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16 figures, 10 tables., The deployment of hydrogen as an energy carrier is found to be a vital alternative fuel for the future. It is expected that water electrolysis, powered by renewable energy sources, be able to scale‐up hydrogen production. However, the reaction kinetic of oxygen evolution reaction (OER) is a sluggish process, which predominantly limits the efficiency of water electrolysis. This review recapitulates the recent progress and efforts made in the design and development of two selected earth-abundant bimetallic electrocatalysts (NiCo and CoFe) for alkaline OER. Each bimetal electrocatalyst is thoroughly outlined and discussed in five sub-sections, including bimetal (oxy) hydroxides, Layered double hydroxides (LDHs) structures, oxides, composites, alloy and nanostructured electrocatalysts, and assembled with heteroatoms. Furthermore, a brief introduction to an in situ/operando characterization techniques and advantages for monitoring the structure of the electrocatalysts is provided. Finally, a summary outlining the challenges and conceivable approaches to advance OER performance is highlighted and discussed., Financial support from the European Union’s Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie Actions-Innovative Training Networks (MSCA-ITN) Grant Agreement 813748 (Bike project) are gratefully acknowledged. The authors also wish to acknowledge the Ministerio de Ciencia, Innovación y Universidades (MICINN), and FEDER for the received funding in the project of reference ENE2017-83976-C2-1-R.

9 figures, 5 tables.-- Supplementary information available, Active and durable electrocatalysts for the oxygen evolution reaction (OER), capable of replacing noble metal catalysts, are required to develop efficient and competitive devices within the frame of the water electrolysis technology for hydrogen production. In this work, we have investigated tantalum based catalysts supported on carbon nanofibers (CNF) for the first time. The effect of CNF characteristics and the catalyst annealing temperature on the electrochemical response for the OER have been analyzed in alkaline environment using a rotating ring disc electrode (RRDE). The best OER activity and oxygen efficiency were found with a highly graphitic CNF, despite its lower surface area, synthesized at 700 °C, and upon a catalyst annealing temperature of 800 °C. The ordering degree of carbon nanofibers favors the production of oxygen in combination with a low oxygen content in tantalum oxides. The most active catalyst exhibited also an excellent durability., The authors want to thank the Ministerio de Economía, Industria y Competitividad (MICINN) and FEDER for the received funding in the project of reference ENE2017-83976-C2-1-R, and to the Gobierno de Aragón (DGA) for the funding to Grupo de Investigación Conversión de Combustibles (T06_17R). J.C. Ruiz-Cornejo acknowledges DGA for his PhD grant. D. Sebastián acknowledges the MICINN for the Ramón y Cajal research contract (RyC-2016-20944).

8 figures, 2 tables.-- Supplementary information available., The stainless steel mesh (SSM) has received remarkable attention for hydrogen and oxygen evolution reactions. It was demonstrated that the SSM exhibits admirable performance towards oxygen evolution reaction (OER) electrocatalysis, while its catalytic activity for hydrogen evolution reaction (HER) remains quite low. This obstructs the utilization of SSM-based catalysts for sustainable complete water electrolysis. In this study, a facile hydrothermal route followed by a phosphorization process was adopted to transform commercially available SSM materials into high-performance and stable electrocatalysts for alkaline HER. We report an interconnected NiCoP-CoP sponge-like structure on SSM substrate without polymer binder. Benefiting from the 3D construction with high exposed surface area, close contact between electroactive species and conductive surface, and facilitated infiltration of electrolyte, the as-prepared NiCoP@SSM electrocatalyst brought an improved catalytic activity for HER, required a low overpotential of 138 mV to derive a current density of 10 mAcm−2 in 1.0 M KOH aqueous solution. The high performance of the NiCoP@SSM catalyst has also unveiled fast reaction kinetics (presents a small Tafel slope of 74 mV/dec), a relatively large electrochemical active surface area (ECSA), and small charge transfer resistance. Furthermore, the NiCoP@SSM electrode also presented excellent stability during long-term measurements, making it one of the most encouraging HER electrodes to date. This research study paves the way for the development of HER-active electrocatalysts made from SSMs that are commercially available, low-cost, and highly active., The authors wish to acknowledge the grants PID2020-115848RB-C21 and PID2020-115848RB-C22 funded by MCIN/AEI/10.13039/501100011033.

Electrochemical water splitting is an environmentally benign technology employed for H

10 figures, 7 tables.-- Supplementary information available., Highly efficient, low-cost and stable bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desirable for the development of green electrochemical energy storage and conversion devices. Here, we report the synthesis of sulfur-doped carbon nanofibers (CNF) as support for tantalum oxide nanoparticles. Carbon nanofibers and tantalum oxides represent a durable choice for oxygen electrocatalysis, but an improvement of catalytic activity is required. Upon doping, sulfur is found to be mainly bonded to carbon as C–S–C species (more than 80%). The results show that the effective incorporation of sulfur in the support has a clear positive effect on the electroactivity of the tantalum oxide catalysts. It causes a decrease of OER/ORR overpotential of 80 mV with respect to the undoped counterpart, with special improvement in the ORR. The new catalysts have shown an interesting bifunctional behavior for the OER and ORR, as well as a good stability through time., The authors wish to acknowledge the grants PID2020-115848RB-C21 and PID2020-115848RB-C22 funded by MCIN/AEI/10.13039/501100011033, and to the Gobierno de Aragón (DGA) for the funding to Grupo de Conversión de Combustibles (T06_17R). J.C. Ruiz-Cornejo acknowledges also DGA for his PhD grant.

11 figures, 2 tables.-- Supplementary information available., High performance, durable and inexpensive electrocatalyst for oxygen evolution reaction (OER) is of great importance for tenable hydrogen production via water electrolysis. Although spinel oxides (AB2O4, A, B = metal) represent a class of promising candidates for OER, their intrinsically poor electrical conductivity impacts their electrochemical performance. Herein, we employed a facile approach to transform an intrinsically low active NiFe2O4 into nitrogen-doped carbon decorated Ni3Fe@Fe3O4 catalyst with improved activity and stability for alkaline OER. Initially, a pristine NiFe2O4 octahedron-like structure was synthesized by a hydrothermal route. Then, series electrocatalysts were prepared by incorporating the pristine NiFe2O4 with different dopamine concentrations via in-situ polymerizations of dopamine followed by carbonization. The morphology, crystalline structure, and chemical composition of the catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP). The OER electrocatalysis performance was measured in a standard three-electrode system. The effect of the carbonized dopamine on the electrocatalytic activity and structure of the NiFe2O4 precursor was systematically investigated. Among several NiFe electrocatalysts, the one with 10 wt% of dopamine (NiFe/NC10%) exhibited a relatively higher catalytic activity for OER tested in 1.0 M KOH; unveiled low overpotential (350 mV at 10 mAcm−2 current density), a low Tafel slope (56 mVdec−1), low charge transfer resistance, relatively higher electrochemically active surface area. Most prominently, it remained stable for at least 12 h. This work provides a new perspective for functionalizing metal oxides and affords a facile synthesis approach, low-cost, high-performance, and robust electrocatalyst for alkaline OER electrodes., Financial support from the European Union's Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie Actions–Innovative Training Networks (MSCA-ITN) Grant Agreement 813748 are gratefully acknowledged.

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

The hybrid methylammonium (MA) lead halide MAPbX 3 perovskites present an appealing optoelectronic behavior with applications in high-efficiency solar cells. The orientation of the organic MA units may play an important role in the properties, given the degrees of freedom for internal motion of MA groups within the PbX 6 network. The present neutron powder diffraction study reveals the dynamic features of the MA units in the hybrid perovskite series MAPb(Br 1−x Cl x ) 3 , with x=0, 0.33, 0.5, 0.67, and 1. From difference Fourier maps, the H and C/N positions were located within the PbX 6 lattice; the refinement of the crystal structures unveiled the MA conformations. Three different orientations were found to exist as a function of the chlorine content (x) and, therefore, of the cubic unit-cell size. These conformations are stabilized by H-bond interactions with the halide ions, and were found to agree with those reported from theoretical calculations. Fil: Lopez, Carlos Alberto. Instituto de Ciencia de Materiales de Madrid; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentina Fil: Álvarez Galván, María Consuelo. Consejo Superior de Investigaciones Científicas; España Fil: Martínez Huerta, María Victoria. Consejo Superior de Investigaciones Científicas; España Fil: Fernández Díaz, María Teresa. Institut Laue Langevin; Francia Fil: Alonso, José Antonio. Instituto de Ciencia de Materiales de Madrid; España

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).

The effect of titanium carbonitride (TiCN) as a new support for platinum-tin nanoparticulated catalysts for the ethanol oxidation reaction (EOR) in acid medium was evaluated. For that purpose, two platinum-tin catalysts supported on TiCN and carbon black (Vulcan XC-72R) were synthesized following the ethylene glycol method. XRD, TEM, ICP-OES and XPS techniques revealed that both catalysts exhibit similar physicochemical properties. However, the EOR and the CO tolerance were enhanced at the catalyst supported on TiCN. In situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) were used in order to get more information on the reaction mechanism and product selectivity. Main results indicate an improvement of the CO oxidation reaction by facile water dissociation on PtSn/TiCN, and elevated current output during the EOR on PtSn/TiCN since the acetaldehyde path is the favored, meanwhile the CO and acetic acid pathways are suppressed at this catalytic material. Significant differences were observed between both catalysts, indicating an extraordinary impact of the support in the catalytic performance.

7 figures, 2 tables., The development of active and low-cost electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the sustainable commercialization of fuel cell technologies. In this study, we have synthetized Me/Mo2C (Me = Fe, Co, Cu)-based composites embedded in N- and P-dual doped carbon by means of inexpensive industrial materials, such as melamine and chitosan, as C and N sources, and the heteropolyacid H3PMo12O40 as P and Mo precursor. The effect of the transition metal (Fe, Co, and Cu) on the ORR in alkaline medium has been investigated. The physicochemical properties of the electrocatalysts were performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). Activity towards ORR was carried out in a three-electrode cell using a ring-disk electrode in 0.1M NaOH. The results obtained clearly show the important role played by each transition metal (Fe, Co, and Cu) in the electrochemical activity. Among them, Fe gives rise to the best performing composite in carrying out the oxygen reduction reaction. The formation Fe3C/Mo2C species embedded in N- and P-dual doped carbon seems to be the determining role in the increase of the ORR performance., The authors acknowledge the Ministerio de Ciencia, Innovación y Universidades (MCIU), and FEDER for the funding received for the project, with references ENE2017-83976-C2-1-R, Spanish National Research Council COOPB20202, and MERC project 721399002.

8 figures, Polymer electrolyte fuel cells with alkaline anion exchange membranes (AAEMs) have gained increasing attention because of the faster reaction kinetics associated with the alkaline environment compared to acidic media. While the development of anion exchange polymer membranes is increasing, the catalytic layer structure and composition of electrodes is of paramount importance to maximize fuel cell performance. In this work, we examine the preparation procedures for electrodes by catalyst-coated substrate to be used with a well-known commercial AAEM, Fumasep® FAA-3, and a commercial ionomer of the same nature (Fumion), both from Fumatech GmbH. The anion exchange procedure, the ionomer concentration in the catalytic layer and also the effect of membrane thickness, are investigated as they are very relevant parameters conditioning the cell behavior. The best power density was achieved upon ion exchange of the ionomer by submerging the electrodes in KCl (isopropyl alcohol/water solution) for at least one hour, two exchange steps, followed by treatment in KOH for 30 min. The optimum ionomer (Fumion) concentration was found to be close to 50 wt%, with a relatively narrow interval of functioning ionomer percentages. These results provide a practical guide for electrode preparation in AAEM-based fuel cell research., This research was funded by the Ministry of Economy, Industry and Innovation (MICINN) and FEDER, grant number ENE2017-83976-C2-1-R and by the Government of Aragón and FEDER for supporting ‘Grupo de Conversión de Combustibles’, grant number T06_17R. D.S. and J.M.L.-C. acknowledge also MICINN for their Ramón y Cajal research contract (RyC-2016-20944) and Ph.D. grant, respectively. G.L. acknowledges as well Aragón Government for his Ph.D. grant.

The structures of vanadium oxide molecularly dispersed on oxide supports are unlike bulk phases, vanadium or its organometallic compounds. The dispersion of vanadium oxide triggers its exposure, which is the driving force for its applications in catalysis and surface science. The presence of an oxide support modifies the properties of the supported oxide, which in combination with coverage effect and the presence of additives helps creating a plethora of properties, with high relevance in catalysis, sensors and many other applications. This chapter presents a perspective essentially from the experience of the authors over the past 25 years. It addresses the nature of supported oxides and how these are affected by environmental conditions, loading and the presence of additives. Since environmental conditions may range from ambient hydrated to extreme pressure and atmospheres, the use of in-situ techniques is of paramount relevance to know the actual structure that supported vanadia species possess at given conditions. For catalyst materials, and functional materials in general, there is no point in knowing the structure at work if we do not know its performance. Among in-situ studies, operando methodology addresses this by providing simultaneous determination of material performance at genuine operation conditions and knowledge of its structure while working (“operando” in Latin). These aspects are considered from the perspective of catalytic application of supported vanadium oxides.

Pt80Rh20 and Pt60Rh40 alloy catalysts were electrodeposited at constant current density from different electrolytic baths on commercial carbon paper in order to be tested for the ethanol oxidation reaction (EOR) and as anodes in a direct ethanol fuel cell (DEFC). Pt and Rh anodes prepared in the same form were also examined for comparison. As measured by energy-dispersive X-ray microanalyses, the electrodeposited Pt:Rh atomic ratios were the same as those of the precursors in the bath. X-ray diffraction showed the PtRh alloy formation with mean particle sizes of 8.3 and 7.0 nm for Pt80Rh20 and Pt60Rh40, respectively, and a Pt lattice contraction caused by the Rh addition. The X-ray photoelectron spectroscopy analyses suggested a Pt lattice strain due to Rh alloying because the Pt4f binding energies were shifted to higher values with respect to that of pure Pt. The onset potentials of the alloy oxidation, CO stripping and ethanol oxidation in the cyclic and linear sweep voltammograms indicated that Pt60Rh40 was the most active for the CO and the ethanol electrooxidation. The apparent activation energies for the EOR on that alloy were also the lowest one, in agreement with its highest activity. These results were explained by the bifunctional mechanism, assuming that Rh contributed with hydroxylated species to favor the removal of the CO-type adsorbed species on Pt sites, and by the effect of Rh on the Pt electronic structure, the lattice strain being dominating over the charge transfer between Rh and Pt. Tests carried out in single DEFCs showed the feasibility of using the Pt60Rh40 electrodeposited electrodes on carbon as the anode in a real fuel cell environment.

Hybrid organic-inorganic perovskites, MAPbX (MA: methylammonium, CH-NH; X = halogen), are active absorption materials in the new generation of solar cells. The triiodide specimen (MAPbI) remains the most widely studied perovskite due to its ability to absorb broadband light below its band gap of 1.6 eV, but its degradation in a humid atmosphere has remained a major obstacle for commercialization. Here we found that CHNHPbIBr (x = 0.0, 1.0) perovskites, prepared by ball milling, exhibit superior stability, showing no signs of degradation after several months of exposure to humid air. A synchrotron X-ray diffraction (SXRD) investigation was useful to determine some peculiar structural features that may account for the improved stability. The crystal structure was analysed to be in the I4/mcm and acentric I4cm space groups, yielding similar agreement factors. In both, the inorganic framework presents a conspicuously lower tilting effect than that observed in samples prepared by wet methods; an additional difference arises since the tetragonal structure is stable down to 140 K. The orientation of the organic MA units may play an important role in the properties, given the degrees of freedom for internal motion of MA groups within the PbX network. From the refined C/N positions, the MA units lie along the c axis with 25% probability. The structure at 140 K shows that the MA contribution along the c axis vanishes at this temperature. By contrast, MAPbIBr crystallizes in the cubic phase with the space group Pm3m, also with a larger unit-cell volume than that previously described. The absence of phase transitions down to 120 K suggests that the anion disorder prevents the localization of MA units upon cooling., The authors acknowledge the financial support given by the Spanish Ministry of Economy and Competitiveness (MAT2017-84496-R) and KIC RAW MATERIALS from the European Union (OPTNEWOPT project). C. A. L. acknowledges ANPCyT and UNSL, Argentina, for the financial support (projects PICT2017-1842 and PROICO 2-2016, respectively), We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

This work investigates the effect of changing the vanadia/support interface on the redox properties of the material for the oxidative dehydrogenation reaction of small alkanes. In particular, ternary V2O5/CeO2/SiO2 catalysts are compared to vanadia on ceria and CeVO4 catalysts. Modifications in the CeO2 phase by the effect of the silica support and the creation of new V–Ce–Si interfaces induce substantial changes in the phases and behavior of vanadium species as well as CeO2, thus modifying the reaction mechanism. Powerful characterization techniques, XRD, in situ XANES, and Raman, as well as studies of ethane oxidative dehydrogenation catalytic activity provide a solid description of the phenomena associated with the different interfaces on a molecular level. Bulk CeO2 entities react with the vanadium species, leading to the formation of vanadate inhibiting the redox pair of V. These centers are very active but selective to ethane total oxidation. However, smaller ceria domains achieved by dispersion on ...

Iron and cobalt materials have attracted enormous interest as low-cost alternatives to noble-metal catalysts able to catalyse oxygen reduction reaction. Here, the effect of the heteropolyacid H3PMo12O40 (HPMo) into the structure of new composites formed by Fe, Co and reduced-graphene oxide/chitosan (rGOCS) has been investigated. Chitosan was used as a nitrogen precursor for nanocarbon, while reduced graphene oxide was introduced to tune the electrical conductivity. The physicochemical properties of electrocatalysts were performed by Raman, XRD, XPS and TEM. Activity toward ORR was carried out in a three-electrode electrochemical cell using a rotating disk electrode (RDE). The molybdophosphoric acid incorporation into the structure of Fe/rGOCS composites resulted in an increase of the activity of the oxygen reduction reaction in alkaline medium. Furthermore, the replacement of iron by cobalt yielded in a great improvement of the activity and stability, which may open new avenues for the design of nanomaterials utilizing HPMo/reduced-graphene oxide/chitosan composites., This work was supported by the Spanish Government under the MINECO projectENE2014-52158-C2-1R (co-funded by FEDER), Spanish National Research CouncilCOOPB20202 and MERC project721394002. M.R.A acknowledges the FPU-2012 program for financial support.

Low temperature fuel cells technologies are currently shifting very fast from fundamental research to real growth. The development of electrocatalysts plays a vital role in the electrocatalytic reactions involved in these devices, because the catalyst determines the overall reaction efficiency, durability and cost. This article review progress in the research and development of electrocatalysts for low temperature fuel cells technologies, with especial attention in the contribution of our research teams over the last 15 years or so. The intensive research efforts in reducing or replacing Pt-based electrodes in fuel cells have been focus in the use of carbon nanomaterials as electrocatalytic supports, including carbon nanostructures tailored by surface modification or building in particular dopants/defects. Recent research effort has also led to the use of electronic conductivity noncarbon support materials. In addition, carbon-composite materials are proving to be a robust, inexpensive and active electrocatalysts, where the synergetic effect between the carbon nanomaterials and the ceramic or polymer nanostructures can lead to a superior electrocatalytic performance and durability for low temperature fuel cells. Perspectives on these catalysts and possible pathways to address current remaining challenges are also discussed., Authors thank the Ministry of Economy and Competitiveness (MINECO) and FEDER through the Project ENE2014-52158-C2-1-R for financial support.

Cost-efficient and sustainable electrocatalysts for oxygen evolution reaction (OER) is highly desired in the search for clean and renewable energy sources. In this study, we develop a new one-step synthesis strategy of novel composites based on Ni and molybdenum carbide embedded in N- and P-dual doped carbon matrices using mainly chitosan biopolymer as the carbon and nitrogen source, and molybdophosphoric acid (HMoP) as the P and Mo precursor. Two composites have been investigated through annealing a mixture of Ni/chitosan and HMoP with two unlike carbon matrices, melamine and graphene oxide, at a high temperature. Both composites exhibit similar multi-active sites with high electrocatalytic activity for OER in an alkaline medium, which is comparable to the IrO2 catalyst. For this study, an accurate measurement of the onset potential for O2 evolution has been used by means of a rotating ring-disk electrode (RRDE). The use of this method allows confirming a better stability in the chitosan/graphene composite. This work serves as a promising approach for the conversion of feedstock and renewable chitosan into desired OER catalysts., By the Spanish Ministry of Science, Innovation and Universities, through project ENE2017-83976-C2-1-R (co-founded by FEDER), the Spanish National Research Council (CSIC) through project iCOOP20202 and MERC grant project 99392002.

[EN] IrO 2 and IrRuO x (Ir:Ru 60:40 at%), supported by 50 wt% onto titania nanotubes (TNTs) and (3 at% Nb) Nb-doped titania nanotubes (Nb-TNTs), as electrocatalysts for the oxygen evolution reaction (OER), were synthesized and characterized by means of structural, surface analytical and electrochemical techniques. Nb doping of titania significantly increased the surface area of the support from 145 (TNTs) to 260 m 2 g −1 (Nb-TNTs), which was significantly higher than those of the Nb-doped titania supports previously re- ported in the literature. The surface analytical techniques showed good dispersion of the catalysts onto the supports. The X-ray photoelectron spectroscopy analyses showed that Nb was mainly in the form of Nb(IV) species, the suitable form to behave as a donor introducing free electrons to the conduction band of titania. The redox transitions of the cyclic voltammograms, in agreement with the XPS results, were found to be reversible. Despite the supported materials presented bigger crystallite sizes than the unsupported ones, the total number of active sites of the former was also higher due to their better cat- alyst dispersion. Considering the outer and the total charges of the cyclic voltammograms in the range 0.1–1.4 V, stability and electrode potentials at given current densities, the preferred catalyst was IrO 2 sup- ported on the Nb-TNTs. The electrode potentials corresponding to given current densities were between the smallest ones given in the literature despite the small oxide loading used in this work and its Nb doping, thus making the Nb-TNTs-supported IrO 2 catalyst a promising candidate for the OER. The good dispersion of IrO 2 , high specific surface area of the Nb-doped supports, accessibility of the electroactive centers, increased stability due to Nb doping and electron donor properties of the Nb(IV) oxide species were considered the main reasons for its good performance., The authors would like to thank to EU FP7 SUSHGEN Network project No. 238678 and project ENE2017-83976-C2-1-R (AEI/FEDER, EU)). The facilities of the Centres Científics i Tecnològics de la Universitat de Barcelona (CCiT-UB) are also acknowledged for the struc- tural and surface analyses.

11 Figuras.- 2 Tablas.- Material suplementario disponible en línea en la página web del editor.-- Título del postprint: Crystal growth, structural phase transitions and optical gap evolution of CH3NH3Pb(Br1-xClx)3 powders, Chemically tuned inorganic–organic hybrid halide perovskites based on bromide and chloride anions CH3NH3Pb(Br1–xClx)3 have been crystallized and investigated by synchrotron X-ray diffraction (SXRD), scanning electron microscopy, and UV–vis spectroscopy. CH3NH3PbBr3 and CH3NH3PbCl3 experience successive phase transitions upon cooling, which are suppressed for intermediate compositions probably due to compositional disorder. For CH3NH3PbCl3, a transient phase, formerly described as tetragonal, was identified at 167.5 K; the analysis of SXRD data demonstrated that it is indeed orthorhombic, with space group Pnma, and a ≈ √2ap; b ≈ 2ap; c ≈ √2ap (ap is the ideal cubic perovskite unit-cell parameter). The band gap engineering brought about by the chemical management of CH3NH3Pb(Br1–xClx)3 perovskites can be controllably tuned: the gap progressively increases with the concentration of Cl ions from 2.2 to 2.9 eV, and shows a concomitant variation with the unit-cell parameters of the cubic phases at 295 K. This study provides an improved understanding of the structural and optical properties of the mixed CH3NH3Pb(Br1–xClx)3 perovskites., Authors acknowledge financial support given by KIC RAW MATERIALS from European Union (OPTNEWOPT project) and the Spanish Ministry of Economy and Competitiveness (ENE2014-52158-C2-1-R project and MAT2017-84496-R) cofounded by FEDER. C.A.L. acknowledges ANPCyT and UNSL for financial support (Projects PICT2014-3576 and PROICO 2-2016), Argentine. C.A.L. is a member of CONICET.

The hybrid methylammonium (MA) lead halide MAPbX

In the current work the concept of the active site is analyzed. With this end, Pt was deposited on Au(111) electrode assisted by water in oil microemulsion, in which the micelles confine the formation of small Pt clusters. The presence of highly and lowly coordinated Pt atoms was finely tuned by controlling the annealing processes and confirmed by CO stripping voltammetry in conjunction with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). This procedure allowed for the individuation of the effects of materials free and rich of catalytic defect sites on the CO electrochemical oxidation profile. Thus, a clear correlation between low-coordinated Pt atoms and the appearance of CO oxidation peaks at more negative potentials (peaks at 0.26 and 0.59 V vs. RHE) compared to high-coordinated Pt atoms (ca. 1.1 V vs. RHE) was identified.

Recent development on new anionic exchange membranes for alkaline membrane fuel cells has led to an increase on electrocatalyst testing measurements in three-electrode half-cells in alkaline media. However, there is not yet any commercial alkaline ionomer widely used, comparing to Nafion® in acidic media. In this work, two different commercial alkaline ionomers (I2 from Acta and Fumion® FAA-3 from Fumatech) are tested. Different catalyst: ionomer ratios are employed in order to adjust the ink composition for a correct evaluation of the catalyst activity. For this purpose, a commercial 20 wt.% Pt/C catalyst was tested for CO electrooxidation and oxygen reduction reaction in thin layer RDE configuration.

For the first time, a low cost, high performance and environmentally friendly heterogeneous catalyst derived from waste filter press cake (FPC) from a sugar manufacturing facility was used for the production of biodiesel. This industrial waste was calcined in air at 900 °C for 2 h to convert it into an active CaO-based catalyst (FPC-HT). In addition, the calcium oxide nanoparticles (FPC-NAC) were synthesized by surfactant-hydration treatment of FPC-HT. The synthesized catalysts were characterized by XRD, FTIR, SEM, TEM and BET analysis. These calcium oxide catalysts were used for a transesterification reaction between canola oil and methanol to produce biodiesel. The results show that the FPC-NAC has higher catalytic activity than FPC-HT under optimized reaction conditions. Therefore, this economic catalyst is able to catalyze the transesterification of canola oil to its methyl esters in 1.5 h with yields above 96 %.

The oxygen electrode plays a crucial role in performance and lifetime of water electrolyzers and regenerative fuel cells due to its slow electrochemical processes under rigorously oxidizing or reducing environments. Herein, we report the use of titanium carbonitride as an efficient and stable support in acidic media. Pt3M (M = Ru, Ir, Ta) nanoparticles supported on titanium carbonitride were synthesized by the ethylene glycol method and characterized by transmission electron microscopy, X-ray diffraction and inductively coupled plasma optical emission spectrometry. The electrochemical activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as well as the stability of the catalysts, was tested employing a rotating ring-disk electrode. The activity of the three catalysts is similar for the ORR. However, for the OER, Pt3Ru/TiCN appears to be the best catalyst by far. Pt3Ru/TiCN was also compared with a commercial RuO2 catalyst, obtaining a better performance for the supported catalyst even though the low amount of Ru/RuO2 present in the supported sample. The high activity and stability of the Pt3Ru/TiCN catalyst for the ORR and OER is due to an interesting promotion effect of the titanium carbonitride support, so that this electrocatalyst has a great potential for the application in unitized regenerative fuel cells.

One of the most important aliphatic diacids is adipic acid, which is produced industrially because of its application in the manufacture of nylon-6 and nylon-66. In the present work, a green methodology for the direct oxidation of cyclohexanol to adipic acid in a one-step reaction using ZnO nanoparticles supported on hydroxyapatite was developed. This work could be one of the very few articles on the use of ZnO nanoparticles for preparing adipic acid by using molecular oxygen as the greenest oxidant. The ZnO nanoparticles were prepared using different methods, such as reverse micelle, osmosis, alkaline hydrolysis, and impregnation, to compare their catalytic performances. We believe that oxygen deficiency in the ZnO nanocatalyst plays the main role in this oxidation reaction. The catalysts were characterized by different methods, such as FESEM, XRD, TEM, BET, and ICP. Among all the investigated catalysts, ZnO nanoparticles prepared by the reverse micelle method exhibited superior activity over all the other tested catalysts. To obtain the optimized conditions for the maximum conversion and selectivity, the reaction parameters, such as temperature, time, oxygen pressure, the amount of catalyst, amount of ZnO loaded on hydroxyapatite, and the method of preparation of the catalyst, were optimized. Under the found optimized conditions, a maximum conversion of 86% and selectivity of 96% was achieved for the production of adipic acid with ZnO/hydroxyapatite catalyst prepared by the reverse micelle method. The optimum conditions for the oxidation of cyclohexanol were 25 mg of catalyst, 120 °C, 15 bar oxygen pressure, and 8 h. Furthermore, this catalyst retained its catalytic activity with 84% conversion and 70% selectivity for adipic acid production after four cycles.

11 Figuras, 3 Tablas.-- Material suplementario disponible en línea en la página web del editor., Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts play an important role in energy conversion and storage devices, but highly active and robust nonprecious metal catalysts are required to address the cost and durability issues. In this work, a modified gel methodology has been used to obtain nanocomposites of perovskite CoTiO3 and N-doped reduced graphene oxide (NrGO). Moreover, the influence of the annealing extent in the synthesis has been studied. The composites show higher activity in oxygen evolution and reduction reactions in alkaline environment compared to sole ilmenite, which is related to a strong interaction between cobalt titanate and NrGO carbon matrix. The annealing duration appears as a key variable to modulate the physicochemical properties and the electrochemical behavior. The composite prepared at the largest duration (3 h) exhibit enhanced bifunctional properties for ORR and OER, with onset potentials of 0.93 V and 1.53 V vs. RHE respectively, which is mainly attributed to higher concentration of nitrogen, larger extent of defects and/or the presence of more oxidized Co species in the nanocomposite., The authors wish to acknowledge the Ministerio de Ciencia, Innovación y Universidades (MICINN) and FEDER for the received funding in the project of reference ENE2017-83976-C2-1-R. Thanks also to the Gobierno de Aragón (DGA) the funding for the Grupo de Investigación Conversión de Combustibles (T06_17R). J. M. Luque also thanks MICINN for its Ph.D. grant. D. Sebastián acknowledges the MICINN for the contract Ramón y Cajal (RyC-2016-20944).

Hybrid organic-inorganic perovskites, MAPbX3 (X= halogen), containing methylammonium (MA: CH3-NH3+) in the large voids conformed by the PbX6 octahedral network, are the active absorption materials in the new generation of solar cells. CH3NH3PbBr3 is a promising alternative with a large band-gap that gives rise to a high open circuit voltage. A deep knowledge of the crystal structure and, in particular, the MA conformation inside the perovskite cage across the phase transitions undergone below room temperature, seems essential to establish structure-property correlations that may drive to further improvements. The presence of protons requires the use of neutrons, combined with synchrotron XRD data that help to depict subtle symmetry changes undergone upon cooling. We present a consistent picture of the structural features of this fascinating material, in complement with photocurrent measurements from a photodetector device, demonstrating the potential of MAPbBr3 in optoelectronics., Comment: Authors' version of the peer-reviewed manuscript. 19 pages, 7 figures

Developing efficient, durable, and low cost catalysts based on earth-abundant elements for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for renewable energy conversion and energy storage devices. We report herein a simple one-pot procedure for the synthesis of non-precious metals N-doped graphene composites employing urea as nitrogen source, and their application as bifunctional catalysts for both the ORR and OER in alkaline environment. In this study, the effects of the addition of Ti and Co on the structure and performance of the N-doped graphene composites are investigated. The incorporation of Ti leads to a composite with both anatase and rutile TiO2 crystalline phases as well as Ti3+ species stabilized upon hybridization with N-doped reduced graphene oxide. The ORR onset potential for the Ti-based composite is 0.85 V (vs. RHE) and the number of electrons transferred is 3.5, showing superior stability than Pt/C after accelerated potential cycling in alkaline solution. However, this composite shows low activity and stability for the OER. On the other hand, the composite consisting of metallic Co and Co3O4 nanocrystals grown on N-doped reduced graphene oxide exhibits the best performance as bifunctional catalyst, with ORR and OER onset potentials of 0.95 V and 1.51 V (vs. RHE), respectively, and a number of electrons transferred of 3.6 (ORR). The results reveal the presence of important structural features such as metallic Co as the predominant crystalline component, amorphous Co3O4 phase and the coordination of Co-N-doped graphene. All of them seem to be fundamental for the high activity and stability towards ORR and OER., Authors acknowledge financial support given by Spanish Ministry of Economy and Competitiveness (MINECO) through projects ENE2014-52158-C2-1-R and 2-R (co-founded by FEDER). J. M. Luque and G. Lemes also thank MINECO and Aragon Government, respectively, for their Ph.D. grants.

The catalytic activity of VOx species supported on TiO2 was investigated in the simultaneous destruction of NO and 1,2-dichlorobenzene (o-DCB), as typical pollutants molecules in the off-gases from municipal waste incinerator (MWI) plants. Catalysts with different vanadium loading were prepared in order to obtain different VOx species and characterized by ICP-AES, XPS, N2 adsorption at −196 °C, XRD, H2-TPR, Raman and UV–vis–NIR DRS spectroscopy. The characterization results show that molecularly dispersed isolated and polymeric vanadia species form below the dispersion limit loading (“monolayer coverage”), while crystalline species form above it. We used moderate HNO3 treatment to partially leach vanadium oxide species, creating a series of catalysts with variable vanadia loading. The catalytic activity of the VOx/TiO2 catalyst shows that it is able to catalyze the destruction of both pollutants, although higher temperature is required for o-DCB oxidation than for NO reduction. Surface vanadia coverage has a clear effect on TOF and activation energy values, which underline that isolated vanadia species are more efficient for o-DCB oxidation, while the polymeric ones are more efficient for NO reduction., This research was funded by Basque Government though the Grant to Consolidated Research Groups (GIC-07/67-JT-450-07) and the SAIOTEK program (S-PE11UN074), by University of the Basque Country UPV/EHU through the UFI (UFI 11/39) and the Grant for the acquisition and renovation of scientific infrastructure (INF12/37) and by the Spanish Ministry of Economy and Competitiveness (CTM2012-31576). One of the authors (MGV) acknowledges also the Basque Government for the PhD Research Grant (BFI-2011-238).

In the present work, the selective liquid phase oxidation of cyclohexene mainly to 2-cyclohexe-1-one has been investigated over gold nanoparticles (GNPs) with molecular oxygen in a solvent-free condition. Gold nanoparticles were synthesised on two modified supports of silica and bentonite. In this respect the surface of silica and bentonite was modified with organic ligands consist of thiol and thioester groups. The catalysts were characterized by TEM, XPS, N2 adsorption/desorption, FT-IR, and CHNS techniques. TEM images show that the gold nanoparticles over modified bentonite and silica have diameters in the range 0f 50 and less than 10 nm, respectively. The results show that the catalytic activity of gold nanoparticles over modified silica, SiO2-pA-Acrylate-Thioamide-Au (0), is much better than the gold nanoparticles immobilized on the modified bentonite, MEDPT@CP-bentonite-Au (0). The catalytic activity over SiO2-pA-Acrylate-Thioamide-Au (0) recycled catalyst remained at a satisfactory state after at least 4 cycles. Activity tests were carried out in an autoclave under solvent-free conditions. In order to obtain maximum conversion, the reaction parameters such as reaction temperature and time were optimized. Under optimized conditions, a maximum of 92% conversion and 97% selectivity was achieved with the SiO2-pA-Acrylate-Thioamide-Au (0) catalyst., Thanks are due to the Iranian Nanotechnology Initiative and the Research Council of Isfahan University of Technology and Centre of Excellence in the Chemistry Department of Isfahan University of Technology for supporting of this work.

Hybrid organic-inorganic perovskites, MAPbX

The review article discusses the current status and recent findings of our investigations on the synthesis and characterization of carbon-supported PtRuMo electrocatalysts for direct alcohol fuel cells. In particular, the effect of the carbon support and the composition on the structure, stability and the activity of the PtRuMo nanoparticles for the electrooxidation of CO, methanol and ethanol have been studied. Different physicochemical techniques have been employed for the analysis of the catalysts structures: X-ray analytical methods (XRD, XPS, TXRF), thermogravimetry (TGA) and transmission electron microscopy (TEM), as well as a number of electrochemical techniques like CO adsorption studies, current-time curves and cyclic voltammetry measurements. Furthermore, spectroscopic methods adapted to the electrochemical systems for in situ studies, such as Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS), have been used to evaluate the oxidation process of CO, methanol and ethanol over the carbon-supported PtRuMo electrocatalysts., This work has been supported by the Spanish Science and Innovation Ministry under projects ENE2010-15381 and CTQ2011-28913-CO2-O2.

The role of two intermetallic phases of PtSn, namely Pt 3 Sn (fcc phase) and PtSn (hcp phase) for the electrooxidation of CO and methanol has been evaluated. Carbon supported Pt 3 Sn and PtSn nanosized particles have been prepared by controlled surface reactions. The actual structure of the PtSn alloys has been evaluated and confirmed by means of XRD and HR-TEM studies which reveal the predominance of either the hcp or the fcc phase in each catalyst. The catalysts have been further characterized to identify the actual metal loading and Pt/Sn atomic ratio in order to eliminate particle size or metal loading effects on their electrocatalytic performance. The performance of the catalysts for the electrooxidation of CO and methanol has been evaluated by electrochemical techniques along with in situ techniques such as electrochemical coupled Infrared Reflection Absorption Spectroscopy (EC-IRAS) and differential electrochemical mass spectrometry (DEMS). Altogether, the results presented in this work reveal that Pt 3 Sn fcc is more active than PtSn hcp for the electrooxidation of CO and methanol and that the contribution of the hcp phase in those electrocatalytic processes is negligible.

The electrooxidation of ethanol on carbon supported PtRuMo nanoparticles of different Mo compositions has been studied in the temperature range of 30–70 °C. Current–time curves have shown an increase of the current density with the Mo introduction during the ethanol oxidation at 0.5 V in a whole temperature range. The incorporation of different amount of MoOx (∼Mo5+) like species over PtRu systems produces ternary catalyst with similar structural characteristics as particle size or crystal phases, but the catalytic behavior depended on both the surface amount of Mo and on the applied potential. In situ spectroelectrochemical studies have been used to identity adsorbed reaction intermediates and products (in situ Fourier transform infrared spectroscopy, FTIR) and volatile reaction products (differential electrochemical mass spectrometry, DEMS). For all catalysts, incomplete ethanol oxidation to C2 products (acetaldehyde and acetic acid) prevails under the conditions selected in this study. The higher CO tolerance of PtRuMo/C catalysts at very low potentials (

This fundamental study deals with the electrochemical stability of several non-conventional carbon based catalyst supports, intended for low temperature proton exchange membrane fuel cell (PEMFC) cathodes. Electrochemical surface oxidation of raw and functionalized carbon nanofibers, and carbon black for comparison, was studied following a potential step treatment at 25.0 °C in acid electrolyte, which mimics the operating conditions of low temperature PEMFCs. Surface oxidation was characterized using cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Cyclic voltammograms clearly showed the presence of the hydroquinone/quinone couple. Furthermore, identification of carbonyl, ether, hydroxyl and carboxyl surface functional groups were made by deconvolution of the XPS spectra. The relative increase in surface oxides on carbon nanofibers during the electrochemical oxidation treatment is significantly smaller than that on carbon black. This suggests that carbon nanofibers are more resistant to the electrochemical corrosion than carbon black under the experimental conditions used in this work. This behaviour could be attributed to the differences found in the microstructure of both kinds of carbons. According to these results, carbon nanofibers possess a high potential as catalyst support to increase the durability of catalysts used in low temperature PEMFC applications.

Carbon supported PtRuMo nanoparticles for CO and methanol electrooxidation have been prepared using different Mo precursors (MoCl5, (NH4)6Mo7O24 and MoO3). Electrocatalysts as well as support characterization has been carried out through various physicochemical (XRD, TEM, XPS, TPR and TXRF) and electrochemical techniques as cyclic voltammetries and current–time curves, applied in combination with differential electrochemical mass spectrometry (DEMS). MoO3 precursor was mainly used as representative of Mo6+ species in the electrocatalyst. The results of this work pointed out that irrespectively of the similar structure and particle size are obtained using MoCl5 and (NH4)6Mo7O24, the final composition and homogeneity of the ternary catalysts were found to depend markedly on these precursors. MoCl5 led to a dramatic loss of Mo, while (NH4)6Mo7O24 appeared to be more stable and handy for synthesis of PtRuMo nanoparticles. Once the catalysts have been stabilized in the electrode, similar Mo species, mainly Mo5+, are formed on the catalysts surface of all PtRuMo catalysts. This is indicative that similar metal–support and metal–metal interactions are likely developed in carbon supported PtRuMo nanoparticles at these potential conditions. The possible metal interactions that take place and the lower oxidation states of surface Mo species may be responsible of the high activity in CO and methanol electrooxidation as compared with binary and ternary catalysts obtained with MoO3. The higher activity observed using (NH4)6Mo7O24 as precursor could be finally attributed to the composition and a remarkable Ru–Mo interaction detected by TPR. Finally, the MoO3-loaded catalyst proves that high oxidation states of Mo not only result in high losses of metals during the stabilization of the system and lower activities but also affect negatively the development of Pt–Ru interactions.

The factors controlling the behavior and the stability of electrocatalysts based on Pt, Ru and Mo nanoparticles during exhaustive electrochemical treatment are examined. Along this treatment, it has been observed that in the case of ternary catalysts there are pronounced changes in the structure of their surface resulting in electrode activation for methanol and CO electrooxidation, whereas the activity of binary PtRu/C and PtMo/C catalysts decreases. Therefore, the role of both Ru and Mo is crucial for the electrochemical activation of the catalyst, though metal losses do occur during electrochemical process. For the first time a detailed study of this phenomenon is presented, including characterization by HRTEM, TXRF, XRD, electrochemical measurements and in situ Fourier transform infrared spectroscopy (FTIR). In order to get a deeper insight into the surface structure, chemical state, and stability of the electrocatalyst under reaction conditions, a combination of cyclic voltammetry, chronoamperometry and X-ray photoelectron spectroscopy (XPS) has been used. By comparing bulk and surface composition, our results point out to the key role of the geometric effect enhanced by previous reduction of the nanoparticles. At the end of the electrochemical treatment, Mo-PtRu/C catalysts surface was restructured with substantial enrichment in Pt and a less pronounced Mo surface enrichment, while Ru is incorporated into the Pt-Mo overlayer. These results underline the possibility of further optimization of the surface structure and composition producing PtRuMo nanoparticles with high methanol and CO oxidation activity.

The influence of thermal treatment under different environments of PtRuMo/C catalyst has been investigated for CO and methanol electrooxidation in a half cell and in a DMFC single cell. The PtRuMo/C catalysts were synthesized following two step procedure while the thermal treatments consisted of heating at 300 °C in H2 or He atmosphere for 1 h. Structural characteristics of the electrocatalysts have been studied employing a wide range of instrumental methods, including physicochemical techniques like X-ray diffraction, TEM, TPR, XPS, and electrochemical techniques like single cell studies and Fourier Transform Infrared Spectroscopy adapted to the electrochemical system for in situ studies. These electrocatalysts exhibited good dispersion and small particle size, which increased upon increasing thermal treatment. Moreover, thermal treatment, mainly under H2 is responsible for the decrease of the lattice parameter and the increase of the spill over effect to Mo sites. These effects were also accompanied by increasing the proportion of the more reduced Ru species in this catalyst. The electrochemical characterization revealed that although all ternary catalysts were more active towards CO and methanol oxidation than the binary catalyst, the catalyst treated with H2 improves its performance by ca. 15% higher with respect to the ternary catalysts treated either in He treatment or with no treatment. The enhancement in activity is associated with a change in the reaction path, which promotes the direct oxidation of CHO species to CO2 without the production of the CO poisoning species. The synergistic effect of the three metals seems to be improved and the Mo–Pt and Mo–Ru interaction strengthened.

Novel carbonaceous supports for electrocatalysts are being investigated to improve the performance of polymer electrolyte fuel cells. Within several supports, carbon nanofibers blend two properties that rarely coexist in a material: a high mesoporosity and a high electrical conductivity, due to their particular structure. Carbon nanofibers have been obtained by catalytic decomposition of methane, optimizing growth conditions to obtain carbon supports with different properties. Subsequently, the surface chemistry has been modified by an oxidation treatment, in order to create oxygen surface groups of different nature that have been observed to be necessary to obtain a higher performance of the electrocatalyst. Platinum has then been supported on the as-prepared carbon nanofibers by different deposition methods and the obtained catalysts have been studied by different electrochemical techniques. The influence of carbon nanofibers properties and functionalization on the electrochemical behavior of the electrocatalysts has been studied and discussed, obtaining higher performances than commercial electrocatalysts with the highest electrical conductive carbon nanofibers as support.

CO electrooxidation on nanocrystalline molybdenum carbide has been studied through CO stripping measurements using cyclic voltammetry. The active molybdenum carbide was obtained from the carbothermic reduction of really very small molybdenum oxide particles supported on Vulcan XC-72 carbon black (CB). In order to obtain highly dispersed molybdenum carbide particles, low molybdenum loading and control of the carbothermic reduction conditions of CB-supported molybdenum oxide were employed to avoid Mo sintering during the carburization process. This work provides experimental evidence on the CO electrooxidation capability of the Mo carbide phase, which to the best of our knowledge is reported for the first time. The small particle size of carbide electrocatalyst exhibited better performance for CO electrooxidation than the commercial bulk molybdenum carbide sample.

The synthesis of carbon nanocoils (CNCs) by the catalytic graphitization of composites has been studied. Resorcinol-formaldehyde gel was used as the carbon precursor; a mixture of cobalt and nickel salts was used as the graphitization catalysts in the synthesis; and silica sol was added to the reaction mixture to obtain carbon materials with high specific surface area and to achieve a good dispersion of the transition-metal nanoparticles. Different molar ratios of the reagents were used with the purpose of obtaining carbon materials with different structural and textural properties, seeking a compromise between the graphitization degree and surface area. X-ray diffraction (XRD), Raman spectrometry, transmission electron microscopy (TEM), temperature-programmed oxidation (TPO), N 2 physisorption, and temperature-programmed desorption (TPD) were used to characterize the morphology, textural properties, and surface chemistry of such materials. Results showed that obtained CNCs had good crystallinity and well-defined porosity, which depended upon the preparation conditions.

The influence of vanadium oxide on the TiO2 (anatase) to rutile transformation for supported VOx/TiO2 catalysts under different environments (oxidizing, reducing and ethane oxidative dehydrogenation (ODH)) was investigated. The supported VOx/TiO2 catalysts were synthesized by incipient wetness impregnation and characterized with XPS surface analysis, Raman spectroscopy and temperature-programmed oxidation and reduction. The XPS surface analysis and Raman spectroscopy demonstrate that the supported vanadium oxide phase is initially present as surface VOx species on the titania (anatase) support below monolayer coverage (∼9 V/nm2) and that crystalline V2O5 nanoparticles are also present above monolayer coverage. The TiO2 anatase-to-rutile transformation is found to depend both on the gaseous environment and presence of vanadia. The anatase-to-rutile transformation is accelerated by the presence of vanadium oxide and the incorporation of V+4 cations into the TiO2 (rutile) lattice. The incorporation of the V+4 cations decreases the catalytic activity since the active sites are removed from the surface into the bulk, which is not accessible to the reactant gases. Although the titania anatase-to-rutile transformation readily occurs in oxidizing environments (O2 and ODH reaction), the solid-state transformation does not take place under reducing environments (H2) since large V3+ ions form prior to the transition temperature and cannot enter the titania lattice.

A relationship between the chemical state of Ru on bimetallic PtRu bulk samples and their performance in both CO and methanol electrooxidation has been established. The nature of the Ru species in the bimetallic samples has been scrutinized by means of XPS, XRD and TPR. The following Ru species were detected; reduced ruthenium (Ru 0 ), anhydrous RuO 2 and hydrous Ru oxide. The actual nature of the latter species consists of two amorphous oxides of general formula RuO 2 · x H 2 O and RuO x (OH) y as determined from the XPS analysis. Irrespective of the Ru phases, all PtRu catalyst studied display a similar CO oxidation pattern. However, methanol electrooxidation was found dependent on the Ru phases. Thus, catalysts containing Ru 0 are more active in the methanol oxidation reaction, at least during the early stages of the reaction. More stable catalyst are obtained if amorphous Ru oxide phases are the predominant ones.

The influence of the structure and morphology of PtRu nanoparticles supported on functionalized carbon black has been investigated for CO and methanol electrooxidation in a half-cell and in a DMFC single cell. Carbon black was treated with HNO3 to obtain an oxidized surface (Vulcan-N), and PtRu nanoparticles supported on Vulcan-N were prepared via impregnation, Bonnemann's method and the sulfito-complex route. Temperature programmed reduction (TPR) measurements evidence the presence of RuO2·xH2O phase in the catalyst obtained by the sulfito-complex route. This phase was stabilized by metal–support interaction, whereas alloy characteristics were estimated for PtRu catalyst obtained by impregnation and Bonnemann's method. The nature of the precursor–support interaction, induced by the nature of the functional groups on the carbon surface, affects the structure of the electrocatalyst and subsequent behavior in electroactivity. When synthesized through Bonnemann's method, the surface oxygen-containing groups of the support seem to be unable to stabilize the anhydrous precursors of platinum and ruthenium, yielding crystalline RuO2. Methanol electrooxidation performance was clearly different in the three catalysts, whereas only a few negligible differences were observed in CO oxidation. The superior performance in DMFC of the catalysts obtained by the sulfito-complex route accounts for both the presence of RuO2·xH2O species and the functionalization of carbon black.

Novel nanostructured catalysts based on PtRu–MoO x nanoparticles supported on carbon nanofibers have been investigated for CO and methanol electrooxidation. Carbon nanofibers are prepared by thermocatalytic decomposition of methane (NF), and functionalized with HNO 3 (NF.F). Electrocatalysts are obtained using a two-step procedure: (1) Pt and Ru are incorporated on the carbon substrates (Vulcan XC 72R, NF and NF.F), and (2) Mo is loaded on the PtRu/C samples. Differential electrochemical mass spectrometry (DEMS) analyses establish that the incorporation of Mo increases significantly the CO tolerance than respective binary counterparts. The nature of the carbon support affects considerably the stabilization of MoO x nanoparticles and also the performance in methanol electrooxidation. Accordingly, a significant increase of methanol oxidation is obtained in PtRu–MoO x nanoparticles supported on non-functionalized carbon nanofiber, in parallel with a large reduction of the Pt amount in comparison with binary counterparts and commercial catalyst.

The roles of the different sites and structures of supported V 5+/CeO 2 catalysts have been studied by the operando Raman-GC methodology during ethane oxidative dehydrogenation (ODH) to obtain a molecular understanding of the structure−activity/selectivity relationships in this system. A remarkable deactivation takes place at high vanadia coverage during reaction. The remarkable effect of surface vanadia species on ceria on catalytic activity is due to a solid-state reaction between surface V 5+ species and CeO 2 support to form crystalline CeVO 4 nanoparticles, which consume the surface vanadia sites. The catalytic activity does not decrease upon the transformation of surface vanadia species into an incipient crystalline tetragonal CeVO 4 phase, but due to the growth of a well-defined bulk crystalline tetragonal CeVO 4 phase. The activation energy is not affected by these changes, only the number of active sites. Therefore, the nature of the active site for ethane ODH on supported V 5+/CeO 2 and on CeVO ...

Carbon-supported PtRu—MoOx nanoparticles with significant CO tolerance were prepared by a new two-step procedure: in the first step, molybdenum oxide was deposited on a carbon substrate (MoOx/C) by impregnation, and in the second one, Pt and Ru were incorporated following a colloidal method with NaHSO3. The composition, particle size, and crystallinity of the catalysts were determined by X-ray analytical methods (X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and total-reflection X-ray fluorescence (TXRF)), transmission electron microscopy (TEM), and thermogravimetry (TG). Conventional electrochemical techniques such as cyclic voltammetry (CV) and chronoamperometry were applied in combination with spectroscopic methods adapted to the electrochemical systems for in situ studies, such as Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS). The results of this work are highly encouraging, as it is proved that a reduction of the amount of...

The effect of vanadium oxide loading on CeO2 support for ethane oxidative dehydrogenation (ODH) is studied. Surface vanadia species are highly dispersed on CeO2. The interaction with surface vanadia species significantly changes the structural and reactive properties of ceria support. VOx/CeO2 suffers an important change during ethane ODH due to a solid-state reaction between CeO2 and surface vanadia species resulting in the formation of CeVO4. Such a solid-state reaction is promoted by high temperature, high vanadium loading, and reducing environments. Raman in situ temperature-programmed studies under reduction and oxidation conditions reveal that the catalytic cycle involves oxidation−reduction of the Ce4+ ↔ Ce3+ species, while the V5+ species remain stable.