Nitrogen-doped reduced graphene oxide electrodes for electrochemical supercapacitors.

Herein we use Nitrogen-doped reduced Graphene Oxide (N-rGO) as the active material in supercapacitor electrodes. Building on a previous work detailing the synthesis of this material, electrodes were fabricated via spray-deposition of aqueous dispersions and the electrochemical charge storage mechanism was investigated. Results indicate that the functionalised graphene displays improved performance compared to non-functionalised graphene. The simplicity of fabrication suggests ease of up-scaling of such electrodes for commercial applications.

Carbon Thin-Film Electrodes as High-Performing Substrates for Correlative Single Entity Electrochemistry.

Correlative methods to characterize single entities by electrochemistry and microscopy/spectroscopy are increasingly needed to elucidate structure-function relationships of nanomaterials. However, the technical constraints often differ depending on the characterization techniques to be applied in combination. One of the cornerstones of correlative single-entity electrochemistry (SEE) is the substrate, which needs to achieve a high conductivity, low roughness, and electrochemical inertness. This work shows that graphitized sputtered carbon thin films constitute excellent electrodes for SEE while enabling characterization with scanning probe, optical, electron, and X-ray microscopies. Three different correlative SEE experiments using nanoparticles, nanocubes, and 2D Ti3C2Tx MXene materials are reported to illustrate the potential of using carbon thin film substrates for SEE characterization. The advantages and unique capabilities of SEE correlative strategies are further demonstrated by showing that electrochemically oxidized Ti3C2Tx MXene display changes in chemical bonding and electrolyte ion distribution.

Porous N-doped carbon-encapsulated iron as a novel catalyst architecture for the electrocatalytic hydrogenation of benzaldehyde.

Carbon porous materials containing nitrogen functionalities and encapsulated iron-based active sites have been suggested as electrocatalysts for energy conversion, however their applications to the hydrogenation of organic substrates via electrocatalytic hydrogenation (ECH) remain unexplored. Herein, we report on a Fe@C:N material synthesized with an adapted annealing procedure and tested as electrocatalyst for the hydrogenation of benzaldehyde. Using different concentrations of the organic, and electrolysis coupled to gas chromatography experiments, we demonstrate that it is possible to use such architectures for the ECH of unsaturated organics. Potential control experiments show that ECH faradaic efficiencies >70% are possible in acid electrolytes, while maintaining selectivity for the alcohol over the pinacol dimerization product. Estimates of product formation rates and turnover frequency (TOF) values suggest that these carbon-encapsulated architectures can achieve competitive performance in acid electrolytes relative to both base and precious metal electrodes.

Nitrogen-doped pyrolytic carbon films as highly electrochemically active electrodes.

Nitrogen-doped Pyrolytic Carbon (N-PyC) films were employed as an electrode material in electrochemical applications. PyC was grown by via non-catalysed chemical vapour deposition and subsequently functionalised via exposure to ammonia-hydrogen plasma. The electrochemical properties of the N-PyC films were investigated using the ferri/ferro-cyanide and hexaamine ruthenium(III) chloride redox probes. Exceptional electron transfer properties were observed and quantified for the N-PyC compared to the as-grown films. X-ray photoelectron spectroscopy confirmed the presence of nitrogen in edge plane graphitic configurations and the surface of the N-PyC was investigated using scanning electron microscopy and atomic force microscopy. The excellent electrochemical performance of the N-PyC, in addition to its ease of preparation, renders this material ideal for applications in electrochemical sensing.

Isolation of pseudocapacitive surface processes at monolayer MXene flakes reveals delocalized charging mechanism.

Pseudocapacitive charge storage in Ti3C2Tx MXenes in acid electrolytes is typically described as involving proton intercalation/deintercalation accompanied by redox switching of the Ti centres and protonation/deprotonation of oxygen functional groups. Here we conduct nanoscale electrochemical measurements in a unique experimental configuration, restricting the electrochemical contact area to a small subregion (0.3 µm2) of a monolayer Ti3C2Tx flake. In this unique configuration, proton intercalation into interlayer spaces is not possible, and surface processes are isolated from the bulk processes, characteristic of macroscale electrodes. Analysis of the pseudocapacitive response of differently sized MXene flakes indicates that entire MXene flakes are charged through electrochemical contact of only a small basal plane subregion, corresponding to as little as 3% of the flake surface area. Our observation of pseudocapacitive charging outside the electrochemical contact area is suggestive of a fast transport of protons mechanism across the MXene surface.

Magnetically activated adhesives: towards on-demand magnetic triggering of selected polymerisation reactions.

On-demand initiation of chemical reactions is becoming increasingly popular in many areas. The use of a magnetic field to trigger reactions is an intriguing concept, with vast potential in both research and industrial settings, though it remains a challenge as yet unsolved. Here we report the first example of on-demand magnetic activation of a polymerisation process using an anaerobic adhesive formulation as an example of this new approach toward triggering polymerisation reactions using an external magnetic field. Our strategy involves the use of a colloidal system comprising functional methacrylate ester monomers, peroxide and CuII-salt as polymerisation initiators and magnetic nanoparticles coated with an oxidising shell. This unique combination prevents reduction of the reactive transition metal (CuII) ion by the metal substrates (steel or aluminium) to be joined - hence inhibiting the redox radical initiated cationic polymerisation reaction and efficiently preventing adhesion. The polymerisation and corresponding adhesion process can be triggered by removal of the functional magnetic particles using a permanent external magnet either prior to formulation application or at the joint to be adhered, enabling the polymerisation to proceed through CuII-mediated reduction. This new approach enables on-demand magnetically-triggered reaction initiation and holds potential for a range of useful applications in chemistry, materials science and relevant industrial manufacturing.

Molybdenum disulfide/pyrolytic carbon hybrid electrodes for scalable hydrogen evolution.

The electrochemical generation of hydrogen fuel via the proton reduction in the Hydrogen Evolution Reaction (HER) in aqueous media is currently dependent on the use expensive noble metal catalysts for which alternatives must be sought. Molybdenum disulfide (MoS2) has shown great promise as a suitable electrocatalyst in this regard. While many lab-scale experiments on the HER activity of this material have demonstrated its viability and explored some fundamental mechanistic features of HER at MoS2, these experimental techniques are often ill-suited to large scale production of such electrodes. In this study we present work on the fabrication of MoS2/pyrolytic carbon (PyC) electrodes via vapour phase sulfurization of Mo thin films. These hybrid electrodes combine the catalytic activity of MoS2 with the conductivity and stability of PyC, whilst using industrially compatible processing techniques. Structural defects in the sulfur lattice were found to be key catalytically active sites for HER and thinner MoS2 films displayed a higher quantity of these defects and, hence, an improved HER activity. The observed Tafel slope of 95 mV decade(-1) is comparable to previous literature works on MoS2 HER performance.