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Preparation of new ironzeolite modified electrodes for the oxidation of pollutants via an electro-Fenton-like process is reported in this work. Alizarin Red S (ARS) is chosen as the model dye compound for anodic oxidation in an aqueous acidic medium. A minimal metal loading ranging from 0.2 to 0.8 wt% of ferrous/ferric (Fe2+/Fe3+) ions was introduced inside the ZSM-5 zeolite (Si/Al ratio of 15.0) via an ion-exchange process and the presence of iron species in the zeolite framework was determined using several physicochemical techniques. The ironzeolite samples obtained under different experimental conditions were employed in order to study the textural and structural properties, and electrocatalytic activity. Cyclic voltammetry measurements showed that the textural properties of zeolite do not mainly affect the electrocatalytic reaction. However, the differences observed in catalytic peaks were a consequence of different iron ions present in zeolite. The structurecatalytic activity relationship is highlighted by the identification of the degradation products like oxalic acid (C2H2O4) and formic acid (HCOOH). Consequently, the degradation of ARS reached an optimum value of ca. 30% at 2 V vs. SCE for Fe(iii)TTZSM-5 with a catalyst loading of 5.0 mg cm2. This study shows that ironzeolite modified electrodes are highly active for dye compound degradation without the addition of H2O2 and have potential application in the treatment of effluents., FCT (Fundação para a Ciência e a Tecnologia, Portugal) for the PhD grant to Marta Ferreira. This work was developed under the scope of the projects: BioTecNorte (operation NORTE-01-0145-FEDER-000004), supported by the Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). This work also has been funded by national funds (FCT), through the projects: PTDC/AAG-TEC/5269/2014, Centre of Chemistry (UID/QUI/00686/2013 and UID/QUI/0686/2016). The authors also thank the graduate student João P. M. Fernandes for his contribution to the electrocatalytic tests., info:eu-repo/semantics/publishedVersion

International audience; Selective electrochemical conversion of CO2 to HCOOH is obtained at the surface of a carbon-supported bimetallic cathode material composed of copper and palladium nanoparticles. Polycrystalline copper or large copper particles are well-known to catalyze CO2 reduction to hydrocarbons at relatively negative potentials, or when their surface is covered by copper oxides (Cu2O and CuO). Cu-based materials modified by various palladium contents (0

International audience; Copper-supported mesoporous carbon nanocatalysts (Cu/FDU-15) were synthesized using an easy and convenient one-pot soft-template method for low-overvoltage CO2 electroreduction. TEM imaging revealed the presence of large Cu nanoparticles (diameter 140nm) with Cu2O nanoparticles (16nm) as an additional phase. From the electron tomography observations, we found that the copper particles were placed inside and on the exterior surface of the porous FDU-15 support, providing an accessible surface for electrocatalytic reactions. CO2 electrolyses showed that the mesostructured Cu/FDU-15-350 cathode materials were active towards CO2 conversion to formic acid with 22% Faradaic efficiency at a remarkably low overpotential of 290mV, hydrogen being the only side-product. The catalyst's activity correlates to the calculated metallic surface area, as determined from a geometrical model, confirming that the mesoporous channels act as a diffusion path for the CO2 molecule, and that the whole Cu surface is accessible to CO2, even if particles are entrapped in the carbon matrix.

Mesoporous carbon structures containing copper particles were synthesized according to different synthesis methods in order to tune the morphostructural properties of these electrocatalysts for the CO2 reduction reaction. Microwave polyol synthesis, hard templating, one pot soft templating and evaporation induced self assembly gave access to different mesoporous structures. Copper particles were identified inside the mesoporous structures, while the porous channels remained unaffected leading to confined nano reactors. Bulk electrolyses showed that only two CO2 reduction products are obtained: HCOOH as the main product with a low amount of CO, H2 completing the faradaic balance. Differences in steady state current densities during electrolyses were correlated to the Cu metallic specific surface area. The latter was determined according to a geometrical model based on truncated octahedron clusters developed for copper clusters. This correlation evidences that confined Cu particles remains still electroactive and paves a way for the efficient development of 3D electrodes.

The role of the nanostructured iron catalysts hosted by different type of zeolite structures (NaY and ZSM5) on the electrochemical degradation of Congo Red dye (C32H22N6Na2O6S2) was investigated. Here, the nano-iron zeolite catalysts with high surface areas (up to 853 m2 g-1) were prepared by ion-exchange method1 serving tunable particle size and acidity that is highly sensitive to the local reaction environment at the electrode surface. The structural and morphological analysis was carried out using scanning electron microscopy (SEM), X-ray diffraction and N2-sorption techniques. In order to clarify the electrocatalytic trend observed by constant potential electrolysis, we further considered the acidity properties of the zeolites determined by microcalorimetric measurements. Moreover, it was noted that the presence of NH4 +, H+ and Na+ ions in the case of ZSM5 zeolite allows the rearrangement of the iron-zeolite architecture, resulting in a more favorable stabilization of the degradation process as a function of the production rate. Compared with the FeNaY catalysts, the FeZSM5 catalysts (Fe(Na)ZSM5, Fe(H)ZSM5 and Fe(NH4)ZSM5) exhibited excellent activity and stability, with a maximum dye degradation around 64% on the Fe(H)ZSM5 catalyst. This work, revealing the synergetic interactions between the acid sites of the zeolite and the catalytic active sites, provides a new route for the development of electrochemical sensing low-metal content zeolite structures. Acknowledgements: This work was conducted in the framework of the BioTecNorte projects: NORTE-01-0145-FEDER-000004, PTDC/AAGTEC/5269/2014, UID/QUI/00686/2013, and UID/QUI/0686/2016. Z. B. is grateful for ERASMUS research grant. Reference: 1. M. Ferreira, F. Pinto, O. S. G. P. Soares, M. F. R. Pereira, J. J. M. Órfão, J. L. Figueiredo, I. C. Neves, A. M. Fonseca, P. Parpot, Chemical Engineering Journal, 228 (2013) 374.

Low-temperature proton exchange membrane fuel cells (PEMFCs), offering significantly higher efficiency compared to conventional heat engines play a crucial role in responding to the growing energy demand, especially for transportation applications. The fundamental understanding of bulk electrocatalysis both in acidic and alkaline media at nanostructured electrodes that possess compositional and structural heterogeneity has a profound effect on electrode kinetics and reaction mechanisms. Because the electrocatalytic activity depends mainly upon the nanoscale size, composition as well as surface properties of the prepared catalyst, development and engineering of advanced electrocatalysts is needed for giving a lead towards unprecedented improvements in electrode performance so in fuel cell systems1. It has hypothesized2 and reported3 that alloying Pt with different metal components (herein Sn and Ni) brings about modifying the electrotonic states such as the d-band centers as well as geometric factors, which has attracted a great deal of attention in electrocatalysis. Moreover, the superior catalytic synergy of nanostructured binary4 and ternary5 electrocatalysts towards oxygen reduction activity was previously reported. To this end, highly active, robust and low-cost carbon-supported ternary nanoparticles (Pt2Sn1Ni1/C) were synthesized using a modified microwave-assisted polyol method6 in diethylene glycol (DEG) without additional protective agents. The morphostructural properties of the catalyst were determined via various advanced-characterization techniques. Cyclic voltammetry (CV) and rotating (ring) disk electrode (RRDE) measurements reveal that the alloying of Pt with Sn-Ni significantly boosts the catalytic activity towards oxygen reduction reaction (ORR) in O2-saturated 0.1M HClO4 electrolyte. The kinetic parameters were assessed through Koutecky-Levich approach. The influence of the alloying structure on the kinetic parameters such as exchange current density, limiting current density, Tafel slopes, reaction rate, and the number of exchanged electrons is extensively discussed. References: M. Shao, Q. Chang, J. P. Dodelet, R. Chenitz, Chem. Rev., (2016), 116, 3594. J. K. Norskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J.R. Kitchin, T. Bligaard, H. Jonsson, J. Phys. Chem. B, (2004), 108, 17886. T. Toda, H. Igarashi, H. Uchida, M. Watanabe, J. Electrochem. Soc., (1999), 146, (10), 3750. C. C. Bakir, N. Sahin, R. Polat, Z. Dursun, Journal of Electroanalytical Chemistry, (2011), 662, 275. S. Beyhan, N. E. Sahin, S. Pronier, J. M. Leger, F. Kadirgan, Electrochimica Acta, (2015), 151, 565. N. Sahin, T. Napporn, L. Dubau, F. Kadirgan, J. M. Leger, K. B. Kokoh, Applied Catal. B: Environ., (2017), 203, 72.

Copper-supported mesoporous carbon nanocatalysts (Cu/FDU-15) were synthesized using an easy and convenient one-pot soft-template method for low-overvoltage CO

This work reports first the synthesis of carbon supported Pt and Pt-Cr electrode materials from microwave-heated diethylene glycol (DEG) without additional protective agents. The prepared electro-catalysts have superior electrochemical activity and stability than those previously reported in acidic medium. Transmission electron microscopy (TEM) characterizations of these materials reveal uniformly dispersed particles with a mean size of ca. 1.20 nm. The morphological changes of these two materials were investigated by identical location-transmission electron microscopy (IL-TEM) after classical durability test. The electrocatalytic activity towards the oxygen reduction reaction (ORR) was investigated using rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) techniques in 0.1 mol L-1 HClO4. The kinetic parametdrs were assessed through the Koutecky-Levich equation at 20, 30 and 40 degrees C. Electrochemical measurements demonstrate that significantly higher catalytic activity was observed on the Pt-Cr/C electrocatalyst than on Pt/C. The RRDE analysis shows that the ORR mainly involves a four-electron reduction mechanism to water with the formation of a very low H2O2 amount as reaction intermediate. (C) 2016 Elsevier B.V. All rights reserved.

Besides producing clean energy via fuel cells, the costs and activations of catalysts have a great importance. In order to reduce cathode activation losses due to comparably sluggish kinetics of oxygen reduction reaction, more active catalysts than Pt should be used. Mostly, noble metals are alloyed with second or third metal as cathode catalysts in order to obtain a synergistic effect. The objective of this study is to improve and enhance the electrocatalytic activities and to lower costs of Pt-based cathode catalysts. Microwave assisted polyol synthesis is used to synthesize bimetallic or ternary catalysts in a very short time with particle size smaller than 10 nm. PtCo/C and PtSnCo/C electrocatalysts is shown ORR activities higher than Pt/C catalyst. Effect of the addition of Co and/or Co and Sn catalyst to Pt/C over ORR kinetic is investigated. Characterization of catalysts is carried out by electrochemical, spectroscopic and microscopic methods.

Ethanol is a molecule of considerable interest because of its potential renewable use in fuel cells without reforming. Therefore, bifunctional electrocatalysts were proposed to decrease the precious noble metal content in the catalyst composition and to promote the conversion of this fuel, leading to the preparation of Pt-based materials containing oxophilic co-catalysts such as tin, osmium, iridium and ruthenium. They allow the ethanol oxidation to occur at low potentials, and also remove CO-like adsorbed species from the electrode surface. The knowledge of the mechanism is important to propose new materials and design that are able to promote the cleavage of the C-C bond in large extent. This chapter discusses the performances obtained in a single direct ethanol fuel cell (DEFC) using various Pt-based anode nanomaterials for oxidizing ethanol in acidic environment. It shows the recent progress in catalyst preparation, particularly the thermal decomposition and microwave heating methods. The activity of the electrocatalysts is discussed by examining their capability of converting ethanol to different reaction products. Great attention is paid to the identification of the reaction intermediate species and those in the bulk by using in situ infrared spectroscopy and other analytical techniques. Performance in a DEFC is a direct measurement between the anodic and cathodic potentials which depends on the ethanol oxidation occurring at low overpotentials and also on the oxygen reduction reaction (ORR) at higher ones. Determination of the kinetic parameters for the ORR and quantitative detection of hydrogen peroxide formation with rotating ring disk electrode technique are herein proposed as an overview of the electrode kinetics.

The kinetics of oxygen reduction reaction (ORR) on carbon supported Pt, Pt-Sn, Pt-Ni, and Pt-Sn-Ni catalysts, prepared by Bonnemann method, is investigated by using rotating ring disk electrode (RRDE) measurements in 0.1 M HClO4 solution. Physical characterization of the catalysts is performed by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS) techniques. The cyclic voltammetry (CV) measurement has been used to estimate the electrochemical active surface (EAS) area of the catalyst. The enhancement in the ORR activity of the Pt/C observed in the presence of either Sn or Ni, leading to more than 99% of water formation. However, Pt-Sn/C catalyst shows a higher ORR performance as compared to the Pt-Ni/C and Pt-Sn-Ni/C catalysts. This can be explained by the presence of optimal amount of Sn oxides as an unalloyed state in Pt-Sn/C, which plays a beneficial role for both adsorption oxygen and water. On the other hand, it is found that the alloying Pt with Ni seems to be less favourable for the ORR performance. (C) 2014 Elsevier Ltd. All rights reserved.

Multiwalled carbon nanotubes (MWCNTs) were functionalized with acid treatment and thereafter gold-copper nanoparticles were electrodeposited on the MWCNTs by applying several repetitive scans, thus forming a Cu-Au-MWCNT/GCE interface. The electrochemical reduction of oxygen was studied on this modified electrode in 0.1 M NaOH solution. The electrocatalytic activity on the Cu-Au-MWCNT/GCE showed a tendency towards the O-2 reduction. The peak potential of O-2 reduction on the Cu-Au-MWCNT/GCE shifted ca. 70 mV higher positive potentials as compared to that of a polished glassy carbon electrode. A significant current enhancement was obtained on the Cu-Au-MWCNT/GCE compared to that of bare GCE, MWCNT/GCE, Cu-MWCNT/GCE and Au-MWCNT/GCE. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed in order to investigate the surface morphology and elemental composition of the modified electrode, respectively. (C) 2011 Elsevier B.V. All rights reserved.