Platinum deposition on functionalised graphene for corrosion resistant oxygen reduction electrodes

Graphene-related materials are promising supports for electrocatalysts due to their stability and high surface area. Their innate surface chemistries can be controlled and tuned via functionalisation to improve the stability of both the carbon support and the metal catalyst. Functionalised graphenes were prepared using either aryl diazonium functionalisation or non-destructive chemical reduction, to provide groups adapted for platinum deposition. XPS and TGA-MS measurements confirmed the presence of polyethyleneglycol and sulfur-containing functional groups, and provided consistent values for the extent of the reactions. The deposited platinum nanoparticles obtained were consistently around 2 nm via reductive chemistry and around 4 nm via the diazonium route. Although these graphene-supported electrocatalysts provided a lower electrochemical surface area (ECSA), functionalised samples showed enhanced specific activity compared to a commercial platinum/carbon black system. Accelerated stress testing (AST) showed improved durability for the functionalised graphenes compared to the non-functionalised materials, attributed to edge passivation and catalyst particle anchoring

Carbon foams from emulsion-templated reduced graphene oxide polymer composites: electrodes for supercapacitor devices

Amphiphilic reduced graphene oxide (rGO) is an efficient emulsifier for water-in-divinylbenzene (DVB) high internal phase emulsions. The polymerisation of the continuous DVB phase of the emulsion template and removal of water results in macroporous poly(divinylbenzene) (polyDVB). Subsequent pyrolysis of the poly(DVB) macroporous polymers yields ‘all-carbon’ foams containing micropores alongside emulsion templated-macropores, resulting in hierarchical porosity. The synthesis of carbon foams, or ‘carboHIPEs’, from poly(DVB) produced by polymerisation of rGO stabilised HIPEs provides both exceptionally high surface areas (up to 1820 m2 g−1) and excellent electrical conductivities (up to 285 S m−1), competing with the highest figures reported for carboHIPEs. The use of a 2D carbon emulsifier results in the elimination of post-carbonisation treatments to remove standard inorganic particulate emulsifiers, such as silica particles. It is demonstrated that rGO containing carboHIPEs are good candidates for supercapacitor electrodes where carboHIPEs derived from more conventional polymerised silica-stabilised HIPEs perform poorly. Supercapacitor devices featured a room-temperature ionic liquid electrolyte and electrodes derived from either rGO- or silica-containing poly(DVB)HIPEs demonstrated a maximum specific capacitance of 26 F g−1, an energy density of 5.2 W h kg−1 and a power density of 280 W kg−1

Biphasic epoxy-ionic liquid structural electrolytes: minimising feature size through cure cycle and multifunctional block-copolymer addition

Structural electrolytes provide mechanical properties approaching structural resin combined with a high degree of ionic conductivity. Here, structural electrolytes based on bisphenol A diglycidyl ether and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM-TFSI) were synthesised through reaction induced phase separation (RIPS) using isophorone diamine (iPDA) as a curing agent. The microstructure and properties of the resulting materials were controlled through both the initial formulations and the curing temperature. Curing at room temperature generated a bi-continuous structure and improved both mechanical performance and ionic conductivity of the resulting structural electrolytes. The balance between properties can be systematically adjusted; for example, a promising Young's modulus of 800 MPa was obtained simultaneously with an ionic conductivity of 0.28 mS cm−1, for a formulation containing 35 vol% EMIM-TFSI. The lengthscale of the structural features was reduced by an order of magnitude by introducing multifunctional block-copolymers (MF-bcP) based on glycidyl methacrylate (GMA) and quaternised (2-dimethylamino)ethyl methacrylate (DMAEMA). Small angle neutron scattering (SANS), obtained during curing, identified at least two structural phases of different length scale, for the formulations containing MF-bcP, in agreement with microstructures observed using scanning electron microscopy. Such structural electrolytes may be required when using structural electrodes that also have finer characteristic lengthscales. The addition of the MF-bcP to formulations containing 35 vol% EMIM-TFSI produced structural electrolytes with a Young's modulus of 530 MPa and an ionic conductivity of 0.64 mS cm

Quantitative evaluation of electrophoretic deposition kinetics of graphene oxide

\u3cp\u3eThe electrophoretic deposition (EPD) technique is an attractive approach for development of graphene and graphene oxide (GO) films for a variety of applications. However, in order to establish the influence of the EPD parameters on the properties of the deposited films, a deeper investigation of the fundamental GO-EPD kinetics is required. Previous studies have reported a simultaneous anodic reduction of GO flakes during EPD, complicating the kinetics and process control. Therefore, in this study, low voltages were used to prevent significant GO reduction during EPD, as confirmed by XPS and FTIR. Accordingly, the GO-EPD kinetics was established as a function of deposition time and voltage, accompanied by microscopic characterization of the deposited films. The experimental results show that the deposition follows a linear growth law, in good agreement with the predictions of Hamaker's law. Comparisons of optical absorbance and profilometry provide estimates of (reduced) GO deposition rate, extinction coefficient, and density.\u3c/p\u3

White light-activated bactericidal coating using acrylic latex, crystal violet, and zinc oxide nanoparticles

In this study, a white light-activated bactericidal coating consisting of acrylic latex, zinc oxide nanoparticles (ZnO NPs) and crystal violet (CV) was produced through a two-step dipping process. CV molecules and ZnO NPs were incorporated into an acrylic latex coating deposited onto a glass substrate. After the incorporation, the colour of the coating surface changed to purple from colourless and XPS sputtering analysis showed the existence of ZnO NPs within the coating. In a bactericidal test, the CV dyed samples showed an intrinsic bactericidal activity (0.7–0.88 log reduction in viable bacteria number) against S. aureus whereas it was not observed on E. coli in the dark. Upon white light irradiation (light intensity: 512 lux), the bactericidal activity of the CV-dyed sample was significantly enhanced. Compared to the control, the CV-dyed samples showed 1.16–2.51 log reduction against both bacterial strains in white light. In terms of the testing against S. aureus in white light, ZnO NPs addition into the CV-dyed sample showed enhanced bactericidal activity. The bactericidal activity of the CV-dyed sample with ZnO NPs was 1.34 log higher than the CV-dyed sample. Based on data obtained from TR-EPR spectroscopy, it is speculated that the addition of ZnO NPs into the dye induces an alternative photoredox pathway, resulting in more generation of reactive oxygen species lethal to bacterial cells. It is expected that this technique could be used to transform a wide range of surfaces into bactericidal surfaces and contribute to maintaining low pathogen levels on hospital surfaces related to healthcare-associated infection

Layered zinc hydroxide monolayers by hydrolysis of organozincs.

2D inorganic materials and their exfoliated counterparts are both of fundamental interest and relevant for applications including catalysis, electronics and sensing. Here, a new bottom-up synthesis route is used to prepare functionalised nanoplatelets, in apolar organic solvents, via the hydrolysis of organometallic reagents; the products can be prepared in high yield, at room temperature. In particular, a series of layered zinc hydroxides, coordinated by aliphatic carboxylate ligands, were produced by the hydrolysis of diethyl zinc and zinc carboxylate mixtures, optimally at a molar ratio of [COOR]/[Zn] = 0.6. Layered zinc hydroxides coordinated by oleate ligands form high concentration solutions of isolated monolayers (3 nm thick x ∼ 26 nm) in apolar organic solvents (up to 23 mg mL-1 in toluene), as confirmed by both atomic force and transmission electron microscopies of deposited species. The high solubility of the product allows the synthetic pathway to be monitored directly in situ through 1H NMR spectroscopy. The high solubility also provides a route to solution deposition of active functional materials, as illustrated by the formation of nanoporous films of optically transparent porous zinc oxide (1 μm thickness) after annealing at 500 °C. This new organometallic route to 2D materials obviates common complications of top-down exfoliation syntheses, including sonochemical-degradation and low yields of aggregated polydispersed layers, and may potentially be extended to a wide range of systems

Layered zinc hydroxide monolayers by hydrolysis of organozincs.

2D inorganic materials and their exfoliated counterparts are both of fundamental interest and relevant for applications including catalysis, electronics and sensing. Here, a new bottom-up synthesis route is used to prepare functionalised nanoplatelets, in apolar organic solvents, via the hydrolysis of organometallic reagents; the products can be prepared in high yield, at room temperature. In particular, a series of layered zinc hydroxides, coordinated by aliphatic carboxylate ligands, were produced by the hydrolysis of diethyl zinc and zinc carboxylate mixtures, optimally at a molar ratio of [COOR]/[Zn] = 0.6. Layered zinc hydroxides coordinated by oleate ligands form high concentration solutions of isolated monolayers (3 nm thick x ∼ 26 nm) in apolar organic solvents (up to 23 mg mL-1 in toluene), as confirmed by both atomic force and transmission electron microscopies of deposited species. The high solubility of the product allows the synthetic pathway to be monitored directly in situ through 1H NMR spectroscopy. The high solubility also provides a route to solution deposition of active functional materials, as illustrated by the formation of nanoporous films of optically transparent porous zinc oxide (1 μm thickness) after annealing at 500 °C. This new organometallic route to 2D materials obviates common complications of top-down exfoliation syntheses, including sonochemical-degradation and low yields of aggregated polydispersed layers, and may potentially be extended to a wide range of systems