Nitrogen-Doped Partially Reduced Graphene Oxide Rewritable Nonvolatile Memory

As memory materials, two-dimensional (2D) carbon materials such as graphene oxide (GO)-based materials have attracted attention due to a variety of advantageous attributes, including their solution-processability and their potential for highly scalable device fabrication for transistor-based memory and cross-bar memory arrays. In spite of this, the use of GO-based materials has been limited, primarily due to uncontrollable oxygen functional groups. To induce the stable memory effect by ionic charges of a negatively charged carboxylic acid group of partially reduced graphene oxide (PrGO), a positively charged pyridinium N that served as a counterion to the negatively charged carboxylic acid was carefully introduced on the PrGO framework. Partially reduced N-doped graphene oxide (PrGO_DMF) in dimethylformamide (DMF) behaved as a semiconducting nonvolatile memory material. Its optical energy band gap was 1.7–2.1 eV and contained a sp² CC framework with 45–50% oxygen-functionalized carbon density and 3% doped nitrogen atoms. In particular, rewritable nonvolatile memory characteristics were dependent on the proportion of pyridinum N, and as the proportion of pyridinium N atom decreased, the PrGO_DMF film lost memory behavior. Polarization of charged PrGO_DMF containing pyridinium N and carboxylic acid under an electric field produced N-doped PrGO_DMF memory effects that followed voltage-driven rewrite-read-erase-read processes

Highly Bendable, Conductive, and Transparent Film by an Enhanced Adhesion of Silver Nanowires

Recently, silver nanowires (AgNWs) have attracted considerable interest for their potential application in flexible transparent conductive films (TCFs). One challenge for the commercialization of AgNW-based TCFs is the low conductivity and stability caused by the weak adhesion forces between the AgNWs and the substrate. Here, we report a highly bendable, conductive, and transparent AgNW film, which consists of an underlying poly­(diallyldimethyl-ammonium chloride) (PDDA) and AgNW composite bottom layer and a top layer-by-layer (LbL) assembled graphene oxide (GO) and PDDA overcoating layer (OCL). We demonstrated that PDDA could increase the adhesion between the AgNW and the substrate to form a uniform AgNW network and could also serve to improve the stability of the GO OCL. Hence, a highly bendable, conductive, and transparent AgNW–PDDA–GO composite TCF on a poly­(ethylene terephthalate) (PET) substrate with Rs ≈ 10 Ω/sq and <i>T</i> ≈ 91% could be made by an all-solution processable method at room temperature. In addition, our AgNW–PDDA–GO composite TCF is stable without degradation after exposure to H₂S gas or sonication

Highly Bendable, Conductive, and Transparent Film by an Enhanced Adhesion of Silver Nanowires

Recently, silver nanowires (AgNWs) have attracted considerable interest for their potential application in flexible transparent conductive films (TCFs). One challenge for the commercialization of AgNW-based TCFs is the low conductivity and stability caused by the weak adhesion forces between the AgNWs and the substrate. Here, we report a highly bendable, conductive, and transparent AgNW film, which consists of an underlying poly­(diallyldimethyl-ammonium chloride) (PDDA) and AgNW composite bottom layer and a top layer-by-layer (LbL) assembled graphene oxide (GO) and PDDA overcoating layer (OCL). We demonstrated that PDDA could increase the adhesion between the AgNW and the substrate to form a uniform AgNW network and could also serve to improve the stability of the GO OCL. Hence, a highly bendable, conductive, and transparent AgNW–PDDA–GO composite TCF on a poly­(ethylene terephthalate) (PET) substrate with Rs ≈ 10 Ω/sq and <i>T</i> ≈ 91% could be made by an all-solution processable method at room temperature. In addition, our AgNW–PDDA–GO composite TCF is stable without degradation after exposure to H₂S gas or sonication

Dual Functions of Highly Potent Graphene Derivative–Poly‑l‑Lysine Composites To Inhibit Bacteria and Support Human Cells

Dual-function poly(l-lysine) (PLL) composites that function as antibacterial agents and promote the growth of human cell culture have been sought by researchers for a long period. In this paper, we report the preparation of new graphene derivative–PLL composites <i>via</i> electrostatic interactions and covalent bonding between graphene derivatives and PLL. The resulting composites were characterized by infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The novel dual function of PLL composites, specifically antibacterial activity and biocompatibility with human cells [human adipose-derived stem cells and non-small-cell lung carcinoma cells (A549)], was carefully investigated. Graphene–DS–PLL composites composed of 4-carboxylic acid benzene diazonium salt (DS) generated more anionic carboxylic acid groups to bind to cationic PLLs, forming the most potent antibacterial agent among PLL and PLL composites with high biocompatibility with human cell culture. This dual functionality can be used to inhibit bacterial growth while enhancing human cell growth

Vertical Alignments of Graphene Sheets Spatially and Densely Piled for Fast Ion Diffusion in Compact Supercapacitors

Supercapacitors with porous carbon structures have high energy storage capacity. However, the porous nature of the carbon electrode, composed mainly of carbon nanotubes (CNTs) and graphene oxide (GO) derivatives, negatively impacts the volumetric electrochemical characteristics of the supercapacitors because of poor packing density (<0.5 g cm^–3). Herein, we report a simple method to fabricate highly dense and vertically aligned reduced graphene oxide (VArGO) electrodes involving simple hand-rolling and cutting processes. Because of their vertically aligned and opened-edge graphene structure, VArGO electrodes displayed high packing density and highly efficient volumetric and areal electrochemical characteristics, very fast electrolyte ion diffusion with rectangular CV curves even at a high scan rate (20 V/s), and the highest volumetric capacitance among known rGO electrodes. Surprisingly, even when the film thickness of the VArGO electrode was increased, its volumetric and areal capacitances were maintained

Oxygen-Bridged Vanadium Single-Atom Dimer Catalysts Promoting High Faradaic Efficiency of Ammonia Electrosynthesis

Single-atom catalysts have already been widely investigated for the nitrogen reduction reaction (NRR). However, the simplicity of a single atom as an active center encounters the challenge of modulating the multiple reaction intermediates during the NRR process. Moving toward the single-atom-dimer (SAD) structures can not only buffer the multiple reaction intermediates but also provide a strategy to modify the electronic structure and environment of the catalysts. Here, a structure of a vanadium SAD (V-O-V) catalyst on N-doped carbon (O-V2-NC) is proposed for the electrochemical nitrogen reduction reaction, in which the vanadium dimer is coordinated with nitrogen and simultaneously bridged by one oxygen. The oxygen-bridged metal atom dimer that has more electron deficiency is perceived to be the active center for nitrogen reduction. A loop evolution of the intermediate structure was found during the theoretical process simulated by density functional theory (DFT) calculation. The active center V-O-V breaks down to V-O and V during the protonation process and regenerates to the original V-O-V structure after releasing all the nitrogen species. Thus, the O-V2-NC structure presents excellent activity toward the electrochemical NRR, achieving an outstanding faradaic efficiency (77%) along with the yield of 9.97 μg h–1 mg–1 at 0 V (vs RHE) and comparably high ammonia yield (26 μg h–1 mg–1) with the FE of 4.6% at −0.4 V (vs RHE). This report synthesizes and proves the peculiar V-O-V dimer structure experimentally, which also contributes to the library of SAD catalysts with superior performance

Inductive Effect of Lewis Acidic Dopants on the Band Levels of Perovskite for a Photocatalytic Reaction

Band-edge modulation of halide perovskites as photoabsorbers plays significant roles in the application of photovoltaic and photochemical systems. Here, Lewis acidity of dopants (M) as the new descriptor of engineering the band-edge position of the perovskite is investigated in the gradiently doped perovskite along the core-to-surface (CsPbBr3–CsPb1–xMxBr3). Reducing M–bromide bond strength with an increase in hardness of acidic M increases the electron ability of basic Br, thus strengthening the Pb–Br orbital coupling in M–Pb–Br, noted as the inductive effect of dopants. Especially, the highly hard Lewis acidic Mg localized in the outer position of the perovskite induces the increase of work function and then shifts band edge upward along the core-to-surface of the perovskite. Thus, charge separation driven by the dopant-induced internal electric field induces the slow annihilation of the excited holes, improving the slow aromatic Csp3–H dissociation in the photocatalytic oxidation process by ∼211% (491.39 μmol g–1 h–1) enhancements, compared with undoped nanocrystals