Hubert H. Girault

A nanoporous molybdenum carbide nanowire as an electrocatalyst for hydrogen evolution reaction

A highly active and stable electrochemical catalyst of nanoporous molybdenum carbide nanowires (np-Mo2C NWs) has been developed for hydrogen evolution reaction (HER). The np-Mo2C NWs were synthesized simply by pyrolysis of a MoOx/amine hybrid precursor with sub-nanosized periodic structure under an inert atmosphere. The enriched nanoporosity and large reactive surface of these highly dispersed nanowires with uniform Mo2C nanocrystallites provide an efficient electrocatalysis, leading to their superior HER activity with lower onset overpotential and higher current densities than Mo2C microparticles. This study opens a new perspective for the development of highly active non-noble electrocatalysts for hydrogen production from water splitting.

UV laser machined polymer substrates for the development of microdiagnostic systems

This report describes a UV laser photoablation method for the production of miniaturized liquid-handling systems on polymer substrate chips. The fabrication of fluid channel and reservoir networks is accomplished by firing 200 mJ pulses from an UV excimer laser at substrates moving in predefined computer-controlled patterns. This method was used for producing channels in polystyrene, polycarbonate, cellulose acetate, and poly(ethylene terephthalate). Efficient sealing of the resulting photoablated polymer channels was accomplished using a low-cost film lamination technique. After fabrication, the ablated structures were observed to be well defined, i.e., possessing high aspect ratios, as seen by light, scanning electron, and atomic force microscopy. Relative to the original polymer samples, photoablated surfaces showed an increase in their hydrophilicity and rugosity as a group, yet differences were noted between the polymers studied. These surface characteristics demonstrate the capability of generating electroosmotic flow in the cathodic direction, which is characterized here as a function of applied electric field, pH, and ionic strength of common electrophoretic buffer systems. These results show a correlation between the ablative changes in surface conditions and the resulting electroosmotic flow. The effect of protein coatings on ablated surfaces is also demonstrated to significantly dampen the electroosmotic flow for all polymers. All of these results are discussed in terms of developing liquid-handling capability, which is an essential part of many μ-TAS and chemical diagnostic systems.

Electrochemistry at liquid/liquid interfaces: methodology and potential applications

Electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) gains more and more interest due to its wide range of applications. The present review encompasses the various domains of charge transfer reactions in biphasic systems, with some emphasis on certain studies that marked the advances of electrochemistry at ITIES and that, in a noticeable manner, have been presented in large majority at the ISE meetings during the last two decades. These studies, as well as some subjects in which our recent research interest is concerned, are used here to describe the fundamental aspects of charge transfer reactions at liquid:liquid interfaces and to outline their various applications. This overview presents the methodologies offered by the ITIES in the fields of amperometric sensors, solvent extraction, pharmacokinetics, thermo-electricity and solar energy conversion, and the accent is put on the perspectives of their potential development in the coming years.

Assisted ion transfer at micro-ITIES supported at the tip of micropipettes

Abstract Micro liquid-liquid interfaces supported at the tip of glass micropipettes have been used to study the assisted transfer of potassium by dibenzo-18-crown-6 at the water-1,2-dichloroethane interface. This technique allows the measurement of the ratio of the diffusion coefficients of the free ionophore and of the complexed ion. It also shows that the transfer occurs by an interfacial complexation-dissociation process. A new nomenclature for assisted ion transfer is also proposed.

The measurement of interfacial tension of pendant drops using a video image profile digitizer

Abstract A video image processor designed for the automatic digital measurement of the external coordinates of an object with a resolution of 1066 (pixels/line) × 575 lines is described. This profile digitizer has been used for the measurement of the interfacial tension of pendant drops. A new computational method based on the processing of the drop coordinates acquired in real time (25 video frames per second) is presented. This method utilizes the Laplace equation at the inflexion plane of the drop located by a polynomial fitting technique. The results at different organic liquid-water interfaces show that the method is capable of giving an absolute accuracy of better than 1% when using a standard video camera. The application of this technique for adsorption kinetics is described.

Analytical and Physical Electrochemistry

The study electrochemistry is pertinent to a wide variety of fields, including bioenergetics, environmental sciences, and engineering sciences. Intended both as a basic course for undergraduate students and as a reference work for graduates and researchers, this book covers two fundamental aspects of electrochemistry: electrochemistry in solution and interfacial electrochemistry. By bringing these two subjects together into a single volume, the author clearly establishes the links between the physical foundation and the analytical applications of electrochemistry. With this rigorous approach, the author has provided a book of reference constructed from first principles. In this respect, the nomenclature and standards of the IUPAC (International Union of Pure and Applied Chemistry) are observed.

Molecular electrocatalysis for oxygen reduction by cobalt porphyrins adsorbed at liquid/liquid interfaces.

Molecular electrocatalysis for oxygen reduction at a polarized water/1,2-dichloroethane (DCE) interface was studied, involving aqueous protons, ferrocene (Fc) in DCE and amphiphilic cobalt porphyrin catalysts adsorbed at the interface. The catalyst, (2,8,13,17-tetraethyl-3,7,12,18-tetramethyl-5-p-amino-phenylporphyrin) cobalt(II) (CoAP), functions like conventional cobalt porphyrins, activating O(2) via coordination by the formation of a superoxide structure. Furthermore, due to the hydrophilic nature of the aminophenyl group, CoAP has a strong affinity for the water/DCE interface as evidenced by lipophilicity mapping calculations and surface tension measurements, facilitating the protonation of the CoAP-O(2) complex and its reduction by ferrocene. The reaction is electrocatalytic as its rate depends on the applied Galvani potential difference between the two phases.

Cyclic voltammetry at a regular microdisc electrode array

A simulation of cyclic voltammetric responses has been performed to study the diffusion process of a regular array of microdisc interfaces by the use of finite element software. The effect of centre-to-centre distance between the active electrodes on the current response and also their voltammetric shape and characteristics have been investigated.

Electrochemical Detection in Polymer Microchannels

A method, using UV laser photoablation, is presented for the fabrication and the integration of an electrochemical detector in a microchannel device, where carbon microband electrodes are placed either in the bottom or in the side walls of the rectangular microchannel. The different electrochemical cell geometries are tested with a model compound (ferrocenecarboxylic acid) in 40- and 100-μm-wide capillaries fabricated in planar polymer substrates. The experimental results are compared to numerical simulations for stagnant stream conditions. Depending on the scan rate and on the microchannel depth, the system behaves as a microband electrode until a linear diffusion field develops within the channel. The limit of detection for a one electron redox species within the 120-pL detection volume is ∼1 fmol with both cyclic voltammetry and chronoamperometric detection.

Protein purification by Off-Gel electrophoresis

A novel free‐flow protein purification technique based on isoelectric electrophoresis is presented, where the proteins are purified in solution without the need of carrier ampholytes. The gist of the method is to flow protein solutions under an immobilised pH gradient gel (IPG) through which an electric field is applied perpendicular to the direction of the flow. Due to the buffering capacity of the IPG gel, proteins with an isoelectric point (pI) close to pH of the gel in contact with the flow chamber stay in solution because they are neutral and therefore not extracted by the electric field. Other proteins will be charged when approaching the IPG gel and are extracted into the gel by the electric field. Both a demonstration experiment with pI markers and a simulation of the electric field distribution are presented to highlight the principle of the system. In addition, an isoelectric fractionation of an Escherichia coli extract is shown to illustrate the possible applications.