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Two new boundary correction techniques are proposed in order to mitigate the order reduction phenomenon associated to the numerical solution of initial boundary value problems for parabolic Partial Differential Equations in arbitrary spatial dimensions with time dependent Dirichlet boundary conditions. The new techniques are based on the idea of discretizing the PDE problem at the boundary points as similarly as possible as for the interior points of the domain. These new techniques are considered for the time integration with W-methods based on Approximate Matrix Factorization. By suitably modifying the internal stages of the methods on the boundary points, it is illustrated by numerical testing with time dependent boundary conditions that the new boundary correction techniques are able to keep the same accuracy and order of convergence that the method reaches in the case of homogeneous boundary conditions.

Membrane processes, whose low energy and operating costs make them competitive for gas separation compared to other conventional methods such as pressure swing adsorption, cryogenic distillation or amine absorption, allows high-purity gas to be obtained in a sustainable and continuous manner. Similarly, resin-derived carbon membranes with molecular sieving properties have improved the selectivity and permeability of conventional dense membranes, as well as having high chemical and thermal resistance. In this review, an overview of the preparation of phenolic resin-based carbon membranes and their performance in gas separation is presented, particularly in processes involving permanent gases such as hydrogen purification, air separation, natural gas/biogas sweetening or carbon dioxide capture. Moreover, bioresources already proven for the synthesis of “greener” phenolic resins and the separation performance of some carbon membranes based on bioresource-derived phenolic resins are also reported and discussed in this work. This review will summarise the development and gas separation performance of phenolic resin-based carbon membranes and will provide a clear future direction in “green” carbon membranes research.

Lithium battery materials can be advantageously used for the selective sequestration of lithium ions from natural resources, which contain other cations in high excess. However, for practical applications, this new approach for lithium production requires the battery host materials to be stable over many cycles while retaining the high lithium selectivity. Here, a nearly symmetrical cell design was employed to show that LiFePO4 shows good capacity retention with cycling in artificial lithium brines representative of brines from Chile, Bolivia and Argentina. A quantitative correlation was identified between brine viscosity and capacity degradation, and for the first time it was demonstrated that the dilution of viscous brines with water significantly enhanced capacity retention and rate capability. The electrochemical and X-ray diffraction characterisation of the cycled electrodes also showed that the high lithium selectivity was preserved with cycling. Raman spectra of the cycled electrodes showed no signs of degradation of the carbon coating of LiFePO4 , while scanning electron microscopy images showed signs of particle cracking, thus pointing towards interfacial reactions as the cause of capacity degradation.

6 figures, 4 tables.-- Supplementary information available.-- © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/, Porous carbon materials are promising electrocatalysts for the oxygen reduction reaction (ORR). Their active sites, involving porosity and surface chemistry, are different from those of metal-doped carbons. The latter have been widely studied and are adapted to today's popular electrochemical devices, the rotating disk electrode being the most useful preliminary tool to evaluate their activity in ORR. However, porous carbon materials have been less explored, and experimental parameters need to be adjusted to achieve the best ORR performance. Therefore, in this study, the optimization of different key factors was investigated to evaluate their effect on the ORR performance of porous carbon electrocatalysts in alkaline medium. The parameters considered were: (i) the relevance of using RRDE or Koutecky-Levich equations for estimating the number of electrons transferred; (ii) the amount of ionomer (Nafion®); (iii) the carbon loading on the electrode; (iv) the carbon grinding method; and (v) the selection of the upper potential of ORR experiments. We conclude that an optimization of the experimental conditions should be done for each material studied, and we give important benchmarks for the appropriate evaluation of the catalytic activity in ORR of carbon-based catalysts., This study was partly supported by the French PIA project “Lorraine Université d’Excellence”, reference ANR-15-IDEX-04-LUE and the TALiSMAN project funded by ERDF (2019-000214). SPR acknowledges MCIN/AEI/10.13039/501100011033 for her Juan de la Cierva Incorporación research contract (IJC2019-041874-I).

11 figures.-- Supplementary information available., Bifunctional oxygen electrocatalysts are essential in the development of low-temperature unitized regenerative fuel cells (URFCs), as a promising alternative for storing energy via hydrogen. TiO2, as a semiconductor material, is commonly not established as an active electrocatalyst for oxygen reduction and oxygen evolution due to its poor electrical conductivity and low reactivity. Here, we demonstrated that composites composed of TiO2 and N-doped graphene can be active in oxygen reduction and evolution reactions in an alkaline environment. Combination factors such anatase/rutile interaction, N-doping graphene, and the presence of Ti3+/Ti–N species raise the active sites and improve the electrochemical activity. Our results may afford an opportunity to develop a non-noble and promising electrocatalyst in energy storage technology., This research was funded by the Ministry of Science, Innovation and Universities and FEDER, grant number ENE2017-83976-C2-1-R

Direct ethanol fuel cells are a promising technology for clean energy production. The ethanol oxidation reaction (EOR) is surface sensitive and, hence, the study of single-crystal electrodes provides fundamental knowledge of the different activity of the metal crystal planes. However, for practical applications, metal nanoparticles dispersed on a porous support are generally used to enhance the efficiency and to reduce the catalyst cost. Although some research has been devoted to the development of shape-controlled nanoparticles, the finding of an efficient, cost-effective, and easily scaled-up catalytic system remains a challenge. Furthermore, the use of a suitable support with a well-defined nanoarchitecture is essential for the control of the catalyst reactivity. In this Review, a general overview of the performance of single-crystal electrodes and unsupported/supported shape-controlled nanoparticles for the EOR is presented, paying special attention to Pt surfaces. Finally, the major challenges and directions for future research are also discussed to guide the design of efficient shape-controlled catalysts for the EOR.

11 figures, 4 tables.-- Información suplementaria., Biomass from agricultural by-products is gaining increasing interest as cheap and abundant precursor in the development of active materials for efficient and environmentally friendly devices like fuel cells. Herein, we investigated iron and nitrogen co-doped nanoporous carbons derived from aronia, peach stones and coal tar pitch/furfural as electrocatalysts for the electrochemical oxygen reduction reaction (ORR) in alkaline media. Urea was used as nitrogen precursor and two annealing steps with intermediate acid leaching served to activate the catalysts. Within the series, the peach stone-derived catalyst exhibited a catalytic activity for the ORR close to the benchmark Pt/C, with a 60 mV dec−1 Tafel slope upon the incorporation of 0.57 wt% Fe and proper combination of N-Fe species (20%) with pyridinic/pyridonic moieties (49%). We concluded that the microporosity and a certain content of meso/macro-pores of the activated carbon, together with the creation of graphitic domains result in a high relative amount of Fe-N4 and nitrogen functionalities, which determine the electrocatalytic performance., The authors gratefully acknowledge financial support given by the project BLOW UP "Balkans Waste to Products: transfer of NoI model to Balkan area: de-siloing new waste-derived raw materials and developing new applications" from EIT RAW MATERIAL EIT16320, Horizon 2020. D. Sebastián and C. Alegre acknowledge the Ministry of Economy, Industry and Competitiveness for their Ramón y Cajal (RyC-2016-20944) and Juan de la Cierva Incorporación (IJCI-2017-32354) research contracts, respectively.

8 figures, 1 table.-- Supplementary information available.-- © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Biochar derived from the pyrolysis of pine tannin is a green and available by-product of oil manufacturing that presents interesting features after having been activated by KOH at 650 °C. Different weight ratios of KOH to biochar were used and the resulting activated carbons (ACs) presented highly developed specific surface areas of up to 2190 m2 g−1, well-connected porosity and high oxygen content, leading to enhanced electrochemical performance when used as electrochemical capacitor electrodes in a 1 M H2SO4 aqueous electrolyte. Galvanostatic charge/discharge experiments evidenced that the best material achieved a maximum electrode capacitance of up to 232 F g−1 (at 0.5 A g−1) with a capacitance retention of 70% at 10 A g−1 using commercial mass loadings (i.e., approx. 10 mg cm−2). In addition, long cycling stability with a residual capacitance of 92 to 94% after 10,000 cycles at 5 A g−1 was achieved. These results prove that ACs derived from pine tannin biochars have great potential for their commercial use as electrochemical energy storage devices., This study was partly supported by the French PIA project “Lorraine Université d’Excellence”, reference ANR-15-IDEX-04-LUE and the TALiSMAN project funded by ERDF. O. Pinto thanks ANID - Subdirección de Capital Humano/Doctorado, # 2019/21190633. P.S. Poon and C. Segura thank ANID-PIA/APOYO CCTE AFB170007 project. J. Matos acknowledges the funds from the Chilean projects ANID-FONDEF ID19I10003; ANID-FONDECYT 1190591; and Millennium Science Initiative Program-NCN17-040. J. Matos also thanks the Technological Development UNIT (UDT) from the University of Concepción (Chile), for supplying the tannin-derived chars. The authors finally thank Philippe Gadonneix for his technical assistance in laboratory measurements at Université de Lorraine.

Splitting-based time integration approaches such as fractional steps, alternating direction implicit, operator splitting, and locally one-dimensional methods partition the system of interest into components and solve individual components implicitly in a cost-effective way. This work proposes a unified formulation of splitting time integration schemes in the framework of general-structure additive Runge-Kutta (GARK) methods. Specifically, we develop implicit-implicit (IMIM) GARK schemes, provide the order conditions and stability analysis for this class, and explain their application to partitioned systems of ordinary differential equations. We show that classical splitting methods belong to the IMIM GARK family, and therefore can be studied in this unified framework. New IMIM-GARK splitting methods are developed and tested using parabolic systems.

5 figures., Carbonaceous materials have always played an important role in history of electrochemical processes, from the fabrication of solid electrodes to the development of porous matrixes in the conversion and storage of energy and chemicals. This book chapter provides a general overview of emerging carbon nanostructures potentially used in electrochemistry. One-dimensional carbon nanofilaments, such as carbon nanotubes and carbon nanofibers, two-dimensional graphene, and three-dimensional materials, such as carbon gels and ordered mesoporous carbons, are reviewed. The chapter focuses on the physicochemical properties and synthesis methodologies of these carbon nanostructures together with their application to cutting-edge technologies for electrochemical energy conversion and storage, such as fuel cells, electrolyzers, supercapacitors, or batteries. The major challenges and directions for future research are also discussed to guide the design of efficient carbon-based electrodes and catalysts for electrochemical devices., Authors acknowledge financial support given by Spanish Ministry of Science, Innovation and University (MICINN) through project ENE2017-83976-C2-1-R (cofounded by FEDER). C. Alegre and D. Sebastián acknowledge also MICINN for their Juan de la Cierva (IJCI-2017-32354) and Ramón y Cajal (RyC-2016-20944) research contracts, respectively.

© 2020 by the authors., Ordered mesoporous carbons (OMCs) have been used as catalyst supports of Pd nanoparticles for the electrochemical reduction of CO2 in 0.1 M KHCO3. OMC with tunable porosity and morphology were obtained by the hard-template approach using synthesized SBA-15 templates. SBA-15 materials were prepared using a mass ratio of the silica precursor (TEOS) and the surfactant (P123) of 2 or 5. After removing silica particles by a purification treatment with NaOH-ethanol or HF, different OMCs were obtained, with a developed porosity (up to 1050 m2 g−1) and ordered 2D hexagonal mesostructure (p6 mm). An increase in the TEOS/P123 ratio as well as the treatment with HF resulted in a decrease in the structural ordering of the materials. Pd nanoparticles with an average size of around 3 nm were deposited on the OMC. However, larger nanoparticles were also observed, especially for the materials obtained using a mass ratio TEOS/P123 of 5. Despite these differences, electrochemical experiments showed that CO2 was successfully reduced to other species (mainly COad) for all Pd/OMC electrocatalysts. These reduced species were adsorbed on Pd active sites, inhibiting the hydrogen evolution reaction, The authors gratefully acknowledge the financial support given to the Fuel Conversion Group by the Aragón Government (T06).

Nanocarbon materials present sp2-carbon domains skilled for electrochemical energy conversion or storage applications. In this work, we investigate graphene oxide nanofibers (GONFs) as a recent interesting carbon material class. This material combines the filamentous morphology of the starting carbon nanofibers (CNFs) and the interlayer spacing of graphene oxide, and exhibits a domain arrangement accessible for fast transport of electrons and ions. Reduced GONFs (RGONFs) present the partial removal of basal functional groups, resulting in higher mesoporosity, turbostratic stacking, and surface chemistry less restrictive for transport phenomena. Besides, the filament morphology minimizes the severe layer restacking shown in the reduction of conventional graphene oxide sheets. The influence of the reduction temperature (140&ndash, 220 &deg, C) on the electrochemical behaviour in aqueous 0.5 M H2SO4 of RGONFs is reported. RGONFs present an improved capacitance up to 16 times higher than GONFs, ascribed to the unique structure of RGONFs containing accessible turbostratic domains and restored electronic conductivity. Hydrothermal reduction at 140 &deg, C results in the highest capacitance as evidenced by cyclic voltammetry and electrochemical impedance spectroscopy measurements (up to 137 F&middot, g&minus, 1). Higher temperatures lead to the removal of sulphur groups and slightly thicker graphite domains, and consequently a decrease of the capacitance.

8 Figuras.- 4 Tablas, Pd and PdM (M = Fe or Co) nanostructured electrocatalysts were synthesized by the impregnation method and supported on carbon black Vulcan XC-72R for the formic acid oxidation reaction, FAOR, in acid medium. Nitrates or chlorides were used as Fe and Co precursors to study the counter ion role on the physicochemical features and electrochemical performance of the electrocatalysts. TEM analysis showed that PdM was deposited on the carbon material with a particle size around 2–3 nm. From XRD, peaks associated with the fcc palladium planes were observed along with evidence of PdM alloy formation, particularly when the nitrate salts were used as metal precursors. Furthermore, XPS analyses indicated that nitrates promote the metal oxide formation to a greater extent than chlorides, mainly for Pd. PdCo electrocatalyst obtained from nitrates exhibited the highest performance for FAOR with a steady state current density of 451 and 313 μA cm−2 at 200 and 400 mV respectively, which is in both cases, 3 times larger than that developed for a commercial Pd/C catalyst., LJM is grateful to CONACYT for the grant awarded for this research, as well as to the UAM-A and the ICB for the support provided. MGMY, MRR, MPP and AEM thank the SNI for the distinction of their membership and the stipend provided. MGMY is indebted to L'oreál-UNESCO-CONACyT-AMC for the grant Women in Science 2016. MJL and SPR gratefully acknowledge financial support given by Spanish MINECO (ENE2014-52158-C2-1-R).

2 Figuras. 1 Tabla., Differential electrochemical mass spectrometry (DEMS) was used to establish the difference in surface acidity in sulfuric acid solution between commercially available carbon black (Vulcan) and Vulcan which had been chemically modified with concentrated nitric acid (VulcanO). The mass signal for the m/z = 2 associated with H2 formation was observed to be influenced by functional groups at the carbon surfaces. Analysis of the mass spectra with the help of the Nernst equation allowed us to quantitatively find the difference in surface pH between the two carbon-based materials in acid media. The elevated concentration of functional groups at the VulcanO surface results in a decrease in the local acidity of the surface under these conditions (0.5 M H2SO4), and consequently the hydrogen evolution reaction (HER) is delayed., The authors gratefully acknowledge financial support given by Spanish MINECO (ENE2014-52158-C2-2-R and 1-R). GG acknowledges the Viera y Clavijo program (ACIISI & ULL) for financial support.

The present work considers the numerical solution of differential equations that are obtained by space discretization (method of lines) of parabolic evolution equations. Main emphasis is put on the presence of mixed derivatives in the elliptic operator. An extension of the alternating-direction-implicit (ADI) approach to this situation is presented. Our stability analysis is based on a scalar test equation that is relevant to the considered class of problems. The novel treatment of mixed derivatives is implemented in third-order W-methods. Numerical experiments and comparisons with standard methods show the efficiency of the new approach. An extension of our treatment of mixed derivatives to 3D and higher dimensional problems is outlined at the end of the article.

A technique to stabilize standard explicit Runge-Kutta methods by associating them with W-methods is proposed. The main point to get the associated family of W-methods for a given explicit Runge-Kutta method is to require commutativity for the coefficient matrices of the W-method in order to reduce the large number of order conditions that must be satisfied to get a pre-fixed order.Based on this idea, for any given explicit four-stage Runge-Kutta method of order four, two uniparametric families of third order W-methods are obtained. The free parameter can be used to increase the stability regions of the W-methods in case of d ź 1 splittings in the derivative function when a von Neumann stability analysis is carried out. Additionally, it is possible to find L-stable ROW-methods (W-methods with exact Jacobian) for some specific values of the free parameter.The new family of W-methods is also equipped with the splitting provided by the Approximate Matrix Factorization (AMF), which converts a W-method into some kind of ADI-method (Alternating Direction Implicit method). The AMF-W-methods so obtained are mainly used to solve large time-dependent PDE systems (in 2D or 3D spatial variables) discretized in space by using finite differences or finite volumes. Some stability properties of the family of AMF-W-methods are also supplied for the case of d -splittings ( d ź 1 ).Numerical experiments in connection with the proposed AMF-W-methods on a few interesting stiff problems coming from PDE discretizations illustrate the stabilization approach in comparison with some relevant methods in the literature.

10 figuras, 2 tablas. Datos asociados suplementarios están disponibles en la versión en línea del editor., In the present work, a wide variety of electrocatalysts, involving different metals, synthesis routes and oxidation states, have been prepared and the response towards the CO2 reduction on carbon-supported established. In particular, catalysts based on non-noble metals (Cu, Co, Fe and Ni) supported on carbon black (Vulcan XC-72R) were tested in the electrochemical reduction of CO2. Amorphous oxides of magnetite/maghemite and crystalline CuO and Cu2O oxides obtained by different methodologies were also studied. Previously, the efficiency of the catalysts for the hydrogen formation was evaluated in 0.1 M NaHCO3 since it takes place as a competitive reaction during CO2 reduction in aqueous electrolytes. By comparison of the voltammograms in the absence and presence of CO2, an inhibition of the hydrogen evolution was showed for all (metal and oxide-based) catalysts due to the adsorption of species from CO2 reduction (CO2,red). Interestingly, the CO2,red formation on Co and Fe-surfaces operating under these conditions has not been stated before. A strong current decrease, and consequently, a higher adsorbate amount, was observed on copper-oxides (75–85%) vs. the metal catalyst (45%)., The authors gratefully acknowledge financial support given by Spanish MINECO (CTQ2011-28913-C02-01 and 02) and Gobierno de Aragon (T07). S. Pérez-Rodríguez acknowledges also Gobierno de Aragón for the DGA grant. Authors thank Advanced Microscopy Laboratory at Instituto de Nanociencia de Aragón and Electronic Microscopic Service at Universidad de Zaragoza for offering access to STEM and TEM facilities, respectively.

6 Figures, 3 Tables., Ordered mesoporous carbon materials (OMC) present a developed porosity, making them promising candidates for electrochemical energy-conversion devices. However, OMC undergo electrochemical oxidation causing the degradation of electrodes and exhibit low electrical conductivities due to their amorphous carbon structure. To address these issues, OMC can be graphitized by thermal treatments. Herein, the electrooxidation behavior of different OMC, prior and upon graphitization, is studied by chronoamperometry in a highly acidic electrolyte (0.5 M H2SO4). Several oxidation potentials and temperatures are used to gain insights on the electrooxidation mechanism. Potential holding tests evidenced differences in the oxidation behavior of as-synthesized and graphitized materials. Graphitization results in a strong decrease of the oxidation charge from 93 to 7% depending on the carbon properties, applied potential and temperature. Temperature plays an important role on carbon degradation of not-graphitized OMC, with a strong electrochemical capacitance loss (90%–93%) after tests at 40 °C and 60 °C. Conversely, graphitized materials present a raise of the capacitance by the creation of oxygen-functionalities as confirmed by post-mortem X-ray photoelectron spectra analysis. Additionally, graphitized materials show an increase of the apparent activation energy associated to electrooxidation (7 times higher), indicative of their improved resistance., The authors gratefully acknowledge financial support given by Spanish Ministry of Science, Innovation and Universities MICINN (ENE2017-83976-C2-1-R) and to the Aragón Government to the Fuel Conversion Group (T06_17R). DS acknowledges also MICINN for his Ramón y Cajal contract (RyC-2016-20944).

5 figures, 2 tables., In the present work, Pd and PdFe nanoparticles supported on CNT with and without functionalization (CNT and CNTox) were used for Formic Acid Oxidation Reaction (FAOR) in acid media. Electrocatalysts were synthesized by the borohydride reduction method with 20 wt.% metal loading. The CNTs were synthesized by the methane catalytic decomposition, and subjected to an oxidation treatment with nitric acid, named as CNTox. Themorphology, composition and structural properties were studied by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) and X-Ray Diffraction (XRD). The FAOR was evaluated in acid media in a conventional three-electrode cell by means of cyclic voltammetry and chronoamperometry. From the steady state current density, it was found that Pd and PdFe supported at CNTox allowed improving the catalytic activity in comparison with the nonoxidized support., The authors thank the organizers of the meeting. LJM is grateful to CONACYT for the scholarship granted for the completion of the PhD studies and the ECS for the support given to attend the meeting. MGMOY, MARR, MEPP and EMAE thank the SNI for the distinction of their membership and the stipend received.

A facile and straightforward methodology for the preparation of monometallic (copper and palladium) and bimetallic nanocatalysts (NiCu and PdCu) stabilized by a N-heterocyclic carbene ligand is reported. Both colloidal and supported nanoparticles (NPs) on carbon nanotubes (CNTs) were prepared in a one-pot synthesis with outstanding control on their size, morphology and composition. These catalysts were evaluated in the selective hydrogenation of alkynes and alkynols. PdCu/CNTs revealed an efficient catalytic system providing high selectivity in the hydrogenation of terminal and internal alkynes. Moreover, this catalyst was tested in the semi-hydrogenation of acetylene in industrially relevant acetylene/ethylene-rich model gas feeds and showed excellent stability even after 40 h of reaction.

The combination of Approximate Matrix Factorization (AMF), W-methods and iterative refinement in the solution of linear systems leads to the definition of AMFR-W-methods. This method class provides stable and accurate time integrators for parabolic PDEs with mixed derivatives discretized in space by means of Finite Differences (or Finite Volumes) in an arbitrary number of spatial dimensions. When the coefficients of the PDE actually depend on the spatial variables, the approximation of the pure diffusion coefficients by its respective maximum value produces simplified AMFR-W-methods requiring only a reduced number of LU decompositions of banded matrices with small bandwidth. The new class of methods is shown to be unconditionally stable regardless of the spatial dimension on a linear test problem relevant for homogeneous or periodic boundary conditions. Furthermore, high orders of convergence in PDE sense are observed when homogeneous boundary conditions are assumed. For general Robin boundary conditions, a simple algorithm is provided to convert a PDE problem into one where such conditions are homogeneous. Numerical experiments with the new simplified AMFR-W-methods on a linear parabolic problem with variable coefficients and the Heston problem from financial option pricing are presented.

This contribution reports a novel “Magnetic Paper – Based ELISA” using core–shell magnetite@polydopamine nanoparticles supported on a Whatman paper-like new solid immunoassay platform specifically for IgM-dengue antibodies recognition as the proof-of-concept target for antibodies isotype IgM detection. Affordable procedures to deposit magnetite nanoparticles on cellulose paper sheets (Whatman type-1 and ss903) and to conjugate such nanoparticles with anti human-IgM antibodies using polydopamine as linker are reported. Structural features, magnetic behavior, coating homogeneity, and the nanoparticles/linked antibodies ratio were determined. Additionally, “Magnetic Paper – Based ELISA” for IgM-dengue antibodies detection provides a system with improved analytical response (two orders more sensitive with a 700 times lower limit of detection (LOD) than traditional ELISA or using magnetic beads without depositing), appropriate accuracy for real sample detection, low cost, easy manufacturing, and effortless and easy handling.

An electrochemical reactor, with a membrane-electrode-assembly technology, has been developed for the electrochemical reduction of CO2 in gas phase. The reactor was carefully designed to prevent the strong corrosion by the high overpotentials required for addressing CO2 reduction. In addition, electrodes based on Fe and Pt supported on Vulcan XC-72R (the commercial carbon black often used for electrochemical applications) were used as cathode. These electrodes favor the CO2 confinement in the nanoporous structure of the carbon support, resulting in higher pressures at the electrocatalytic surface, and consequently, enhancing the performance. The behavior of the electrodes for CO2 reduction was studied in both acid media (0.5 M H2SO4) and in gas phase using the designed reactor in order to establish a correlation of the results. A higher current density was developed for the Pt-based electrode due to a significant formation of H2 by the water reduction, whereas the CO2 conversion could be favored on the Fe electrode, in both acid media and gas phase.

Palladium–nickel catalysts supported on carbon blacks containing similar metal contents (25 wt. %) and Pd:Ni atomic ratios (1:1 and 1:2) were synthesized. Carbon supports were chemically treated to create different oxygen and nitrogen groups on surface. X ray patterns revealed a weak alloying between Pd and Ni, whereas crystallite sizes were between 2.1 and 3.2 nm, being consistent with the values detected by transmission electron microscopy (TEM). CO strippings demonstrated a higher poisoning tolerance of the Pd–Ni catalysts than that observed for a Pd catalyst supported on Vulcan carbon black. The methanol oxidation on Pd–Ni catalysts suggested that presence of Ni increase the activity of the materials, considering that Pd/CB exhibited the lowest methanol oxidation current densities. Nevertheless, no effects associated to the presence of surface functional groups on carbon supports were observed in the performance of this reaction.

In this paper new three-stage W-methods for the time integration of semi-discretized advection diffusion reaction Partial Differential Equations (PDEs) are provided. In particular, two three-parametric families of W-methods of order three are obtained under a realistic assumption regarding the commutator of the exact Jacobian and the approximation of the Jacobian which defines the corresponding W-method. Specific methods are selected by minimizing error coefficients, enlarging stability regions or increasing monotonicity factors, and embedded methods of order two for an adaptive time integration are derived by further assuming first order approximations to the Jacobian. The relevance of the newly proposed methods in connection with the Approximate Matrix Factorization technique is discussed and numerical illustration on practical PDE problems revealing that the new methods are good competitors over existing integrators in the literature is provided.

8 Figures, 3 Tables.-- Supplementary material.-- © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, We report the electrochemical properties of a novel nanocarbon material obtained by chemical oxidation and ultrasound-assisted exfoliation of fishbone carbon nanofibers (CNF). The resulting material maintains its tubular morphology and presents a characteristic interlayer spacing of graphene oxide (above 0.75 nm). Thus, this is called graphene oxide nanofibers (GONF). The new rearrangement of the accessible sp2-carbon domains makes the GONF a potential alternative for electrochemical energy conversion/storage applications, showing a developed porosity and tuneable surface chemistry. The influence of the oxidation degree of GONF on its electrochemical behaviour in 0.5 M H2SO4 is reported. Cyclic voltammetry and electrochemical impedance spectroscopy evidenced a significant increase of the capacitance for GONF, being 4–27 times higher than that obtained for pristine CNF. An optimum in the capacitance (49.2 F g−1) was obtained using an oxidation ratio (OR = KMnO4/Sample) of 6 and 60 min of sonication. The latter is ascribed to the unique structure of this material containing both graphitic and graphene oxide domains. Higher OR or longer sonication times led to a partial loss of graphitic domains and higher contribution of micropores, which worsen the fast ion/electrolyte transport. Additionally, the optimized material exhibited an improved activity for the hydrogen evolution reaction., This work was funded by FEDER, the Spanish Ministry of Science, Innovation and Universities MICINN (ENE2017-83976-C2-1-R & ENE2017-83854-R) and by the Aragón Government to the Fuel Conversion Group (T06_17R). DS thanks MICINN for his Ramon y Cajal research contract (RyC-2016-20944).

6 Figuras.- 4 Tablas.- Datos suplementarios disponibles en línea en la página web del editor., Ordered mesoporous carbon materials (OMC), obtained by the template carbonization pathway from silica templates (sacrificial method), exhibit promising features for many applications mainly due to their large surface area. Graphitization is a common approach to improve the electrical conductivity and degradation resistance. We have investigated the graphitization of two different OMC at 1500 °C and the electrochemical oxidation by potential holding at 1.4 V vs. reversible hydrogen electrode (RHE) in acidic electrolyte. Graphitization conducts to a significant reduction of the electrooxidation associated charge, between 50 and 90% depending on the carbon properties, together with a decrease of surface area of 35–48%. The materials still exhibit a large electrochemical surface area, according to electrochemical impedance and cyclic voltammetry experiments. Upon electrooxidation, the relative amount of oxygen increases according to a comparative analysis of X-ray photoelectron spectroscopy test of the electrodes before and after potential holding. The results are of interest to define strategies towards the amelioration of carbon degradation by electrooxidation in electrochemical devices., The authors gratefully acknowledge financial support given by Spanish Ministry of Science, Innovation and Universities MICINN (ENE2017-83976-C2-1-R) and to the Aragón Government to the Fuel Conversion Group (T06_17R). DS acknowledges also MICINN for his Ramón y Cajal contract (RyC-2016-20944).

The low oxidation kinetics of alcohols and the need for expensive platinum group metals are still some of the main drawbacks for the commercialization of energy efficient direct alcohol fuel cells. In this work, we investigate the influence of nitrogen doping of ordered mesoporous carbon (CMK) as support on the electrochemical activity of PtRu nanoparticles. Nitrogen doping procedures involve the utilization of pyrrole as both nitrogen and carbon precursor by means of a templating method using mesoporous silica. This method allows obtaining carbon supports with up to 14 wt. % nitrogen, with an effective introduction of pyridinic, pyrrolic and quaternary nitrogen. PtRu nanoparticles were deposited by sodium formate reduction method. The presence of nitrogen mainly influences the Pt:Ru atomic ratio at the near surface, passing from 50:50 on the bare (un-doped) CMK to 70:30 for the N-doped CMK catalyst. The electroactivity towards the methanol oxidation reaction (MOR) was evaluated in acid and alkaline electrolytes. The presence of nitrogen in the support favors a faster oxidation of methanol due to the enrichment of Pt at the near surface together with an increase of the intrinsic activity of PtRu nanoparticles., The work has received financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through projects ENE2014-52158-C2-1-R and 2-R (co-founded by FEDER) and from Aragon Government to the Fuel Conversion Group. M.J. Nieto-Monge has also received funding for her Ph.D. grant from MINECO. D. Sebastián acknowledges also MINECO for his Ramón y Cajal research contract (RYC-2016-20944).

The effect of chemical surface oxidation of the carbon black Vulcan XC-72R on the capacitance, tolerance to corrosion and electrochemical activity toward the hydrogen evolution reaction (HER) has been studied in 0.1 M NaHCO3. Acid treatments with HNO3 or a HNO3H2SO4 mixture resulted in a progressive introduction of oxygen-containing groups which led to a strong increase of the capacitance and a higher tendency to carbon corrosion. In contrast, an inhibition of the hydrogen evolution current (at potentials more negative than −1.0 V) was observed for oxidized samples in comparison to the un-treated material. HER was also tested in the presence of dissolved CO2 to study the influence of the surface chemistry on the CO2 electroreduction. An inhibition of the H2 evolution current was evidenced in the CO2 saturated electrolyte due to the adsorption of species from CO2 reduction. A strong hydrogen current decrease (65–78%), and thus a higher tendency to adsorb (CO2)red species, was obtained on the original Vulcan and the HNO3-treated samples, in comparison to the carbon oxidized with HNO3H2SO4 (15%), which could be related to the highest content of basic groups of the last carbon., The authors gratefully acknowledge financial support given by Spanish MINECO (ENE2014-52158-C2-1-R and 2-R). S. Pérez-Rodríguez thanks Gobierno de Aragón for the DGA grant. Furthermore, the authors wish to acknowledge Dra. Ana Beatriz García for the TPD measurements.

The convergence of a family of AMF-Runge-Kutta methods (in short AMF-RK) for the time integration of evolutionary Partial Differential Equations (PDEs) of Advection Diffusion Reaction type semi-discretized in space is considered. The methods are based on very few inexact Newton Iterations applied to Implicit Runge-Kutta formulas by combining the use of a natural splitting for the underlying Jacobians and the Approximate Matrix Factorization (AMF) technique. This approach allows a very cheap implementation of the Runge-Kutta formula under consideration. Particular AMF-RK methods based on Radau IIA formulas are considered. These methods have given very competitive results when compared with important formulas in the literature for multidimensional systems of non-linear parabolic PDE problems. Uniform bounds for the global time-space errors on semi-linear PDEs when simultaneously the time step-size and the spatial grid resolution tend to zero are derived. Numerical illustrations supporting the theory are presented.

This paper summarizes the main results obtained by the Fuel Combustion Group in three applications: (1) carbon-based catalysts for the selective catalytic reduction (SCR) process of NOx, (2) Pt and Pt–Ru catalysts for direct alcohol fuel cells, (3) carbon-supported catalysts for the electroreduction of CO2. Concerning the first aspect, low-cost catalysts able to work at lower temperatures have been prepared and compared with commercial catalysts; for the second one, new catalysts for methanol and ethanol electrochemical oxidation exhibiting current densities that are double those of the commercial ones have been developed; as regards the third one, carbon-supported catalysts for the electroreduction of CO2 based on Fe and Pd were synthesized and tested. Formic acid was obtained as the main product on all Fe/C electrodes.

6 Figuras. 4 Tablas.-- Datos suplementarios sobre el artículo disponibles en la versión en línea del editor.-- © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, This work reports a study of the electrical conductivity under compression of nanostructured carbon powders with different physicochemical properties (texture, chemical-surface and morphology): a commercial carbon black (Vulcan XC-72R) and synthesized ordered mesoporous carbon (OMC), carbon nanocoils (CNC) and carbon nanofibers (CNF). The electrical conductivity was determined from the sample resistance under compaction (from 0.5 to 140 MPa) using the four-probe technique. A comparison of intrinsic and grain electrical conductivities (calculated according to the percolation theory and the general effective media approximation) was performed. Additionally, samples were subjected to chemical oxidation or graphitization treatments to evaluate the effect of oxygen content and structural properties on the electrical conductivity. In spite of the physicochemical differences of carbon materials, an exponential decrease of the electrical conductivity with the oxygen amount was stated. Finally, thermal treatment of OMC at 1500 °C led to a surprising increase in its conductivity due to the graphitization of the amorphous carbon structure of the original material and the oxygen removal., The authors gratefully acknowledge financial support given by Spanish MINECO (ENE2014-52158-C2-1-R). Furthermore, the authors wish to thank Dra. Ana Beatriz García (INCAR-CSIC) for the graphitization treatment of OMC and the TPD measurements.

RESUMEN Fundamento. Un adecuado control de la glucemia y de los factores de riesgo cardiovascular (FRCV) es fundamental en los pacientes con diabetes mellitus tipo 2 (DM2). Sin embargo, diversos estudios han demostrado que el porcentaje de pacientes que alcanzan dichos objetivos es escaso. Hemos evaluado el grado de control de FRCV en pacientes DM2 que acuden con regularidad a una consulta monográfica de diabetes. Pacientes y métodos. Se han estudiado los pacientes con DM2 que acudían a revisión al departamento de Endocrinología de la Clínica Universidad de Navarra con un seguimiento mínimo de un año. Se presentan las características clínicas, complicaciones crónicas y tratamiento médico, así como la clasificación en grupos según el cumplimiento de los objetivos de hemoglobina glicada (HbA1c), perfil lipídico (LDL-colesterol) y presión arterial (PA) individualizados según comorbilidades y años de evolución de la DM2. Resultados. Se han analizado 137 pacientes (75% hombres) con DM2, 67 años de edad media y 12,7 años de evolución. Durante el seguimiento, se encontraron dentro del rango objetivo individualizado de HbA1c el 83,9% de los pacientes, el 67,2% en cuanto a LDL-colesterol y el 76,6% considerando PA. Además, el 68% presentaron las tres variables principales dentro del objetivo. Conclusiones. En nuestra población de DM2 la consecución de objetivos de HbA1c, LDL-colesterol y PA se alcanza en una importante proporción de pacientes (67-91%). Posiblemente la intensa e individualizada atención ofrecida a través de una unidad de diabetes especializada pueda explicar estos resultados. ABSTRACT Background. Achieving an adequate control of glycaemic and cardiovascular risk factors (CVRFs) is essential in patients with type 2 diabetes mellitus (T2DM). However, several studies have shown that the percentage of patients achieving these goals is scarce. We evaluated the degree of control of CVRFs target goals in T2DM patients who regularly attend a specialized diabetic clinic. Methods. We studied T2DM patients who attended the specialized Diabetic Unit at the Department of Endocrinology of Clínica Universidad de Navarra with a minimum follow-up of one year. Clinical characteristics, chronic complications and treatments were collected and patients were classified into groups according to the fulfilment of target glycated haemoglobin (HbA1c), LDL cholesterol and blood pressure (BP) levels, predefined according to the presence of different comorbidities and the duration of T2DM. Results. We analysed 137 patients (75% men) with T2DM, with an average age of 67 years and a 12.7 year duration of diabetes. During follow-up, 83.9% of the patients were within the individualized HbA1c target, 76.6% considering BP and 67.2% in terms of LDL-cholesterol. In addition, 68% had concomitantly the three main variables within the target. Conclusions. In our population of T2DM, HbA1c, LDL cholesterol and BP targets were achieved in a substantial proportion of patients (67-91%). Perhaps the intense and individualized care offered through a specialized diabetes unit may explain these results.

9 Figuras. 4 Tablas. Datos suplementarios pueden encontrarse en la versión en línea del editor., This work reports a study of the electrocatalytic properties and stability of nanostructured carbon electrodes by on-line differential electrochemical mass spectrometry (DEMS). A wide electrochemical characterization in 0.1 M NaHCO3 involving anodic (carbon corrosion and oxygen evolution reaction, OER) and cathodic (CO2 reduction and hydrogen evolution reaction, HER) key reactions in energy-conversion devices was performed. DEMS studies showed that the faradaic current from 1.3 to 1.6 V vs. RHE of carbons was only associated to CO2 formation by corrosion and not to OER, the stability being improved by the graphitic character of carbon. H2 evolution was also enhanced with graphitic carbon nanofilaments, even though metal traces might positively influence their catalytic activity. By comparison of the faradaic currents and the H2 formation signals, in the absence and presence of CO2, a high inhibition of the HER was established for all carbon electrodes due to the species adsorption from CO2 reduction., The authors gratefully acknowledge financial support given by Spanish MINECO (CTQ2011‐28913‐C02‐01 and 02). S. Pérez-Rodríguez acknowledges Gobierno de Aragón for the DGA grant.

The numerical integration of PDEs of Advection-Diffusion-Reaction type in several spatial variables in the MoL framework is considered. The spatial discretization is based on Finite Differences and the time integration is carried out by using splitting techniques applied to Rosenbrock-type methods. The focus here is to provide a way of making some refinements to the usual Approximate Matrix Factorization (AMF) when it is applied to some well-known Rosenbrock-type methods. The proposed AMF-refinements provide new methods in a natural way and some of these methods belong to the class of the W-methods. Interesting stability properties of the resulting methods are proved and a few numerical experiments on some important non-linear PDE problems with applications in Physics are carried out.

For the efficient solution of large stiff systems resulting from semidiscretization of multi-dimensional partial differential equations two methods using approximate matrix factorizations (AMF) are discussed. In extensive numerical tests of Reaction Diffusion type implemented in Matlab they are compared with integration methods using Krylov techniques for solving the linear systems or to approximate exponential matrices times a vector. The results show that for low and medium accuracy requirements AMF methods are superior. For stringent tolerances peer methods with Krylov are more efficient.

12 páginas.- 5 figuras.- 4 tablas.- Published: 21 August 2013, Different advanced nanostructured carbon materials, such as carbon nanocoils, carbon nanofibers, graphitized ordered mesoporous carbons and carbon xerogels, presenting interesting features such as high electrical conductivity and extensively developed porous structure were synthesized and used as supports in the preparation of electrocatalysts for direct methanol fuel cells (DMFCs). The main advantage of these supports is that their physical properties and surface chemistry can be tailored to adapt the carbonaceous material to the catalytic requirements. Moreover, all of them present a highly mesoporous structure, diminishing diffusion problems, and both graphitic character and surface area can be conveniently modified. In the present work, the influence of the particular features of each material on the catalytic activity and stability was analyzed. Results have been compared with those obtained for commercial catalysts supported on Vulcan XC-72R, Pt/C and PtRu/C (ETEK). Both a highly ordered graphitic and mesopore-enriched structure of these advanced nanostructured materials resulted in an improved electrochemical performance in comparison to the commercial catalysts assayed, both towards CO and alcohol oxidation., The authors want to thank the Spanish Ministry of Economy and Competitiveness (Secretaría de Estado de I+D+I, previously Spanish Ministry of Science and Innovation) and FEDER for financial support under the project CTQ2011-28913-C02-01 and 02. Verónica Celorrio acknowledges the financial support by CSIC/ESF for her JAE Grant. Sara Pérez Rodríguez acknowledges Gobierno de Aragon for her PhD grant. María Elena Gálvez is indebted as well to the Spanish Ministry of Economy and Competitiveness (Secretaria de Estado de I+D+i) for her “Ramón y Cajal” contract.

The numerical integration of time-dependent PDEs of Advection-Diffusion-Reaction type, for two and three spatial variables (in short, 2D and 3D problems) in the MoL framework is considered. The spatial discretization is made by using Finite Differences and the time integration is carried out by means of the L-stable, third-order formula known as the two stage Radau IIA method. The main point for the solution of the large-dimensional ODEs is not to solve for the stage values of the Radau method until convergence (because the convergence is very slow on the stiff components), but only giving a very few iterations and take as advancing solution the latter stage value computed. The iterations are carried out by using the Approximate Matrix Factorization (AMF) coupled to a Newton-type iteration (SNI) as indicated in Perez-Rodriguez et al. (2009) [10], which turns out in an acceptably cheap iteration. Some stability results for the whole process (AMF)-(SNI) and a local error estimate for an adaptive time-integration are also given. Numerical results on four standard PDEs are presented and some conclusions about our method and other well-known solvers are drawn.

This paper is concerned with the time integration of semi-discretized, multi-dimensional PDEs of advection-diffusion-reaction type. To cope with the stiffness of these ODEs, an implicit method has been selected, viz., the two-stage, third-order Radau IIA method. The main topic of this paper is the efficient solution of the resulting implicit relations. First, a modified Newton process has been transformed into an iteration process in which the 2 stages are decoupled and, moreover, can exploit the same LU-factorization of the iteration matrix. Next, we apply a so-called Approximate Matrix Factorization (AMF) technique to solve the linear systems in each Newton iteration. This AMF approach is very efficient since it reduces the ‘multi-dimensional’ system to a series of ‘one-dimensional’ systems. The total amount of linear algebra work involved is reduced enormously by this approach. The idea of applying AMF to two-dimensional problems is quite old and goes back to Peaceman and Rachford in the early fifties. The situation in three space dimensions is less favourable and will be analyzed here in more detail, both theoretically and experimentally. Furthermore, we analyze a variant in which the AMF-technique has been used to really solve (‘until convergence’) the underlying Radau IIA method so that we can rely on its excellent stability and accuracy characteristics. Finally, the method has been tested on several examples. Also, a comparison has been made with the existing codes VODPK and IMEXRKC, and the efficiency (CPU time versus accuracy) is shown to be at least competitive with the efficiency of these solvers.

We consider some important aspects about the implementation of high order implicit formulas (specially the Gauss methods) for solving second-order differential systems having high frequencies and small amplitudes superimposed. The choice of an appropriate iterative scheme is discussed in detail. Important topics about the predictors (initial guesses) are analyzed and a variable order strategy to select the best predictor at each integration step is supplied. A few numerical experiments on some standard test problems confirm the theory presented.

This paper is concerned with local error estimation in the numerical integration of stiff systems of ordinary differential equations by means of Runge--Kutta methods. With implicit Runge--Kutta methods it is often difficult to embed a local error estimate with the appropriate order and stability properties. In this paper local error estimation based on the information from the last two integration steps (that are supposed to have the same steplength) is proposed. It is shown that this technique, applied to Radau IIA methods, lets us get estimators with proper order and stability properties. Numerical examples showing that the proposed estimate improves the efficiency of the integration codes are presented.

In this paper, we propose a technique to stabilize some starting algorithms often used in the Newton-type iterations appearing when collocation Runge-Kutta methods are applied to solve stiff initial value problems. By following the ideas given in [1], we analyze the order (classical and stiff) of the new starting algorithms and pay special attention to their error amplifying functions. From the computational point of view, the new algorithms require the solution of an additional linear system per integration step, but as shown in the numerical experiments, this extra cost is compensated in most of the problems by their better stability properties.

This paper deals with starting algorithms for Newton-type schemes for solving the stage equations of implicit s-stages Runge-Kutta methods applied to stiff problems. We present a family of starting algorithms with orders from 0 to s + 1 and, with estimations of the error in these algorithms, we give a technique for selecting, at each step, the most convenient in the family. The proposed algorithms, that can be expressed in terms of divided differences, are based on the Lagrange interpolation of the stages of the last two integration steps. We also analyse the orders of the starting algorithms for the non-stiff case, for the Prothero and Robinson model and the stiff order. Finally, by means of some numerical experiments we show that this technique allows, in general, to greatly improve the performance of implicit Runge-Kutta methods on stiff problems.

The convergence of a family of AMF-Radau methods for the time integration of evolutionary semilinear Partial Differential Equations (PDEs) of Advection Diffusion Reaction type semi-discretized in space is considered. The methods are based on very few inexact Newton Iterations of Aproximate Matrix Factorization type (AMF) applied to the two-stage Radau IIA method. Uniform bounds for the global time-space errors on semi-linear PDEs when simultaneously the time step-size and the spatial grid resolution tend to zero are derived. Numerical illustrations supporting the theory are presented.

Pd nanoparticles have been supported onto different novel carbon materials to be used in the electroreduction of CO2 to high-added value products. Carbon nanocoils (CNCs), carbon nanofibers (CNFs) and ordered mesoporous carbon materials (OMCs) have been studied as support of the catalysts. In addition, Pd catalyst supported onto Vulcan XC-72R has been synthesized in order to establish a comparison with the commercial support. In this way, the influence of the carbon material on the physicochemical and electrochemical properties of the catalysts for the CO2 electroreduction process can be analyzed. Supports presented different morphologies and structures. CNFs and CNCs exhibited a crystalline structure with well-aligned graphitic layers and OMCs a hexagonal ordered structure composed of not crystalline carbon. Finally, Vulcan presented an intermediate structure between amorphous and graphitic. These differences do not affect significantly the average Pd crystallite size,although a different metal dispersion was found depending on the carbon material. On the other hand, cyclic voltammetry studies showed that CO2 was effectively reduced to other species at the surface of Pd/C catalysts. Additionally, it was proved that these species were adsorbed onto Pd at -1.0 V vs Ag/AgCl. Finally, a different catalytic activity towards the CO2 reduction reaction was observed for the different electrocatalysts, indicating an influence of the carbon support., The authors gratefully acknowledge financial support given by Spanish MINECO (CTQ2011‐28913‐C02‐01 and 02). S. Pérez-Rodríguez acknowledges Gobierno de Aragón for the DGA grant.