A review in rational design of graphene toward advanced Li–S batteries

For lithium–sulfur (Li–S) batteries, the problems of polysulfides shuttle effect, slow dynamics of sulfur species and growth of lithium dendrite during charge/discharge processes have greatly impeded its practical development. Of core importance to advance the performances of Li–S batteries lies in the selection and design of novel materials with strong polysulfides adsorption ability and enhanced redox electrocatalytic behavior. Graphene, affording high electrical conductivity, superior carrier mobility, and large surface area, has presented great potentials in improving the performances of Li–S cells. However, the properties of intrinsic graphene are far enough to achieve the multiple management toward electrochemical catalysis of energy storage systems. In addition, a general and objective understanding of its role in Li–S systems is still lacking. Along this line, we summarize the design routes from three aspects, including defect engineering, dimension adjustment, and heterostructure modulation, to perfect the graphene properties. Thus-synthesized graphene materials are explored as multifunctional electrocatalysts targeting high-efficiency and long-lifespan Li–S batteries, based on which the regulating role of graphene is comprehensively analyzed. This project provides a perspective on the effective engineering management of graphene materials to boost Li–S chemistry, meanwhile promote the practical application process for graphene materials

High-Performance 3D Vertically Oriented Graphene Photodetector Using a Floating Indium Tin Oxide Channel

Vertically oriented graphene (VG), owing to its sharp edges, non-stacking morphology, and high surface-to-volume ratio structure, is promising as a consummate material for the application of photoelectric detection. However, owing to high defect and fast photocarrier recombination, VG-absorption-based detectors inherently suffer from poor responsivity, severely limiting their viability for light detection. Herein, we report a high-performance photodetector based on a VG/indium tin oxide (ITO) composite structure, where the VG layer serves as the light absorption layer while ITO works as the carrier conduction channel, thus achieving the broadband and high response nature of a photodetector. Under the illumination of infrared light, photoinduced carriers generated in VG could transfer to the floating ITO layer, which makes them separate and diffuse to electrodes quickly, finally realizing large photocurrent detectivity. This kind of composite structure photodetector possesses a room temperature photoresponsivity as high as ~0.7 A/W at a wavelength of 980 nm, and it still maintains an acceptable performance at temperatures as low as 87 K. In addition, a response time of 5.8 s is observed, ~10 s faster than VG photodetectors. Owing to the unique three-dimensional morphology structure of the as-prepared VG, the photoresponsivity of the VG/ITO composite photodetector also presented selectivity of incidence angles. These findings demonstrate that our novel composite structure VG device is attractive and promising in highly sensitive, fast, and broadband photodetection technology

Transparent Electrothermal Heaters Based on Vertically-Oriented Graphene Glass Hybrid Materials

Transparent heating devices are widely used in daily life-related applications that can be achieved by various heating materials with suitable resistances. Herein, high-performance vertically-oriented graphene (VG) films are directly grown on soda-lime glass by a radio-frequency (rf) plasma-enhanced chemical vapor deposition (PECVD) method, giving reasonable resistances for electrothermal heating. The optical and electrical properties of VG films are found to be tunable by optimizing the growth parameters such as growth time, carrier gas flow, etc. The electrothermal performances of the derived materials with different resistances are thus studied systematically. Specifically, the VG film on glass with a transmittance of ~73% at 550 nm and a sheet resistance of ~3.9 KΩ/□ is fabricated into a heating device, presenting a saturated temperature up to 55 °C by applying 80 V for 3 min. The VG film on the glass at a transmittance of ~43% and a sheet resistance of 0.76 KΩ/□ exhibits a highly steady temperature increase up to ~108 °C with a maximum heating rate of ~2.6 °C/s under a voltage of 60 V. Briefly, the tunable sheet resistance, good adhesion of VG to the growth substrate, relative high heating efficiency, and large heating temperature range make VG films on glass decent candidates for electrothermal related applications in defrosting and defogging devices

Confining MOF-derived SnSe nanoplatelets in nitrogen-doped graphene cages via direct CVD for durable sodium ion storage

Tin-based compounds are deemed as suitable anode candidates affording promising sodium-ion storages for rechargeable batteries and hybrid capacitors. However, synergistically tailoring the electrical conductivity and structural stability of tin-based anodes to attain durable sodium-ion storages remains challenging to date for its practical applications. Herein, metal-organic framework (MOF) derived SnSe/C wrapped within nitrogen-doped graphene (NG@SnSe/C) is designed targeting durable sodium-ion storage. NG@SnSe/C possesses favorable electrical conductivity and structure stability due to the “inner” carbon framework from the MOF thermal treatment and “outer” graphitic cage from the direct chemical vapor deposition synthesis. Consequently, NG@SnSe/C electrode can obtain a high reversible capacity of 650 mAh·g−1 at 0.05 A·g−1, a favorable rate performance of 287.8 mAh·g−1 at 5 A·g−1 and a superior cycle stability with a negligible capacity decay of 0.016% per cycle over 3,200 cycles at 0.4 A·g−1. Theoretical calculations reveal that the nitrogen-doping in graphene can stabilize the NG@SnSe/C structure and improve the electrical conductivity. The reversible Na-ion storage mechanism of SnSe is further investigated by in-situ X-ray diffraction/ex-situ transmission electron microscopy. Furthermore, assembled sodium-ion hybrid capacitor full-cells comprising our NG@SnSe/C anode and an active carbon cathode harvest a high energy/power density of 115.5 Wh·kg−1/5,742 W·kg−1, holding promise for next-generation energy storages.[Figure not available: see fulltext.]

Fast Growth of Strain-Free AIN on Graphene-Buffered Sapphire

We study the roles of graphene acting as a buffer layer for growth of an A1N film on a sapphire substrate. Graphene can reduce the density of A1N nuclei but increase the growth rate for an individual nucleus at the initial growth stage. This can lead to the reduction of threading dislocations evolved at the coalescence boundaries. The graphene interlayer also weakens the interaction between AIN and sapphire and accommodates their large mismatch in the lattice and thermal expansion coefficients; thus, the compressive strain in A1N and the tensile strain in sapphire are largely relaxed. The effective relaxation of strain further leads to a low density of defects in the AIN films. These findings reveal the roles of graphene in III-nitride growth and offer valuable insights into the efficient applications of graphene in the light-emitting diode industry