Flexible Piezoresistive Polystyrene Composite Sensors Filled with Hollow 3D Graphitic Shells.

The objective of this research was to develop highly effective conductive polymer composite (CPC) materials for flexible piezoresistive sensors, utilizing hollow three-dimensional graphitic shells as a highly conductive particulate component. Polystyrene (PS), a cost-effective and robust polymer widely used in various applications such as household appliances, electronics, automotive parts, packaging, and thermal insulation materials, was chosen as the polymer matrix. The hollow spherical three-dimensional graphitic shells (GS) were synthesized through chemical vapor deposition (CVD) with magnesium oxide (MgO) nanoparticles serving as a support, which was removed post-synthesis and employed as the conductive filler. Commercial multi-walled carbon nanotubes (CNTs) were used as a reference one-dimensional graphene material. The main focus of this study was to investigate the impact of the GS on the piezoresistive response of carbon/polymer composite thin films. The distribution and arrangement of GS and CNTs in the polymer matrix were analyzed using techniques such as X-ray diffraction and scanning electron microscopy, while the electrical, thermal, and mechanical properties of the composites were also evaluated. The results revealed that the PS composite films filled with GS exhibited a more pronounced piezoresistive response as compared to the CNT-based composites, despite their lower mechanical and thermal performance.

Fast synthesis of large-area bilayer graphene film on Cu.

Bilayer graphene (BLG) is intriguing for its unique properties and potential applications in electronics, photonics, and mechanics. However, the chemical vapor deposition synthesis of large-area high-quality bilayer graphene on Cu is suffering from a low growth rate and limited bilayer coverage. Herein, we demonstrate the fast synthesis of meter-sized bilayer graphene film on commercial polycrystalline Cu foils by introducing trace CO2 during high-temperature growth. Continuous bilayer graphene with a high ratio of AB-stacking structure can be obtained within 20 min, which exhibits enhanced mechanical strength, uniform transmittance, and low sheet resistance in large area. Moreover, 96 and 100% AB-stacking structures were achieved in bilayer graphene grown on single-crystal Cu(111) foil and ultraflat single-crystal Cu(111)/sapphire substrates, respectively. The AB-stacking bilayer graphene exhibits tunable bandgap and performs well in photodetection. This work provides important insights into the growth mechanism and the mass production of large-area high-quality BLG on Cu.

Applications of Graphene in Five Senses, Nervous System, and Artificial Muscles.

Graphene remains of great interest in biomedical applications because of biocompatibility. Diseases relating to human senses interfere with life satisfaction and happiness. Therefore, the restoration by artificial organs or sensory devices may bring a bright future by the recovery of senses in patients. In this review, we update the most recent progress in graphene based sensors for mimicking human senses such as artificial retina for image sensors, artificial eardrums, gas sensors, chemical sensors, and tactile sensors. The brain-like processors are discussed based on conventional transistors as well as memristor related neuromorphic computing. The brain-machine interface is introduced for providing a single pathway. Besides, the artificial muscles based on graphene are summarized in the means of actuators in order to react to the physical world. Future opportunities remain for elevating the performances of human-like sensors and their clinical applications.

Strain Regulating and Kinetics Accelerating of Micro-Sized Silicon Anodes via Dual-Size Hollow Graphitic Carbons Conductive Additives.

Micro-sized silicon (µSi) anode features fewer interfacial side reactions and lower costs compared to nanosized silicon, and has higher commercial value when applied as a lithium-ion battery (LIB) anode. However, the high localized stress generated during (de)lithiation causes electrode breakdown and performance deterioration of the µSi anode. In this work, hollow graphitic carbons with tailored dual sizes are employed as conductive additives for the µSi anode to overcome electrode failure. The dual-size hollow graphitic carbons (HGC) additives consist of particles with micrometer size similar to the µSi particles; these additives are used for strain regulation. Additionally, nanometer-size particles similar to commercial carbon black Spheron (SP) are used mainly for kinetics acceleration. In addition to building an efficient conductive network, the dual-size hollow graphitic carbon conductive additive prevents the fracture of the electrode by reducing local stress and alleviating volume expansion. The µSi anode with dual-size hollow graphitic carbons as conductive additives achieves an impressive capacity of 651.4 mAh g-1 after 500 cycles at a high current density of 2 A g-1 . These findings suggest that dual-size hollow graphitic carbons are expected to be superior conductive additives for micro-sized alloy anodes similar to µSi.

Synergized N, P dual-doped 3D carbon host derived from filter paper for durable lithium metal anodes.

Lithium metal is deemed a promising anode material for the next-generation batteries with high specific energy. Unfortunately, the growth of Li dendrites and infinite volume change during cycling, caused by the "hostless" feature of metallic Li, have posed a great challenge to the commercialization of Li metal anode. The introduction of appropriate host materials for Li metal is highly desirable. In this work, a N, P dual-doped 3D carbon derived from low-cost quantitative filter paper (NPCQP) is designed and fabricated for direct using as a host for Li metal anode. The resulting NPCQP host achieves a high deposition/stripping Coulombic efficiency of above 97.5 % with a low nucleation overpotential. Moreover, the NPCQP@Li symmetric cells enable an excellent long-term cycling performance (1000 h) with an ultralow voltage hysteresis (12 mV) and stable interface behavior. When paired with the commercial LiFePO4 cathode, the full cell with NPCQP@Li anode displays impressive long-term cyclic stability and rate capability, outperforming the counter cell with bare Li anode. This contribution sheds light on the rational design of viable host for practical lithium metal anodes.

Mosaic Nanocrystalline Graphene Skin Empowers Highly Reversible Zn Metal Anodes.

Constructing a conductive carbon-based artificial interphase layer (AIL) to inhibit dendritic formation and side reaction plays a pivotal role in achieving longevous Zn anodes. Distinct from the previously reported carbonaceous overlayers with singular dopants and thick foreign coatings, a new type of N/O co-doped carbon skin with ultrathin feature (i.e., 20 nm thickness) is developed via the direct chemical vapor deposition growth over Zn foil. Throughout fine-tuning the growth conditions, mosaic nanocrystalline graphene can be obtained, which is proven crucial to enable the orientational deposition along Zn (002), thereby inducing a planar Zn texture. Moreover, the abundant heteroatoms help reduce the solvation energy and accelerate the reaction kinetics. As a result, dendrite growth, hydrogen evolution, and side reactions are concurrently mitigated. Symmetric cell harvests durable electrochemical cycling of 3040 h at 1.0 mA cm-2 /1.0 mAh cm-2 and 136 h at 30.0 mA cm-2 /30.0 mAh cm-2 . Assembled full battery further realizes elongated lifespans under stringent conditions of fast charging, bending operation, and low N/P ratio. This strategy opens up a new avenue for the in situ construction of conductive AIL toward pragmatic Zn anode.

Copper acetate-facilitated transfer-free growth of high-quality graphene for hydrovoltaic generators.

Direct synthesis of high-quality graphene on dielectric substrates without a transfer process is of vital importance for a variety of applications. Current strategies for boosting high-quality graphene growth, such as remote metal catalyzation, are limited by poor performance with respect to the release of metal catalysts and hence suffer from a problem with metal residues. Herein, we report an effective approach that utilizes a metal-containing species, copper acetate, to continuously supply copper clusters in a gaseous form to aid transfer-free growth of graphene over a wafer scale. The thus-derived graphene films were found to show reduced multilayer density and improved electrical performance and exhibited a carrier mobility of 8500 cm2 V-1 s-1. Furthermore, droplet-based hydrovoltaic electricity generator devices based on directly grown graphene were found to exhibit robust voltage output and long cyclic stability, in stark contrast to their counterparts based on transferred graphene, demonstrating the potential for emerging energy harvesting applications. The work presented here offers a promising solution to organize the metal catalytic booster toward transfer-free synthesis of high-quality graphene and enable smart energy generation.

Plasma Surface Engineering of NiCo2S4@rGO Electrocatalysts Enables High-Performance Li-O2 Batteries.

The sluggish redox reaction kinetics for aprotic Li-O2 batteries (LOBs) caused by the insulating discharge product of Li2O2 could result in the poor round-trip efficiency, low rate capability, and cyclic stability. To address these challenges, we herein fabricated NiCo2S4 supported on reduced graphene oxide (NiCo2S4@rGO), the surface of which is further modified via a unique low-pressure capacitive-coupled nitrogen plasma (CCPN-NiCo2S4@rGO). The high ionization environment of the plasma could etch the surface of NiCo2S4@rGO, introducing effective nitrogen doping. The as-prepared CCPN-NiCo2S4@rGO has been employed as an efficient catalyst for advanced LOBs. The electrochemical analysis, combined with theoretical calculations, reveals that the N-doping can effectively improve the thermodynamics and kinetics for LiO2 adsorption, giving rise to a well-knit Li2O2 formation on CCPN-NiCo2S4@rGO. The LOBs based on the CCPN-NiCo2S4@rGO oxygen electrode deliver a low overpotential of 0.75 V, a high discharge capacity of 10,490 mA h g-1, and an improved cyclic stability (more than 110 cycles). This contribution may pave a promising avenue for facile surface engineering of the electrocatalyst in LOBs and other energy storage systems.

General synthesis of 2D rare-earth oxide single crystals with tailorable facets.

Two-dimensional (2D) rare-earth oxides (REOs) are a large family of materials with various intriguing applications and precise facet control is essential for investigating new properties in the 2D limit. However, a bottleneck remains with regard to obtaining their 2D single crystals with specific facets because of the intrinsic non-layered structure and disparate thermodynamic stability of different facets. Herein, for the first time, we achieve the synthesis of a wide variety of high-quality 2D REO single crystals with tailorable facets via designing a hard-soft-acid-base couple for controlling the 2D nucleation of the predetermined facets and adjusting the growth mode and direction of crystals. Also, the facet-related magnetic properties of 2D REO single crystals were revealed. Our approach provides a foundation for further exploring other facet-dependent properties and various applications of 2D REO, as well as inspiration for the precise growth of other non-layered 2D materials.

Copper dendrite stabilized NiFe(OH)x electrocatalyst for durable alkaline hydrogen evolution over 1000 h.

Durable Cu/NiFe(OH)x electrocatalyst was designed for hydrogen evolution reaction in alkaline media. The in situ generated Cu nanodendrites protect the NiFe(OH)x from being hydrogenated, giving it a > 1000 h lifetime for high-performance water splitting (1.51 V, 10 mA cm-2 in 1 M KOH) when coupled with a NiFe-layered double hydroxide anode.

Accelerating O-Redox Kinetics with Carbon Nanotubes for Stable Lithium-Rich Cathodes.

Lithium-rich cathodes (LRCs) show great potential to improve the energy density of commercial lithium-ion batteries owing to their cationic and anionic redox characteristics. Herein, a complete conductive network using carbon nanotubes (CNTs) additives to improve the poor kinetics of LRCs is fabricated. Ex situ X-ray photoelectron spectroscopy first demonstrates that the slope at a low potential and the following long platform can be assigned to the transition metal and oxygen redox, respectively. The combination of galvanostatic intermittent titration technique and electrochemical impedance spectroscopy further reveal that a battery with CNTs exhibited accelerated kinetics, especially for the O-redox process. Consequently, LRCs with CNTs exhibit a much better rate and cycling performance (≈89% capacity retention at 2 C for over 200 cycles) than the Super P case. Eventually, TEM results imply that the improved electrochemical performance of the CNTs case also benefits from its more stable bulk and surface structures. Such a facile conductive additive modification strategy also provides a universal approach for the enhancement of the electron diffusion properties of other electrode materials.

Photocatalytic Abstraction of Hydrogen Atoms from Water Using Hydroxylated Graphitic Carbon Nitride for Hydrogenative Coupling Reactions.

Employing pure water, the ultimate green source of hydrogen donor to initiate chemical reactions that involve a hydrogen atom transfer (HAT) step is fascinating but challenging due to its large H-O bond dissociation energy (BDEH-O =5.1 eV). Many approaches have been explored to stimulate water for hydrogenative reactions, but the efficiency and productivity still require significant enhancement. Here, we show that the surface hydroxylated graphitic carbon nitride (gCN-OH) only requires 2.25 eV to activate H-O bonds in water, enabling abstraction of hydrogen atoms via dehydrogenation of pure water into hydrogen peroxide under visible light irradiation. The gCN-OH presents a stable catalytic performance for hydrogenative N-N coupling, pinacol-type coupling and dehalogenative C-C coupling, all with high yield and efficiency, even under solar radiation, featuring extensive impacts in using renewable energy for a cleaner process in dye, electronic, and pharmaceutical industries.

Eliminating Graphite Exfoliation with an Artificial Solid Electrolyte Interphase for Stable Lithium-Ion Batteries.

Although graphite materials with desirable comprehensive properties dominate the anode market of commercial lithium-ion batteries (LIBs), their low capacity during fast charging precludes further commercialization. In the present work, natural graphite (G) is reported not only to suffer from low capacity during fast charging, but also from charge failure after many charging cycles. Using different characterization techniques, severe graphite exfoliation, and continuously increasing solid electrolyte interphase (SEI) are demonstrated as reasons for the failure of G samples. An ultrathin artificial SEI is proposed, addressing these problems effectively and ensuring extremely stable operation of the graphite anode, with a capacity retention of ≈97.5% after 400 cycles at 1 C. Such an artificial SEI modification strategy provides a universal approach to tailoring and designing better anode materials for next-generation LIBs with high energy densities.

Au-activated N motifs in non-coherent cupric porphyrin metal organic frameworks for promoting and stabilizing ethylene production.

Direct implementation of metal-organic frameworks as the catalyst for CO2 electroreduction has been challenging due to issues such as poor conductivity, stability, and limited > 2e- products. In this study, Au nanoneedles are impregnated into a cupric porphyrin-based metal-organic framework by exploiting ligand carboxylates as the Au3+ -reducing agent, simultaneously cleaving the ligand-node linkage. Surprisingly, despite the lack of a coherent structure, the Au-inserted framework affords a superb ethylene selectivity up to 52.5% in Faradaic efficiency, ranking among the best for metal-organic frameworks reported in the literature. Through operando X-ray, infrared spectroscopies and density functional theory calculations, the enhanced ethylene selectivity is attributed to Au-activated nitrogen motifs in coordination with the Cu centers for C-C coupling at the metalloporphyrin sites. Furthermore, the Au-inserted catalyst demonstrates both improved structural and catalytic stability, ascribed to the altered charge conduction path that bypasses the incoherent framework. This study underlines the modulation of reticular metalloporphyrin structure by metal impregnation for steering the CO2 reduction reaction pathway.

An effective formaldehyde gas sensor based on oxygen-rich three-dimensional graphene.

Three-dimensional (3D) graphene with a high specific surface area and excellent electrical conductivity holds extraordinary potential for molecular gas sensing. Gas molecules adsorbed onto graphene serve as electron donors, leading to an increase in conductivity. However, several challenges remain for 3D graphene-based gas sensors, such as slow response and long recovery time. Therefore, research interest remains in the promotion of the sensitivity of molecular gas detection. In this study, we fabricate oxygen plasma-treated 3D graphene for the high-performance gas sensing of formaldehyde. We synthesize large-area, high-quality, 3D graphene over Ni foam by chemical vapor deposition and obtain freestanding 3D graphene foam after Ni etching. We compare three types of strategies-non-treatment, oxygen plasma, and etching in HNO3solution-for the posttreatment of 3D graphene. Eventually, the strategy for oxygen plasma-treated 3D graphene exceeds expectations, which may highlight the general gas sensing based on chemiresistors.

Ultrafast Single-Crystal-to-Single-Crystal Transformation from Metal-Organic Framework to 2D Hydroxide.

Single-crystal-to-single-crystal (SCSC) transformations have received considerable interest in crystal engineering, owing to providing a key platform for creating new materials. However, because of the limited tolerance of chemical bonds against the lattice strains, it is challenging to maintain the crystallinity when the structure changes dramatically. Here, a peculiar SCSC transformation from organic crystals to inorganic crystals, simultaneously achieving a drastic change in structure, connectivity, and dimension, is reported. As a demonstration, after reacting with liquid gallium, zeolitic imidazolate framework-8 (ZIF-8) can easily transform to 2D hydroxide single crystals. Interestingly, long-range ordered metallic atoms of hydroxide inherited from the ordered atomic arrangement of ZIF-8, but the connectivity is distinct. With good universality and extensibility, this transformation vastly expands the research scope of the SCSC transformations and provides a novel pathway for the synthesis of crystalline materials.

Mildly Oxidized MXene (Ti3C2, Nb2C, and V2C) Electrocatalyst via a Generic Strategy Enables Longevous Li-O2 Battery under a High Rate.

Lithium-oxygen batteries (LOBs) with ultrahigh theoretical energy density have emerged as one appealing candidate for next-generation energy storage devices. Unfortunately, some fundamental issues remain unsettled, involving large overpotential and inferior rate capability, mainly induced by the sluggish reaction kinetics and parasitic reactions at the cathode. Hence, the pursuit of suitable catalyst capable of efficiently catalyzing the oxygen redox reaction and eliminating the side-product generation, become urgent for the development of LOBs. Here, we report a universal synthesis approach to fabricate a suite of mildly oxidized MXenes (mo-Nb2CTx, mo-Ti3C2Tx, and mo-V2CTx) as cathode catalysts for LOBs. The readily prepared mo-MXenes possess expanded interlayer distance to accommodate massive Li2O2 formation, and in-situ-formed light metal oxide to enhance the electrocatalytic activity of MXenes. Taken together, the mo-V2CTx manages to deliver a high specific capacity of 22752 mAh g-1 at a current density of 100 mA g-1, and a long lifespan of 100 cycles at 500 mA g-1. More impressively, LOBs with mo-V2CTx can continuously operate for 90, 89, and 70 cycles, respectively, under a high current density of 1000, 2000, and 3000 mA g-1 with a cutoff capacity of 1000 mAh g-1. The theoretical calculations further reveal the underlying mechanism lies in the optimized surface, where the overpotentials for the formation/decomposition of Li2O2 are significantly reduced and the catalytic kinetics is accelerated. This contribution offers a feasible strategy to prepare MXenes as efficient and robust electrocatalyst toward advanced LOBs and other energy storage devices.

Promoting ethylene production over a wide potential window on Cu crystallites induced and stabilized via current shock and charge delocalization.

Electrochemical CO2 reduction (CO2RR) in a product-orientated and energy-efficient manner relies on rational catalyst design guided by mechanistic understandings. In this study, the effect of conducting support on the CO2RR behaviors of semi-conductive metal-organic framework (MOF) - Cu3(HITP)2 are carefully investigated. Compared to the stand-alone MOF, adding Ketjen Black greatly promotes C2H4 production with a stabilized Faradaic efficiency between 60-70% in a wide potential range and prolonged period. Multicrystalline Cu nano-crystallites in the reconstructed MOF are induced and stabilized by the conducting support via current shock and charge delocalization, which is analogous to the mechanism of dendrite prevention through conductive scaffolds in metal ion batteries. Density functional theory calculations elucidate that the contained multi-facets and rich grain boundaries promote C-C coupling while suppressing HER. This study underlines the key role of substrate-catalyst interaction, and the regulation of Cu crystalline states via conditioning the charge transport, in steering the CO2RR pathway.

Mechanistic Probing of Encapsulation and Confined Growth of Lithium Crystals in Carbonaceous Nanotubes.

Encapsulation of lithium in the confined spaces within individual nanocapsules is intriguing and highly desirable for developing high-performance Li metal anodes. This work aims for a mechanistic understanding of Li encapsulation and its confined growth kinetics inside 1D enclosed spaces. To achieve this, amorphous carbon nanotubes are employed as a model host using in situ transmission electron microscopy. The carbon shells have dual roles, providing geometric/mechanical constraints and electron/ion transport channels, which profoundly alter the Li growth patterns. Li growth/dissolution takes place via atom addition/removal at the free surfaces through Li+ diffusion along the shells in the electric field direction, resulting in the formation of unusual Li structures, such as poly-crystalline nanowires and free-standing 2D ultrathin (1-2 nm) Li membranes. Such confined front-growth processes are dominated by Li {110} or {200} growing faces, distinct from the root growth of single-crystal Li dendrites outside the nanotubes. Controlled experiments show that high lithiophilicity/permeability, enabled by sufficient nitrogen/oxygen doping or pre-lithiation, is critical for the stable encapsulation of lithium inside carbonaceous nanocapsules. First-principles-based calculations reveal that N/O doping can reduce the diffusion barrier for Li+ penetration, and facilitate Li filling driven by energy minimization associated with the formation of low-energy Li/C interfaces.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection.

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.