Designing energy storage devices from thick carbon electrodes with high areal/volumetric energy density via a simple and green way is very attractive but still challenging. Cellulose, as an excellent ...precursor for thick carbon electrodes with abundant sources and low cost, is usually activated by a chemical activator and pyrolysis route to achieve high electrochemical performance. However, there are still some problems to be addressed, such as the harsh activation conditions, easy collapse of porous structures, and the high cost. Herein, a 3D self‐supporting thick carbon electrode derived from wood‐based cellulose is proposed for high areal and volumetric energy density of supercapacitor from a mild, simple, and green enzymolysis treatment. Benefiting from the high specific surface area (1418 m2 g−1) and abundant active sites on the surface of wood‐derived hierarchically porous structures and enzymolysis‐induced micropores and mesopores, the assembled symmetry supercapacitor from the thick carbon electrode can realize the high areal/volumetric energy density of 0.21 mWh cm−2/0.99 mWh cm−3 with excellent stability of 86.58% after 15 000 long‐term cycles at 20 mA cm−2. Significantly, the simple and universal strategy to design material with high specific surface area, provides a new research idea for realizing multi‐functional application.
Thick carbon electrode with high specific surface area (1418 m2 g−1) and abundant active sites is fabricated from the enzymolysis of bass wood. The assembled symmetry supercapacitor from such a thick carbon electrode can realize the high areal/volumetric energy density of 0.21 mWh cm−2/0.99 mWh cm−3 with an excellent stability of 86.58% after 15 000 long‐term cycles at 20 mA cm−2.
To address the problem of the serious capacity fading in lithium–sulfur batteries, a multi‐functional PEO(polyethylene oxide)/LiFSI (lithium bis(fluorosulfonyl)imide)/PVDF (polyvinylidene fluoride) ...(PLP) gel polymer electrolyte is exploited by coating PLP on a carbon nanotubes (CNTs) based sulfur cathode (PLP‐S/CNTs) with a controlled thermal annealing process. The annealing process leads to the conformal infusion of PLP through the matrix of S/CNTs with retaining the amorphous phase of the PLP, which enhance the rate performance compared to the bare S/CNTs. The PLP coating drives the transformation of more elemental sulfur to Li2S2/Li2S without forming intermediary product by restraining soluble‐polysulfides formation. Furthermore, the PLP coating successfully inhibits the dissolution of Li2Sx (x > 4) in PEO and prevents the loss of active material in the cathode, which is confirmed by density functional theory calculations. Comprehensively, the PLP coating applied to the surface of the S/CNTs cathode exhibit significantly suppressed shuttle effect and greatly improve long‐term cycle stability of the lithium–sulfur battery. The synthesized PLP‐coated S/CNTs composite cathode demonstrates a high specific capacity of 573.6 mAh g−1 at a current density of 0.5 C after 1 000 cycles, even achieving 318.1 mAh g−1 at an extremely high C‐rate (6 C). which is unprecedented performance among the reported studies on coating technology.
A PEO‐LiFSI‐PVDF (PLP)‐coated S/CNTs retains high discharge capacity (573.6 mA h−1 at 0.5 C) after long‐term operation (1000 cycles) and even achieves a high discharge capacity of 318.1 mA h−1 at high rate operation of 6 C. Notably, simple coating of PLP may help bridge the gap between lab‐scale studies and industrialization of Li–S batteries.
For the proliferation of the supercapacitor technology, it is essential to attain superior areal and volumetric performance. Nevertheless, maintaining stable areal/volumetric capacitance and rate ...capability, especially for thick electrodes, remains a fundamental challenge. Here, for the first time, a rationally designed porous monolithic electrode is reported with high thickness of 800 µm (46.74 mg cm−2, with high areal mass loading of NiCo2S4 6.9 mg cm−2) in which redox‐active Ag nanoparticles and NiCo2S4 nanosheets are sequentially decorated on highly conductive wood‐derived carbon (WC) substrates. The hierarchically assembled WC@Ag@NiCo2S4 electrode exhibits outstanding areal capacitance of 6.09 F cm−2 and long‐term stability of 84.5% up to 10 000 cycles, as well as exceptional rate capability at 50 mA cm−2. The asymmetric cell with an anode of WC@Ag and a cathode of WC@Ag@NiCo2S4 delivers areal/volumetric energy density of 0.59 mWh cm−2/3.93 mWh cm−3, which is much‐improved performance compared to those of most reported thick electrodes at the same scale. Theoretical calculations verify that the enhanced performance could be attributed to the decreased adsorption energy of OH− and the down‐shifted d‐band of Ag atoms, which can accelerate the electron transport and ion transfer.
High conductivity wood‐based carbon WC@Ag@NiCo2S4 thick composite electrodes show high areal/volumetric energy density. The electrode exhibits outstanding areal capacitance of 6.09 F cm−2 and supercapacitance retention of 84.5% up to 10 000 cycles (50 mA cm−2). The assembled asymmetric supercapacitor with WC@Ag anode and WC@Ag@NiCo2S4 cathode delivers areal and volumetric energy density of 0.59 mWh cm−2 and 3.93 mWh cm−3, respectively.
Highly sensitive and selective chemical sensors are needed for use in a wide range of applications such as environmental toxic gas monitoring, disease diagnosis, and food quality control. Although ...some chemiresistive sensors have been commercialized, grand challenges still remain: ppb-level sensitivity, accurate cross-selectivity, and long-term stability. Metal-organic frameworks (MOFs) with record-breaking surface areas and ultrahigh porosity are ideal sensing materials because chemical sensors rely highly on surface reactions. In addition, MOFs can be used as a membrane to utilize their unique gas adsorption and separation characteristics. Furthermore, the use of MOFs as precursors to enable facile production of various nanostructures is further combined with other functional materials. Based on these fascinating features of MOFs, there have been great efforts to elucidate reaction mechanisms and address limitations in MOF-based chemiresistors. In this review, we present a comprehensive overview and recent progress in chemiresistive sensors developed by using pure MOFs, MOF membranes, and MOF derivatives.
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Metal-organic frameworks (MOFs) have attracted much attention in diverse research communities because of their ultrahigh surface areas, high porosity, and tunable structures. In particular, MOFs are considered one of the most ideal sensing materials since chemical sensing properties are mainly influenced by surface reactions. Recently, the use of MOFs in chemiresistive sensors that transduce electrical signals from surface reactions has rapidly emerged. The development of conductive MOFs has fueled the use of pure MOFs as a new class of chemiresistors. MOFs with unique gas adsorption and separation properties also enable their use in gas sensors as selective filtration layers. In addition, as sacrificial templates, MOFs can be converted to various types of gas-sensitive nanomaterials such as carbon composites and metal oxides via controlled pyrolysis or calcination. In this review, we summarize the latest studies on MOF-based chemiresistive sensors and suggest future research directions.
Metal-organic frameworks (MOFs) have rapidly emerged in the field of chemiresistive sensors because of their ultrahigh surface area with high porosity, unique gas adsorption and separation properties, and ability to serve as sacrificial templates to produce various nanomaterials. In this review, we summarize a comprehensive overview and recent studies on MOFs for chemiresistive sensors, including pure MOFs, MOF membranes, and MOF derivatives.
Humidity sensors are essential components in wearable electronics for monitoring of environmental condition and physical state. In this work, a unique humidity sensing layer composed of ...nitrogen‐doped reduced graphene oxide (nRGO) fiber on colorless polyimide film is proposed. Ultralong graphene oxide (GO) fibers are synthesized by solution assembly of large GO sheets assisted by lyotropic liquid crystal behavior. Chemical modification by nitrogen‐doping is carried out under thermal annealing in H2(4%)/N2(96%) ambient to obtain highly conductive nRGO fiber. Very small (≈2 nm) Pt nanoparticles are tightly anchored on the surface of the nRGO fiber as water dissociation catalysts by an optical sintering process. As a result, nRGO fiber can effectively detect wide humidity levels in the range of 6.1–66.4% relative humidity (RH). Furthermore, a 1.36‐fold higher sensitivity (4.51%) at 66.4% RH is achieved using a Pt functionalized nRGO fiber (i.e., Pt‐nRGO fiber) compared with the sensitivity (3.53% at 66.4% RH) of pure nRGO fiber. Real‐time and portable humidity sensing characteristics are successfully demonstrated toward exhaled breath using Pt‐nRGO fiber integrated on a portable sensing module. The Pt‐nRGO fiber with high sensitivity and wide range of humidity detection levels offers a new sensing platform for wearable humidity sensors.
Nitrogen‐doped graphene fiber functionalized by Pt nanoparticles (Pt‐nRGO fiber) is integrated on a flexible and transparent polyimide substrate for application in real‐time and on‐site monitoring of humidity. This work demonstrates the humidity sensing characteristic of Pt‐nRGO fiber, which further expands versatility of graphene‐based fiber in wearable sensing electronics.
Two-dimensional (2D) nanostructures are gaining tremendous interests due to the fascinating physical, chemical, electrical, and optical properties. Recent advances in 2D nanomaterials synthesis have ...contributed to optimization of various parameters such as physical dimension and chemical structure for specific applications. In particular, development of high performance gas sensors is gaining vast importance for real-time and on-site environmental monitoring by detection of hazardous chemical species. In this review, we comprehensively report recent achievements of 2D nanostructured materials for chemiresistive-type gas sensors. Firstly, the basic sensing mechanism is described based on charge transfer behavior between gas species and 2D nanomaterials. Secondly, diverse synthesis strategies and characteristic gas sensing properties of 2D nanostructures such as graphene, metal oxides, transition metal dichalcogenides (TMDs), metal organic frameworks (MOFs), phosphorus, and MXenes are presented. In addition, recent trends in synthesis of 2D heterostructures by integrating two different types of 2D nanomaterials and their gas sensing properties are discussed. Finally, this review provides perspectives and future research directions for gas sensor technology using various 2D nanomaterials.
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Though highly promising as powerful gas sensors, oxide semiconductor chemiresistors have low surface reactivity, which limits their selectivity, sensitivity, and reaction kinetics, particularly at ...room temperature (RT) operation. It is proposed that a hybrid design involving the nanostructuring of oxides and passivation with selective gas filtration layers can potentially overcome the issues with surface activity. Herein, unique bi‐stacked heterogeneous layers are introduced; that is, nanostructured oxides covered by conformal nanoporous gas filters, on ultrahigh‐density nanofiber (NF) yarns via sputter deposition with indium tin oxide (ITO) and subsequent self‐assembly of zeolitic imidazolate framework (ZIF‐8) nanocrystals. The NF yarn composed of ZIF‐8‐coated ITO films can offer heightened surface activity at RT because of high porosity, large surface area, and effective screening of interfering gases. As a case study, the hybrid sensor demonstrated remarkable sensing performances characterized by high NO selectivity, fast response/recovery kinetics (>60‐fold improvement), and large responses (12.8‐fold improvement @ 1 ppm) in comparison with pristine yarn@ITO, especially under highly humid conditions. Molecular modeling reveals an increased penetration ratio of NO over O2 to the ITO surface, indicating that NO oxidation is reliably prevented and that the secondary adsorption sites provided by the ZIF‐8 facilitate the adsorption/desorption of NO, both to and from ITO.
A multifunctional chemiresistive gas sensor composed of nanofiber yarn sputter‐deposited with indium tin oxide (ITO) as a sensing layer is designed, and then coated with zeolitic imidazolate framework (ZIF‐8) for nanofiltration of gas analytes. Through comprehensive sensing experiments and molecular modeling, it is demonstrated that yarn@ITO@ZIF‐8 exhibits highly sensitive and selective sensing properties toward NO at room temperature with accelerated responding speeds.
Achieving an improved understanding of catalyst properties, with ability to predict new catalytic materials, is key to overcoming the inherent limitations of metal oxide based gas sensors associated ...with rather low sensitivity and selectivity, particularly under highly humid conditions. This study introduces newly designed bimetallic nanoparticles (NPs) employing bimetallic Pt‐based NPs (PtM, where M = Pd, Rh, and Ni) via a protein encapsulating route supported on mesoporous WO3 nanofibers. These structures demonstrate unprecedented sensing performance for detecting target biomarkers (even at p.p.b. levels) in highly humid exhaled breath. Sensor arrays are further employed to enable pattern recognition capable of discriminating between simulated biomarkers and controlled breath. The results provide a new class of multicomponent catalytic materials, demonstrating potential for achieving reliable breath analysis sensing.
Effective strategy to readily synthesize highly dispersed Pt‐based bimetallic (PtM, where M = Pd, Rh, and Ni) NPs as a new class of active catalysts is successfully developed on the highly porous architecture of 1D WO3 nanofibers via a protein template, i.e., apoferritin, in combination with the electrospinning method for superior exhaled‐breath sensors.
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