The development of a simple, scalable and reproducible technique for the synthesis of two-dimensional metallic phase MoS2nanosheets is of paramount importance in the field of catalysis and energy storage devices.

H 2 oxidation and O 2 reduction have been studied as a function of temperature at Pt electrodes in the protic ionic liquid diethylmethylammonium trifluoromethanesulfonate. Hydrodynamic voltammetry showed that the H 2 oxidation reaction (HOR) became hindered at positive potentials (>1.0 V). Electrochemical analysis and X-ray photoelectron spectroscopy revealed that this drop in HOR activity was due to the formation of an adsorbed blocking oxide layer, which formed on the Pt surface due to trace H 2 O oxidation at positive potentials. Electrochemical analysis also revealed that the O 2 reduction reaction (ORR) occurred at an appreciable rate only when pre-existing surface oxides were reduced. As the temperature increased, the potential at which the surface oxides were reduced shifted to more positive potentials and the reduction peak narrowed. The net result was significantly higher rates of the ORR at positive potentials at higher temperatures. Finally, even when Pt surfaces were not initially covered with an oxide adlayer, the rate of the ORR increased significantly upon increasing the temperature and some possible reasons for this temperature dependence are discussed.

The effects of electrode-adsorbate interactions on electrocatalysis at Pt in ionic liquids are described. The ionic liquids are diethylmethylammonium trifluoromethanesulfonate, [dema][TfO], dimethylethylammonium trifluoromethanesulfonate, [dmea][TfO], and diethylmethylammonium bis(trifluoromethanesulfonyl)imide, [dema][Tf 2 N]. Electrochemical analysis indicates that a monolayer of hydrogen adsorbs onto Pt during potential cycling in [dema][[TfO] and [dmea][TfO]. In addition, a pre-peak is observed at lower potentials than that of the main oxidation peak during CO oxidation in the [TfO]-based liquids. In contrast, hydrogen does not adsorb onto Pt during potential cycling in [dema][Tf 2 N] and no pre-peak is observed during CO oxidation. By displacing adsorbed ions on Pt surfaces with CO at a range of potentials, and measuring the charge passed during ion displacement, the potentials of zero total charge of Pt in [dema][TfO] and [dmea][TfO] were measured as 271 ± 9 mV and 289 ± 10 mV vs. RHE, respectively. CO displacement experiments also indicate that the [Tf 2 N]ion is bound to the Pt surface at potentials above-0.2 V and the implications of ion adsorption on electrocatalysis of the CO oxidation reaction and O 2 reduction reaction in the protic ionic liquids are discussed.

ABSTRACT

The oxygen reduction reaction (ORR) has been studied at Pt surfaces in the protic ionic liquid diethylmethylammonium trifluoromethanesulfonate. Water content measurements suggested that the ORR proceeded in the ionic liquid predominantly via a 4-electron reduction to water. A mechanistic analysis using rotating ring-disk electrode (RRDE) voltammetry confirmed that negligible amounts of hydrogen peroxide were formed during the ORR. A kinetic analysis of the ORR was performed using rotating disk electrode (RDE) voltammetry and the importance of correcting for ohmic (iR) drop prior to performing kinetic measurements in the ionic liquid is demonstrated. A Tafel analysis of the RDE voltammetry data revealed a change in the ORR Tafel slope from 70 mV per decade at low ORR overpotentials to 117 mV per decade at high overpotentials, and the reason for this change is discussed. The change in the Tafel slope for the ORR with increasing overpotential meant that the exchange current density for the ORR varied from 0.007 nA cm(-2) to 10 nA cm(-2), depending on the applied potential. Finally, the implications of these results for the development of protic ionic liquid fuel cells are discussed.

The development of vanadium redox flow batteries (VRFBs) is partly limited by the sluggishness of the electrochemical reactions at conventional carbon-based electrodes. The VO 2+ /VO 2 + redox reaction is particularly sluggish and improvements in battery performance require the development of new electrocatalysts for this reaction. In this study, synergistic Electrochemical analysis shows that the electrocatalytic activity of the composite material is significantly higher than those of the individual components due to synergism between the Mn 3 O 4 nanoparticles and the carbonaceous support material. The electrocatalytic activity is highest when the Mn 3 O 4 loading is ~24% but decreases at lower and higher loadings.Furthermore, electrocatalysis of the redox reaction is only observed when nitrogen is present within the support framework, demonstrating that the metal-nitrogen-carbon coupling is key to the performance of this electrocatalytic composite for VO 2+ /VO 2 + electrochemistry.

Development of applications for graphene are currently hampered by its poor dispersion in common, low boiling point solvents. Covalent functionalization is considered as one method for addressing this challenge. To date, approaches have tended to focus upon producing the graphene and functionalizing subsequently. Herein, we describe simultaneous electrochemical exfoliation and functionalization of graphite using diazonium salts at a single applied potential for the first time. Such an approach is advantageous, compared to postfunctionalization of premade graphene, as both functionalization and exfoliation occur at the same time, meaning that monolayer or few-layer graphene can be functionalized and stabilized in situ before they aggregate. Furthermore, the N generated during in situ diazonium reduction is found to aid the separation of functionalized graphene sheets. The degree of graphene functionalization was controlled by varying the concentration of the diazonium species in the exfoliation solution. The formation of functionalized graphene was confirmed using Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The functionalized graphene was soluble in aqueous systems, and its solubility was 2 orders of magnitude higher than the nonfunctionalized electrochemically exfoliated graphene sheets. Moreover, the functionalization enhanced the charge storage capacity when used as an electrode in supercapacitor devices with the specific capacitance being highly dependent on the degree of graphene functionalization. This simple method of in situ simultaneous exfoliation and functionaliztion may aid the processing of graphene for various applications.

The stability of water-in-salt electrolyte systems is investigated using highly concentrated solutions of KF(aq) with graphite as a model system.