Oxygen vacancy enriched hollow cobaltosic oxide frames with ultrathin walls for efficient energy storage and biosensing

Surface passivation strategies for CsPbBr3 quantum dots aiming at nonradiative suppression and enhancement of electroluminescent light-emitting diodes

With many fascinating characteristics, such as color-tunability, narrow-band emission, and low-cost solution processability, all-inorganic lead halide perovskite quantum dots (QDs) have attracted keen attention for electroluminescent light-emitting diodes (QLEDs) and display applications. However, the performance of perovskite QLED devices is intrinsically limited by the inefficient electrical carrier transport capacity. Herein, one facile but effective method is proposed to enhance the perovskite QLED performance by incorporating a short carbon chain ligand of 2-phenethylammonium bromide (PEABr) to passivate the CsPbBr3 QD surface. With the PEABr ligand, the Br- vacancies are passivated, which could eliminate nonradiative recombination of perovskite QDs; thus their optical properties are enhanced. Meanwhile, PEABr can interact with perovskite QDs to adjust the perovskite film morphology, resulting in low current leakage and efficient electron injection. After the PEABr treatment, the CsPbBr3 QD film exhibits strong green emission located at 516 nm, with an average photoluminescence lifetime of 45.71 ns and a photoluminescence quantum yield of up to 78.64%. In addition, the surface roughness of the CsPbBr3 QD film is reduced from 3.61 nm to 1.38 nm, which is essential to prepare a QD film with high surface coverage. As a result, the QLED device with PEABr treated CsPbBr3 QDs exhibits a maximum current efficiency of 32.69 cd A-1 corresponding to an external quantum efficiency of 9.67%, 3.88-fold higher than that of the control device (pure QDs as an emission layer). This research provides an effective strategy for the improvement of the perovskite QLED performance and may be helpful for extending their actual applications.

Design and regulation of defective electrocatalysts

Electrocatalysts are the key components of electrochemical energy storage and conversion devices. High performance electrocatalysts can effectively reduce the energy barrier of the chemical reactions, thereby improving the conversion efficiency of energy devices. The electrocatalytic reaction mainly experiences adsorption and desorption of molecules (reactants, intermediates and products) on a catalyst surface, accompanied by charge transfer processes. Therefore, surface control of electrocatalysts plays a pivotal role in catalyst design and optimization. In recent years, many studies have revealed that the rational design and regulation of a defect structure can result in rearrangement of the atomic structure on the catalyst surface, thereby efficaciously promoting the electrocatalytic performance. However, the relationship between defects and catalytic properties still remains to be understood. In this review, the types of defects, synthesis methods and characterization techniques are comprehensively summarized, and then the intrinsic relationship between defects and electrocatalytic performance is discussed. Moreover, the application and development of defects are reviewed in detail. Finally, the challenges existing in defective electrocatalysts are summarized and prospected, and the future research direction is also suggested. We hope that this review will provide some principal guidance and reference for researchers engaged in defect and catalysis research, better help researchers understand the research status and development trends in the field of defects and catalysis, and expand the application of high-performance defective electrocatalysts to the field of electrocatalytic engineering.

Mechanisms for self-templating design of micro/nanostructures toward efficient energy storage

The ever-growing demand in modern power systems calls for the innovation in electrochemical energy storage devices so as to achieve both supercapacitor-like high power density and battery-like high energy density. Rational design of the micro/nanostructures of energy storage materials offers a pathway to finely tailor their electrochemical properties thereby enabling significant improvements in device performances and enormous strategies have been developed for synthesizing hierarchically structured active materials. Among all strategies, the direct conversion of precursor templates into target micro/nanostructures through physical and/or chemical processes is facile, controllable, and scalable. Yet the mechanistic understanding of the self-templating method is lacking and the synthetic versatility for constructing complex architectures is inadequately demonstrated. This review starts with the introduction of five main self-templating synthetic mechanisms and the corresponding constructed hierarchical micro/nanostructures. Subsequently, the structural merits provided by the well-defined architectures for energy storage are elaborately discussed. At last, a summary of current challenges and future development of the self-templating method for synthesizing high-performance electrode materials is also presented.

Metal-Organic Framework (UiO-66)-Based Temperature-Responsive Pesticide Delivery System for Controlled Release and Enhanced Insecticidal Performance against Spodoptera frugiperda

Spodoptera frugiperda is a global pest that brings about great disasters to crops. Conventional pesticide formulations often suffer from poor water solubility, low stability, burst release, weak leaf adhesion, and low efficiency. To improve the insecticidal activity of pesticides, a stimuli-responsive controlled release pesticide delivery system (PDS) has attracted extensive attention in recent years. This paper reports a temperature-responsive controlled release PDS based on poly(N-isopropyl acrylamide) (PNIPAm)-modified indoxacarb (IDC)-loaded UiO-66-(COOH)₂ (IDC@UiO-66-(COOH)₂-PNIPAm) and studies its insecticidal activities against S. frugiperda. The UiO-66-(COOH)₂ nanocarrier has an excellent pesticide loading performance, and the loading rate for IDC is 78.69%. The as-prepared PDS has good stability, temperature-responsive controllable release performance, and enhanced leaf affinity, so it can effectively improve the utilization rate of IDC. The insecticidal experiment indicates that the PDS has an enhanced control effect against S. frugiperda. In addition, biosafety analysis further verifies that the PDS exhibits no obvious negative effects on the germination of maize seeds and the growth of maize seedlings. In view of this, we believe that this PDS will have a broad application in the field of pesticide formulation innovation, pest management, and sustainable agricultural development.

Engineering Sulfur Vacancies in Spinel-Phase Co3S4 for Effective Electrocatalysis of the Oxygen Evolution Reaction

Restricted by the sluggish kinetics of the oxygen evolution reaction (OER), efficient OER catalysis remains a challenge. Here, a facile strategy was proposed to prepare a hollow dodecahedron constructed by vacancy-rich spinel Co₃S₄ nanoparticles in a self-generated H₂S atmosphere of thiourea. The morphology, composition, and electronic structure, especially the sulfur vacancy, of the cobalt sulfides can be regulated by the dose of thiourea. Benefitting from the H₂S atmosphere, the anion exchange process and vacancy introduction can be accomplished simultaneously. The resulting catalyst exhibits excellent catalytic activity for the OER with a low overpotential of 270 mV to reach a current density of 10 mA cm^-2 and a small Tafel slope of 59 mV dec^-1. Combined with various characterizations and electrochemical tests, the as-proposed defect engineering method could delocalize cobalt neighboring electrons and expose more Co²⁺ sites in spinel Co₃S₄, which lowers the charge transfer resistance and facilitates the formation of Co³⁺ active sites during the preactivation process. This work paves a new way for the rational design of vacancy-enriched transition metal-based catalysts toward an efficient OER.

Universal Strategy for Preparing Highly Stable PBA/Ti3C2Tx MXene toward Lithium-Ion Batteries via Chemical Transformation

Prussian blue analogues (PBAs) are believed to be intriguing anode materials for Li⁺ storage because of their tunable composition, designable topologies, and tailorable porous structures, yet they suffer from severe capacity decay and inferior cycling stability due to the volume variation upon lithiation and high electrical resistance. Herein, we develop a universal strategy for synthesizing small PBA nanoparticles hosted on two-dimensional (2D) MXene or rGO (PBA/MX or PBA/rGO) via an in situ transformation from ultrathin layered double hydroxides (LDH) nanosheets. 2D conductive nanosheets allow for fast electron transport and guarantee the full utilization of PBA even at high rates; at the meantime, PBA nanoparticles effectively prevent 2D materials from restacking and facilitate rapid ion diffusion. The optimized Ni_0.8Mn_0.2-PBA/MX as an anode for lithium-ion batteries (LIBs) delivers a capacity of 442 mAh g^-1 at 0.1 A g^-1 and an excellent cycling robustness in comparison with bare PBA bulk crystals. We believe that this study offers an alternative choice for rationally designing PBA-based electrode materials for energy storage.

NiMoO4@NiMnCo2O4 Heterostructure: A Poly(3,4-propylenedioxythiophene) Composite-Based Supercapacitor Powers an Electrochromic Device

The hierarchical heterostructure of NiMoO₄@NiMnCo₂O₄ (NMO@NMCO) with furry structures of NMCO juxtaposed with NMO nanowires are endowed with multiple electrochemically active and accessible sites for ion storage, thus delivering an ultrahigh specific capacitance of 2706 F g^-1, nearly two-fold times greater than that of sole NMCO. Electrodeposition of an overlayer of a highly robust and electrically conducting polymer, poly(3,4-propylenedioxythiophene) (PProDOT), not only improves the energy storage performance but also assists the binary oxide cathode in retaining its structural integrity during redox cycling. Coupling with an anode of porous flaky carbon (FC) derived from groundnut shells results in an asymmetric supercapacitor of FC//PProDOT@NiMoO₄@NiMnCo₂O₄, which delivers an outstanding capacitance of 552 F g^-1, energy and power density ranges of 172-40 Wh kg^-1 and 0.75-10 kW kg^-1, respectively, and a remarkable cycle life of 50 000 cycles, with ∼97.8% capacitance retention, over an operational voltage window of 1.5 V. From an application perspective, the charged supercapacitor was connected to a complementary coloring reversible electrochromic device (ECD) of Prussian blue//PProDOT, and the ECD state transformed from a pale-blue to a deep blue hue, thus signaling the efficient utilization of energy stored in the supercapacitor. The energy-saving attribute of the ECD was realized in terms of an integrated visible-light modulation of 39% that accompanied the optical transition. Deployment of low-cost devices at homes and commercial spaces, capable of storing and saving energy, is the way forward, and this is one significant step in this direction.

Sulfur vacancies enriched Nickel-Cobalt sulfides hollow spheres with high performance for All-Solid-State hybrid supercapacitor

To pursue excellent performance of supercapacitor, an electrode material with designed morphology and tailored intrinsic properties is indeed desired. Herein, nickel-cobalt sulfides hollow spheres decorated with rich sulfur vacancies r-NiCo₂S₄ HSs) are prepared via an anion exchange of Ni-Co coordination polymer spheres, combined with wet chemical reduction. The r-NiCo₂S₄ HSs sample delivers excellent performance as an electrode: it possesses a high specific capacity (763.5C g^-1 at 1 A/g), favorable cyclability (91.40% after 5000 cycles at 10 A/g) and rate capacity (522.68C g^-1 at 15 A/g). Additionally, an all-solid-state hybrid supercapacitor device, assembled with r-NiCo₂S₄ HSs as the positive electrode and N/S co-doped activated carbon nanosheets as the negative electrode, presents an excellent energy density of 50.76 Wh kg^-1 under 800 W kg^-1 and feasible stability. Thus, combining hollow structure with sulfur vacancies could not only increase more active sites and ensure sufficient redox reactions, but also enhance electronic conductivity, facilitate ions / electrons transport and shorten diffusion path, which could be regarded as a promising approach to develop electrode materials with outstanding performance.

Site-Selective Transformation for Preparing Tripod-like NiCo-Sulfides@Carbon Boosts Enhanced Areal Capacity and Cycling Reliability

Flexible power supply systems for future wearable electronics desperately require high areal capacity (C_a) and robust cycling reliability due to the limited surface area of the human body. Transition metal sulfides are preferred as cathode materials for their improved conductivity and rich redox centers, yet their practical applications are severely hindered by the sluggish charge transport kinetics and unavoidable capacity decay due to the phase transformation during charge/discharge processes. Herein, we develop a site-selective transformation strategy for preparing tripod-like NiCo-sulfides@carbon (T-NCS@C) arrays on carbon cloth. The mass loading of active materials is balanced with charge (electron and ion) transport efficiency. The optimized T-NCS@C delivers a superior C_a of 494 μA h/cm² (corresponding to 235 mA h/g) at 3 mA/cm². Due to the protection of the carbon layer that is derived from transformed metal-organic framework (MOF) sheath, the T-NCS@C displays excellent stability with 92% retention over 5000 charge/discharge cycles. The flexible full cell adopting Fe₂O₃ as the anode and T-NCS@C as the cathode exhibits an improved E_a (areal energy density) of 389 μW h/cm² at a P_a (areal power density) of 4.22 mW/cm² together with robust cycling reliability.

Ammonium Intercalation Induced Expanded 1T-Rich Molybdenum Diselenides for Improved Lithium Ion Storage

Transition metal dichalcogenides (TMDs), particularly molybdenum diselenides (MoSe₂), have the merits of their unique two-dimensional (2D) layered structures, large interlayer spacing (∼0.64 nm), good electrical conductivities, and high theoretical capacities when applied in lithium-ion batteries (LIBs) as anode materials. However, MoSe₂ remains suffering from inferior stability as well as unsatisfactory rate capability because of the unavoidable volume expansion and sluggish charge transport during lithiation-delithiation cycles. Herein, we develop a simultaneous reduction-intercalation strategy to synthesize expanded MoSe₂ (e-MoSe₂) with an interlayer spacing of 0.98 nm and a rich 1T phase (53.7%) by rationally selecting the safe precursors of ethylenediamine (NH₂C₂H₄NH₂), selenium dioxide (SeO₂), and sodium molybdate (Na₂MoO₄). It is noteworthy that NH₂C₂H₄NH₂ can effectively reduce SeO₂ and MoO₄^2- forming MoSe₂ nanosheets; in the meantime, the generated ammonium (NH₄⁺) efficiently intercalates between MoSe₂ layers, leading to charge transfer, thus stabilizing 1T phases. The obtained e-MoSe₂ exhibits high capacities of 778.99 and 611.40 mAh g^-1 at 0.2 and 1 C, respectively, together with excellent cycling stability (retaining >90% initial capacity at 0.2 C over 100 charge-discharge cycles). It is believed that the material design strategy proposed in this paper provides a favorable reference for the synthesis of other transition metal selenides with improved electrochemical performance for battery applications.

Direct Growth of Oxygen Vacancy-Enriched Co3O4 Nanosheets on Carbon Nanotubes for High-Performance Supercapacitors

Ultrathin Co₃O₄ nanosheets (NSs) with abundant oxygen vacancies on conductive carbon nanotube (CNT) nanocomposites (termed as Co₃O₄-NSs/CNTs) are easily achieved by an effective NaBH₄-assisted cyanogel hydrolysis strategy under ambient conditions. The specific capacitance of Co₃O₄-NSs/CNTs with 5% CNT mass can reach 1280.4 F g^-1 at 1 A g^-1 and retain 112.5% even after 10 000 cycles, demonstrating very high electrochemical capability and stability. When assembled in the two-electrode Co₃O₄-NSs/CNTs-5%//reduced graphene oxide (rGO) system, a maximum specific energy density of 37.2 Wh kg^-1 (160.2 W kg^-1) is obtained at room temperature. Ultrathin structure of nanosheets, abundant oxygen vacancies, and the synergistic effect between Co₃O₄-NSs and CNTs are crucial factors for excellent electrochemical performance. Specifically, these characteristics favor rapid electron transfer, complete exposure of the active interface, and sufficient adsorption/desorption of electrolyte ions within the active material. This work gives insights into the efficient construction of two-dimensional hybrid electrodes with high performance for the new-generation energy storage system.

Mechanistic insight in site-selective and anisotropic etching of prussian blue analogues toward designable complex architectures for efficient energy storage

Engineering coordination compounds, e.g., prussian blue (PB) and its analogues (PBAs), with designable complex nanostructures via chemical etching holds great opportunities for improving energy storage performances by adjusting topological geometry, selectively exposing active sites, tuning electronic properties and enhancing accessible surface area. Unfortunately, it remains ambiguous particularly on site-selective and anisotropic etching behaviors. Herein, for the first time, we propose that two distinct regions are formed inside NiCo PBA (NCP) cubes due to the competition between classical ion-by-ion crystallization and non-classical crystallization based on aggregation. Such a unique structure ultimately determines not only the etching position but also the anisotropic pathway by selectively exposing unprotected Ni sites. According to this principle, complex PBA architectures, including nanocages, open nanocubes (constructed by six cones sharing the same apex), nanocones, and chamfer nanocubes can be intentionally obtained. After thermal annealing, NCP nanocones are converted to morning glory-like porous architectures composed of NiO/NiCo2O4 heterostructures with a mean particle size of 5 nm, which show improved rate performance and cycling stability.

A good-performance glucose sensor fabricated via rationally designing a new cobalt–metal–organic framework precursor

A good-performance glucose sensor based on Co₃O₄ has been first synthesized by rationally designing a new cobalt–metal–organic framework precursor.

Nanotechnology and nanomaterial-based no-wash electrochemical biosensors: from design to application

Nanotechnology and nanomaterial based electrochemical biosensors (ECBs) have achieved great development in many fields, such as clinical diagnosis, food analysis, and environmental monitoring. Nowadays, the single-handed pursuit of sensitivity and accuracy cannot meet the demands of detection in many in situ and point-of-care (POC) circumstances. More and more attention has been focused on simplifying the operation procedure and reducing detection time, and thus no-wash assay has become one of the most effective ways for the continuous development of ECBs. However, there are many challenges to realize no-wash detection in the real analysis, such as redox interferences, multiple impurities, non-conducting protein macromolecules, etc. Furthermore, the complex detection circumstance in different application fields makes the realization of no-wash ECBs more complicated and difficult. Thanks to the updated nanotechnology and nanomaterials, in-depth analysis of the obstacles in the detection process and various methods for fabricating no-wash ECBs, most issues have been largely resolved. In this review, we have systematically analyzed the nanomaterial based design strategy of the state-of-the-art no-wash ECBs in the past few years. Following that, we summarized the challenges in the detection process of no-wash ECBs and their applications in different fields. Finally, based on the summary and analysis in this review, we also evaluated and discussed future prospects from the design to the application of ECBs.

Electrostatically Assembling 2D Nanosheets of MXene and MOF-Derivatives into 3D Hollow Frameworks for Enhanced Lithium Storage

As an essential member of 2D materials, MXene (e.g., Ti₃ C₂ T_x ) is highly preferred for energy storage owing to a high surface-to-volume ratio, shortened ion diffusion pathway, superior electronic conductivity, and neglectable volume change, which are beneficial for electrochemical kinetics. However, the low theoretical capacitance and restacking issues of MXene severely limit its practical application in lithium-ion batteries (LIBs). Herein, a facile and controllable method is developed to engineer 2D nanosheets of negatively charged MXene and positively charged layered double hydroxides derived from ZIF-67 polyhedrons into 3D hollow frameworks via electrostatic self-assembling. After thermal annealing, transition metal oxides (TMOs)@MXene (CoO/Co₂ Mo₃ O₈ @MXene) hollow frameworks are obtained and used as anode materials for LIBs. CoO/Co₂ Mo₃ O₈ nanosheets prevent MXene from aggregation and contribute remarkable lithium storage capacity, while MXene nanosheets provide a 3D conductive network and mechanical robustness to facilitate rapid charge transfer at the interface, and accommodate the volume expansion of the internal CoO/Co₂ Mo₃ O₈ . Such hollow frameworks present a high reversible capacity of 947.4 mAh g^-1 at 0.1 A g^-1 , an impressive rate behavior with 435.8 mAh g^-1 retained at 5 A g^-1 , and good stability over 1200 cycles (545 mAh g^-1 at 2 A g^-1 ).

Polarity-assisted formation of hollow-frame sheathed nitrogen-doped nanofibrous carbon for supercapacitors

Heteroatom-doped carbon nanostructures with uniform size and morphology, well-designed architectures, and minimized interfacial resistance have been recognized as promising electrode materials for energy storage, but remain a crucial challenge. Herein, we develop a general approach of polarity-induced decoration of a monolayer sheath of metal-organic framework (MOF) particles with excellent uniformity in size and morphology on electrospun polymer nanofibers. These hybrid nanofibers are facilely converted into nitrogen-doped nanofibrous carbon (denoted as N-NFC) during pyrolysis. The thus-obtained N-NFC features (1) a one-dimensional nanofibrous structure with a highly conductive core, (2) a monolayer sheath of hollow carbon-frames with uniform size and morphology, (3) plenty of micro/mesopores with a highly accessible surface area, and (4) a high N-doping level, all of which guarantee its good electrochemical performance with a high capacitance of 387.3 F g-1 at 1 A g-1. In a solid-state supercapacitor, it delivers excellent rate capability (78.0 F g-1 at 0.2 A g-1 and 64.0 F g-1 at 1 A g-1), an enhanced energy density of 7.9 W h kg-1 at a power density of 219 W kg-1, and outstanding cycling stability with 90% capacity retained over 10 000 cycles at 1 A g-1.