Understanding nanoparticle porosity via nanoimpacts and XPS: electro-oxidation of platinum nanoparticle aggregates

The porosity of platinum nanoparticle aggregates (PtNPs) is investigated electrochemically via particle-electrode impacts and by XPS. The mean charge per oxidative transient is measured from nanoimpacts; XPS shows the formation of PtO and PtO2 in relative amounts defined by the electrode potential and an average oxidation state is deduced as a function of potential. The number of platinum atoms oxidised per PtNP is calculated and compared with two models: solid and porous spheres, within which there are two cases: full and surface oxidation. This allows insight into extent to which the internal surface of the aggregate is ‘seen’ by the solution and is electrochemically active

How can electrode surface modification benefit electroanalysis?

This Perspective critically evaluates the ways in which electrode surface modification affects the effectiveness of electroanalytical techniques. The use of various voltammetric techniques, the role of modification in increasing selectivity, the manipulation of electron transfer kinetics, as well as the impact of increased surface area are discussed. It is critical that the motivations and physical implications of altering the electrode surface are properly understood before intricate, impractical modifications are employed that do not significantly improve the performance of the sensor

Circus Perfomers

Photograph of a woman in a sports car with a man standing beside, another man is stood further behind. The photograph appears to be next to the steps of a theatre . Posters in the background refer to 'Hippodrome' and 'Billy Cotton's Band'

Adsorption on graphene: flat to edge to end transitions of phenyl hydroquinone

The adsorption of phenyl hydroquinone (PHQ) on graphene surfaces at the liquid–solid interface is investigated revealing a flat orientation and two different vertically adsorbed states of PHQ on graphene nanoplatelets (GNPs), namely edgewise or endwise adsorption. The transition between these states is driven by increasing concentrations of PHQ in solution leading to increased absolute coverages on the graphene surface. At low adsorbate concentrations (≤21 mM), the adsorption process is also shown to be Langmuirian with an adsorption constant of (9.5 ± 0.2) mM−1. Independent measurements are conducted using a single particle electrochemical technique to confirm the surface coverage of PHQ on GNPs at low concentrations, showing excellent agreement with the UV-Vis studies

Adsorption on graphene: flat to edge to end transitions of phenyl hydroquinone

The adsorption of phenyl hydroquinone (PHQ) on graphene surfaces at the liquid–solid interface is investigated revealing a flat orientation and two different vertically adsorbed states of PHQ on graphene nanoplatelets (GNPs), namely edgewise or endwise adsorption. The transition between these states is driven by increasing concentrations of PHQ in solution leading to increased absolute coverages on the graphene surface. At low adsorbate concentrations (≤21 mM), the adsorption process is also shown to be Langmuirian with an adsorption constant of (9.5 ± 0.2) mM−1. Independent measurements are conducted using a single particle electrochemical technique to confirm the surface coverage of PHQ on GNPs at low concentrations, showing excellent agreement with the UV-Vis studies

Single nanoparticle detection in ionic liquids

Nanoimpacts are novelly observed in a room temperature ionic liquid with the oxidation of silver nanoparticles in 1-butyl-3-methylimidazolium tetrafluoroborate. The addition of chloride facilitates the oxidation of the silver nanoparticles to silver chloride, which is observed as spikes in the current that correspond to single nanoparticles occurring via nanoimpacts, whereby random diffusion (Brownian motion) brings particles to within electron tunnelling distance of an electrode. © 2016 American Chemical Society

Electroanalytical study of dopamine oxidation on carbon electrodes: from the macro- to the micro-scale

The oxidation of dopamine in strongly acidic (pH = 0) solution is investigated using microdisc, microcylinder and macro-electrodes together with a range of voltage scan rates. Kinetic and mechanistic analysis over the full range of mass transport conditions show a behaviour consistent with an ECE process with a fast chemical step and in which the second electron transfer is thermodynamically more favourable than the first step. Accordingly the reaction effectively behaves as an EE process

DNA capping agent control of electron transfer from silver nanoparticles

Silver nanoparticles capped with either DNA or citrate are investigated electrochemically using stripping voltammetry and nano-impacts. Whilst the citrate capped particles are readily oxidised to silver cations at 0.7 V, the DNA capped particles undergo electron transfer from the silver core to the electrode in two distinct potential ranges - 0.8 to 1.1 V and 1.125 to 1.2 V, and only undergo complete oxidation at the higher potential range. These potentials reflect the oxidation of guanine and adenine respectively, with a potential sufficient to oxidise both base pairs being necessary to observe full silver oxidation. The DNA thus serves as a tunnelling barrier to electrically insulate the particle, and allows for selective oxidation to occur by controlling the potential applied

One electron oxygen reduction in room temperature ionic liquids: A comparative study of Butler-Volmer and Symmetric Marcus-Hush theories using microdisc electrodes

The voltammetry for the reduction of oxygen at a microdisc electrode is reported in two room temperature ionic liquids: 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([Bmpyrr][NTf2]) and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide ([P 14,6,6,6][NTf2]) at 298 K. Simulated voltammograms using Butler-Volmer theory and Symmetric Marcus-Hush (SMH) theory were compared with experimental data. Butler-Volmer theory consistently provided experimental parameters with a higher level of certainty than SMH theory. A value of solvent reorganisation energy for oxygen reduction in ionic liquids was inferred for the first time as 0.4-0.5 eV, which is attributable to inner-sphere reorganisation with a negligible contribution from solvent reorganisation. The developed Butler-Volmer and Symmetric Marcus-Hush programs are also used to theoretically study the possibility of kinetically limited steady state currents, and to establish an approximate equivalence relationship between microdisc electrodes and spherical electrodes resting on a surface for steady state voltammetry for both Butler-Volmer and Symmetric Marcus-Hush theory. © 2014 Elsevier B.V. All rights reserved

Impact electrochemistry reveals that graphene nanoplatelets catalyse the oxidation of dopamine via adsorption

Graphene nanoplatelets are shown to electrocatalyse the oxidation of dopamine. Single entity measurements (‘nano-impacts’) coupled with microdisc voltammetry and UV-visible spectroscopy reveal that adsorption of dopamine and its oxidised product on the graphene nanoplatelets is the key factor causing the observed catalysis. Genetic implications are drawn both for the study of catalysts in general and for graphene nanoplatelets in particular.</p