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International audience; The electrochemical regeneration of the NADH cofactor was realized in a hybrid flow reactor coupling fuel cell technology and redox flow device, paying attention to the robust immobilization of all catalysts. The rhodium catalyst Rh(Cp∗)(bpy)Cl+ was covalently immobilized on a MWCNT layer and the association with the gas diffusion electrode was carefully optimized. High stability and activity of the electrochemical system were assessed by cyclic voltammetry and amperometry in the flow reactor. Afterwards, the optimal cofactor regeneration was applied to NADH-dependent biosynthesis using immobilized lactate dehydrogenase for the conversion of pyruvate to lactate in the flow cell in the presence of cofactor concentration as low as 10 μM. 79 % faradaic efficiency was achieved and remarkable total turnover number (TTN) were reached: 2500, 18000, and 180000, for the NADH cofactor, the Rh complex and the LDH enzyme, respectively.

International audience; Beta-nicotinamide adenine dinucleotide (NAD + /NADH) is an important enzymatic co-factor that can be efficiently regenerated using a rhodium-based catalyst as electron transfer mediator (i.e. [Cp*Rh(bpy)Cl] + , where Cp* = pentamethylcyclopentadienyl and bpy = 2,2-bipyridine). Here, the above mediated regeneration of NADH is implemented in a redox flow bioreactor hybridized with a gas diffusion electrode for hydrogen oxidation. The reactor was initially optimized with respect to rhodium complex and NAD + concentrations, humidification of the hydrogen gas, flow rates of both H 2 gas and electrolytic solution, and solution pH. The integration of an enzymatic reaction consuming the generated NADH was then investigated in a flow process, combining in series the electrochemical reactor to a biochemical cell with immobilized L-lactic dehydrogenase for the conversion of pyruvate to lactate. A high activity was achieved with a turnover number up to 370 h-1 for NADH regeneration. Coupled electrochemical regeneration to enzymatic reaction led to total turnover number values of 2000 and 6.3*10 6 for NADH electrochemical regeneration and bioconversion, respectively.

Electrochemical stripping analysis (anodic, cathodic, or adsorptive) is usually based on the pre-concentration of a target analyte on the working electrode surface and then measuring its quantity via its direct quantitative electrochemical transformation (with the electrode refreshed afterwards). In this work, we demonstrate a new approach to carry out electrochemical stripping analysis of non-adsorbing species, thus not based on the analyte being directly pre-concentrated on the working electrode (WE), but on the signal obtained indirectly from the counter electrode (CE) where metal ions are reduced and then electrochemically stripped. Different from the CE with large surface area in classical electrochemical measurements, an ultramicroelectrode is chosen here as CE to purposely exploit the polarization effect. The concept is based on oxidizing the analyte on WE in one compartment of the electrochemical cell while reducing Cu2+ on CE from another compartment connected with an ionic bridge or a less common metal “bridge”. The deposited Cu on CE is then analyzed by stripping in another three-electrode cell, and the charge shows good linear relationship with the concentration of analyte in the former cell. As the stripping current response (peak) is much clearer than the small current variations corresponding to the direct oxidation of the analyte, it improves the resolution of raw signal. Besides, it may also reduce the background signal from blank solution by “filtering” the non-Faradaic charge. Like in classical electrochemical stripping analysis, one may also prolong the oxidation time in exchange for higher sensitivity of analysis. This work extends the applications of stripping analysis and offers a new angle of electroanalysis by capturing signals from counter electrode.

International audience; Beta-nicotinamide adenine dinucleotide (NAD + /NADH) is an important enzymatic co-factor that can be efficiently regenerated using a rhodium-based catalyst as electron transfer mediator (i.e. [Cp*Rh(bpy)Cl] + , where Cp* = pentamethylcyclopentadienyl and bpy = 2,2-bipyridine). Here, the above mediated regeneration of NADH is implemented in a redox flow bioreactor hybridized with a gas diffusion electrode for hydrogen oxidation. The reactor was initially optimized with respect to rhodium complex and NAD + concentrations, humidification of the hydrogen gas, flow rates of both H 2 gas and electrolytic solution, and solution pH. The integration of an enzymatic reaction consuming the generated NADH was then investigated in a flow process, combining in series the electrochemical reactor to a biochemical cell with immobilized L-lactic dehydrogenase for the conversion of pyruvate to lactate. A high activity was achieved with a turnover number up to 370 h-1 for NADH regeneration. Coupled electrochemical regeneration to enzymatic reaction led to total turnover number values of 2000 and 6.3*10 6 for NADH electrochemical regeneration and bioconversion, respectively.

International audience

Pseudo-capacitive materials operating with electron-hopping as the charge transfer mechanism are elaborated by the extensive assembly of fixed redox molecules onto the surface of graphene-supported mesoporous silica film. Various physico-chemical techniques are used to characterize the resulting composites. The obtained GO@Fc-MS electrode (ferrocene functionalized silica film coated onto electro-exfoliated graphene) can deliver a specific capacity of 196 mC cm−2 (326 mF cm−2) at a current density of 2 mA cm−2 and a 69% capacity retention even at 3800 C, which is much better than the traditional faradic materials. The electrochemical analyses reveal the energy storage behavior of GO@Fc-MS is a fast surface-controlled redox process. The electrode can be assembled into an asymmetric device which exhibits excellent cycling stability (no noticeable fading after 10 000 cycles) and competitive energy densities (respectively 17.7 or 9.2 µWh cm−2 at power densities of 0.53 or 13.7 mW cm−2). These results open up new opportunities for pseudocapacitive materials based on electroactive inorganic frameworks bearing surface-tethered molecular redox sites with high energy storage capability.

International audience; Vertically aligned mesoporous silica films electrogenerated on indium-tin oxide (ITO) electrodes are used as hardtemplates for the electrochemical growth of polyaniline (PANI) nanofilaments. To ensure proper adhesion ofPANI to the underlying ITO surface, aniline moieties are first covalently attached to the bottom of mesochannelsvia electrografting of aminophenyl diazonium cations, serving in a second step as precursors for PANI growth byelectropolymerization of aniline through the silica mesochannels. This was achieved by cyclic voltammetry orpotentiostatically at an applied potential of +0.85 V (vs. Ag/AgCl), the latter offering a better control of thenanofilaments length by tuning the electropolymerization time. PANI wires remain attached to ITO after etchingof the silica membrane, confirming the importance of initial electrografting. Although PANI nanofilaments in thesilica membrane remain electroactive, enhanced peak currents were observed after silica removal as PANInanofilaments offer a larger effective surface area to the electrolyte solution.

A three-phase junction formed between a solid electrode placed between solutions of the organic phase and the aqueous phase is employed for localized and electrochemically assisted nylon-6,6 deposition. The fluorine-doped tin oxide (FTO) conductive support (serving as the working electrode) is immersed into the cell filled with the aqueous solution of 1,6- hexanediamine (1,6-DAH) and the organic solution of adipoyl chloride (AC) dissolved in 1,2-dichloroethane. The interfacial polycondensation reaction between these two reagents occurs spontaneously at the liquid–liquid interface at elevated pH and is inhibited when diamine is fully protonated. With this in mind, we have designed a system where the pH close to the three-phase junction was increased using electrochemical water reduction triggering very localized polyamide deposition.

International audience; The voltammetric behavior of bulky heteropolyanions belonging to the Dawson family of polyoxometalates, [P2VmW18-mO62] n-(m = 0, 3, 6), has been investigated at electrodes coated with vertically-aligned mesoporous silica thin films with pore openings in the 2-3 nm range. The experiments have been carried out in acidic medium (pH 0.3-1), where the silica surface is positively charged and thus likely to interact with the negatively charged redox probes, and at various ionic strengths of the medium. Better permeability of the films was clearly observed at lower pH values, corresponding to higher densities of positive charges onto the silica walls, and of films with a larger mesopore size, favoring the mass transport rates through the nanoporous membrane. Diffusion of such bulky anionic redox probes was dramatically influenced by the ionic strength of the medium, being especially restricted at low electrolyte concentrations where the thickness of the electrical double layer became of the same order of magnitude or larger than the mesopore radius, giving rise to very low voltammetric signals. The overall negative charge on POMs had few effects on their mass transport through the film, except at low ionic strength where the most highly charged redox probes gave rise to the lowest current responses.

International audience; The mediated electrochemical reduction of NAD(P) + in aerated solution was investigated and exploited for NAD(P)H regeneration in view of biosensing application. Oxygen was locally removed from the electrode surface with an electrochemical oxygen filter made of platinum grids positioned close to the oxygen sensitive reactions. The working electrode was a bucky paper functionalized with [Cp*Rh(bpy)Cl] + by diazonium electrografting. The local oxygen removal was first evaluated, before to be applied to deoxygenation for NAD + and NADP + reduction. A porous silica gel layer encapsulating D-sorbitol dehydrogenase was finally deposited on the top of the modified bucky paper and the resulting bioelectrode was found sensitive to the presence of D-fructose.

Organic-inorganic hybrid membranes, made of a high density of redox active moieties covalently bonded to the internal surfaces of vertically aligned mesoporous silica thin films, are relevant for applications in transparent energy storage devices. This is demonstrated here on the basis of functionalized transparent mesoporous silica thin films prepared on the indium-tin oxide electrode from the combination of an electrochemically induced self-assembly method (to generate azide-functionalized silica) and a copper-catalyzed azide-alkyne click reaction (to derivatize the material with electroactive groups). The very small thickness (105 nm) and the uniformly distributed vertical mesochannels with ultranarrow diameter (2 nm) make the hybrid film a promising substrate that not only achieves a transparency of 82% but also provides large surface area to accommodate a high density of redox active species such as ferrocene. In such rigid and insulating porous membranes, the charge transfer reactions take place through a pure electron-hopping mechanism between adjacent redox sites, which are favored by the ordered and oriented mesostructure containing large amounts of uniformly distributed ferrocene functions in the mesochannels. Their performance results from both high charge transfer rates (electron hopping) and easy mass transport (fast diffusion of counter ions). The most effective system is the ferrocene-functionalized silica film prepared from 40% organosilane, which is able to deliver a capacity of 105 C cm-3 (1.10 mC cm-2) at a current density of 0.4 A cm-3 (with up to 48% capacity retention achieved at a charging time as short as 2.8 s). Such an electrode can be associated to an electrodeposited graphene anode in a solid-state battery-capacitor hybrid device, which can deliver 0.74 mC cm-2 at a potential scan rate of 20 mV s-1. The azide-functionalized mesoporous silica film is actually a versatile platform that can be functionalized with different redox molecules, as shown here for cobaltocenium moieties, which may broaden its application field.

International audience; Unmodified and ferrocene-functionalised mesoporous silica layers exhibiting vertical nanochannels have been grown by electrochemically assisted self-assembly onto indium-tin oxide (ITO) and the resulting film electrodes have been applied to the electrochemical detection of cysteine. When using the unmodified film electrode and ferrocenedimethanol (Fc(MeOH)2) as mediator in solution, both cysteine and glutathione can be oxidised by Fc(MeOH)2 + generated at the electrode surface, following an EC' mechanism, but the electron transfer rates were three times faster with cysteine than with glutathione. This can be exploited for the reagent-free selective detection of cysteine over glutathione by using a ferrocene-functionalised mesoporous silica film on ITO electrode, based on a combination of charge transfer kinetic and mass transport limitations through the oriented nanochannels. This has been demonstrated here by cyclic voltammetry and amperometry in a flow injection analysis mode.

It appeared that either the carbon paste or the screen-printed carbon electrodes that were modified with gold nanoparticles (AuNPs) gave rise to the largest current responses after a rapid screening of various nanomaterials as modifiers of carbon composite electrodes in view of designing an electrochemical sensor for Moxifloxacin Hydrochloride (Moxi). The screen-printed electrode (SPE) support was preferred over the carbon paste one for its ability to be used as disposable single-use sensor enabling the circumvention of the problems of surface fouling encountered in the determination of Moxi. The response of AuNPs modified SPE to Moxi was investigated by cyclic voltammetry (CV) (including the effect of the potential scan rate and the pH of the medium), chronoamperometry, and differential pulse voltammetry (DPV) after morphological and physico-chemical characterization. DPV was finally applied to Moxi detection in phosphate buffer at pH 7, giving rise to an accessible concentration window ranging between 8 &micro, M and 0.48 mM, and the detection and quantification limits were established to be 11.6 &micro, M and 38.6 &micro, M, correspondingly. In order to estimate the applicability of Moxi identification scheme in actual trials, it was practiced in a human baby urine sample with excellent recoveries between 99.8 % and 101.6 % and RSDs of 1.1&ndash, 3.4%, without noticeable interference.

International audience; Mesoporous silica thin films encapsulating a molecular iron-triazole complex, Fe(Htrz)3 (Htrz = 1,2,4,-1H-triazole), have been generated by electrochemically assisted self-assembly (EASA) on indium-tin oxide (ITO) electrode. The obtained modified electrodes are characterized by well-defined voltammetric signals corresponding to the Fe II/III centers of the Fe(Htrz)3 species immobilized into the films, indicating fast electron transfer processes and stable operational stability. This is due to the presence of a high density of redox probes in the material (1.610-4 mol g-1 Fe(Htrz)3 in the mesoporous silica film) enabling efficient charge transport by electron hopping. The mesoporous films are uniformly deposited over the whole electrode surface and they are characterized by a thickness of 110 nm and a wormlike mesostructure directed by the template role played by Fe(Htrz)3 species in the EASA process. These species are durably immobilized in the material (they are not removed by solvent extraction). The composite mesoporous material (denoted Fe(Htrz)3@SiO2) is then used for the electrocatalytic detection of hydrogen peroxide, which can be performed by amperometry at an applied potential of-0.4 V versus Ag/AgCl and by flow injection analysis. The organic-inorganic hybrid film electrode displays good sensitivity for H2O2 sensing over a dynamic range from 5 to 300 μM, with a detection limit estimated at 2 μM.

International audience; The effect of vertically aligned silica nanochannels on the electrochemical response of various cationic redox probes has been investigated. To this end, an oriented mesoporous silica thin film has been generated by electro-assisted self-assembly onto a fluoride-doped tin oxide (FTO) electrode, which was then used to characterize the voltammetric behaviour of redox cations of different nature, size and charge. Methylene Blue (MB +), paraquat (PQ 2+), diquat (DQ 2+), ruthenium trisbipyridine (Ru(bpy)3 2+) and ruthenium hexamine (Ru(NH3)6 3+) were selected for that purpose. Multisweep cyclic voltammetry experiments showed significant accumulation of these cations thanks to favourable electrostatic interactions with the negatively-charge silica surface, but the enhancement of the votammetric signals compared to the bare FTO electrode was strongly dependent on the probe type, according the following trend: MB + > PQ 2+ > DQ 2+ > Ru(bpy)3 2+ > Ru(NH3)6 3+. The accumulation processes were very fast owing to the vertical orientation of the mesopore channels ensuring fast diffusion from the solution to the electrode surface. Operating at various potential scan rates and different probe concentrations enabled to quantify the relative ratio between surface-confined and diffusion-controlled processes, the adsorption phenomena being clearly more prominent in diluted media and also accentuated at high potential scan rates. The mesoporous silica film electrodes exhibited higher sensitivities at lower concentrations, which can give benefits for sensor applications at trace levels.

Caffeine (Caf) is one of the most widespread compounds in food components, beverages and medicines, which drives us to find a simple, fast and convenient method for its determination. The promising Nano-Cobalt (II, III) oxide modified carbon paste (NCOMCP) sensor was fabricated and applied to the sensitive determination of Caf in both aqueous (0.01 mol L−1 H2SO4) and micellar media (0.5 mmol L−1 sodium dodecylsulfate, SDS). Surface characterization was performed utilizing scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDX). The electrochemical behavior of Caf was studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). From these experiments, the apparent diffusion coefficient (Dapp) and catalytic rate constant (kcat) were evaluated to be 4.2 × 10-5 cm2 s-1 and 1.92 × 103 mol−1 L-2 s-1, respectively. Caf can be detected in a concentration range between 5.0 and 600 μmol L−1, with a limit of detection (LOD) of 0.016 μmol L−1, as determined from the calibration plot obtained using differential pulse voltammetry (DPV). The sensor was applicable for Caf sensing in several commercial real samples with recoveries ranging from 98.9% to 101.9%. It exhibited good selectivity in the presence of common interferences.

Ordered mesoporous silica films exhibiting vertically-aligned nanopore channels can be obtained by combining sol-gel chemistry, surfactant physico-chemical properties and electrode polarization, according to an electrochemically induced self-assembly mechanism. The method is based on the application of a cathodic potential likely to organize transient hemi-micelles of cationic surfactant onto the electrode surface and to induce simultaneously a pH increase inducing the polycondensation of silica precursors around the surfactant template at the electrode/solution interface, generating thereby the vertical growth of a mesoporous film.One can also combine this approach with “click chemistry” in order to generate functionalized mesoporous silica films with well-defined properties, giving rise to nanoscale reactors bearing a high number of easily accessible organofunctional groups. The accurate control of orientation and the versatility of the functionalization process open new avenues in applied fields such as sensors, semi-permeable membranes and nanotechnologies., Des films de silice organisés à l’échelle nanométrique et présentant une structure mésoporeuse verticalement orientée peuvent être obtenus en combinant la chimie sol-gel, la physico-chimie des tensioactifs et la polarisation d’électrode, selon un mécanisme d’auto-assemblage induit par électrochimie. La méthode est basée sur une polarisation cathodique conduisant à la formation transitoire d’hémi-micelles de tensioactif cationique à la surface de l’électrode et induisant une montée de pH à l’interface électrode/solution initiant la polycondensation des précurseurs inorganiques autour du porogène, résultant en une croissance orthogonale d’un film mésostructuré.Il est également possible de combiner cette approche avec la « chimie clic » pour générer des films mésoporeux fonctionnalisés à propriétés dédiées, donnant naissance à de véritables nanoréacteurs incorporant un grand nombre de groupements fonctionnels aisément accessibles. Le contrôle de l’orientation et la souplesse de fonctionnalisation ouvrent de nouvelles voies d’application dans des domaines tels que les capteurs, les membranes à perméabilité sélective et les nanotechnologies.

While attempting to confine Fe(Htrz)3 (Htrz = 1,2,4,-1H-triazole) into a mesoporous silica matrix during its formation by electrochemically assisted self-assembly (EASA), we have discovered that such spin crossover complex is likely to act as the template (in place of the surfactant species) to form in one step a composite mesoporous material (Fe(Htrz)3@SiO2). The EASA method usually leads to the vertical growth of mesoporous silica thin films owing to the electroinduced condensation of silica precursors (i.e., tetraethoxysilane, TEOS) around tubular micelles (i.e., made of cetyltrimethylammonium bromide, CTAB) oriented orthogonally to the underlying support. In the presence of Fe(Htrz)3 in the starting sol (in addition to TEOS and CTAB), two distinct situations can be reached. At low Fe(Htrz)3 concentration (≤3 mM), the vertically aligned mesostructure is formed and Fe(Htrz)3 complexes are incorporated along with the surfactant phase, but most of them are released upon surfactant removal. At high Fe(Htrz...

We demonstrate the successful electrodeposition of Cu nanodendrite foams (CuFoams) onto a series of lithographically formed gold band array electrodes at negative overpotentials in an acidic environment. The nanodendrite foams were deposited onto two different integrated microelectrode arrays fabricated using standard lithographic techniques. Each electrode consisted of 17 gold band electrodes deposited onto a silicon wafer substrate, labeled BA5 (with a width of 5 μm and a length of 250 μm) and BA10 (with a width of 10 μm and a length of 500 μm). Prior to Cu deposition the gold electrodes were characterized by scanning electron microscopy (SEM) in order to evaluate the morphology of each design and by cyclic voltammetry (CV) in order to investigate their diffusion profiles. After Cu deposition the resulting 3D foam structures were studied using SEM, XPS, and EDX. The CuFoam/Au microelectrodes were then used for the electrocatalytic detection of glucose via oxidation at a potential of +0.45 V vs Ag/AgCl in an alkaline medium. It was found that both types of electrode arrays used showed excellent analytical performance in terms of sensitivity, reproducibility, and stability in comparison with the best performances reported in the literature. In particular, the BA5-CuFoam electrode exhibited an outstanding sensitivity of 10,630 μA mM–1 cm–2 toward glucose with a wide linear range up to 22.55 mM, while the BA10-CuFoam electrode showed a sensitivity of 4,437 μA mM–1 cm–2. The performance of the proposed electrochemical sensor is attributed to a combination of the use of the very high surface area Cu nanodendrite foam and the enhanced radial distribution profile associated with the use of the smaller band microfabricated electrodes. Additionally, both sensors also showed a strong resistance to the poisoning effects of chlorine ions and excellent stability over a period of three months.

International audience; Single walled carbon nanotubes (SWCNTs) were immobilized on glassy carbon (GC) electrode by drop casting The resulting modified electrode (represented as GC/SWCNTs) efficiently oxidizes acetaminophen (AC), dopamine (DA) and pyridoxine (PY) by decreasing the respective oxidation potentials and increasing peak currents in comparison to bare GC electrode. The extent of lowering overpotentials is in the order of AC > PY > DA, in agreement with the order of decrease in the HOMO-LUMO energy gap (E) of these analytes, as determined from Density Functional Theory (DFT) calculations. DFT calculations further reveal that due to the adsorption of the analytes on the SWCNT(10,10) there is a negative charge density transfer (higher probability of electron transfer, lower E value) to the frontier molecular orbitals of the analytes, which eases their oxidation. Since AC, DA and PY oxidize distinctly at distinct potential values, the present SWCNTs modified electrodes could be used to simultaneously determine them. Cyclic voltammetry, differential pulse voltammetry and amperometry techniques are utilized to understand the electrochemical characteristics of the analytes (AC, DA and PY) and subsequent sensing of them at the GC/SWCNTs electrode. The electrode is then applied to the determination of Ac as a case study. Sensitivity, detection limit and linear calibration range for the AC are found to be 7.9 µA µM-1 cm-2 , 1.1 µM and 2.0-100.0 µM, respectively.

International audience; We revealed a general guidance on preparation of electrochemically stable meso forms of nickel-salen based polymers suitable as new anode materials for electrochemical devices. Electrochemical performance of nickel-salen complexes, used as monomers of nickel-salen based polymers, was directly related to the salen ligand structure. We have considered it in specially designed and synthesized herein a new meso form of the nickel-salen polymer, vis., poly[meso-N,N 0-bis-(3-methylosalicylidene)-2,3butanediaminonickel(II)]. Then, electrochemical conditions for providing the environment appropriate for electropolymerization and charge transfer were optimized. In dependence upon the purpose of the use of the poly(meso-Ni-salen) films coated electrodes, it was possible to increase the amount of the charge stored in these conjugated polymer systems by proper tuning of both the chemical structure of the polymer and electrochemical conditions. Apparently, the charge transfer through nickel-salen polymers strongly depended upon steric hindrance between polymer layers, thus ensuring efficient counter ion doping. Therefore, this hindrance was carefully selected. We have defined steric requirements with respect to the type and position of moderately electrodonating substituents on imine bridges and phenolic rings of the nickel-salen polymers that must be met to achieve high conductivity and stability/durability during potential multi-cycling of the polymer films prepared.

International audience; Layer-by-Layer (LbL) deposition of multi-walled carbon nanotubes (MWCNT) was used to modify porous electrodes for vanadium redox flow batteries. Preliminary studies performed over glassy carbon electrodes (GCEs) showed that assemblies obtained with MWCNT displayed better mechanical stability than those prepared with other carbon nanoforms. The LbL process involved successive deposition of a positively-charged polymer (in our case polyethylenimine, PEI) and carbon nanotubes modified in such a way to get their surface negatively-charged, and it was found that the use of MWCNT dispersed with poly(acrylic acid) (PAA) allowed a faster and more homogenous film growth than-COOH functionalized SWCNT. The thickness of the MWCNT assembly deposited onto a GCE strongly influenced the electrochemistry of VO 2+ /VO2 + species. The thicker the film, the better the electrochemical reversibility resulted. An electron transfer rate constant k0 of 5x10-4 cm s-1 was determined for the electrode prepared with one hundred bi-layers and treated at 650 °C in inert atmosphere. After optimizing the process on GCEs, the LbL technique was applied to the modification of graphite felt electrodes (GFEs). GF electrodes modified with ten bilayers of PEI-PAA(MWCNT) were tested in a vanadium redox flow battery, showing a net decrease in the charge and discharge overpotentials with respect to the unmodified graphite felt. Lower overpotentials for charge-discharge resulted in higher energy and voltage efficiencies for the battery with modified GF electrodes. Furthermore, cyclability of the system was tested and no fading was observed in the battery performance after one hundred cycles.

International audience

International audience; Electronics, and nanoelectronics in particular, represent one of the most promising branches of technology. The search for novel and more efficient materials seems to be natural here. Thus far, silicon-based devices have been monopolizing this domain. Indeed, it is justified since it allows for significant miniaturization of electronic elements by their densification in integrated circuits. Nevertheless, silicon has some restrictions. Since this material is applied in the bulk form, the miniaturization limit seems to be already reached. Moreover, smaller silicon-based elements (mainly processors) need much more energy and generate significantly more heat than their larger counterparts. In our opinion, the future belongs to nanostructured materials where a proper structure is obtained by means of bottom-up nanotechnology. A great example of a material utilizing nanostructuring is mesoporous silica, which, due to its outstanding properties, can find numerous applications in electronic devices. This focused review is devoted to the application of porous silica-based materials in electronics. We guide the reader through the development and most crucial findings of porous silica from its first synthesis in 1992 to the present. The article describes constant struggle of researchers to find better solutions to supercapacitors, lower the k value or redox-active hybrids while maintaining robust mechanical properties. Finally, the last section refers to ultra-modern applications of silica such as molecular artificial neural networks or super-dense magnetic memory storage.

Cyclic voltammetry has been applied to characterize mass transport of a Keggin-type polyoxometalates ([SiW12O40]4-) through vertically-aligned mesoporous silica thin films in aqueous media. The results indicate a drastic influence of pH and the ionic strength which may be rationalized in terms of electrostatic interactions and confinement effects. Diffusion of such bulky anionic electroactive species is considerably restricted at pH values higher than the point of zero charge of the silica for which the walls of the nanochannels are negatively charged. On the other hand, the positive charge density generated in more acidic solutions favors the ingress of [SiW12O40]4- species through the mesochannels, enhancing considerably the electrochemical response, except at high ionic strength due to competition for the binding sites. The accumulation of POM anions into the silica films can be even promoted by functionalization of the silica surface with propylammonium groups. In summary, pH tuning induced gating of the ionic flux through the silica nanopores, which can be somewhat modulated by the ionic strength by varying the thickness of the electrical double layer generated at the silica walls surface.

Hydrogen has concerned interest universally as an environmentally nontoxic and renewable fuel. Electrocatalytic hydrogen evolution reaction (HER) is one of the utmost favorable methods for hydrogen creation on a vast scale; however, the high cost of Pt-based supplies, which demonstrate the highest activity for HER, forced investigators to look for cheaper electro-catalysts. Tungsten has been considered as an effective, active and low cost electrocatalyst for the hydrogen evolution reaction, mostly in alkaline media, and we have investigated here its behavior in acid electrolytes. HER has been studied utilizing linear polarization technique and electrochemical impedance spectroscopy (EIS). It happens on W at rather low overpotential (−0.32 V vs. NHE at 10 mA cm−2, in 0.5 M H2SO4), yet more cathodic than the widely used Pt/C catalyst, but not so far from more sophisticated systems developed recently. The effect of acid concentration on the HER rate and the electrode stability was investigated. Cathodic transfer coefficient and exchange current density were calculated for the HER from Tafel curves obtained in H2SO4 solution at concentrations ranging from 0.1 to 3.0 M. EIS experiments were performed under both open circuit and/or cathodic polarization. It was found that the hydrogen evolution rate is relatively high under low overpotential, confirming that W is a possible applicant to substitute more expensive electrocatalysts usually used for the HER under acidic conditions. The process is economic and appropriate with no need for specific treatments, as supported by additional X-ray diffraction (XRD), Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) characterization of the tungsten electrode surface.

International audience; The morphological and electrocatalytic properties of ITO and nanostructured carbon screen printed electrodes (nanoSPCE) modified with thin films of MnO2 particles, alone or as hybrid with SiO2, as obtained using electrodeposition techniques, were studied. The time and potential of MnO2 electrodeposition influenced the electrocatalytic properties of the modified electrodes towards H2O2. The highest electrocatalytic current was observed at deposition potential E=-0.8 V and deposition time of 10 s. MnO2 particles with uniform distribution were obtained onto the electrode surface when prepared under optimal conditions. The nanoSPCE-MnO2 has demonstrated larger effective surface area and faster charge transfer rates compared to ITO-MnO2. The electrodeposited silica, in addition to MnO2, improved the operational stability of the electrodes without noticeable decreasing of their performance. Modified electrodes were used for hydrogen peroxide determination.

Vertically aligned mesoporous silica films can be generated by electrochemically assisted self-assembly (EASA) but the accurate control of their thickness is essentially restricted to the 100 nm range. Here we have developed a wet etching approach using dilute ammonium fluoride to gradually decrease the thickness of ferrocene-functionalized films down to 20 nm by increasing the etching time. The effectiveness of the process was followed by monitoring the decrease in the voltammetric response of ferrocene moieties that are progressively removed from the electrode surface upon silica etching. Film thickness variations have also been confirmed by profilometry and were consistent with the electrochemical measurements. Electron microscopy analyses indicated a uniform thickness decrease but also some loss in the integrity of the mesostructure after prolonged etching. Keywords: Oriented mesoporous silica membrane, Ferrocene functionalized thin film, Wet etching, Film thickness control, Electroactive organic-inorganic hybrid

International audience; A novel method for fabrication of precisely functionalized nanomaterials was developed. Presented here multi-step functionalization procedure can be applied for vertically-aligned mesoporous silica thin films. As an example, we presented the syntheses of films, precisely functionalized by the propyl-copper-phosphonate and the propyl-silver-carbonate groups located exclusively at the pores bottom. Obtained functional materials were characterized by a few physical and chemical techniques: transmission electron microscopy, X-ray scattering, differential pulse voltammetry and infrared spectroscopy supported by the numerical simulations. On this base, we prove the efficiency of the synthesis method. We expect that presented multi-step functionalization procedure can be easily generalized and applied for fabrication of the novel porous silica-based functional materials.

SGECM potentiometric measurements are developed with a novel Ag/AgCl-gel micro-reference electrode. The electrode is prepared by electrodeposition of chitosan on Ag micro-disk electrode followed by anodic chlorination of Ag. It is approached to the sample by shear force feedback, and the potential between the electrode and the sample is recorded with a highly sensitive voltammeter. Based on this, simultaneous mapping of topography and electrochemical potential is achieved, with the sample exposed in air. Tests of model samples indicate that the electrode is reliable and stable for potentiometry, and two different metals (Al and Cu) are clearly identified from the topography and potential maps. Keywords: Micro-reference electrode, Hydrogel, Potential mapping, Topography, Scanning gel electrochemical microscopy

International audience; A generic approach has been developed for sequential heterogeneous surface modification of electrodes. The strategy, which is applicable for a wide range of functional groups, involves two main steps. In the first one, azide‐alkene bifunctionalized electrodes are obtained by electrochemical reduction of a mixture of diazonium salts generated in situ from the corresponding 4‐azidoaniline and 4‐vinylaniline. In that way, we provide reactive sites that are available for further selective functionalization in a sequential process based on ‘click reactions’, in which subsequent immobilization of the targeted molecules is achieved by the azide‐alkyne cycloaddition Huisgen reaction and alkene‐thiol coupling. Feasibility of the method has been first demonstrated for the coimmobilization of two distinct redox moieties (cobaltocenium and ferrocene) as evidenced by cyclic voltammetry and X‐ray photoelectron spectroscopy measurements. The versatility of the sequential method has then been exploited for the coimmobilization of a molecular electrocatalyst [Cp*Rh(bpy) Cl]+ and a biological catalyst, a NAD‐dependent dehydrogenase, that were proved to act in cascade in the electroenzymatic reduction of D‐fructose to D‐sorbitol. Such simple combination of diazonium chemistry and robust chemical reactions (‘click chemistry’) is promising for the environmentally friendly heterogeneous modification of electrodes with multiple chemical and biological catalysts.

International audience; Notwithstanding their insulating properties, silica-based materials have become ubiquitous in electrochemistry. Thanks to the versatility of the sol–gel process to manufacture materials with controlled composition, structure and morphology, their use as electrode modifier has offered new avenues in electrochemical sensing and biosensing. This review highlights some of the most recent developments in the field, focusing especially on devices based on engineered nanoparticles and ordered mesoporous silica thin films, and discussing their interest in designing sensors and biosensors for improved electrochemical detection.

International audience; Scanning electrochemical probe techniques have been widely applied for analyzing the local electrochemical activity of surfaces and interfaces. In this work, we develop a new concept of carrying out local electrochemical measurements by localizing both the electrode and the electrolyte. This is achieved through a gel probe, which is prepared by electrodepositing chitosan-gelatin gel on a microdisk electrode. It is positioned in contact with the sample surface by shear force feedback. The preliminary results indicate that the topography of the sample can be mapped by tapping the probe and recording the coordinates at a given normalized shear force signal, while the local electrochemical activity can be retrieved from local measurements with the probe touching the sample surface. The technique is denoted as scanning gel electrochemical microscopy. As compared with existing techniques, it has a major advantage of operating in air with the electrolyte immobilized in gel. This would prevent the spreading and leakage of solution on the sample surface and may lead to field applications.

An electrochemical method was developed for rapid and sensitive detection of the herbicide paraquat in aqueous samples using mesoporous silica thin film modified glassy carbon electrodes (GCE). Vertically aligned mesoporous silica thin films were deposited onto GCE by electrochemically assisted self-assembly (EASA). Cyclic voltammetry revealed effective response to the cationic analyte (while rejecting anions) thanks to the charge selectivity exhibited by the negatively charged mesoporous channels. Square wave voltametry (SWV) was then used to detect paraquat via its one electron reduction process. Influence of various experimental parameters (i.e., pH, electrolyte concentration, and nature of electrolyte anions) on sensitivity was investigated and discussed with respect to the mesopore characteristics and accumulation efficiency, pointing out the key role of charge distribution in such confined spaces on these processes. Calibration plots for paraquat concentration ranging from 10 nM to 10 μM were constructed at mesoporous silica modified GCE which were linear with increasing paraquat concentration, showing dramatically enhanced sensitivity (almost 30 times) as compared to nonmodified electrodes. Finally, real samples from Meuse River (France) spiked with paraquat, without any pretreatment (except filtration), were analyzed by SWV, revealing the possible detection of paraquat at very low concentration (10-50 nM). Limit of detection (LOD) calculated from real sample analysis was found to be 12 nM, which is well below the permissible limits of paraquat in drinking water (40-400 nM) in various countries.

International audience

SDS is commonly employed as BGE additive in CZE analysis of non-enveloped icosahedral viruses. But the way by which SDS interacts with the surface of such viruses remains to date poorly known, making complicate to understand their behavior during a run. In this article, two related bacteriophages, MS2 and Qβ, are used as model to investigate the migration mechanism of non-enveloped icosahedral viruses in SDS-based CZE. Both phages are characterized by similar size and surface charge but significantly different surface hydrophobicity (Qβ > MS2, where ‘>’ means ‘more hydrophobic than’). By comparing their electrophoretic mobility in the presence or not of SDS on both sides of the CMC, we show that surface hydrophobicity of phages is a key factor influencing their mobility and that SDS-virus association is driven by hydrophobic interactions at the surface of virions. The CZE analyses of heated MS2 particles, which over-express hydrophobic domains at their surface, confirm this finding. The correlations between the present results and others from the literature suggest that the proposed mechanism might not be exclusive to the bacteriophages examined here. This article is protected by copyright. All rights reserved

International audience; The interface formed between two immiscible electrolyte solutions (ITIES) constitutes a fantastic playground for the investigation of charge (under the form of either ion or electron) transfer processes. We have reviewed here the routes for the modification of such soft interfaces by an accurate electrochemical control. The three main strategies developed in the past four decades include (i) the electrochemically controlled assembly of molecules and nano-objects; (ii) the in-situ electrogeneration of nanomaterials and (iii) the use of ex-situ synthesised membranes. Applications of functionalized ITIES in the fields of redox catalysis and electroanalysis of modified soft interfaces are also discussed.

International audience; Two commercial formulations of apatitic calcium phosphate cements (CPCs), Graftys Ò Quickset (QS) and Graftys Ò HBS (HBS), similar in composition but with different initial setting time (7 and 15 min, respectively), were combined to ovine whole blood. Surprisingly, although a very cohesive paste was obtained after a few minutes, the setting time of the HBS/blood composite dramatically delayed when compared to its QS analogue and the two blood-free references. Using solid state NMR, scanning electron microscopy and high frequency impedance measurements, it was shown that, in the particular case of the HBS/blood composite, formation of a reticulated and porous organic network occurred in the intergranular space, prior to the precipitation of apatite crystals driven by the cement setting process. The resulting microstructure conferred unique biological properties to this material upon implantation in bone defects, since its degradation rate after 4 and 12 weeks was more than twice that for the three other CPCs, with a significant replacement by newly formed bone. Statement of Significance A major challenge in the design of bone graft substitutes is the development of injectable, cohesive, resorbable and self-setting calcium phosphate cement (CPC) that enables rapid cell invasion with initial mechanical properties as close as bone ones. Thus, we describe specific conditions in CPC-blood composites where the formation of a 3D clot-like network can interact with the precipitated apatite crystals formed during the cement setting process. The resulting microstructure appears more ductile at short-term and more sensitive to biological degradation which finally promotes new bone formation. This important and original paper reports the design and in-depth chemical and physical characterization of this groundbreaking technology.

International audience; Covalent bonding of (2,2′-bipyridyl) (pentamethylcyclopentadienyl)-rhodium complex at the surface of a carbon-based porous electrode was achieved by combining diazonium electrografting, Huisgen cycloaddition, and metal complexation. The immobilized catalyst was applied to electrochemical regeneration of the reduced form of nicotinamide adenine dinucleotide (NADH). The different steps of surface functionalization were characterized by X-ray photoelectron spectroscopy and electrochemistry. The Faradaic efficiency of NADH regeneration was 87%. The chemical bonding provided good stability in solution under convection over 14 days, which is much better than the simple adsorption of the Rh complex on the electrode surface. Finally, the system was tested in the presence of NAD-dependent dehydrogenases that were immobilized in a sol–gel film on the top of the functionalized porous carbon electrode. A total turnover of 3790 and turnover frequency of 164 h–1 was observed. Two enzymatic reactions were considered: d-fructose reduction to d-sorbitol catalyzed by d-sorbitol dehydrogenase and hydroxyacetone reduction to 1,2-propanediol with galactitol dehydrogenase. The electrocatalytic regeneration of 1 mM NADH by the immobilized rhodium species was kept after 90 h electrolysis in the conditions of electroenzymatic synthesis.

International audience; The growth of vertically aligned and ordered polyaniline nanofilaments is controlled by potentiostatic polymerization through hexagonally packed and oriented mesoporous silica films. In such small pore template (2 nm in diameter), quasi-single PANI chains are likely to be produced. From chronoamperometric experiments and using films of various thicknesses (100–200 nm) it is possible to evidence the electropolymerization transients, wherein each stage of polymerization (induction period, growth, and overgrowth of polyaniline on mesoporous silica films) is clearly identified. The advantageous effect of mesostructured silica thin films as hard templates for the generation of isolated polyaniline nanofilaments is demonstrated from enhancement of the reversibility between the conductive and the nonconductive states of polyaniline and the higher electroactive surface areas displayed for all mesoporous silica/PANI composites. The possibility to control and tailor the growth of conducting polymer nanofilaments offers numerous opportunities for applications in various fields including energy, sensors and biosensors, photovoltaics, nanophotonics, or nanoelectronics.

International audience; Diffusion of anionic species through ordered mesoporous silica films is considerably restricted due to electrostatic repulsion by the negatively charged silica surface and this effect is even worse in low ionic strength media (owing to Donnan exclusion effects). This is at the origin of the poor electrochemical response of anionic redox probes at electrodes modified with such mesoporous thin films. Here, by using indium–tin oxide (ITO) electrodes covered with vertically aligned mesoporous silica films generated by electrochemically assisted self‐assembly (EASA), we show that charge transfer for anionic redox probes [i.e. Fe(CN)63−/4−] can be dramatically amplified by using a neutral [ferrocene dimethanol, Fc(MeOH)2] or cationic [(Ru(NH3)63+] redox mediator. This has been observed by cyclic voltammetry, showing current enhancement in the presence of the mediator, which acts as a mobile electron shuttle between the charge‐excluded Fe(CN)63−/4− species from the mesoporous silica film and the underlying ITO surface owing to the ability of the mediator species to diffuse freely through the oriented mesopore channels. This behavior was significantly affected by the relative contents of Fe(CN)63−/4− probe to Fc(MeOH)2 mediator, the potential scan rate, and the supporting electrolyte concentration. The most effective improvements were reached at low Fe(CN)63−/4− concentration, high mediator content, low potential scan rate, and low ionic strength.

International audience; Macroporous carbon nanotube-carbon composite electrodes (CNT-C) have been fabricated and characterized. CNT/polystyrene beads assembly was first prepared by electrophoretic co-deposition. Polypyrrole (PPy) was then polymerized electrochemically in the pore volume generated by the CNT assembly. After removal of the polystyrene template and pyrolysis of the conductive polymer between 650 and 950 °C, a macroporous composite material made of CNT and an amorphous carbon binder (quoted as C) was obtained. Increasing the amount of PPy allowed to improve the mechanical properties of the composite, as measured by the Young's modulus extending from 7 (CNT alone) to 663 GPa (CNT-C composite). CNT-C composite was characterized by Raman and X-ray photoelectron spectroscopies. Its surface area was dramatically enhanced, as evidenced by the increase in capacitance from 6 mF cm−2 to 199 mF cm−2 in the presence of the largest content of amorphous carbon. The influence of the amount of deposited carbon was discussed regarding the VO2+/VO2+ electrochemistry (i.e., the most critical redox couple in vanadium redox flow batteries). A 50 μm thick macroporous CNT-C composite gave rise to 5 times enhancement of the electrochemical response compared to a nonmacroporous CNT-layer).

International audience; A smectite-based inorganic-organic hybrid material was prepared by a one-step intercalation of cetyltrimethylammonium ions and thiourea within the interlayer space of montmorillonite (MT). The surface and textural properties of the resulting material were examined using several techniques (X-ray diffraction, elementary analysis and N-2 adsorption-desorption experiments (BET method)) that demonstrated the presence of both modifiers in the clay mineral structure. The presence of thiourea molecules in the modified MT greatly improved its ability towards the fixation of Pb2+ and Cd-2+ ions when the organoclay material was used for sensing purposes as a glassy carbon electrode modifier. The electro-analytical procedure was based on the chemical accumulation of both analytes under open-circuit conditions, followed by the detection of the pre-concentrated species using square wave voltammetry. Upon optimization of different parameters likely to influence the electrode response, linear calibration graphs were obtained in the concentration ranges from 0.1 to 1 mu M and 0.01 to 0.1 mu M for Cd2+ and Pb2+, respectively, leading to low limits of detection (4.2 x 10(-1) M for Pb2+ and 1.2 x 10(-9) M for Cd2+).

International audience; Thiol–ene click chemistry can be exploited for the immobilization of cysteine-tagged dehydrogenases in an active form onto carbon electrodes (glassy carbon and carbon felt). The electrode surfaces have been first modified with vinylphenyl groups by electrochemical reduction of the corresponding diazonium salts generated in situ from 4-vinylaniline. The grafting process has been optimized in order to not hinder the electrochemical regeneration of NAD+/NADH cofactor and soluble mediators such as ferrocenedimethanol and [Cp*Rh(bpy)Cl]+. Having demonstrated the feasibility of thiol–ene click chemistry for attaching ferrocene moieties onto those carbon surfaces, the same approach was then applied to the immobilization of d-sorbitol dehydrogenases with cysteine tag. These proteins can be effectively immobilized (as pointed out by XPS), and the cysteine tag (either 1 or 2 cysteine moieties at the N terminus of the polypeptide chain) was proven to maintain the enzymatic activity of the dehydrogenase upon grafting. The bioelectrode was applied to electroenzymatic enantioselective reduction of d-fructose to d-sorbitol, as a case study.

International audience; Vertically oriented mesoporous silica has proven to be of interest for applications in a variety of fields (e.g., electroanalysis, energy, and nanotechnology). Although glassy carbon is widely used as an electrode material, the adherence of silica deposits is rather poor, causing mechanical instability. A solution to improve the adhesion of mesoporous silica films onto glassy carbon electrodes without compromising the vertical orientation and the order of the mesopores will greatly contribute to the use of this kind of modified carbon electrode. We propose here the electrografting of 3-amino-propyltriethoxysilane on glassy carbon as a molecular glue to improve the mechanical stability of the silica film on the electrode surface without disturbing the vertical orientation and the order of the mesoporous silica obtained by electrochemically assisted self-assembly. These findings are supported by a series of surface chemistry techniques such as X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, and cyclic voltammetry. Finally, methylviologen was used as a model redox probe to investigate the cathodic potential region of both glassy carbon and indium tin oxide electrodes modified with mesoporous silica in order to demonstrate further the interest in the approach developed here.

International audience; The proof-of-concept for enzymatic electrosynthesis with simultaneous energy production has been demonstrated by using the regioselective conversion of D-sorbitol to D-fructose by D-sorbitol dehydrogenase as a model reaction. The bioreactor was composed of two electrodes, a carbon felt bioanode modified by multi-walled carbon nanotubes (MWCNT) containing D-sorbitol dehydrogenase immobilized in a silica matrix and an oxygen gas-flow cathode. The electrochemical regeneration of the NAD+ cofactor at the bioanode was achieved by using a poly(methylene green) mediator electrodeposited on the carbon felt/MWCNT electrode. The conversion rate was 1.18 mg day−1 cm−3 and an energy power output up to 14.6 μW cm−3 at 0.1 V was reached.

International audience; no abstract

International audience; Getting oriented mesoporous thin films with functionalized pores accessible from the substrate surface remains one key challenge in materials science, and jumping the step forward to multifunctional layers with perpendicular nanochannels has still to be achieved. Here, a general method is introduced combining the electrochemically assisted deposition of ordered and oriented azide- and thiol-functionalized mesoporous silica with a selective sequential azide-alkyne and thiol-ene "click chemistry" approach to prepare nanostructured and vertically aligned hybrid films bearing tunable amounts of organofunctional groups. High-resolution electron microscopy is used to evidence the high level of mesostructural order and pore orientation, while the effectiveness of the functionalization processes is proven from spectroscopic and electrochemical measurements. Voltammetric data also demonstrate that both the accessibility through the films and the properties of the incorporated functions are maintained upon derivatization. Feasibility of this simple and generic strategy is illustrated here for two couples of model derivatives (ethynylcobaltocenium/vinylferrocene and propargyl alcohol/allyl cyanide) but such stepwise postfunctionalization can be extensively used for the incorporation of a variety of organic functions in mesoporous silica films.

International audience; In this work, the array of miniaturized interfaces between two immiscible electrolyte solutions was modified with a mesoporous silica material. The electrochemical behavior of such silica deposits was evaluated with six analytes: 3 tetraalkylammonium cations of different sizes, the anionic 4-octylbenzenesulfonate and two poly(aminoamide) dendrimers (generation 0 and 1). Presence of silica deposits affects the ion transfer across the liquid/liquid interface for all six probes with the effect greater for species possessing higher hydrodynamic radius. Analytical parameters (sensitivity and detection limit) were extracted from the calibration curves plotted in the presence and in the absence of silica deposits. Results indicate that silica constitutes an obstacle for interfacial transfer reaction and becomes limiting factor for interfacial mass transfer. Three main conclusions can be drawn from the experimental observations: (i) for tetraalkylammonium species, the larger species (tetrabutylammonium) is more affected by the presence of silica deposits than the smaller species (tetramethylammonium); (ii) due to the negative charge of silica walls, anions are more affected than cations of the same size; (iii) multiply charged cationic dendrimers are less affected by the presence of silica deposits than smaller single charge cations. Apparent diffusion coefficients for all species were also extracted from calibration curves plotted after modification.

International audience; The influence of the supporting electrolyte on the electrochemical response of ordered and oriented, ferrocene-functionalized, mesoporous silica films has been investigated. The ferrocene-functionalized films were prepared by electrochemically-assisted self-assembly, leading to azide-functionalized silica materials in a first step, which were then allowed to react with ethynylferrocene according to a Huisgen azide-alkyne cycloaddition to get the final films bearing various amounts of ferrocene groups covalently attached to the mesopore channels. In such organic-inorganic hybrid redox polymer, the charge transfer mechanism involves electron hopping between adjacent redox sites and transport of electrolyte ions through the film to maintain charge balance (i.e., ingress of anions to compensate the positive charges generated by the oxidation of ferrocene moieties). The electrochemical behavior of the ferrocene-functionalized films is thus likely to be affected by the density of redox sites in the material as well as the supporting electrolyte nature and concentration. This has been analyzed here, showing that electron transfer processes are favored in mesopore channels containing great amounts of ferrocene groups, in an electrolyte-rich medium, and for counter-anions of small size and big charge. Electron transfer kinetics are primarily governed by the density of redox sites in the material while the intensity of voltammetric signals is mainly controlled by the transport of counter-anions in the confined space of mesopore channels.