Copper oxides are promising photocathodes for solar hydrogen production, but the role of the metastable intermediate phase, paramelaconite (Cu4O3), remains obscure due to its narrow thermodynamic stability window. Herein, we report the controllable synthesis of pure Cu2O, Cu4O3 and CuO thin films via radio-frequency reactive magnetron sputtering by precisely manipulating the oxygen partial pressure. A systematic phase diagram was established to isolate the challenging Cu4O3 phase, facilitating comprehensive comparative studies of the inherent correlations between crystal structure, electronic properties, and photoelectrochemical (PEC) behaviors. Mott-Schottky plots and band alignment analysis reveal that Cu2O exhibits the most favorable electronic properties, featuring the highest hole carrier density (similar to 3.1 & times; 10(19) cm(-3)) and the most negative conduction band potential, providing the strongest thermodynamic driving force for hydrogen evolution. In contrast, although the Cu4O3 also demonstrates a high carrier density (similar to 2.7 & times; 10(19) cm(-3)), comprehensive PEC evaluations identify its rapid surface recombination and significant photocorrosion. This stems from a high density of deep-level traps acting as recombination centers, which drives severe surface charge recombination and consequently triggers rapid photocorrosion. Conversely, the Cu2O phase shows superior kinetic stability with rectangular photoresponses and distinctive self-activation behavior. This work unravels the trade-off between conductivity and stability, affirming that the defect tolerance and phase purity of Cu2O render it as the optimal candidate material for durable solar water splitting.

A nanocomposite of reduced graphene oxide, polydopamine, and Co3O4 was developed via a one-step hydrothermal process, which showed remarkable electrochemical properties, when used as electrodes in a current collector-free μ-supercapacitor device.

Chondrocyte hypertrophic differentiation is a main event leading to articular cartilage degradation in osteoarthritis. It is associated with matrix remodeling and mineralization, the dynamics of which is not well characterized during chondrocyte hypertrophic differentiation in articular cartilage. Based on an in vitro model of progressive differentiation of immature murine articular chondrocytes (iMACs) into prehypertrophic (Prehyp) and hypertrophic (Hyp) chondrocytes, we performed kinetics of chondrocyte differentiation from Prehyp to Hyp to follow matrix mineralization and remodeling by immunofluorescence, biochemical, molecular, and physicochemical approaches, including atomic force microscopy, scanning electron microscopy associated with energy-dispersive X-ray spectroscopy (SEM–EDS), attenuated total reflection infrared analyses, and X-ray diffraction. Chondrocyte apoptosis was determined by TUNEL assay. The results show the formation of a mineral phase 7 days after Hyp induction, which spreads within the matrices to form poorly crystalline carbonate-substituted hydroxyapatite after 14 days, then the proportions of crystalline relative to amorphous content increases over time. Hyp differentiation also induced a matrix turnover that occurs over the first 7 days, characterized by a decrease in type II collagen and aggrecan and the concomitant appearance of type X collagen. This is accompanied by an increase in the enzymatic activity of MMP-13, the main collagenase in cartilage. The number of apoptotic chondrocytes slightly increased with Hyp differentiation and SEM–EDS analyses detected phosphorus-rich structures that could correspond to apoptotic bodies. Our findings highlight the mechanisms of matrix remodeling events leading to the mineralization of articular cartilage that may occur in osteoarthritis.

Herein, the development and the characterization of an all-solid-state symmetrical and current collector-free microsupercapacitor based on a new reduced graphene oxide-polydopamine (rGO-PDA) composite are reported. The rGO-PDA composite is synthesized by a facile, eco-friendly and scalable hydrothermal approach in the presence of dopamine which can not only contribute to the oxygen functional groups removal from graphene oxide but also polymerize onto the rGO sheets reducing their restacking and improving the wettability of the electrode. The optimized rGO-PDA composite material exhibits excellent capacitance and cycling stability as well as an improved rate capability compared to the pristine rGO in Na2SO4 solution. This performance enhancement can be linked to the higher transfer kinetic and lower transfer resistance values of the ions involved in the charge storage process of rGO-PDA, as determined by ac-electrogravimetry. Furthermore, an all-solid-state microsupercapacitor was prepared employing the optimized rGO-PDA composite as electrode material. Interdigitated electrodes were obtained thanks to a CO2 laser and a Na2SO4/PVA hydrogel was employed, no current collector was used. This device achieves a noteworthy energy density of 6.2 mWh & sdot; cm-3 at a power density of 0.22 W & sdot; cm-3. Moreover, it exhibits exceptional cycling stability, retaining 104 % of its initial capacity even after undergoing 10,000 cycles at 2 V & sdot; s-1. A new reduced graphene oxide-polydopamine (rGO-PDA) material was obtained by an hydrothermal treatment of an aqueous solution containing GO and dopamine. The optimised rGO-PDA composite reveals superior transfer ion kinetics at the electrode/electrolyte interface compared to pristine rGO, probed by advanced electrogravimetry. A current collector-free device composed of interdigitated rGO-PDA electrodes was tested using a Na2SO4/PVA hydrogel electrolyte. It achieves remarkable energy and power densities with exceptional cycle stability.image

Carrier density of electrodeposited methylammonium lead iodide perovskite (CH3NH3PbI3) can be modulated inside the 1017 to 1020 cm-3 range by carefully selecting the experimental parameters used during the last two chemical conversion steps of their synthesis. This finding has been made possible by performing systematically Mott-Schottky (MS) plots in aqueous solution on various semi-conducting CH3NH3PbI3 perovskite samples. These latter were produced by a three-step synthesis method combining an electrodeposition step with two consecutive chemical conversion steps. In a first step, the galvanostatic electrodeposition of a lead dioxide (PbO2) thin film is carried out. This latter is then converted into lead (II) iodide (PbI2) by immersion in a HI/ethanol solution, this latter being then itself turned in a third and last step into the well-known CH3NH3PbI3 perovskite by a new immersion step in a methylammonium iodide (MAI)/isopropanol solution. This very simple and highly repro-ducible synthesis method allows the production of perovskite thin films on large surfaces, unlike many other synthesis methods of perovskite thin films. In parallel to the determination of p-type character, carrier con-centration and flat band potential of the perovskite samples using Mott-Schottky plots, their chemical compo-sition, their morphology and their crystallinity were characterized by using scanning electron microscopy (SEM) and X-Ray Diffraction (XRD) and compared with those of the products obtained at the end of each of the two first steps, i.e. PbO2 and PbI2 respectively. Interestingly, it was shown that the final product is not always a pure p -type perovskite thin film as various amounts of lead (II) iodide (PbI2) can be detected depending on the experimental parameters used during the two consecutive chemical conversion steps. The main result of this study is that the dopant concentration of perovskite thin films was shown to be inversely proportional to the amount of the remaining PbI2 impurities detected in the bulk of perovskite thin films.

In an aqueous electrolyte under an anodic polarization, most of the conductive polymers could undergo an overoxidation due to the hydroxyl radicals formed during water oxidation. Regarding poly(3,4ethylenedioxythiophene) (PEDOT) only a few reports studied its overoxidation. In this paper, we propose a facile and rapid strategy to prepare an ultrathin (15 nm), pinhole-free and non-conductive overoxidized PEDOT film by electropolymerization of EDOT under potentiostatic conditions in the presence of solely weak-acid anions in the monomer solution. The influence of the pH of this solution as well as the applied potential was studied notably by electrochemical impedance spectroscopy. It was pointed out that the PEDOT film is overoxidized when its electrosynthesis is performed in an aqueous monomer solution of pH 10.5, at 1.1 V/SCE, the monomer solution containing only weak-acid ions as anions (phosphates or carbonates). XPS analyses show that some C and S atoms of the film are oxidized leading to a break of the polymer conjugation and therefore to a decrease of its electronic conductivity. Finally, after adding in the monomer phosphate solution of pH 10.5 perchlorate ions that allow to avoid total overoxidation of the film formed at the very beginning of the process, PEDOT nanowires were obtained. (c) 2021 Elsevier Ltd. All rights reserved.

For thermal management applications, copper (Cu) metal matrixes reinforced by carbon are undoubtedly one of the most promising composites for heat spreaders In the frame of this work, hard Cu matrix composites having anisotropic thermal conductivity were fabricated by using Cu flakes coated with carbonized polydopamine. The flakes were coated by simply immersing them into a dopamine aqueous solution, then they were submitted to a thermal treatment under dihydrogen. This easy synthesis method results in a asymptotic to 10 nm thick N-doped graphenelike film surrounding the Cu flakes. The subsequently densified composites that contains about 0.23 wt % of C show an increase of hardness up 44% and 172% as compared to pure Cu in the parallel and perpendicular sintering direction, respectively. In addition an anisotropic thermal conductivity is obtained with an anisotropy ratio of 2.75.

Thickness variations of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films placed under potential conditioning were measured with the help of electrochemical atomic force microscopy (EC-AFM). In this purpose, in-situ AFM operating in the contact mode was coupled with either cyclic voltammetry (CV) or advanced cyclic voltammetry (AdCV). A PEDOT functionnalized platinum electrode was used simultaneously as a sample for in-situ AFM measurements and a working electrode in a usual three electrode electrochemical setup. PEDOT films were electrodeposited with the help of the CV technique from lithium perchlorate aqueous solutions. From these EC-AFM investigations, brand new PEDOT films were found to be anion exchangers, in good agreement with conclusions of investigations reported in literature. Unexpectedly, PEDOT films having undergone a comprehensive electrochemical cycling (i.e. an electrochemical aging) in a potential range encompassing narrowly their redox process by using tens of CV or AdCV potential cycles behave as cation exchangers. Such observation strongly suggests that the electrochemo-mechanical and ion exchange behaviours of PEDOT can be both switched by simply using a potential cycling. Interestingly, the initial steps of this switching process were observed on a brand new PEDOT film during 26 consecutive CV scans. In the course of this process still ongoing at the end of the 26th cycle, a second swelling peak appears and grows progressively beside the initial swelling peak attributed to an anion exchange behaviour. This leads to a dual ion exchange behaviour for the resulting PEDOT film within the explored potential range. Indeed, this new swelling peak can be attributed to a cation exchange behaviour from the comparison of the potential dependant chronothicknograms and corresponding voltathicknograms with those obtained previously in this work.

This work concerns the preparation and modification of mesoporous silica SBA-15 with different amine-copper complexes in order to study their impact on the catalytic behavior via Aza Michael addition. Firstly, SBA-15 was prepared hydrothermally, then functionalized by mono-, di- and tri-amine, and in the second step, copper (II) was anchored. The catalytic activity of these solids was evaluated at room temperature under liquid-phase conditions. Effects of catalyst nature, catalyst mass, reaction time and the starting reagents nature were investigated. Cu@SBA-15 (non-aminated) was shown to be efficient in the Aza Michael addition, but after its second re-use, a progressive decrease in the product yield was obtained due to copper leaching. The catalytic behavior of all prepared catalysts showed a selective reaction via the mono-Aza-Michael addition. Amongst all the catalysts, the one containing the monoamine-copper complex led to the highest yield. This catalyst was used in four consecutive cycles without significant loss of activity, which confirms its stability.

Mesoporous silica SBA-15 was functionalized with various amines and then doped with copper II cation (Cu2+). The modified materials were tested for the retention of CO2 at room temperature using temperature-programmed desorption (CO2-TPD). Several parameters affecting the CO2 retention capacity (CRC) such as the nature of amine groups, repetitive adsorption-desorption cycles and dispersion of copper were investigated. CO2-TPD and H2O-TPD allowed correlating the hydrophilic character with the CO2 retention capacity. The obtained results showed that amine-functionalized mesoporous materials containing their own moisture exhibit higher effectiveness in the retention of CO2. Triamine-functionalized SBA-15 displayed the highest CRC value as a result of the increase of the number of adsorption sites. Material reuse in three adsorption/desorption cycles revealed high stability with a slight decrease in CRC. The dispersion of copper induced a progressive decrease in the CRC value. The CRC decreased with increasing Cu2+ content due to competitive complexation of Cu2+ by the amino groups.

The purpose of this paper is to show that it is possible to increase the diameter and length of the nanostructures of a framework formed of oriented polypyrrole nanowires that has been prepared by a templateless electrochemical method based on the use of a pyrrole solution containing a high concentration of weak-acid anion and a low concentration of non-acidic anion. The dimensions of the initial nanowires are increased by performing an additional electrosynthesis in a ‘classical’ monomer solution. Depending on the polarization time of this last synthesis (a few tens of seconds), wires with various diameters, from one hundred up to several hundred nanometers, are obtained. In addition to the variation of the nanowire size, these findings confirm, as outlined in the reaction mechanism we have proposed, that the base of the nanowires is surrounded by a thin non-conductive polymer i.e. by an overoxidized polypyrrole film. Actually this paper shows a proof-of-concept. Indeed one can imagine that the second polymeric electrodeposit could be performed using an organic monomer solution, using functionalized pyrrole monomer to fabricate a biosensor having large specific area, and/or using anions which could be drugs.

A nanostructured polypyrrole powder was synthesized in a previous work from the oxidation of pyrrole by a nanostructured MnO2 powder used simultaneously as an oxidizing agent and a sacrificial template in a redox heterogeneous mechanism. In this study, this original PPy powder was used as an active additive material with different ratio in carbon/carbon symmetrical supercapacitors whose performances were studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) using a Swagelok-type cell. From the EIS spectra, the complex capacitance was extracted using a model involving two Cole–Cole type complex capacitances linked in series. The specific capacitance values evaluated by EIS and cyclic voltammetry are in a good agreement between them. The results show that the addition of nanostructured polypyrrole powder improves significantly the specific capacitance of the carbon electrode and consequently the performances of carbon/carbon supercapacitors. The original and versatile synthesis method used to produce this polypyrrole powder appears to be attractive for large scale production of promising additives for electrode materials of supercapacitors.

The development of alternative energy sources, especially green energy sources for traditional fossile fuels is a major challenge that humankind is currently facing. The conversion of solar energy into chemical fuels is a promising method. Inspired by photosynthesis taking place in the green plants, artificial photosynthesis was proposed. The targeted reaction is as follows: 2 H2O (l) → 2 H2 (g) + O2 (g) Theoretically, the half redox equation related to water oxidation, also called oxygen evolution reaction (OER), which is a key step for water splitting, needs a high potential bias, as a consequence of the very slow kinetics of this reaction. This latter could be improved by employing a catalyst in order to make it energetically less expensive. Catalysts based on metal oxides have shown bright prospects for this application [1]. As a consequence of the determination of the fine structure of photosystem II in charge of this redox process in plants, it was revealed that the oxygen evolving complex (OEC) was a Mn4CaO5 entity resembling strongly the one that can be found in manganese oxides. These latter attracted consequently a considerable attention of scientists over the last years as possible OER photoelectrocatalysts. After comparison with traditional catalysts based on precious metals, manganese oxides, and mainly MnO2, have the advantages of being abundant on Earth, and therefore inexpensive, and also environmentally friendly. In particular, many investigations reported in literature showed in a rather convincing manner that MnO2 is a promising candidate as OER photoelectrocatalysis. In a work published in 2011, T. F. Jaramillo et al. showed that birnessite-type MnO2 could be a good solar water splitting catalyst [2], whereas S.S. Stahl et al. found that the OER activity of manganese oxides depends on their crystalline structure [3]. D.G. Nocera and co-workers investigated the nucleation and growth mechanism of MnOx thin films electrodeposited in potentiostatic conditions using a potential value selected inside a narrow potential range [4]. Few studies were thus focused on large variations of the potential used during the electrodeposition of MnO2thin films in potentiostatic conditions, and on the corresponding performances of these films towards photoelectrocatalysis of water oxidation. In this work, manganese dioxide (MnO2) thin films with different morphologies were prepared by one-step potentiostatic deposition using an aqueous electrolyte containing MnSO4 and NaClO4 in a traditional three-electrode cell. Fluorine doped tin oxide (FTO) substrates were used as working electrodes, and a platinum grid and a K2SO4 saturated Hg/Hg2SO4 electrode (SSE) were used as counter- and reference electrodes, respectively. The same setup was used during the OER tests except that a 0.1 M KOH Hg/HgO reference electrode (MOE) and a 0.1 M NaOH electrolyte were used instead of SSE and NaClO4respectively. Our results show that the value of the electrodeposition potential has a strong influence on the morphology and crystallinity of resulting MnO2 thin films, as evidenced by SEM-FEG and XRD characterisations. The birnessite type crystalline structure was obtained only for films electrodeposited at potential values close to the peak potential related to MnO2 electrodeposition, whereas MnO2thin layers electrodeposited at potential values situated far beyond this peak potential value and before the foot of the anodic wall related to water oxidation were found to be amorphous, which clearly promoted their activity towards OER, by comparison with those of the birnessite variety. In the course of our investigations, chronoamperometry experiments were carried out for all the samples. They allowed us to find out that the stability of the electrocatalytic behaviour, as well as the adherence on the underlying substrate, were both better for amorphous films. Electrochemical impedance spectroscopy (EIS) experiments were also carried out to develop a better understanding of their electrochemical properties in the course of water oxidation experiments. Moreover, their semi-conductor behaviour was evidenced using water oxidation experiments in the presence of a solar simulator, and deeply investigated with the help of Incident Photon to electron Conversion Efficiency (IPCE), UV-visible spectrophotometry and Current Sensing Atomic Force Microscopy (CS-AFM). References: [1] R. L.Doyle, I.J. Godwin, M.P. Brandon, M.E.G. Lyons, Phys. Chem.Chem. Phys., 2013, 15, 13737-13783 [2] B. A. Pinaud, Z. Chen, D. N. Abram, T. F. Jaramillo, J. Phys. Chem. C, 2011, 115 (23), 11830–11838 [3] R. Pokhrel, M. K. Goetz, S. E. Shaner, X. Wu, S. S. Stahl, J. Am. Chem. Soc., 2015, 137 (26), 8384–8387 [4] M. Huynh, D. K. Bediako, Y. Liu, D. G. Nocera, J. Phys. Chem. C, 2014, 118 (30), 17142–17152

Mesoporous WO3 thin films were prepared electrochemically by using an ionic surfactant during the synthesis, and the electrochemical properties are investigated in comparison with their dense analogues. This report specifically highlights the suitability of a time resolved coupled electrogravimetric method to follow meticulously the ion intercalation/extraction phenomena which revealed the enhanced ion intercalation/extraction behavior of electrodeposited mesoporous WO3 thin films for diverse applications in energy storage and electrochromism. This methodology (electrochemical impedance spectroscopy (EIS) and its coupling with a fast quartz crystal microbalance (QCM)) has the ability to detect the contribution of the charged or uncharged species during the electrochemical processes, and to deconvolute the global EQCM responses into the anionic, cationic, and the free solvent contributions. Our study identifies the involvement of several charged species (Li(+), Li(+)·H2O) in the compensation of charge, and H2O molecules indirectly contribute to the process in both dense and mesoporous WO3 thin films. Even a slight contribution of ClO4(-) ions was detected in the case of mesoporous analogues. The results of the study indicate that the transfer resistances of Li(+) and Li(+)·H2O are decreased when the WO3 films are mesoporous. A more significant difference is observed for the larger and partially dehydrated Li(+)·H2O ions, suggesting that increased surface area and pore volume created by mesoporous morphology facilitate the transfer of larger charged species. The relative concentration changes of cations are also magnified in the mesoporous films. The final concentration variations are higher in mesoporous films than that in the dense analogues; ∼4 times and ∼10 times higher for Li(+) and for Li(+)·H2O, respectively. To the best of our knowledge, an unambiguous identification of species other than desolvated cations (e.g. Li(+) ions), the information on their transfer dynamics and quantification of the transferred species have never been reported in the literature to describe the charge compensation process in WO3 based electrodes.

To propose a picture of plaster hydration at a submicrometric scale, we have developed a kinetic Monte Carlo simulation model of gypsum crystal growth. Raman spectroscopy is used to check the model and to assign physical values to the parameters. Special focus is put on the effects of increasing plaster-to-water ratio and using citric acid as an additive. The hypothesis about the autocatalytic growth of gypsum needles during the first stage of the reaction is confirmed by the correct simulation of the induction period preceding the fast growth regime. The aspect ratio of gypsum needles, defined as the ratio of needle length and width, emerges as a relevant parameter to control both dynamics and material structure. Addition of citric acid is known to produce compact gypsum crystals instead of long needles. The choice of a small aspect ratio is sufficient for the simulations to reproduce the effects of citric acid, including the slowing down of the reaction without recourse to fitting parameters. The kinetic Monte Carlo simulation model proved to be a predictive tool that could assist the rational development of novel additives and reagent treatments with the aim of producing materials with predefined properties.

Cerium oxide (CeO2) nanoparticles (NPs) possessing defined size and crystallinity have been synthesised by a co-precipitation method. The effect of several parameters, such as the nature of the solvent and the calcination process, on the crystallite size was studied by XRD, TEM and BET methods. These CeO2 nanoparticles were then incorporated in dodecylsulfate (DS) doped PPy films during their electrodeposition in potentiodynamic conditions in order to produce PPy-DS/CeO2 NPs nanocomposite thin films on gold coated quartz crystals. Simultaneous EQCM experiments revealed successful incorporation of increasing amounts of cerium oxide nanoparticles in the polypyrrole matrix during each of the consecutive CV scans. This was confirmed using FEG-SEM and EDS microanalysis.The ion exchange phenomena occurring in the resulting nanocomposite materials were studied by ac-electrogravimetry in NaCl aqueous electrolyte. PPy-DS films appear to be mainly cation exchangers, independently from the incorporation of CeO2 nanoparticles (NPs), even though chloride anions in smaller amounts, and free water molecules, are simultaneously transferred at the film/electrolytic solution interface. This study also reveals that the kinetics of Cl- ion insertion occurring at the film/electrolyte interface upon oxidation is persistently slower in PPy-DS/CeO2 NPs films than in PPy-DS films throughout the entire potential window of investigation. However, the relative concentration changes of Cl- ions in PPy-DS/CeO2 NPs films is about two times greater than that occurring in pristine PPy-DS films. Such conclusion tends to demonstrate that CeO2 NPs have the ability to modify the morphology of electrodeposited PPy-DS thin films as well as their subsequent permeability towards ions contained in the electrolytic solution, possibly via the perturbation of polymer chain interactions and organisation. (C) 2014 Elsevier Ltd. All rights reserved.