S. Tiewcharoen, C. Warakulwit, V. Lapeyre, P. Garrigue, L. Fourier, C. Elissalde, S. Buffière, P. Legros, M. Gayot, J. Limtrakul, A. Kuhn

Angew.Chem.Int.Ed. (2017) 56, 11431-11435, COVER, HOT PAPER

see also CNRS press release

Deposition of metals on TiO2 semiconductor particles (M-TiO2) results in hybrid Janus objects combining the interesting properties of both materials. One of the techniques that have been proposed to generate Janus particles is bipolar electrochemistry (BPE). The concept can be applied in a straightforward way for the site selective modification of conducting particles, but is much less obvious to use for semiconductors. In this work we report the bulk synthesis of anisotropic M-TiO2 particles based on the synergy of BPE and photochemistry, allowing to overcome intrinsic limitations when they are used separately. When applying electric fields during irradiation, electrons and holes can be efficiently separated, thus breaking the symmetry of particles by modifying them selectively and in a wireless way on one side with either gold or platinum. Such hybrid materials are an important first step towards high performance designer catalyst particles for example for photosplitting of water.

2017 16

A. G. Mark, E. Suraniti, J. Roche, H. Richter, A. Kuhn, N. Mano, P. Fischer

Lab Chip, 2017, 17, 1761 HOT PAPER

see also CNRS press release

A variety of diagnostic and therapeutic medical technologies rely on long term implantation of an electronic device to monitor or regulate a patient's condition. One proposed approach to powering these devices is to use a biofuel cell to convert the chemical energy from blood nutrients into electrical current to supply the electronics. We present here an enzymatic microbiofuel cell whose electrodes are directly integrated into a digital electronic circuit. Glucose oxidizing and oxygen reducing enzymes are immobilized on microelectrodes of an application specific integrated circuit (ASIC) using redox hydrogels to produce an enzymatic biofuel cell, capable of harvesting electrical power from just a single droplet of 5 mM glucose solution. Optimisation of the fuel cell voltage and power to match the requirements of the electronics allow self-powered operation of the on-board digital circuitry. This study represents a step towards implantable self-powered electronic devices that gather their energy from physiological fluids.

2017 14

 

L. Bouffier, S. Reculusa, V. Ravaine, A. Kuhn.


ChemPhysChem 2017, 18, 2637-2642.

 

A new simple and versatile method for the preparation of surface wetting gradients is proposed. It is based on the combination of electrode surface structuration introduced by a sacrificial template approach and the formation of a tuneable molecular gradient by bipolar electrochemistry. The gradient involves the formation of a self-assembled monolayer on gold surface by selecting an appropriate thiol molecule and the subsequent reductive desorption by means of bipolar electrochemistry. Under these conditions, the completion of the reductive desorption process evolves along the bipolar surface with a maximum strength localized at the cathodic edge and a decreasing driving force toward the middle of the surface. The remaining quantity of surface-immobilized thiol does therefore vary in function of the axial position, resulting in the formation of a molecular gradient. The surface of the bipolar electrode is characterized at each step of the modification by recording heterogeneous electron transfer. Also, the evolution of static contact angles measured with a water droplet deposited on the surface directly reveals the presence of the wetting gradient which can be modulated by changing the properties of the thiol. This is exemplified with a long hydrophobic alkane-thiol and a short hydrophilic mercaptan.

 

2017 12

Faraday Discuss., 2017, in press,doi 10.1039/C7FD00130D

We study the optical response of individual nm-wide plasmonic nanocavities using a nanoparticle-on-mirror design utilised as an electrode in an electrochemical cell. In this geometry Au nanoparticles are separated from a bulk Au film by an ultrathin molecular spacer, giving intense and stable Raman amplification of 100 molecules. Modulation of the plasmonic spectra and the SERS response is observed with applied voltage under a variety of electrolytes. Different scenarios are discussed to untangle the various mechanisms that can be involved in the electronic interaction between NPs and electrode surfaces.

2017 15

I. Malytska, C. Mézière, M. Keilar, L. Hirsch, G. Wantz, N. Avarvari, A. Kuhn, L. Bouffier.


Journal of Physical Chemistry C 2017, 121, 12921-12927.

 

Bipolar electrochemistry has recently emerged as a very unique method to address conducting particles in a wireless manner. The technic is often applied to the fabrication of Janus particles, however the chemical nature of the bipolar electrode has been essentially limited to carbon or metal-based materials. Here, we report for the first time the use of conducting organic single crystals as bipolar electrodes for the preparation of a new generation of Janus objects. Fabre and Bechgaard salts involving respectively tetrathia- and tetraselenafulvalene were selected for proof-of-concept experiments. Such an approach allows to preserve the integrity of these fragile substrates because it neither necessitates electronic wiring nor mechanical contact. The site-selective electrodeposition of copper is successfully achieved, leading thus to a new metal-organic Janus structure. Subsequently asymmetric generation of photovoltage under illumination is achieved due to the anisotropic presence of copper, making this approach interesting for the design of novel hybrid objects with applications in organic electronics or photocatalysis.

 

2017 13