Rational Design of a Low-Dimensional and Metal-free Heterostructure for Efficient Water Oxidation: DFT and Experimental Studies.

A nitrogen-doped fullerene dimer is synthesized and compounded with multi-walled carbon nanotubes (MWCNTs) to construct a low-dimensional and metal-free 0D-1D heterostructure for electrocatalytic water oxidation. The (C59N)2/MWCNTs heterostructure exhibits a highly efficient performance, as verified by both first-principles density functional theory and experimental studies. The *O → *OOH process is confirmed as the rate-determining step of water oxidation. The negatively charged N-doping leads to electronic redistribution and intermolecular charge transfer and thus reduces the uphill free energies of intermediates on the (C59N)2/MWCNTs interface. Therefore, the (C59N)2/MWCNTs heterostructure has great potential to emit light and heat in metal-free-based electrocatalytic water oxidation.

Metal Oxide/Nitrogen-Doped Carbon Nanosheet Heteronanostructures as Highly Efficient Electromagnetic Wave Absorbing Materials.

In this paper, we will discuss the excellent broadband microwave absorption behaviors of Cu/CuO/carbon nanosheet composites: traces of copper and oxide embedded in a carbon nano-sheet not only cut down the high permittivity of adsorbs but also induce more interfacial polarization centers. The results showed that at a cracking temperature of 900 °C, the fabricated material has a unique ripple-like structure, which promotes the hierarchical interfacial polarization. The prepared material has a maximum absorption bandwidth of 4.48 GHz at an exceedingly thin thickness of 1.7 mm and a maximum reflection loss of -25.3 dB at a thickness of 2 mm. It is a relatively ideal material for electromagnetic wave absorption.

Synchronous Sound Recognition and Energy Harvesting by Flexible Piezoelectric PLLA/VB2 Composites.

In the present study, poling-free PLLA/VB2 piezoelectric composites are fabricated to achieve synchronous sound recognition and energy harvesting. The addition of VB2 can interact with PLLA by intermolecular hydrogen bonding, inducing the dipole orientation of C=O in PLLA. Meanwhile, VB2 can promote crystallization of PLLA through heterogeneous nucleation. The combination of the two strategies significantly improves the piezoelectric performance of PLLA/VB2 composites. The PLLA/VB2 can detect the sound frequency with an accuracy of 0.1% in the range of 0-20 kHz to recognize characteristic sounds from a specific source. PLLA/VB2 can also convert sound into electrical energy synchronously with an energy density of 0.2 W/cm-3 to power up LEDs. Therefore, PLLA/VB2 shows great potential in the field of information and energy synchronous collection.

Plasma-induced oxygen defects in titanium dioxide to address the long-term stability of pseudocapacitive MnO2 anode for lithium ion batteries.

In this work, we developed Manganese and Titanium based oxide composites with oxygen defects (MnOx@aTiOy) via plasma processing as anodes of lithium ion batteries. By appropriately adjusting the defect concentration, the ion transport kinetics and electrical conductivity of the electrodes are significantly improved, showing stable capacity retention. Furthermore, the incremental capacity is further activated and long-term stable cycling performance is achieved, with a specific capacity of 829.5 mAh/g at 1 A/g after 2000 cycles. To scrutinize the lithium migration paths and energy barriers in MnO2 and Mn2O3, the density functional theory (DFT) calculations is performed to explore the lithium migration paths and energy barriers. Although the transformation of MnO2 into Mn2O3 through oxygen defects was initially surmised to inhibit Li ions along their standard routes, our results indicate quite the contrary. In fact, the composite's lithium diffusion rate saw a substantial increase. This can be accredited to the pronounced enhancement of conductivity and ion transport efficiency in the amorphous and porous TiOy.

Fabrication of an Ultralight Ni-MOF-rGO Aerogel with Both Dielectric and Magnetic Performances for Enhanced Microwave Absorption: Microspheres with Hollow Structure Grow onto the GO Nanosheets.

An ultralight Ni-MOF-rGO aerogel which possess the merits of not only broad bandwidth and strong absorption but also lightweight and thin matching thickness is fabricated through a hydrothermal treatment, freeze-drying, and annealing procedure. The Ni@C microspheres are dispersed randomly and evenly on the graphene oxide (GO) nanosheets, which can be proved through SEM and TEM results. The electromagnetic parameters of the composite can be adjusted by changing the mass ratio of the MOF and GO to endow the material with both good impedance matching and superior electromagnetic wave absorption performances. Consequently, the resulting composite shows outstanding microwave absorption performance, which achieves strong absorption (-51.19 dB) and broad effective absorption bandwidth (6.32 GHz) with a thickness of 1.9 mm while the filling content is only 2 wt %. In addition, the multiple loss mechanisms of the Ni-MOF-rGO aerogel are illustrated, including conduction loss, dipolar polarization, interfacial polarization, magnetic resonance, and eddy current loss. In a word, the extraordinary microwave absorption performance is ascribed to the synergistic effects of the unique multiple layered structure of GO and the hollow core-shell structure of the Ni@C microsphere. This work demonstrates that the ultralight aerogel with excellent electromagnetic wave absorption performance is a promising strategy for microwave absorption application.

Modulation of electromagnetic wave absorption via porosity in Pechini-derived carbon guided by a random network model.

It is well established that porosity in carbon materials can benefit electromagnetic wave absorption by providing stronger interfacial polarization, better impedance matching, multiple reflections, and lower density, but an in-depth assessment is still lacking on this issue. The random network model describes the dielectric behavior of a conduction-loss absorber-matrix mixture with two parameters related to the volume fraction and conductivity, respectively. In this work, the porosity in carbon materials was tuned by a simple, green, and low-cost Pechini method, and the mechanism of how porosity affects EM wave absorption was investigated quantitatively based on the model. It was discovered that porosity was crucial for the formation of a random network, and a higher specific pore volume led to a larger volume fraction parameter and a lower conductivity parameter. Guided by the high throughput parameter sweeping based on the model, the Pechini-derived porous carbon could achieve an effective absorption bandwidth of 6.2 GHz at 2.2 mm. This study further verifies the random network model, unveiling the implication and influencing factors of the parameters, and opens a new path to optimize the electromagnetic wave absorption performance of conduction-loss materials.

Metal-organic framework-derived self-supporting metal boride for efficient electrocatalytic oxygen evolution reaction.

Metal boride has been verified as the highly efficient catalyst for oxygen evolution reaction. However, the design and synthesis of self-supporting metal borides remain a big challenge. Herein, metal-organic framework-derived metal boride electrode is in-situ formed on 3D framework via controllable boronation strategy, which is of great significance to the construction of self-supporting metal borides. This strategy not only produces the metal boride materials but also achieves the metal borides based self-supporting electrode with multiple structures. The as-fabricated CoFe-PBA-B exhibits a low overpotential of 255 mV at the current density of 10 mA cm-2 and a low Tafel slope of 51 mV dec-1 due to the enhanced active sites of multiple structures and effective electronic interaction between metal atoms and boron atom. In addition, CoFe-PBA-B shows good stability with negligible weaken in current density for 40 h. This work provides new boulevard for the design and synthesis of self-supporting metal borides for electrochemical OER.

Ultra-thin graphene cube framework@TiO2 heterojunction as high-performance anode materials for lithium ion batteries.

Here, we proposed a new strategy to build the integrated graphene cube (Gr) framework@TiO2 composite to improve the ion transport kinetics and electrical conductivity of TiO2 as a long-life and high-capacity anode for lithium ion batteries. Combined with the salt template method for ultra-thin framework, the distinct structure of Gr@TiO2 shows an excellent electrochemical performance, e.g., initial coulombic efficiency (ICE), rate performance and specific capacity, due to the increased kinetics of lithium ions. Through this method, the integrity is dramatically improved and the pulverization and agglomeration of the anode after long-term cycles are restrained. The optimized Gr@TiO2 displays a high stable reversible capacity of 179.5 mAh g-1 after 4000 cycles at 1 A g-1, excellent rate performance (125.5 mAh g-1 at 5 A g-1). Kinetic studies through Electrochemical Impedance Spectra, Galvanostatic Intermittent Titration Technique and Linear Sweep Voltammetry confirm that the electrical conductivity and ion transport kinetics are dramatically improved through the ultra-thin graphene cube framework as a heterojunction structure of Gr@TiO2.

Bismuth activated succulent-like binary metal sulfide heterostructure as a binder-free electrocatalyst for enhanced oxygen evolution reaction.

Oxygen evolution reaction (OER) is the key to achieve highly efficient hydrogen production during water splitting. Herein, flexible nanorods-integrated succulent-like Bi2S3/Ni3S2/NF heterostructure has been prepared by a facile solvothermal method and applied for OER. We highlight the unique nonequivalent sp3 hybridization of P-region metal based sulfides, which makes a possibility of electronic inductive effect and enhanced electrocatalytic performance. The Bi2S3/Ni3S2/NF catalyst shows low overpotential 268 mV at 10 mA cm-2 and low Tafel slope of 82 mV dec-1. Long-term stability evaluated at high current density suggests that succulent-like Bi2S3/Ni3S2 could be a promising alternative to noble-metal based electrocatalysts for water oxidation reaction in alkaline medium.

Long-range oriented graphene-like nanosheets with corrugated structure.

A facile molten-salt (MS) route for the scalable synthesis of free-standing, long-range oriented and corrugated graphene-like sheets from a copper phthalocyanine (CuPc) precursor is reported. Their unique arrangement and transformation behavior in molten potassium chloride (KCl) play a key role in promoting the successful synthesis of the anisotropic nanostructure.