Jixin Zhu

2D Black Phosphorus for Energy Storage and Thermoelectric Applications

Recent progress in the currently available methods of producing black phosphorus bulk and phosphorene are presented. The effective passivation approaches toward improving the air stability of phosphorene are also discussed. Furthermore, the research efforts on the phosphorene and phosphorene-based materials for potential applications in lithium ion batteries, sodium ion batteries, and thermoelectric devices are summarized and highlighted. Finally, the outlook including challenges and opportunities in these research fields are discussed.

General solution-processed formation of porous transition-metal oxides on exfoliated molybdenum disulfides for high-performance asymmetric supercapacitors

The combination of hierarchical porous transition-metal oxides with ultrathin two-dimensional (2D) transition-metal dichalcogenides (TMDs) with a favorable electrochemical performance beyond single-component materials is still very challenging. The present work demonstrates the general and targeted synthesis of hybrid heterostructures by the integration of porous transition-metal oxides (TMOs, e.g. NiO, Co3O4 and Fe2O3) and 2D MoS2 nanosheets. The as-prepared vertically aligned MoS2–NiO hybrids exhibit an excellent pseudocapacitive performance, such as a high specific capacitance of 1080.6 at 1 A g−1 and long cycling durability with 101.9% capacitance retention after 9000 cycles at 2 A g−1. This facile strategy using low-cost precursors is regarded as a general method to hybridize 2D MoS2 with other porous TMOs, such as Co3O4 and Fe2O3, with largely improved pseudocapacitive performances due to a favorable synergistic effect between MoS2 and TMOs with an enhanced electronic/ionic transport. Asymmetric supercapacitors using MoS2–TMO hybrids as both positive and negative electrodes are also demonstrated. As a proof-of-concept, the as-assembled MoS2–NiO//MoS2–Fe2O3 asymmetric supercapacitor operating within the potential window of 0–1.8 V delivers a high energy density of 39.6 W h kg−1 with a long cycle life and excellent rate capability.

Ultrathin and large-sized vanadium oxide nanosheets mildly prepared at room temperature for high performance fiber-based supercapacitors

Ultrathin vanadium oxide (V2O5) nanosheets with lateral sizes of up to tens of micrometers were synthesized, and then incorporated into multi-walled carbon nanotube (MWCNT) fibers. The solid-state supercapacitor based on such hybrid fibers exhibited an improved volumetric capacitance of 31 F cm−3 at 1.0 A cm−3, and a volumetric energy density of 2.1 mW h cm−3 at 1.5 W cm−3.

Pt nanoparticles grown on 3D RuO2-modified graphene architectures for highly efficient methanol oxidation

Platinum-based electrode catalysts for the methanol oxidation reaction are at the heart of direct methanol fuel cell technology, while their high cost and short lifespan have greatly hindered their large-scale commercial application. Herein, we put forward a facile self-assembly approach to construct 3D porous electrocatalysts made from ultrafine Pt nanoparticles, RuO2 and graphene aerogels. Benefiting from the unique textural features as well as remarkable synergetic effect, the resulting 3D Pt/RuO2/graphene architectures possess exceptional electrocatalytic performance in terms of surprisingly high activity, strong anti-poisoning ability and reliable stability toward methanol electrooxidation, holding great potential as substitutes for conventional Pt/carbon catalysts. This study may offer new insights for the development of various 3D metal oxide-modified graphene supported catalysts for a wide range of applications in the near future.

Leaf-inspired interwoven carbon nanosheet/nanotube homostructures for supercapacitors with high energy and power densities

The rational design and scalable synthesis of hierarchical porous carbon as an electrode material for high-energy-density supercapacitors has drawn wide interest. Herein, we report an environmentally friendly one-pot strategy for the synthesis of interwoven carbon nanotube (CNT)/carbon nanosheet (CNS) sandwiches in a molten salt. Green and cheap biomass glucose was chosen as the precursor for producing CNSs at a pyrolysis temperature of 700 °C in a conventional inorganic salt mixture (LiCl and KCl eutectic), while commercially available CNTs were introduced as veins sandwiched with CNS laminae. Relying on the compositional and structural superiorities benefitting from mimicking net-veined leaves, the unique CNT/CNS sandwiches manifest excellent electrochemical capacitive performance in terms of high specific energy (23.6 W h kg−1), excellent rate capacitance retention (∼75% at 10 A g−1) and exceptional cycling stability (capacitance retention of ∼100% after 5000 cycles).

Carbon Necklace Incorporated Electroactive Reservoir Constructing Flexible Papers for Advanced Lithium–Ion Batteries

Metal-organic frameworks (MOFs) and their derivatives with well-defined structures and compositions show great potential for wide applications such as sensors, catalysis, energy storage, and conversion, etc. However, poor electric conductivity and large volume expansion are main obstacles for their utilization in energy storage, e.g., lithium-ion batteries and supercapacitors. Herein, a facile strategy is proposed for embedding the MOFs, e.g., ZIF-67 and MIL-88 into polyacrylonitrile fibers, which is further used as a template to build a 3D interconnected conductive carbon necklace paper. Owing to the unique structure features of good electric conductivity, interconnected frameworks, electroactive reservoir, and dual dopants, the obtained flexible electrodes with no additives exhibit high specific capacities, good rate capability, and prolonged cycling stability. The hollow dodecahedral ZIF-67 derived carbon necklace paper delivers a high specific capacity of 1200 mAh g-1 and superior stability of more than 400 cycles without capacity decay. Moreover, the spindle-like MIL-88 derived carbon necklace paper shows a high reversible capacity of 980 mAh g-1 . Their unique 3D interconnected structure and outstanding electrochemical performance pave the way for extending the MOF-based interweaving materials toward potential applications in portable and wearable electronic devices.

MoSe2 Nanosheet Array with Layered MoS2 Heterostructures for Superior Hydrogen Evolution and Lithium Storage Performance

Engineering heterostructures of transition metal disulfides through low-cost and high-yield methods instead of using conventional deposition techniques still have great challenges. Herein, we present a conveniently operated and low-energy-consumption solution-processed strategy for the preparation of heterostructures of MoSe2 nanosheet array on layered MoS2, among which the two-dimensional MoS2 surface is uniformly covered with high-density arrays of vertically aligned MoSe2. The unique compositional and structural features of the MoS2-MoSe2 heterostructures not only provide more exposed active sites for sequent electrochemical process, but also facilitate the ion transfer due to the open porous space within the nanosheet array serving as well-defined ionic reservoirs. As a proof of concept, the MoS2-MoSe2 heterostructures serve as promising bifunctional electrodes for both energy conversions and storages, which exhibit an active and acid-stable activity for catalyzing the hydrogen evolution reaction, high specific capacity of 728 F g-1 at 0.1 A g-1, and excellent durability with a remained capacity as high as 676 mA h g-1 after 200 cycles.

Interlayer-Expanded Metal Sulfides on Graphene Triggered by a Molecularly Self-Promoting Process for Enhanced Lithium Ion Storage

A general synthetic approach has been demonstrated to fabricate three-dimensional (3D) structured metal sulfides@graphene, employing few-layered sulfide nanostructures with expanded interlayer spacing of the (002) plane (e.g., 0.98 nm for MoS2 nanoclusters and 0.65 nm for VS4 nanoribbons) and electrically conductive graphene as ideal building blocks. Here, small molecules (thioacetamide) acting as both the sulfur source and, more importantly, the structure-directing agent adjusting the interlayer spacing are wisely selected, further contributing to a sufficient space for ultrafast Li+ ion intercalation. The appealing features of a mechanically robust backbone, ultrathin thickness, abundant exposure of interlayer edges, and good electrical conductivity in such 3D architectures are favorable for providing easy access for the electrolyte to the structures and offering a shortened diffusion length of Li+ when utilized for energy storage. As a proof of concept, the electrochemical behavior of the resulting 3D structured metal sulfides@graphene as an anode material of lithium ion batteries (LIBs) is systematically investigated. As a consequence, high specific capacities, long lifespans, and superior rate capabilities have been realized in such well-designed architectures, e.g. maintaining a specific capacity as high as 965 mAh g-1 for 120 cycles for VS4@graphene and 1100 mAh g-1 for 150 cycles for MoS2@graphene.

Hierarchical Nanostructures of Nitrogen-Doped Porous Carbon Polyhedrons Confined in Carbon Nanosheets for High-Performance Supercapacitors

Interconnected close-packed nitrogen-doped porous carbon polyhedrons (NCPs) confined in two-dimensional carbon nanosheets (CNSs) have been prepared through a sustainable one-pot pyrolysis of a simple solid mixture of zeolitic imidazolate framework-8 (ZIF-8) crystals and with organic potassium as the precursors. The hierarchically organized framework of the NCP-CNS composites enables NCPs and CNSs to act as well-defined electrolyte reservoirs and mechanical buffers accommodating large volume expansions of NCPs, respectively. Among the unique composite nanostructures, the NCPs with vast micropores provide electric double-layer capacitances, while the CNSs bridge the individual NCPs to form a conductive pathway with a hierarchical porosity. As a result, the NCP-CNS composites with high electrical integrity and structural stability are used as electrode materials for high-performance supercapacitors, which exhibit excellent electrochemical capacitive characteristics in terms of an outstanding capacitance of 300 F g-1 at 1 A g-1, large energy density of 20.9 W h kg-1, and great cycling performance of 100% retention after 6000 cycles. This work therefore presents a one-pot and efficient strategy to prepare an ordered arrangement of ZIF-8-derived porous carbons toward new electrode materials in promising energy storage systems.

Ultrasensitive detection of trypsin activity and inhibitor screening based on the electron transfer between phosphorescence copper nanocluster and cytochrome c

Trypsin, as one of important proteases, is specific for catalyzing the hydrolysis of peptide and ester bonds containing lysine and arginine residues at the C-terminus. The level of trypsin in biological fluids can serve as a reliable and specific diagnostic biomarker for pancreatic function and its pathological changes. Herein, we demonstrate the application of phosphorescent Cu NCs for trypsin detection for the first time depending on the electron transfer between Cu NCs and cyt c. Cyt c and Cu NCs were selected as the quencher and the fluorophore, respectively. Cu NCs could bind to the positively charged cyt c through electrostatic and hydrophobic interactions, and the phosphorescence of Cu NCs was efficiently quenched by the metal-containing heme of cyt c. In the presence of trypsin, cyt c was digested, thus phosphorescence of Cu NCs remained. Therefore, a new and continuous phosphorescence assay for the detection of trypsin activity and its inhibitor screening was established. The plot of relative fluorescence versus trypsin concentration obtains a good linear detection range from 0 to 20u202fng/mL (R2 =u202f0.9657), and a detection limit of 2u202fng/mL, which is much lower than 20u202fng/mL of the sensor in buffer solution because of urine amplifying the phosphorescence signal of Cu NCs based on the FRET strategy. This assay still has been successfully applied to trypsin inhibitor screening, demonstrating its potential application in drug discovery.