Highly Conductive and Fracture-Resistant Epoxy Composite Based on Non-oxidized Graphene Flake Aerogel

Graphene aerogel (GA) has shown great promise as reinforcement of polymeric composites with exceptional electrical and mechanical characteristics. Although there has been significant progress in controlling the structure of GAs, no studies have appeared on the enhanced properties of GAs by employing high-quality precursor graphene flakes (GFs). However, the assembly of high-quality GFs is particularly challenging due to their highly hydrophobic and agglomerative nature in aqueous media, and of the few methods available to synthesize high-quality GFs, most produce flakes with very small lateral sizes. Herein, we report the fabrication of highly crystalline GAs using large nonoxidized graphene flakes (NOGFs) prepared by a novel graphite intercalation compound-based method. Bidirectional freeze casting is utilized for aligning NOGFs in two orthogonal directions, vertically and laterally, where the NOGF walls individually function as effective conductive pathways. The as-prepared nonoxidized graphene aerogel (NOGA) exhibits a defect concentration as low as 1.4% of impurity oxygen with an excellent electrical conductivity of 202.9 S/m at a low density of 5.7 mg/cm3. The corresponding NOGA–epoxy composite shows a remarkable electrical conductivity of 122.6 S/m and a fracture toughness of 1.74 MPa·m1/2 at a low filler content of 0.45 vol %

Sulfur-Doped g‑C₃N₄/BiVO₄ Composite Photocatalyst for Water Oxidation under Visible Light

To achieve sustainable utilization of solar energy, development of an efficient photocatalyst for water oxidation, the driving force of reductive solar fuel formation, is strongly needed. Herein, composite photocatalysts with bismuth vanadate (BiVO₄) and sulfur-doped graphitic carbon nitride (SCN) are developed by using a one-pot impregnated precipitation method. Fourier transform infrared and X-ray photoelectron spectroscopy analyses demonstrate that the surface of SCN is oxidized during impregnation and the oxidized surface becomes the synthetic site for BiVO₄ composition. Among the composites with various ratios, the B7S catalyst, which is our best achievement, shows an oxygen evolution rate of 750 μmol h^–1 g^–1 that is >2-fold higher than that of pristine BiVO₄ (i.e., 328 μmol h^–1 g^–1) under identical reaction conditions [0.05 M AgNO₃ aqueous solution under visible light irradiation (λ > 420 nm)]. The photonic efficiency of B7S is also measured as 19%. The mechanism behind this is the enhanced charge carrier lifetime of B7S (3.14 ns), which is lengthened up to 4 times compared to that of BiVO₄ (0.70 ns) because of the facilitated charge separation through the composite

Extraordinary Enhancement of UV Absorption in TiO₂ Nanoparticles Enabled by Low-Oxidized Graphene Nanodots

Titanium oxide (TiO₂) exhibits intrinsically strong absorption of ultraviolet (UV) light, which has been utilized in a variety of applications, such as environmental purification/sterilization, health care, and energies. Accordingly, it is greatly demanded to precisely tune and further improve the UV absorption of TiO₂ to significantly broaden its versatility. Herein, we report an extraordinary enhancement of UV absorption in TiO₂ nanoparticles (NPs) incorporated with graphene nanodots (GNDs) of low oxygen concentration. Chemically bonded TiO₂ NP/GND composites exhibit highly tunable UV absorption, achieving over 243% enhancement of molar extinction coefficient at 336 nm. We found that the drastic improvement is a result of the direct charge transfer from the lowest unoccupied molecular orbitals of GNDs to the conduction bands of TiO₂, enabled by wide/direct band gaps in GNDs with a small amount of oxygen. Also, the significantly improved power conversion efficiency (PCE ∼ 16.74%) and UV stability of the TiO₂ NP/GND composites reveal their high promise for applications benefiting from TiO₂ NP/GND composites, such as solar cells and photolysis

Defect-Free, Size-Tunable Graphene for High-Performance Lithium Ion Battery

The scalable preparation of graphene in control of its structure would significantly improve its commercial viability. Despite intense research in this area, the size control of defect-free graphene (df-G) without any trace of oxidation or structural damage remains a key challenge. Here, we propose a new scalable route for generating df-G with a controllable size of submicron to micron through sequential insertion of potassium and pyridine at low temperature. Structural and chemical analyses confirm that the df-G perfectly preserves the intrinsic properties of graphene. The Co₃O₄ (<50 nm) wrapped by ∼10.5 μm² df-G has unprecedented capacity, rate capability, and cycling stability with capacities as high as 1050 mAh g^–1 at 500 mA g^–1 and 900 mAh g^–1 at 1000 mA g^–1 even after 200 cycles, which suggests enticing potential for the use in high performance lithium ion batteries

Low-Cost Black Phosphorus Nanofillers for Improved Thermoelectric Performance in PEDOT:PSS Composite Films

In recent years, two-dimensional black phosphorus (BP) has seen a surge of research because of its unique optical, electronic, and chemical properties. BP has also received interest as a potential thermoelectric material because of its high Seebeck coefficient and excellent charge mobility, but further development is limited by the high cost and poor scalability of traditional BP synthesis techniques. In this work, high-quality BP is synthesized using a low-cost method and utilized in a PEDOT:PSS film to create the first ever BP composite thermoelectric material. The thermoelectric properties are found to be greatly enhanced after the BP addition, with the power factor of the film, with 2 wt % BP (36.2 μW m^–1 K^–2) representing a 109% improvement over the pure PEDOT:PSS film (17.3 μW m^–1 K^–2). A simultaneous increase of mobility and decrease of the carrier concentration is found to occur with the increasing BP wt %, which allows for both Seebeck coefficient and electrical conductivity to be increased. These results show the potential of this low-cost BP for use in energy devices