mol% of MoSe2 loading) nanocomposite casted a remarkable photocatalytic HER performance, with a rate of 47.3 mmol h−1 g−1. Moreover, MoSe2 nanosheets deformed to generate the piezoelectric polarization field under magnetic stirring, which rendered efficient separation of photogenerated carriers, resulting in a piezo-photocatalytic synergistic effect. As a result, the HER of 20-MS/CSS at 900 rpm for piezo-photocatalysis was 59.1 mmol h−1 g−1, which was 1.25 times that of 20-MS/CSS for photocatalysis. Meanwhile, the photoelectrochemical measurements further visualized the piezo-photoelectric synergy. This study exposes a new way for utilizing mechanical energy to improve photocatalytic performance, and achieving high piezo-photocatalysis.

A hydrangea-like superstructure of ZnS@MoS2 nanosheets as efficient electrocatalyst for hydrogen evolution reaction

The development of low-cost and high active electrocatalysts for hydrogen evolution reaction (HER) is essential for the sustainable energy and environment. Here we report a hydrothermal method to prepare ZnS@MoS2 nanosheets with hydrangea-like superstructure for enhanced HER. Benefiting from their abundant edge sites and facilitated charge transfer, the ZnS@MoS2 exhibited excellent HER performance with low overpotential of 106 mV and small Tafel slope of 73 mV dec−1. In addition, the chronoamperometry measurement results suggested the well-remained current density for 36 h without significant change, which indicated the excellent stability of ZnS@MoS2 superstructure. This work not only provides an effective method for constructing hierarchical heterojunctions, but also gives us a multi-scale strategy for the regulation of metal-based nanomaterials’ structure in energy-related applications.