A Simple and Expeditious Route to Phosphate-Functionalized, Water-Processable Graphene for Capacitive Energy Storage.

Phosphate-functionalized carbon-based nanomaterials have attracted significant attention in recent years owing to their outstanding behavior in electrochemical energy-storage devices. In this work, we report a simple approach to obtain phosphate-functionalized graphene (PFG) via anodic exfoliation of graphite at room temperature with a high yield. The graphene nanosheets were obtained via anodic exfoliation of graphite foil using aqueous solutions of H3PO4 or Na3PO4 in the dual role of phosphate sources and electrolytes, and the underlying exfoliation/functionalization mechanisms are proposed. The effect of electrolyte concentration was studied, as low concentrations do not lead to a favorable graphite exfoliation and high concentrations produce fast graphite expansion but poor layer-by-layer delamination. The optimal concentrations are 0.25 M H3PO4 and 0.05 M Na3PO4, which also exhibited the highest phosphorus contents of 2.2 and 1.4 at. %, respectively. Furthermore, when PFG-acid at 0.25 M and PFG-salt at 0.05 M were tested as an electrode material for capacitive energy storage in a three-electrode cell, they achieved a competitive performance of ∼375 F/g (540 F/cm3) and 356 F/g (500 F/cm3), respectively. Finally, devices made up of symmetric electrode cells obtained using PFG-acid at 0.25 M possess energy and power densities up to 17.6 Wh·kg-1 (25.3 Wh·L-1) and 10,200 W/kg; meanwhile, PFG-salt at 0.05 M achieved values of 14.9 Wh·kg-1 (21.3 Wh·L-1) and 9400 W/kg, with 98 and 99% of capacitance retention after 10,000 cycles, respectively. The methodology proposed here also promotes a circular-synthesis process to successfully achieve a more sustainable and greener energy-storage device.

Super-Anticorrosive Materials Based on Bifunctionalized Reduced Graphene Oxide.

The design of new materials with two or more functional groups must be strongly considered to achieve multifunctional coatings with outstanding properties such as active-passive protection against corrosion, low-friction, antifouling, and sensing, among others. In this sense, nanocomposites based on solvent-free epoxy resin/bifunctionalized reduced graphene oxide layers with NH2 and NH3+ groups (ER/BFRGO) with super-anticorrosive properties are for the first time reported here. The amine groups (-NH2) act as cross-linker agents, which react with epoxy terminal groups from resin, thus closing the gap between the BFRGO layers and the polymeric matrix. Meanwhile, the ammonium ions (-NH3+) are effective trapping agents of negatively charged atoms or molecules (e.g., Cl-). This novel combination enables us to obtain nanocomposite coatings with passive-active protection against corrosion. ER/BFRGO deposited onto A36 mild steel exhibited a remarkably enhanced barrier against corrosion into a saline medium (1 M NaCl; 58.4 g/L), wherein the corrosion current density (icorr) was diminished 6 orders of magnitude (icorr = 5.12 × 10-12 A/cm2), with respect to A36 mild steel coated only with ER (icorr = 2.34 × 10-6 A/cm2). Also, the highest polarization resistance Rp = 6.04 × 107 Ω/cm2 was obtained, which represents the lowest corrosion rate and corresponds to 3 orders of magnitude higher than A36 mild steel coated with ER (Rp = 1.43 × 104 Ω/cm2). The strategy of bifunctionalization proposed herein to obtain bifunctionalized reduced GO with NH2 and NH3+ groups has not been disclosed in the literature before; in consequence, this work opens a new pathway toward the design of smart materials based on multifunctional nanomaterials.

The Role of α, γ, and Metastable Polymorphs on Electrospun Polyamide 6/Functionalized Graphene Oxide.

The present paper describes the addition of nitroxide-functionalized graphene oxide (GOFT) into polyamide 6 (PA6) micro- and nanofibers, which are obtained through electrospinning. Scanning electron microscopy micrographs demonstrate the presence of fibers. Tensile testing presents an unexpected and non-obvious behavior, in which the Young's modulus, tensile strength, and elongation simultaneously and remarkably increase compared to the pristine polymer nanofibers. GOFT induces the hydrogen bonding between the NH group from PA6 with the functional groups, thus promoting higher crystallinity of the polymer matrix. Nonetheless, deconvoluted curves by differential scanning calorimetry reveal the presence of two quasi-steady polymorphs (ß and Î´ phases) contributing to 46% of the total crystallinity. This evidence suggests that their presence and high ratios are responsible for the unexpected and simultaneous enhancement of tensile properties.