A self-assembled organic/metal junction for water photo-oxidation

We report the in situ self-assembly of TTF, TTF ·+ , and BF 4 - or PF 6 - into p-type semiconductors on the surface of Pt microparticles dispersed in water/acetonitrile mixtures. The visible light photoactivation of these self-assemblies leads to water oxidation forming O 2 and H + , with an efficiency of 100% with respect to the initial concentration of TTF ·+ . TTF ·+ is then completely reduced to TTF upon photoreduction with water. The Pt microparticles act as floating microelectrodes whose Fermi level is imposed by the different redox species in solution; here predominantly TTF, TTF ·+ , and HTTF + , which furthermore showed no signs of decomposition in solution.Fil: Olaya, Astrid J.. Swiss Federal Institute Of Technology Epfl; SuizaFil: Omatsu, Terumasa. Kyoto Institute Of Technology; JapónFil: Hidalgo-Acosta, Jonnathan C.. Swiss Federal Institute Of Technology Epfl; SuizaFil: Riva, Julieta Soledad. Swiss Federal Institute Of Technology Epfl; Suiza. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bassetto, Victor Costa. Swiss Federal Institute Of Technology Epfl; SuizaFil: Gasilova, Natalia. Swiss Federal Institute Of Technology Epfl; SuizaFil: Girault, Hubert. Swiss Federal Institute Of Technology Epfl; Suiz

Inkjet Printing Meets Electrochemical Energy Conversion

Inkjet printing is a very powerful digital and mask-less microfabrication technique that has attracted the attention of several research groups working on electrochemical energy conversion concepts. In this short review, an overview is given about recent efforts to employ inkjet printing for the search of new electrocatalyst materials and for the preparation of catalyst layers for polymer electrolyte membrane fuel cell applications. Recent approaches of the Laboratory of Physical and Analytical Electrochemistry (LEPA) at the École Polytechnique Fédérale de Lausanne for the inkjet printing of catalyst layers and membrane electrode assemblies are presented and future energy research directions of LEPA based on inkjet printing in the new Energypolis campus in the Canton of Valais are summarized

Inkjet printing and electrocatalysis

The transition in energy matrix, from fossil to renewable energy sources, will require the utilization of grid levelling alternatives to cope with the intermittent characteristic of renewable energy. Advanced electrochemical energy conversion and storage devices, ranging from batteries to fuel cells, play a crucial role in that process. Many of these electrochemical devices are based on the oxidation and reduction reactions of oxygen, a compound that can conveniently be taken from air and released to the environment. However, sluggish kinetics of the oxygen reactions at current electrode materials require the synthesis and study of more efficient and stable electrocatalysts and catalyst layers made thereof. This thesis focuses on combined drop-on-demand inkjet printing coupled with pulsed light sintering for the fabrication of catalyst layers containing advanced electrocatalyst materials. Inkjet printing allowed the precise control of the material loading inside the catalyst layers and the pulsed light-induced post-processing enabled rapid drying and even material functionalization, such as changing the oxidation state of the metals for improved electrochemical performance. The electrocatalysts were in particular studied for their activity and stability towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). First, an ink with an advanced non-precious metal-based catalyst, nitrogen-doped re-duced graphene oxide supported cobalt oxide nanoparticles (i.e., Co3O4/N-rGO), was prepared and inkjet printed in form of a catalyst layer on large glassy carbon electrodes. The application of the flash lamp reduced in a rapid, non-equilibrium thermal process, the oxidation state of cobalt within a short high intensity light pulse and modified the catalytic properties for the ORR. The electrocatalyst proper-ties are discussed in detail in Chapter III and compared with catalyst layers that were prepared by us-ing equilibrium thermal processing in a furnace. In Chapter IV, the application of inkjet printing and flash light processing for the syn-thesis of nanoparticles from printed, dissolved metal precursors is presented. This concept was recently introduced as "Print-Light-Synthesis" and was herein applied to fabricate Pt nanostructures on glassy carbon substrates. The process is based on the light-induced thermal decomposition of the Pt precursor. It represents a promising, low material consumption and highly controllable alternative to standard wet chemical synthesis of nanoparticles in reactors. Based on the Print-Light-Synthesis, Chapter V describes the development of mixed NiFe nano-composites with well-defined material ratios and loadings in the corresponding inks. Catalyst layer of the composites were fabricated as OER electrocatalysts. A support layer of carbon-nanotubes was used as "light-to-heat-absorber" and alcohols in the ink as reducing agents for the efficient decomposition of the chloride-based Ni and Fe precursors. The last section of this thesis presents future perspectives of the current work. The possibilities in which this research can engender will be discussed. Focus will be drawn to possible industrial applications of the proposed and developed techniques presented in this thesis. Mainly it is demonstrated the possibility of having, through the combination of inkjet printing and flash light processing as two state-of-art techniques the possibility of fabricating in an easily-up scalable

Preparation of copper sphere segment void templates for electrochemical SERS and their use to study the interaction of amino acids with copper under potentiostatic control

We describe a simple method to prepare nanostructured copper electrodes based on electrodeposition of copper through a polystyrene nanosphere template to produce a copper sphere segment void (SSV) structure. We show that the SSV copper electrodes give a large SER enhancement under potentiostatic control and we use the SSV copper electrodes to study the adsorption of aromatic and non-aromatic amino acids in basic solution

Electrochemical Approaches Employed For Sensing The Antioxidant Capacity Exhibited By Vegetal Extracts: A Review.

Vegetal extracts are among the most important source of polyphenols in the diet, highlighting the importance of their characterization and determination. For this reason, analytical methods have gained increasing interest, with many publications devoted to this subject. Among the wide possibilities of analytical methods, electroanalytical techniques can provide valuable information, since the antioxidant activity of polyphenols is related to their electrochemical properties. This review analyzes and highlights the role of electroanalytical approaches for sensing the antioxidant capacity exhibited by vegetal extracts, as well as focuses on their importance for human health. The analytical capacity of the electrochemistry is comprehensively stated with the selected results found in the literature, mainly from 2000 up to the present date.1698-10

Critical view on graphene oxide production and its transfer to surfaces aiming electrochemical applications

Graphene and related materials has been studied aiming their use in several applications including electrochemical sensing systems for a large number of different analytes. However, there have been proportionally only a few studies discussing deeply the implications of the different variables that could be tuned in the preparations of these materials for the development of the electrochemical platforms. In this review it is discussed how the size, number of layers, crystallinity and purity of the graphite starting material affects the final graphene oxide (GO) and reduced graphene oxide (rGO) prepared by chemical exfoliation. The exfoliation process and the most frequently applied transfer methods used to prepare thin films of GO and rGO on surfaces/electrodes of sensing platforms are also discussed. The electrochemical behavior of these materials is evaluated as a role of surface organization and adsorption. Considering the parameters previously presented, it is outlined some of the most relevant sensors and biosensor systems, which employ graphene related materials and attempts to explore different possibilities of deposition14964786496sem informaçã

Assembling Ni-Fe Layered Double Hydroxide 2D thin films for oxygen evolution electrodes

Continuous hydrothermal flow synthesis (CHFS) of Ni-Fe layered double hydroxide (LDH) leads to waterborne dispersions of 2D nanoplatelets in the range of 10-50 nm in lateral size. Conversion of the as-synthesized LDH nanoplatelet dispersion into inkjet printing inks results in high precision patterning and complete substrate coverage with low LDH loadings in the range of mu g cm(-2). The Ni-Fe LDHs' anisotropy induces a preferential inplane alignment to a glassy carbon substrate producing low-porosity films. Thin Ni-Fe LDH films in the submicrometer range exhibit superior electrocatalytic activity for the oxygen evolution reaction (OER), with an overpotential of 270 mV at 10 mA cm(-2) and a Tafel slope of 32 mV dec(-1). The particle alignment creates a compact film and induces a loading-independent electrochemical performance of the Ni-Fe LDH electrodes for loadings above 50 mu g cm(-2). The combination of CHFS and inkjet printing represents a promising hyphenation of large-scale synthesis and electrode production

Print-Light-Synthesis of Ni and NiFe-nanoscale catalysts for oxygen evolution

By hyphenating inkjet printing and flash light irradiation, Ni- and NiFe-nano-electrocatalysts of diameters below 2.5 nm with ultralow loadings below 2 µg·cm–2 are synthesized. To achieve this, nanoliter ink volumes containing Ni and Fe chlorides as catalyst precursors are rapidly printed on large-scale carbon nanotube-coated glassy carbon electrodes and exposed to millisecond-long high intensity light pulses from a Xenon flash lamp. The carbon nanotube coating acts as light-to-heat absorber generating surface peak temperatures of several hundred degrees. The light-induced reduction of the Ni and Fe precursors into chloride-free mixed metal composites is facilitated by alcohols that act as sacrificial electron donors in the printed precursor films. Besides the merging of large-scale electrode production and nanoparticle synthesis into a single robust and rapid process, the adjustability of the precursor ratios using parallel printheads, the operation under ambient conditions, the absence of capping agents as well as surfactants, and the up-scalability to industrial levels are the major advantages of this new electrode fabrication method. Furthermore, the process is superior to standard lab-scale electrocatalyst deposition methods, such as drop casting, and is more flexible to control compared to hydro- and solvothermal syntheses. The electrochemical characterisation of the Ni- and NiFe-based nano-electrocatalysts by voltammetric cycling leads to onset potentials as low as 240 mV (at 0.1 mA·cm–2), overpotentials of 334 mV (at 10 mA·cm–2), Tafel slopes of 41 mV·dec–1 and high turnover frequencies of up to 4.5 s–1 for the oxygen evolution reaction

Printing of NiO-YSZ nanocomposites: from continuous synthesis to inkjet deposition

Water-based inks, containing nanometric NiO and YSZ particles in 66/34 vol. % ratio, are produced by colloidal stabilization of a binary dispersion obtained via continuous hydrothermal synthesis at supercritical conditions, i.e. 280 bar and 400 °C. The method yields single-crystal particles with diameter ≤ 10 nm for both phases in a single-step process, achieving a highly mixed composite. Two different approaches are applied to formulate inks printable with piezoelectric printheads, i.e. an electrostatic and an electrosteric stabilization path. The use of an electrosteric dispersant results in colloids with superior stability > 200 days, more uniform thin films and finely nanostructured porous cermet films with thickness below 500 nm, after reducing NiO to Ni. Particles coarsening to 50-150 nm is obtained at 1000 °C, accompanied by a shrinkage of ca. 43 % in thickness without the formation of cracks or delamination of the zirconia substrates