Faradic Yield Research Articles

Simultaneous exfoliation/fluorination for the preparation of fluorinated exfoliated graphite with high power densities in primary lithium batteries

Fluorinated carbons combining accordion-like morphology, high content of (C2F)n phase (43%), and residual non-fluorinated carbons were synthetized by two routes, i.e. fluorination of expanded graphite and simultaneous exfoliation/fluorination of expandable graphite. The latter allows the synthesis in a one-step process to be achieved. Accordion-like morphology allows the accommodation of LiF without detrimental accumulation onto the fluorocarbon sheet edges during the discharge in primary lithium battery. The faradic yield is then close to 100 % up to a discharge rate of 6C. Residual sp2 carbons (sub-fluorination) ensure the electron flux during the electrochemical process and enhance the power density (9828 W.Kg-1). High content of (C2F)n phase results in a flat galvanostatic discharge curve. The combination of those features results in a good compromise between energy and power densities, making fluorinated exfoliated graphite one of the best cathodes for primary lithium batteries.

Electrochemical and catalytic conversion of CO2 into formic acid on Cu-InO2 nano alloy decorated on reduced graphene oxide (Cu-InO2@rGO)

The catalytic and electrochemical hydrogenation of CO2 offers the option of a carbon-neutral cycle for sustainable energy and synthesis of value-added chemicals. The synthesized noble metal-free Cu-InO2@rGO nanocomposite has been characterized by various techniques such as scanning electron microscopy (SEM) confirming the spherical shape of Cu-InO2 nanoalloy embedded on rGO, the average size calculated by high resolution-transmission electron microscopy (HR-TEM) shows Cu-InO2 (∼ 4 nm) alloy is on rGO surface (∼100 nm). The XRD pattern confirms the Face centered cubic (FCC) crystal structure of Cu-InO2@rGO, and Furrier transform- Infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses of Cu-In-O exist in the nanomaterials. The linear sweep voltammetry (LSV) demonstrates an ultra-low potential of −0.9 V vs. SCE. The bulk electrolysis on Cu-InO2@rGO electrocatalyst demonstrated at a potential of −1.1 V vs. SCE to reach HCOOH with a Faradic yield of 76.10%. Electrochemical CO2 reduction on Cu-InO2@rGO is responsible for the variation of adsorption of CO2 intermediates due to controlled selectivity and inhibiting the formation of H2 and CO. In catalytic hydrogenation used as the same catalyst was found, an excellent yield towards HCOOH is 5.5 mmol. Current studies have highlighted the enhancement in activity along with selectivity for product formation could be due to having a capable active interface from electrocatalysts for low cost and proficient production of fuels.

Electrochemical Deposition in Vertical Tubes : An Hydrodynamic and Mass Transfer Study

The present work is part of the research project NXCHROME led by IRT M2P. It concerns the chemical engineering of metallic hard chromium coatings on internal surface of large tubular parts. These parts are intended to be used in several sectors of activity (aeronautics, armament, energy...). Thus, taking into account severe specifications related to these applications, the parts will be very strongly solicited thermomechanically during their use, which requested high performances to increase substrate's life. In the current process, tubes are treated vertically, by electrodeposition from a hexavalent chromium salt based (chromic acid) electrolyte. These electrolytes have the advantage of being efficient, easy to use, with well known functions. However, they have a low faradic yield (<20%), leading to an important production of bubbles (cathodic and anodic).These bubbles create the fluid motion, and eventually govern hydrodynamic, liquid flow and mass transfer of the species in the tube.It is important to note that the use of CrVI salts has been prohibited since 2017 (except for authorizations for applications without alternatives) by the European regulation REACh (Registration, Evaluation, Authorization and restriction of Chemicals). Indeed, hexavalent chromium is classified in Appendix XIV among SVHC (substances of very high concern), due to its high toxicity (CMR compound : Carcinogenic, Mutagenic and Reprotoxic) and the high danger it represents for coworkers using this compound. The objective of NXCHROME is to find a alternative process with a "REACh compatible" electrolyte based on an innovative trivalent chromium. The modus operandi and the electrochemical mechanisms involved are completely different and less well known, compared to the former electrolyte. Nevertheless, it keeps this low faradic yield and the liquid agitation mode in tubular parts will remains identical.Nevertheless, this change is a good opportunity for a deep investigation in the "bubble induced hydrodynamic" which occurs during plating time, and to collect all reliable information on fluids behavior. Then, two main research axis have been considered. The first one is done via the numerical simulation of the secondary current distribution, i.e. taking into account the electrical phenomena in the electrolyte (ohmic drop), the geometry of the system and the kinetics of the electrochemical reactions. This part is in collaboration with HIVELIX company. The second one trhought the design and elaboration of a large size experimental set-up in stainless steel and PMMA (φ = 40mm, L = 3000mm) Figure 1. This ste-up includes electrochemically active cathode parts (production of bubbles by hydrolysis), and transparent parts (windows of observations of the bubbles, according to the height of the tube). As it is the bubble production which puts in movement the fluid with their vertical displacement towards the surface, informations on their size and behavior are of primary importance. Their speed is determined by their size (depending on the distance covered and the coalescence) and the liquid physical properties.To mimic the chromium electrolyte, a transparent saline solution has been chosen and prepared by adjusting its parameters to be identical to the industrial electrolyte (viscosity, conductivity...), while allowing bubble production on the central electrode surface.Data collection and order of magnitude are done by various means, namely flow rate measurements, gas retention within the liquid and high frequency camera shots (bubble size, bubble velocity, coalescence...). Figure 1

ElectroLeaching-ElectroChemical Deposition (EL-ECD) of gold and palladium in a deep eutectic solvent (DES)

Precious metals (PM) refining from E-waste recycling are based on hazardous hydrometallurgical processes, including cyanide leaching for gold or aqua regia leaching for palladium, which generates an important wastewater production. In this paper, we present an electrochemical process, based on low viscous deep eutectic solvents ChCl:EG 1:2 and ChCl:EG 1:3. Au and Pd electrochemical leaching and deposition parameters, but also gold and palladium speciation were studied. A one-step ElectroLeaching-Electrochemical Deposition Process (EL-ECD) in a single cell is proposed with high faradic yield of metal recovery. This process avoids electrolyte degradation and is advantageous to limit solvent losses and workers exposition.

Halide based ionic liquid mixture for a sustainable electrochemical recovery of precious metals

Precious metal refining from ore or electronic devices includes hydrometallurgical processes with major concern about toxicity or wastewater production. As an alternative, one-step electroleaching-electrochemical deposition process (EL-ECD) using ionic liquid mixtures was evaluated for palladium and gold recovery. A halide based ionic liquid combined with a diluting ionic liquid was chosen among ten electrolytes after cyclic voltammetry and potentiostatic experiments. These low viscous electrolytes allow complexing Au and Pd, leading to metal leaching at low anodic potential. Moreover, the complexes formed could be simultaneously deposited at the cathode. Metal behavior is similar for all halide anions tested (chloride, bromide and iodide). Results show that chloride based mixtures are the more suitable electrolyte providing the highest leaching faradic yield. This process appears more sustainable than conventional processes (chlorination, cyanide leaching) thanks to the electrolyte stability limiting solvent losses but also workers exposition.

Relation between Faradic Yields, Hydrogen Evolution and Pulsed Currents: Morphological and Fe Content Control in Zn and ZnFe Coatings

Long-term protection of metallic parts from atmospheric exposure is an important challenge and one of the most frequent way to ensure their corrosion resistance is the application of sacrificial zinc alloys coatings [1]. Among the various zinc electroplating baths, the alkaline zincate solutions has gained a wide range of applications thanks to its simple bath composition, good dispersion and efficient coverage ability. Nevertheless, its efficiency is very low in absence of additives, which affects the performances of the coatings by modifying the crystal growth and therefore the structural and mechanical properties. This is a result from the competition between dihydrogen production and the reduction of the metallic species present in the bath.The present study deals with the optimization of ZnFe sacrificial coating on steel and aluminum substrate in the frame of the ATLAS project -Alternative TechnoLogies for improved Anticorrosion Solutions- managed by the IRT M2P. After the analysis of the electrochemical behavior of the ZnFe electrolyte patented by the Coventya company and the UTINAM institute, pulsed currents will be implemented to extend the versatility of the coatings. Indeed, pulsed currents are known to act on various parameters such as improving the faradic yield or modifying morphologies and structures [2].The determination of a first panel of pulsed sequences (average current densities, cathodic peak current, cathodic pulse time and off-time) have been based on transient curves analysis from a zincate bath. Three sequences have been selected as they resulted in very different patterns in terms of electrochemical behavior and coatings characteristics. These sequences have been replicated and compared to DC current in several electrolytes, from the zincate bath to the commercial formula. For each set of parameters, the faradic yield has been measured and compared to the hydrogen generated during the electrolysis distributed between the absorbed one (measured by hot extraction) and the dihydrogen released into the reactor atmosphere (measured by mass spectrometry with a dedicated set- up). It is interesting to note that the obtained values strongly depend on pulsed sequences as well as electrolytes composition. Coatings were systematically produced and characterized. Morphology was observed using SEM and microstructure determined from XRD diffractograms: preferential orientation and crystal lattice and crystalline phases. The latest has required a specific methodological development.Finally, the identification of nucleation parameters by model simulation has been undertaken to describe the mechanisms involved in the first steps of zinc electrodeposition [3].[1] B. Chatterjee, « Electrodeposition of Zinc Alloys », p. 31.[2] X. Zhang, K. Tsay, J. Fahlman, and W. Qu, « Journal of Energy Storage, 26 p. 100966 (2019)[3] A. Milche, Electrochimica Acta, 48 p.2903-2913 (2003)

Hydrogen Limitation By Background Salts in the Case of Trivalent Chromium Electrolytes

The toxicity of some chemical compounds for humans and the environment encouraged health authorities to adopt new legislations. This is the case for hexavalent chromium salts, CMR known, which are targeted by the REACH European regulation. These salts are used in various surface treatments processes and their use is subjected to authorization. This situation has severely impacted the 'hard' chromium plating industry. Several projects all over the world deal with alternative solution and most of them are based on non toxic trivalent chromium salts, but more difficult to implement. The present work is undertaken within CRONOS 2024 project supported by a consortium of 20 companies and led by the IRT M2P (Institute for Technological Research Metallurgy Materials Processes in Metz). Trivalent chromium ions form very stable hexa-aqueous complexes in solution, difficult to reduce. It is therefore necessary to introduce complexing agents in order to facilitate their reduction [1]–[3]. These complexing agents, mostly organic, add a difficulty in the realization of trivalent chromium electrolytes since various phenomena must be considered. In addition, the chromium based electrolytes have a low faradic yield which induces permanent competition between its own reduction and the one of protons to dihydrogen. Excessive consumption of protons near the cathode leads to a pH rise which can cause precipitation and incorporation of chromium hydroxides.In order to improve the performance of trivalent chromium electrolytes, it is possible to adjust different parameters such as the nature and concentration of the complexing agents, the pH, the temperature, the addition of additives, etc. In this study, we focused mainly on the nature and concentration of the support salt. Previous works demonstrated that over a given concentration of Na2SO4 or K2SO4 support salts, a diffusion plateau appears, which can be attributed to the reduction of protons to dihydrogen [4]. Irrespective of the substrate nature, the composition and concentration of the support salts have an impact. It has been shown that a modulation of this plateau towards the most negative potential values would be able to help in decreasing the part of current attributed to the generation of dihydrogen. Moreover, as demonstrated by Phuong et al. [5], a comparison is possible with faradaic yields. Finally, the influence of organic and inorganic complexing agents has also been studied.[1] S. Imer et T. Varnali, Applied Organometallic Chemistry, 14(10) p. 660-669, (2000)[2] Z. Zeng, Y. Sun, et J. Zhang, Electrochemistry Communications, 11(2), p. 331-334 (2009)[3] Y. Song et D.-T. Chin, Electrochimica Acta 48(4) p. 349-356 (2002)[4] Y. Mukouyama, M. Kikuchi, et H. Okamoto Journal of Electroanalytical Chemistry 617(2) p. 179-184 (2008)[5] S. De, J. White, T. Brusuelas, C. Patton, A. Koh, et Q. Huang Electrochimica Acta 338 p. 135852 (2020)

Electrocarboxylation of chloroacetonitrile mediated by a Ni(I) terpyridine complex: Voltammetric and spectroscopic studies

Cyclic voltammetry and spectroelectrochemistry (e.p.r.) were used to investigate the mechanisms implied in the electrocarboxylation of chloroacetonitrile (Cl-CH2-CN, noted RCl) mediated by [Ni(II)(terpy)2]2+. The oxidative addition of chloroacetonitrile on the electrogenerated [Ni(I)(terpy)]+ yields an alkyl-nickel R-Ni(III) complex which is reduced into an alkyl-nickel(II). E.p.r study shows that the homolytic nickel-carbon bond cleavage seems to be the more probable pathway to form the organic radical R-which is reduced to R−. Under carbon dioxide atmosphere, cyclic voltammetry studies show that CO2 was added on the alkyl-Ni(III) complex giving probably a CO2 adduct which is reduced to RCO2-Ni(II) complex allowing to release the carboxylate RCO2− and the active [Ni(I)(terpy)]+ complex. Controlled potential electrolyses showed that good carboxylated and faradic yields were obtained.

Hydrogen Limitation By Background Salts in the Case of Trivalent Chromium Electrolytes

The toxicity of some chemical compounds for humans and the environment encouraged health authorities to adopt new legislations. This is the case for hexavalent chromium salts, CMR known, which are targeted by the REACH European regulation. These salts are used in various surface treatments processes and their use is subjected to authorization. This situation has severely impacted the 'hard' chromium plating industry. Several projects all over the world deal with alternative solution and most of them are based on non toxic trivalent chromium salts, but more difficult to implement. The present work is undertaken within CRONOS 2024 project supported by a consortium of 20 companies and led by the IRT M2P (Institute for Technological Research Metallurgy Materials Processes in Metz).Trivalent chromium ions form very stable hexa-aqueous complexes in solution, difficult to reduce. It is therefore necessary to introduce complexing agents in order to facilitate their reduction [1]–[3]. These complexing agents, mostly organic, add a difficulty in the realization of trivalent chromium electrolytes since various phenomena must be considered. In addition, the chromium based electrolytes have a low faradic yield which induces permanent competition between its own reduction and the one of protons to dihydrogen. Excessive consumption of protons near the cathode leads to a pH rise which can cause precipitation and incorporation of chromium hydroxides.In order to improve the performance of trivalent chromium electrolytes, it is possible to adjust different parameters such as the nature and concentration of the complexing agents, the pH, the temperature, the addition of additives, etc. In this study, we focused mainly on the nature and concentration of the support salt. Previous works demonstrated that over a given concentration of Na2SO4 or K2SO4 support salts, a diffusion plateau appears, which can be attributed to the reduction of protons to dihydrogen [4]. Irrespective of the substrate nature, the composition and concentration of the support salts have an impact. It has been shown that a modulation of this plateau towards the most negative potential values would be able to help in decreasing the part of current attributed to the generation of dihydrogen. Moreover, as demonstrated by Phuong et al. [5], a comparison is possible with faradaic yields. Finally, the influence of organic and inorganic complexing agents has also been studied.[1] S. Imer et T. Varnali, « Modeling chromium sulfate complexes in relation to chromium tannage in leather technology: a computational study », Applied Organometallic Chemistry, vol. 14, no 10, p. 660-669, 2000, doi: 10.1002/1099-0739(200010)14:10<660::AID-AOC55>3.0.CO;2-P.[2] Z. Zeng, Y. Sun, et J. Zhang, « The electrochemical reduction mechanism of trivalent chromium in the presence of formic acid », Electrochemistry Communications, vol. 11, no 2, p. 331-334, févr. 2009, doi: 10.1016/j.elecom.2008.11.055.[3] Y. . Song et D.-T. Chin, « Current efficiency and polarization behavior of trivalent chromium electrodeposition process », Electrochimica Acta, vol. 48, no 4, p. 349-356, déc. 2002, doi: 10.1016/S0013-4686(02)00678-3.[4] Y. Mukouyama, M. Kikuchi, et H. Okamoto, « Appearance of new potential oscillation during hydrogen evolution reaction by addition of Na2SO4 and K2SO4 », Journal of Electroanalytical Chemistry, vol. 617, no 2, p. 179-184, juin 2008, doi: 10.1016/j.jelechem.2008.02.006.[5] S. De, J. White, T. Brusuelas, C. Patton, A. Koh, et Q. Huang, « Electrochemical behavior of protons and cupric ions in water in salt electrolytes with alkaline metal chloride », Electrochimica Acta, vol. 338, p. 135852, avr. 2020, doi: 10.1016/j.electacta.2020.135852.

Pulsed Current Vs. Organic Additives on Electrodeposition from Zincate Bath

Among the various zinc electroplating baths, alkaline zincate solution has gained a wider range of applications thanks to its simple bath composition, good dispersion and efficient coverage ability. Nevertheless, alkaline zincate solution cannot be used as such and it is necessary to introduce additives to control the process performances [1]. Otherwise, efficiency is extremely low, and the properties of the coatings are disappointing. Additives can modify the crystal growth and therefore the structural and mechanical properties, the corrosion resistance, and the appearance of coatings [2]. In the absence of additives, the main problem is low efficiency, resulting from the competition between dihydrogen production and the reduction of the metallic species present in the bath.Therefore, pulsed currents constitute an attractive way to eliminate the need for organic additives by significantly improving the Faradic yield. In this study, the influence of various pulsed current sequences versus the addition of organic additives is observed in the characteristics of the coatings as well as in the process execution. A key point in the determination of the pulse sequence is the study of the transient curves with a zincate bath. This allows for the identification of the most influential parameters on dihydrogen production, with direct consequences on the process mechanisms.By knowing the τD i.e. diffusion time preceding hydrogen reduction, it is possible to design pulse sequences with limited gas production. This is confirmed by mass spectrometry measurements which quantify the total dihydrogen production for each pulse sequence. Fig 1.The coating’s characterization consists in SEM analysis topographic pictures and preferential orientations and grain sizes determined through XRD. Results confirm the interest of pulsed currents versus organic additives for zincate baths.[1] J. L. Ortiz-Aparicio, Y. Meas, G. Trejo, R. Ortega, T. W. Chapman, et E. Chainet, « Effects of organic additives on zinc electrodeposition from alkaline electrolytes », J Appl Electrochem, vol. 43, no 3, p. 289-300, mars 2013, doi: 10.1007/s10800-012-0518-x.[2] L. Yuan, Z. Ding, S. Liu, W. Shu, et Y. He, « Effects of additives on zinc electrodeposition from alkaline zincate solution », Transactions of Nonferrous Metals Society of China, vol. 27, no 7, p. 1656-1664, juill. 2017, doi: 10.1016/S1003-6326(17)60188-2. Figure 1

Tuning the Electronic Structure of Monoclinic Tungsten Oxide Nanoblocks by Indium Doping for Boosted Photoelectrochemical Performance.

Photoelectrochemical (PEC) water oxidation, a desirable strategy to meet future energy demands, has several bottle-necks to resolve. One of the prominent issues is the availability of charge carriers at the surface reaction site to promote water oxidation. Of the several approaches, metal dopants to enhance the carrier density of the semiconductors, is an important one. In this work, we have studied the effect of In-doping on monoclinic WO3 nanoblocks, growing vertically over fluorine-doped tin oxide (FTO) without the aid of any seed layer. X-ray photoelectron spectroscopy (XPS) data reveals that In3+ ions are partially occupying the W6+ ions in In-doped WO3 photoanode. In3+ ions are offering better performance by adding additional charge carriers for amplifying the expression of the number of carriers. The maximum current density value of 2.18 mA/cm2 has been provided by the optimized In-doped WO3 photoanode with 3 wt% indium doping at 1.23 V vs. RHE, which is ∼3 times higher than that of undoped monoclinic WO3 photoanode. Mott-Schottky (MS) analysis reveals charge carrier density (ND ) for In-doped WO3 photoanode has been enhanced by a factor of 3. An average Faradic yield of ∼90 percent has been achieved which can serve as a model system using In3+ as a dopant for an inexpensive and attractive method for enhanced WO3 based PEC water oxidation.

Electrocatalytic and catalytic CO2 hydrogenation on ZnO/g-C3N4 hybrid nanoelectrodes

The enhancement of efficiency of electrocatalysts towards the electrochemical reduction of CO2 reaction is always an exploring area of the present days. Herein, we have synthesized g-C3N4 and ZnO decorated g-C3N4 hybrid nanostructures by precipitation followed by calcination method. The as-synthesized nanostructures were well characterized by various spectroscopic techniques. X-ray diffraction suggests the synthesized material in the hexagonal Wurtzite structure. Whereas, scanning electron microscopy and transmission electron microscopy concludes the formation of a g-C3N4 layer with 23.7–71.4 nm and hexagonal decorated ZnO with 2.3 ± 0.5 nm, respectively. Furthermore, the electrochemical reduction of CO2 was observed at −0.504 V vs. RHE in the aqueous KHCO3 medium. The bulk electrolysis has been further carried out at −0.504, −0.734 and −0.934 V vs. RHE and obtained Faradic yield as 40.20, 53.60 and 80.99% respectively. Also, the same catalyst was used for the thermal reduction of CO2 in the batch reaction to confirm the activity and which gave excellent yield (10 mM) of the formate. Based on above investigations, a plausible reaction mechanism for hydrogenation of CO2 to formate synthesis over ZnO/g-C3N4 catalyst is also proposed. This methodology has been applicable for industrial applications for large scale production and hope will overcome the environmental and energy issues i.e., CO2 to formate as a fuel.

Ru-doped 3D flower-like bimetallic phosphide with a climbing effect on overall water splitting

The resplendent prospect of water splitting hydrogen production technology makes the development of efficient and stable hydrogen/oxygen evolution reactions (HER/OER) bifunctional catalysts become urgent. Herein, inspired by the density function theory (DFT) calculation result that Ru-dopants have a climbing effect on both OER and HER processes, we construct a Ru doped three-dimensional flower-like bimetallic phosphide on nickel foam (Ru-NiCoP/NF) derived from Co leaf-like zeolitic imidazolate framework (Co ZIF-L), effectively driving both OER (216mV@20 mA cm−2) and HER (44mV@10 mA cm−2) in 1 M KOH solutions. The overall water splitting device assembled by using Ru-NiCoP/NF as both anode and cathode shows an ultralow cell voltage of 1.515 V to obtain 10 mA cm−2. Interestingly, almost 100 % Faradic yield is achieved for the overall water splitting. This work represents a significant addition to exploring a new class of transition metal phosphides with outstanding performance in producing hydrogen via electrochemical water electrolysis.

(Invited) Pulse Current Currents Transient Curve Study: Hydrogen Discharge and Modeling Attempts

Pulse currents and periodic reverse currents have proven to be of great interest for improving plating rate and coatings properties. Virtually all metals are sensitive to this technique. Pulse plating operates a periodically interrupted direct current. [1] Every short (usually a few milliseconds) cathodic pulse is followed by a short time-off, where no current is applied. Reverse plating implements an additional reverse current, periodically applied to the electrode [2]. Nevertheless, the optimum choice of the pulse current sequence parameters requires preliminary studies. Among them, the use of transient curves in response to pulse currents represents an interesting strategy. In the case of electrolytes with high Faradic yields, a succession of characteristic patterns may be observed. Particularly, two typical plateaus are noticeable, the first corresponds to the Faradic reduction of the metallic species involved below the diffusion limit, while the second, at higher potential, is attributed to the local resistance induced by the depletion of the concentration of the concentration of metal close to the interface. This situation called “diffusion limited range” interferes with the metal reduction, promoting the competitive hydrogen production. A recent work performed with copper during electroforming process show a large influence of the various steps on the hydrogen trapping into the coating [3]. On the contrary, electrolytes with low Faradic yields does not exhibit these two patterns, because the hydrogen discharge starts almost immediately with the current increase. In this case, reverse pulse is a possible solution to keep the possibility to modify the coating properties as for example the microstructure. In this case, the strategy for parameters determination is less obvious. In both situations, modeling constitutes a great help to seek for optimization. [1] J. Cl. Puippe and N. Ibl, J. Appl. Electrochem., 10, (1980) [2] E. J. Taylor, C. Zhou, and J. J. Sun, USPTO Patent Grants, (2005) [3] L. Lain Amador, J Rolet, M-L Doche, P. Massuti-Ballester, M-P Gigandet, V. Moutarlier, M. Taborelli, L. M. A. Ferreira, P. Chiggiato, J-Y Hihn, ECS trans. ECS Transactions 85(13): 815-822 (2018)

High energy density of primary lithium batteries working with sub-fluorinated few walled carbon nanotubes cathode

Fluorinated carbon nanotubes used as cathode material exhibit a capacity exceeding the theoretical value when used in primary lithium battery. The measured experimental capacity, the faradic yield and the energy density were increased, exceeding the expected theoretical values for sub-fluorinated few walled carbon nanotubes (FWCNTs).Although the molar carbon/fluorine ratio was only of 0.37 (i.e CF0.37), an experimental capacity of 900 mAh.g−1 was obtained which is higher than the theoretical value of 521 mAh.g−1. With the same material, an unprecedented energy density of 2565 Wh kg−1 was reached associated with a faradic yield of 172%. The materials were deeply characterized using TEM, Raman and solid state 13C and 19F NMR in order to explain the extra-capacity. Such high electrochemical values can be correlated to the reinforcement effect of the central tube(s), coupled with a low amount of structural defects.

Synthesis of Azanucleosides by Anodic Oxidation in a Lithium Perchlorate–Nitroalkane Medium and Diversification at the 4′‐Nitrogen Position

Azanucleosides, in which the 4'-oxygen atom has been replaced with a nitrogen atom, have drawn much attention owing to their anticancer and antivirus activity, and tolerance towards nucleases. However, the traditional synthetic strategy requires multiple steps and harsh conditions, thereby limiting the structural and functional diversity of the products. Herein we describe the synthesis of azanucleosides by an electrochemical reaction in a lithium perchlorate-nitroethane medium, followed by postmodification at the 4'-N position. N-Acryloyl prolinol derivatives were converted into azanucleosides by anodic activation of the N-α-C-H bond. Moreover, the use of nitroethane instead of nitromethane lowered the oxidation potential of the N-acryloyl prolinols and increased the Faradic yield. The prepared azanucleosides were efficiently functionalized at the 4'-N-acryloyl group with a lipophilic alkanethiol and a fluorescent dye by conjugate addition and olefin cross-metathesis, respectively.

Synthesis of Azanucleosides by Anodic Oxidation in a Lithium Perchlorate–Nitroalkane Medium and Diversification at the 4′‐Nitrogen Position

AbstractAzanucleosides, in which the 4′‐oxygen atom has been replaced with a nitrogen atom, have drawn much attention owing to their anticancer and antivirus activity, and tolerance towards nucleases. However, the traditional synthetic strategy requires multiple steps and harsh conditions, thereby limiting the structural and functional diversity of the products. Herein we describe the synthesis of azanucleosides by an electrochemical reaction in a lithium perchlorate–nitroethane medium, followed by postmodification at the 4′‐N position. N‐Acryloyl prolinol derivatives were converted into azanucleosides by anodic activation of the N‐α‐C−H bond. Moreover, the use of nitroethane instead of nitromethane lowered the oxidation potential of the N‐acryloyl prolinols and increased the Faradic yield. The prepared azanucleosides were efficiently functionalized at the 4′‐N‐acryloyl group with a lipophilic alkanethiol and a fluorescent dye by conjugate addition and olefin cross‐metathesis, respectively.

Facile synthesis of Cu–Ag bimetallic electrocatalyst with prior C2 products at lower overpotential for CO2 electrochemical reduction

In this article, we reported the electrochemical reduction of CO2 at Cu–Ag bimetallic electrocatalysts, which can be facilely and reproducibly synthesized by hydrogen bubble template method and galvanic displacement reaction. An interesting finding was that the faradic yields of products can be tuned by changing the composition of the Ag component. The as-prepared catalyst can maintain higher activity and stability, especially the positively shifted potential to −0.74V (vs. reversible hydrogen electrode) of detectable 14% C2 products and suppression of H2 for the Cu–Ag catalyst with the replacement time of 10s. The synergistic effect of the catalyst has been reported to C2. In addition, the potential dependent rule for products was illustrated as well and volcano shape change towards C2 was worthy to be pointed. Our research will deepen the understanding of the surface electrocatalytic reaction and provide the insight into the factors to design excellent catalysts.

Purification of pentoses from hemicellulosic hydrolysates without neutralization for sulfuric acid recovery

Abstract The agro-industrial sector generates large amounts of coproducts such as lignocellulosic biomass which could be valorized into many chemicals and bio-based intermediates (sugars, paper pulp, surfactants, polymers or bioethanol). However, in the case of biomass hydrolysis by diluted sulfuric acid, current downstream processes involve a partial or complete neutralization which are not satisfactory for economic and environmental reasons. This work presents a purification process of pentoses from hemicellulosic hydrolysates without neutralization for sulfuric acid recovery. Compared to conventional processes, less energy, water and chemicals are required. Very promising results were obtained at pilot scale with 100 L of wheat bran hydrolysates. The process is based on the combination of ultrafiltration, conventional electrodialysis and ion-exchange. Ultrafiltration with a 10 kDa organic membrane totally removed harmful macromolecules which precipitate during electrodialysis operation because of pH rise. Till a volumetric concentration factor 3.6, the average flux kept good for industrial application (27 L·h−1·m−2). However suspended materials have to be filtered before ultrafiltration. Besides, a 2.5 diafiltration is required to recover most of sugars (99%). Then conventional electrodialysis was performed to recover most of sulfuric acid (80%). The average faradic yield was quite good (80%) and the specific energy consumption of the electrodialysis stack was quite interesting (1.1 kW h per kg of H2SO4 recovered and 8.4 kW h per m3 of hydrolysate). Finally, the complete demineralization (conductivity

Pushing the Theoretical Limit of Lithium/Carbone Fluoride Batteries Using Fluorinated Nanostructured Carbon Nanodiscs

The Li/CFx primary battery is the first lithium battery developed since the 1970th, and it possesses the highest energy-density among all primary lithium batteries (theoretically 2180 W h kg-1).When fluorinated carbons (denoted CFx) are used as electrode material in primary lithium battery, the C-F bonds are broken during the electrochemical discharge and carbon and LiF particles are formed. Then, the higher the fluorine content, the higher the theoretical capacity, the maximal value being 865 mAh/g for a CF1 composition. Although this limitation, we found higher capacities (Cexp) than the theoretical ones (Ctheo) for several optimized fluorinated nanocarbons. The faradic yield, defined as 100xCexp/Ctheo, was then higher than 100% and reached even 170%. This means that a second electrochemical process takes place after the defluorination. In order to understand such additional mechanism, a set of carbonaceous nanomaterials, namely carbon nanodiscs, graphitized carbon blacks, double- and multi-walled were fluorinated using either pure F2 gas or a solid fluorinating agent (TbF4) and their electrochemical performances were investigated. After a deep characterization of the material (SEM, TEM, XRD, 19F solid state NMR, EPR), the discharge mechanisms were investigated using the same complementary techniques and compared to conventional graphite fluorides. This systematic study of about ten different CFx underlined that the key point for the extra-capacities lies in both the maintaining of some unfluorinated parts and the ability of the fluorinated carbon to reform its raw structure after electrochemical defluorination are necessary for extra-capacity. LiF particles, which are formed during this process, are then located outside the new carbonaceous matrix and may participate to the second mechanism, similar to the intercalation into the freshly formed carbon matrix. These two processes, electrochemical defluorination and intercalation into the defluorinated carbon are well exemplified by the case of carbon nanodiscs. This sample was fluorinated with TbF4 in order to homogenously locate the fluorine atoms in the whole volume of the discs, except in the central discs, less or not fluorinated. The deep characterization of the fluorinated discs allows this conclusion to be proposed in accordance with the properties of the starting materials. After the defluorination, a shell of agglomerated LiF particles covered the discs. Any exfoliation of the discs has been observed after the defluoration contrary to the studied conventional graphite fluoride. The process similar to an intercalation into the reformed discs may take place thanks to the maintaining of the discotic geometry. The extra-capacity comes from this additional process, which occurs through the LiF shell. In other words, the less or not fluorinated central discs act as a reinforcement that allows the rebuilding of the carbon matrix. Both the unfluorinated carbon and the LiF covering, which is formed outside the carbon lattice during the discharge mechanism, play a key role for the achievement of the extracapacity by the consumption of Li+ to form Li2F+ species stabilized by the carbon host structure formed after the electrochemical defluorination. The necessity of a reinforcement was then confirmed for the cases of fluorinated double and low diameter multi-walled carbon nanotubes, for which the fluorination with F2 gas has been conducted in order to avoid the fluorination of the inner tube, which allows the reinforcement and the carbon rebuilding. The higher faradic yield (170%) was obtained for those samples.