Micrometer‐Thick Graphene Oxide–Layered Double Hydroxide Nacre‐Inspired Coatings and Their Properties

Robust, functional, and flame retardant coatings are attractive in various fields such as building construction, food packaging, electronics encapsulation, and so on. Here, strong, colorful, and fire‐retardant micrometer‐thick hybrid coatings are reported, which can be constructed via an enhanced layer‐by‐layer assembly of graphene oxide (GO) nanosheets and layered double hydroxide (LDH) nanoplatelets. The fabricated GO–LDH hybrid coatings show uniform nacre‐like layered structures that endow them good mechanic properties with Young's modulus of ≈18 GPa and hardness of ≈0.68 GPa. In addition, the GO–LDH hybrid coatings exhibit nacre‐like iridescence and attractive flame retardancy as well due to their well‐defined 2D microstructures. This kind of nacre‐inspired GO–LDH hybrid thick coatings will be applied in various fields in future due to their high strength and multifunctionalities.     

Non‐Volatile ReRAM Devices Based on Self‐Assembled Multilayers of Modified Graphene Oxide 2D Nanosheets

2D nanomaterials have been actively utilized in non‐volatile resistive switching random access memory (ReRAM) devices due to their high flexibility, 3D‐stacking capability, simple structure, transparency, easy fabrication, and low cost. Herein, it demonstrates re‐writable, bistable, transparent, and flexible solution‐processed crossbar ReRAM devices utilizing graphene oxide (GO) based multilayers as active dielectric layers. The devices employ single‐ or multi‐component‐based multilayers composed of positively charged GO (N‐GO(+) or NS‐GO(+)) with/without negatively charged GO(‐) using layer‐by‐layer assembly method, sandwiched between Al bottom and Au top electrodes. The device based on the multi‐component active layer Au/[N‐GO(+)/GO(‐)]_n/Al/PES shows higher ON/OFF ratio of ≈10⁵ with switching voltage of ?1.9 V and higher retention stability (≈10⁴ s), whereas the device based on single component (Au/[N‐GO(+)]_n/Al/PES) shows ≈10³ ON/OFF ratio at ±3.5 V switching voltage. The superior ReRAM properties of the multi‐component‐based device are attributed to a higher coating surface roughness. The Au/[N‐GO(+)/GO(–)]_n/Al/PES device prepared from lower GO concentration (0.01%) exhibits higher ON/OFF ratio (≈10⁹) at switching voltage of ±2.0 V. However, better stability is achieved by increasing the concentration from 0.01% to 0.05% of all GO‐based solutions. It is found that the devices containing MnO₂ in the dielectric layer do not improve the ReRAM performance.     

In Situ Synthesis of MoP Nanoflakes Intercalated N‐Doped Graphene Nanobelts from MoO3–Amine Hybrid for High‐Efficient Hydrogen Evolution Reaction

Molybdenum phosphide (MoP) is a promising non‐noble‐metal electrocatalyst in the hydrogen evolution reaction (HER), but practical implementation is impeded by the sluggish HER kinetics and poor chemical stability. Herein, a novel high‐efficiency HER electrocatalyst comprising MoP nanoflakes intercalated nitrogen‐doped graphene nanobelts (MoP/NG), which are synthesized by one‐step thermal phosphiding organic–inorganic hybrid dodecylamine (DDA) inserted MoO₃ nanobelts, is reported. The intercalated DDA molecules are in situ carbonized into the NG layer and the sandwiched MoO₃ layer is converted into MoP nanoflakes which are intercalated between the NG layers forming the alternatingly stacked MoP/NG hybrid nanobelts. The MoP nanoflakes provide abundant edge sites and the sandwiched MoP/NG hybrid enables rapid ion/electron transport thus yielding excellent electrochemical activity and stability for HER. The MoP/NG shows a low overpotential of 94 mV at 10 mA cm⁻², small Tafel slope of 50.1 mV dec⁻¹, and excellent electrochemical stability with 99.5% retention for over 22 h.     

Direct Growth of Ultrafast Transparent Single‐Layer Graphene Defoggers

The idea flat surface, superb thermal conductivity and excellent optical transmittance of single‐layer graphene promise tremendous potential for graphene as a material for transparent defoggers. However, the resistance of defoggers made from conventional transferred graphene increases sharply once both sides of the film are covered by water molecules which, in turn, leads to a temperature drop that is inefficient for fog removal. Here, the direct growth of large‐area and continuous graphene films on quartz is reported, and the first practical single‐layer graphene defogger is fabricated. The advantages of this single‐layer graphene defogger lie in its ultrafast defogging time for relatively low input voltages and excellent defogging robustness. It can completely remove fog within 6 s when supplied a safe voltage of 32 V. No visible changes in the full defogging time after 50 defogging cycles are observed. This outstanding performance is attributed to the strong interaction forces between the graphene films and the substrates, which prevents the permeation of water molecules. These directly grown transparent graphene defoggers are expected to have excellent prospects in various applications such as anti‐fog glasses, auto window and mirror defogging.     

Graphitic Carbon Nitride (g‐C3N4)‐Derived N‐Rich Graphene with Tuneable Interlayer Distance as a High‐Rate Anode for Sodium‐Ion Batteries

Heteroatom‐doped carbon materials with expanded interlayer distance have been widely studied as anodes for sodium‐ion batteries (SIBs). However, it remains unexplored to further enlarge the interlayer spacing and reveal the influence of heteroatom doping on carbon nanostructures for developing more efficient SIB anode materials. Here, a series of N‐rich few‐layer graphene (N‐FLG) with tuneable interlayer distance ranging from 0.45 to 0.51 nm is successfully synthesized by annealing graphitic carbon nitride (g‐C₃N₄) under zinc catalysis and selected temperature (T = 700, 800, and 900 °C). More significantly, the correlation between N dopants and interlayer distance of resultant N‐FLG‐T highlights the effect of pyrrolic N on the enlargement of graphene interlayer spacing, due to its stronger electrostatic repulsion. As a consequence, N‐FLG‐800 achieves the optimal properties in terms of interlayer spacing, nitrogen configuration and electronic conductivity. When used as an anode for SIBs, N‐FLG‐800 shows remarkable Na⁺ storage performance with ultrahigh rate capability (56.6 mAh g^?1 at 40 A g^?1) and excellent long‐term stability (211.3 mAh g^?1 at 0.5 A g^?1 after 2000 cycles), demonstrating the effectiveness of material design.     

Photoconductivity of Bulk‐Film‐Based Graphene Sheets

Time‐resolved photoconductivity measurements are carried out on graphene films prepared by using soluble graphene oxide. High photocurrent generation efficiency is observed for these graphene‐based films, and the relationships between their photoconductivity and different preparation methods, incident light intensity, external electric field, and photon energies are investigated. Higher photoconductivity is observed with higher photon energy at same incident light intensity. By fitting the experimental data to the Onsager model, the primary quantum yields for charge separation to generate bound electron–hole pairs and the initial ion‐pair thermalization separation distance are calculated.