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Transition metal (Fe, Co, Ni)-doped cryptomelane materials (K-OMS-2) were synthesized and characterized with the use of XRD, Raman spectroscopy, XPS, N2-BET, H2-TPR, and SEM. The electrocatalytic reactivity in oxygen evolution was evaluated with the use of the rotating disk electrode. It was found that the electrocatalytic activity is substantially enhanced for the cobalt-doped material, while iron and nickel doping have no, or even, negative effect on K-OMS-2. The structure of the material bulk is preserved in all cases, but the formation of additional birnessite phases can be evidenced for the iron and cobalt dopants. It is discussed that the reactivity enhancement of Co/K-OMS-2 can be related not only to the formation of cobalt-doped heterophases (cobaltane, birnessite) but also to the changes of the properties of pristine cryptomelane.

Alkaline membrane fuel cells (AMFCs) have started to become more attractive in recent years due to the development of polymeric membranes with good anionic conductivity and durability. However, few studies investigating the performance of H2/O2 fueled AMFCs and alkaline direct ethanol fuel cells (DEFCs) with membrane electrode assemblies (MEAs) fabricated with Pt-group metal (PGM)-free catalysts are available in the literature. In this paper, we synthesized and fully characterized a Fe-Co-N-C electrocatalyst for the oxygen reduction reaction (ORR) by a sacrificial method, using pyrrole as a unique and inexpensive precursor for N-doped carbonaceous materials. Very good ORR activity and stability were obtained in alkaline conditions, most likely due to the presence of Co-Fe@C nanoparticles. We achieved a very high performance in an AMFC, 420 mW cm-2 at 60 °C, among the highest in the literature for PGM-free catalysts, and a good performance in a passive DEFC, 28 mW cm-2 at room temperature.

The influence of three different transition metals (Me = Fe, Co, Cu) on the oxygen reduction reaction (ORR) kinetics in acidic medium of Me–N–C catalysts synthesized using Me(II)-phthalocyanine as precursors is investigated in this work. Through a detailed electrochemical characterization using cyclic voltammetry and rotating ring-disk electrode, several kinetic parameters such as Tafel slope, reaction order for oxygen and proton, apparent activation energy, selectivity toward hydrogen peroxide production, and kinetics of reduction of adsorbed oxygen were determined. The behavior of these three catalysts is analyzed in detail. A comparison between each other of the catalysts, and with a Pt-based catalyst is done. The results obtained provide clear evidence of the important role played by each transition metal in the formation of more or less effective active sites. The ORR kinetics behavior can be well interpreted according to the occurrence of a redox-mediated coverage of the active sites at low overpote...

The performance of a single cell direct methanol fuel cell (DMFC) is optimized by evaluating the effect of the catalyst distribution in the membrane electrode assembly (MEA) via a 3D multi-physics, multi-component, two-phase, and not-isothermal model. The model is computed with Comsol® Multiphysics v4.4 platform, with a finite element analysis solver and simulation software. It consists of Maxwell-Stefan, Stokes-Brinckman, extended two-phase Darcy Law, modified Butler-Volmer and Tafel equations to simulate the performance of the DMFC, and to evaluate the electrochemical, fluid-dynamics and thermal phenomena. The use of a 3D model considering porous equation such as Stokes-Brinkman is helpful for understanding, describing the motions and hydrodynamic forces of interacting particles in Stokes flow, which is more realistic regarding catalyst description and validation. Moreover, the model can be used for evaluating intrinsic parameters of novel electrocatalysts. The model is validated against a set of experimental data, showing congruent and convergent data for a commercial 25 cm 2 MEA consisting of Nafion® 117 and electrodes (Pt/C at the cathode and Pt:Ru at the anode) at different temperatures and inlet methanol concentrations, confirming the accuracy of the model and the equations applied. The model is used to optimize the catalytic layer distribution to obtain a more uniform current density distribution along the anodic catalyst-membrane interface and a better cell performance. The optimized anodic catalytic distribution has been implemented in a 25 cm 2 in-house three-layer MEA and experimentally tested, included a short durability of 26 h, showing better stability compared to a MEA with a classic homogenous catalyst loading distribution.

We report here the synthesis of carbon-supported ZrO2 nanoparticles from zirconium oxyphthalocyanine (ZrOPc) and acetylacetonate [Zr(acac)4]. Using thermogravimetric analysis (TGA) coupled with mass spectrometry (MS), we could investigate the thermal decomposition behavior of the chosen precursors. According to those results, we chose the heat treatment temperatures (T HT) using partial oxidizing (PO) and reducing (RED) atmosphere. By X-ray diffraction we detected structure and size of the nanoparticles; the size was further confirmed by transmission electron microscopy. ZrO2 formation happens at lower temperature with Zr(acac)4 than with ZrOPc, due to the lower thermal stability and a higher oxygen amount in Zr(acac)4. Using ZrOPc at T HT ≥900 °C, PO conditions facilitate the crystallite growth and formation of distinct tetragonal ZrO2, while with Zr(acac)4 a distinct tetragonal ZrO2 phase is observed already at T HT ≥750 °C in both RED and PO conditions. Tuning of ZrO2 nanocrystallite size from 5 to 9 nm by varying the precursor loading is also demonstrated. The chemical state of zirconium was analyzed by X-ray photoelectron spectroscopy, which confirms ZrO2 formation from different synthesis routes.

In this study, the Pt-Cu/C alloy with nominal composition of Pt0.25Cu0.75 was produced via three different methods impregnation, impregnation in the presence of sodium citrate additive and microwave assisted polyol method. Each method produced catalysts with differing structural and electrochemical properties. These catalysts were also heat treated to induce changes in the crystalline structure which in turn altered the activity towards the ethanol oxidation reaction (EOR). The crystalline structure, particle dispersion and chemical composition of the Pt-Cu samples were studied by Thermogravimetric Analysis (TGA), X-ray Powder Diffraction (XRD), Transmission Electron Microscopy (TEM) Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The ICP, XPS, TGA and TEM results indicate each synthetic method produced catalysts with different chemical composition, metal loadings and particle dispersion. The XRD analysis showed that the heat treatment of the Pt-Cu/C samples resulted in ordered intermetallic crystalline structures such as PtCu and PtCu3. The highest EOR activity was observed for samples rich in intermetallic ordered phases, PtCu in particular. XPS and CO stripping measurements indicates that the electronic structure of the Pt-rich surface of the Pt-Cu particles was altered due to formation of intermetallic phases and the Cu-rich core.

A non-noble metal (NNM) catalyst for oxygen reduction reaction (ORR) was synthesized using Fe(II)-phthalocyanine as unique source of Fe, N, and C, and SBA-15 ordered mesoporous silica as templating agent, resulting in a material with an extremely high specific surface area and a high microporosity (around 50%). FESEM, FTIR and Raman analyses were performed to investigate the morphology and the physicochemical properties of the catalyst. The ORR activity and the methanol tolerance were tested in rotating disk electrode (RDE), and the selectivity towards a complete 4-electrons reduction was investigated by rotating ring disk electrode (RRDE) test and hydrogen peroxide reduction test in RDE, showing very promising results. Thus, the Fe-N-C catalyst was tested at the cathode of a DMFC after determination of the optimal electrode formulation regarding catalyst loading and Nafion ® content, showing a maximum power density of 20 mW cm −2 at 90 °C. A short term durability test to assess the behavior of both the Fe-N-C and the Pt/C catalysts was conducted on the DMFC, showing a better performance of the non-noble catalyst. Thus, the Fe-N-C catalyst is a potential good candidate to be used as catalytic material for DMFC cathode, in alternative to Pt. The performance in a H 2 /O 2 PEMFC was tested as well, showing a power density of 105 mW cm −2 at 60 °C.

Iron phthalocyanine (FePc) was used as iron/nitrogen/carbon source and templated with an ordered mesoporous silica (SBA-15), followed by heat treatment and leaching of SiO2 with hydrofluoric acid (sacrificial method). The Fe–N–C catalyst was tested for the oxygen reduction reaction using a rotating disk electrode (three electrode configuration) in the presence of methanol at different concentrations. Furthermore, the catalyst was investigated in a single cell configuration of a direct methanol fuel cell (DMFC) under different methanol concentrations and temperatures. The optimal operating condition was found to be 1 M at 110 °C, reaching 11.2 mW cm−2 using a commercial Pt-Ru black at the anode and the Fe–N–C at the cathode side. Interestingly, the cathodic catalyst was not dramatically affected by the presence of crossovered methanol, showing only a 12% drop in maximum power density with the highest methanol concentration of 10 M at the anode. A 3D multiphysics model was implemented to further explain the experimental DMFC performance data using a commercial platform (Comsol® Multiphysics v4.4a). The model agreed with the experimental data, showing a direct relationship between water saturation, and oxygen consumption, consequently oxygen starvation at the cathodic catalytic layer. The model considered two phases on the cathode side computed by extended Darcy law within the catalytic layer and the gas diffusion layer domains.

In the lithium-oxygen (Li-O2) cell, the porous structure of the cathode is an important issue as well as challenge for its task of accommodating discharge products and providing free paths for oxygen. Clogging of pores and degradation of materials at the cathode affect the discharge rates and cycling performance of Li-O2 cell. Based on the study of five synthesized nanostructured porous carbons, namely, 2-D ordered mesoporous carbon C-15, 3-D ordered mesoporous carbons C-16 and C-16B with larger pores, hollow core mesoporous shell carbon (HCMSC), and reduced graphene oxide (rGO), we found that the type and pore structure of the carbon significantly affect the electrochemical performance of the cell. Both C-15 and rGO cathodes demonstrate good cell cycleability, while the HCMSC, with its interesting bimodal pore system, is not favorable for further improving cycling performance. The C-16B has similar morphology and electrolyte wettability of C-16. However, the former possesses larger pores, and such porosity significantly improves the cell cycleability up to 44 cycles, corresponding to an extended operation life of 850 h.

A 3D multi-physics, multi-component and not isothermal model is developed to analyze the effects of catalyst structures on the performance of a gas diffusion electrode (GDE) cell toward the oxygen reduction reaction using dry oxygen as a reactant. The model includes Stokes–Brinkman, Maxwell–Stefan, and modified Butler–Volmer equations for simulating the performance of the GDE cell, solved by Comsol® Multiphysics v4.4a platform. The model is validated against experimental data, showing congruent and convergent responses for different electrodes based on noble and non-noble metals catalysts, confirming the accuracy of the model and the equations applied. The use of a 3D model incorporating porous materials can be used for evaluating mass transport and diffusivity parameters of the electrocatalyst, identifying the controlling variable in the process. The model can be used as an optimization tool for further improvement of catalyst synthesis, suggesting which properties can be tuned to improve the overall performance in the catalyst design phase.

Three different types of reduced graphene oxide (rGO) were prepared starting from graphite oxide (GO) produced with the Hummers’ method using three different exfoliation-reduction strategies: thermal annealing under N2 atmosphere at 700 °C, thermal annealing under H2–N2 (1:1 vol.) atmosphere at 500 °C and ultrasonication. Then, three non-noble metal catalysts (NNMC) for the oxygen reduction reaction (ORR) were synthesized using these three different rGO as carbon supports, by impregnation of a complex formed between Fe(II) ions and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) as source of nitrogen, followed by a pyrolysis at 800 °C. The physical-chemical properties of rGO and Fe-N/rGO catalysts were characterized by N2 physisorption, XRD, XPS, SEM, and EDX. The capacitive behavior and the ORR activity of rGO and Fe-N/rGO catalysts were measured in alkaline conditions by cyclic voltammetry (CV) and rotating disk electrode (RDE), respectively. The three different reduction-exfoliation methods used for the rGO preparation influenced the physical-chemical properties, as well as the capacitive currents and the ORR activity of both rGO and Fe-N/rGO. This provides an insight about which synthesis process could be the most convenient for the final application.

In this work, polycrystalline platinum-based nanoparticles were deposited onto two different carbon supports: carbon black and multiwalled carbon nanotubes. The samples were characterized by Raman spectroscopy, transmission electron microscopy and tested using a Kelvin probe to measure the work function changes upon oxygen adsorption at different temperatures. The same materials were evaluated as electrocatalysts for the oxygen reduction reactivity under acid conditions, in a three-electrode configuration, in a rotating disc electrode setup. Since both Kelvin probe work function measurements and rotating disc electrode measurements provide the sample averaged surface properties, the correlation of results from these two techniques can be useful for the understanding of the catalysts' performance. A striking correlation between the electrocatalytic activity with the material's ability to activate molecular oxygen was observed. The obtained results were rationalized in terms of electronic interaction between the supporting carbon material, and a metallic component.

In this work a comprehensive study of the activity and stability of a non-precious metal catalyst of type Fe- N- C in acidic media is reported. The catalyst was prepared from polyaniline, dicyandiamide and iron acetate as precursors. Temperature-dependent rotating-disk electrode experiments were performed to determine the activation energy of the catalyst. Besides, load cycle durability tests with and without the addition of methanol show that there is no additional deactivation caused by methanol addition. In a Direct Methanol Fuel Cell (DMFCs) our catalyst performed similarly good in comparison to other Fe-N-C catalysts. Raman and Mossbauer spectroscopy provide valuable information on the structural composition and chemical changes induced by durability and stability testing of the catalyst. While the maximum power density during DMFC operation decreases by 85%, the qualitative distribution of iron sites might indicate the formation of iron and iron oxide clusters as decomposition product associated with the disintegration of FeN4 sites.

Various Pt/TiOx-C catalysts are synthesized by changing the temperature of synthesis of TiOx from 500 to 1000 °C. The carbon support is a commercial multi-wall carbon nanotubes. The synthesis temperature of the TiOx affects the structure and morphology of the support generating different types of suboxides, ranging from TiO2 anatase, TiO2 rutile, Ti3O, and Ti3O5. The catalysts are characterized by means of BET, EDX, XRD, and ICP-MS analyses. The obtained catalysts display a Pt loading of 13.6–19.2 wt.%, with a Pt/Ti atomic ratio of 0.177–0.194. The catalysts are electrochemically characterized by CV, CO stripping, and LSV. The presence of Ti3O5 suboxide positively improves the performance of the catalyst with respect to the oxygen reduction reaction, and enhances the catalyst stability under potential cycling, with an increase of the electrochemical active surface area (ECSA) compared to the commercial Pt/Vulcan catalyst. After stability test for 4000 cycles in range of 0.06–1.26 V vs RHE the ECSA that resulted was equal to 22.73 m2 gPt−1. Moreover, the catalyst is highly methanol tolerant.

A Fe-N-C non-noble metal (NNM) catalyst for oxygen reduction reaction (ORR) was prepared via hard templating method using Fe(II)-phthalocyanine. Its electrochemical behavior towards the ORR was tested in alkaline conditions using cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques. The kinetics of the reduction of the adsorbed oxygen, the selectivity, and the activity towards hydrogen peroxide reduction reaction (HPRR) were investigated. The ethanol tolerance and the stability in alkaline conditions were also assessed with the purpose to verify the good potentiality of this catalyst to be used in an alkaline direct ethanol fuel cell (DEFC). The results evidence that the ORR occurs mainly following the direct 4 e–reduction to OH−, and that the Fe-N-C catalyst is highly ethanol tolerant and shows a promising stability. The alkaline DEFC tests, performed after the optimization of the ionomer amount used for the preparation of the catalyst ink, show good results at low-intermediate currents, with a maximum power density of 62 mW cm−2. The initial DEFC performance can be partially recovered after a purge-drying procedure, This work was supported by the Madrid Regional Research Council (CAM) [RESTOENE-2 grant n. S2013/MAE2882], the Spanish Economy and Competitiveness Ministry [ENE2016 grant n. 77055-C3-1-R], and the Italian Ministry of Education, University and Research [PRIN NAMEDPEM grant n. 2010CYTWAW].

In this work, two series of cobalt-based spinel catalysts, Co3O4 and NiCo2O4, were synthesised by a hard template method with SBA-15 and were investigated as non-noble catalysts for the oxygen evolution reaction (OER) under basic conditions. The effect of synthesis conditions, i.e., heating rate and calcination temperature, and the addition of minor amounts of iron were evaluated with respect to the OER activity. Moreover, the influence of the alkali cation type in the electrolyte (Li, Na, K) was also evaluated. The highest activity was found for the NiCo2O4 obtained with the lowest heating rate. The increase in the heating rate and calcination temperature results in the decrease of the available surface area for the reaction, leading to the deterioration of the activity. The incorporation of 3 wt% of iron in the lattice of NiCo2O4 and Co3O4 resulted in a decrease of the OER activity, however, the deactivation was much less severe in the case of NiCo2O4 than for Co3O4. Among the alkaline electrolytes used, KOH resulted in the highest catalytic activity both for NiCo2O4 and Co3O4.

Recently the use of titanium oxide and titanium suboxides (Magneli phases) has been extensively investigated as an alternative catalyst support to carbon-based materials for the oxygen reduction reaction in low-temperature fuel cells. In this study, a 15 wt.% Pt-based catalyst was developed on a unique, stable mix of titanium suboxides, with a prevailing of the Ti3O5 phase, doped with Mo, as a Ti3O5-Mo carbon-free support and compared to a commercial 20 wt.% Pt/C (E-TEK). The Pt/Ti3O5-Mo catalyst exhibits excellent electroactivity and stability toward the ORR, reaching a performance of 73.3 mA mg−1, slightly more than the double of the commercial Pt/C, with a current density of 1.1 mA cm−2 at 0.9 V vs RHE, and an half-wave potential of 0.86 V vs RHE. A deep accelerated potential cycling between 0 and 1.2 V vs RHE up to 5000 cycles demonstrated the remarkable stability of the Pt/Ti3O5-Mo catalyst, whose electrochemical surface area loss was accounted for only 11%, compared to the more than 81% loss of the commercial Pt/C reference

Four carbonaceous materials (acetylene black, multi-walled carbon nanotubes, and two carbon materials synthesized by hard-template method) were used as a support to synthesize four Fe-N/C non-noble metal (NNM) catalysts for oxygen reduction reaction (ORR) by impregnation with a FeIII–1,10-phenanthroline complex and subsequent pyrolysis in inert atmosphere. The catalysts were characterized by N2 physisorption, XPS, Raman and TGA, and their ORR activity was measured by rotating disk electrode (RDE) in both acidic and alkaline conditions. The catalysts were tested in an acidic direct methanol fuel cell (DMFC) and in an alkaline direct ethanol fuel cell (DEFC). Due to the slower ORR kinetics at low pH, the features of the carbon support have an important influence on the performance in acidic DMFC. Conversely, the enhanced ORR kinetics at high pH, makes the influence of the C-support less evident in alkaline DEFC. Moreover, the short-term durability test in DMFC for our best Fe-N/C catalysts showed better results compared to Pt/C benchmark catalyst. The durability in alkaline DEFC is poor, even though the initial performance can be partially recovered after purge-drying and reactivation.

In this work, a series of Co3O4 spinels were produced by different synthesis routes (precipitation, solution combustion synthesis, and hard template method), and were used as non-noble catalysts for the oxygen evolution reaction (OER) under basic conditions. The investigated catalysts have a proportional relation between electrochemical activity, surface roughness, and specific surface area. The hard template synthesis method resulted in the most active catalyst compared in this work, which we ascribe to its highly porous structure, and concomitant Co3+/Co4+ redox couple at a lower potential, attributed to the OER. The most performant catalyst was compared with a commercial catalyst (Ni@NiO, Alfa Aesar) showing only 0.01 V overpotential difference, evaluated at 10 mA cm− 2 (overpotential 0.44 V).

The present work aims to compare and evaluate the behavior of platinum catalysts supported on different ordered mesoporous carbons (Pt/OMCs). OMCs were templated from two kinds of ordered mesoporou...

A series of Fe–N–C non-noble metal electrocatalysts for oxygen reduction reaction (ORR) are synthesized using mesoporous carbon (MPC) as C source, polypyrrole (PPY) as N source and Fe(II) acetate as Fe source. In the first part, the effects of the addition of polyvinylpyrrolidone (PVP) and performing a heat treatment on the MPC-PPY support before the impregnation with Fe2+ ions are investigated. In the second part, the best catalyst obtained in the first part is used as a support, and the influence of a second pyrolysis treatment performed with or without further impregnation with Fe2+ is investigated. The materials are characterized by FESEM, TEM, EDX, BET-porosimetry, XPS, and FTIR. The electroactivity towards ORR is assessed with a rotating disk electrode (RDE) apparatus in both acidic and alkaline conditions. The different synthesis pathways examined have a direct influence on the ORR activity. The electroactivity and micropores content increases after the second heat treatment.

Low-temperature fuel cells (LTFCs) based on polymer electrolyte membranes (PEMs) fed with hydrogen are being recognized to be among the best candidates as pollution-free and energy-saving power sources for electric or hybrid vehicles or portable apparatuses because of their high-energy conversion efficiency (~58 %) and zero or nearly zero emissions. Currently, cost and durability are the main limitations of FC technology to be commercialized. A significant percentage of the cost of PEMFCs comes from precious group metal (PGM) based catalysts that are used mainly for the oxygen reduction reaction (ORR). Therefore, a breakthrough in the development of cost-effective, highly performing, and durable catalysts has been identified as the determining factor for success toward PEMFC commercialization. In particular, non-noble metal (NNM) cathodic electrocatalyst gained lots of attention in recent years to replace PGM-based catalysts for the ORR. Within various NNM electrocatalysts, the most promising ones seem to be heat-treated Fe(II) and/or Co(II) chelates and macrocycles supported on carbon particles. The formation of metal–nitrogen (M–NX/C) and metal–carbon (M/C) active ensembles after the heat treatment is necessary for ORR. In this chapter we will describe an enhancement of the electrochemical activity toward ORR through a step-by-step understanding of the variables involved during the formation of active Fe–NX NNM catalysts. We adopted different approaches in order to understand the formation of active ensembles and to increase the activity by a rational step-by-step progression.

Different Me–N–C catalysts for oxygen reduction reaction (ORR) are synthesized using Me(II)-phthalocyanines (Me = Fe, Co, Cu, Zn) as a unique precursor molecule, and SBA-15 silica as a sacrificial template. The influence of different transition metals on the pyrolysis process and the consequent physical–chemical properties of the final catalysts were investigated using different characterization techniques such as N2 physisorption, FESEM, EDX, XPS, XRD, and thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The ORR activity and selectivity toward a complete 4-electrons reaction were assessed by RDE analysis in alkaline conditions. The ORR activity of the different Me–N–C catalysts decreases in the order Fe > Co > Cu > Zn ≈ H. Microporosity, pyridinic nitrogen content and temperature at which H2 starts to be detected during the pyrolysis are directly related to the ORR activity of the different catalysts.

Pt 3 Cu nanoparticles are deposited on multi wall carbon nanotubes (MWCNT) according to three different types of synthesis: a thermal reduction using an aprotic solvent (“thermal method”, TM), a chemical reduction using sodium borohydride (“chemical method”, CM), and an alloy method (“alloy method”, AM). The catalysts are characterized by means of BET, FESEM, EDX, XRD, ICP-MS and XPS analyses. The obtained catalysts display a Pt loading of 19.6–19.8 wt.%, with a Pt/Cu atomic ratio of 2.60–2.80. The electrocatalytic activity towards ORR is assessed by RDE in acid conditions (0.1 M HClO 4 ). The best activity belongs to the Pt 3 Cu/C catalyst prepared by chemical reduction method (–10.300 mA mg −1 Pt ) at 900 mV, IR corrected.

a b s t r a c t Three iron-nitrogen-containing non-noble metal electrocatalysts supported on networked graphitic structures, carbon nano-networks (CNNs), were synthesized using a wet-impregnation method. The CNN supports were produced in-house by chemical vapor deposition of ethene over cobalt nanoparticles that were previously synthesized in bicontinuous microemulsions. The three CNN supports differed in cobalt content, ranging from 0.1 to 1.7% in weight. These CNN supports were used to prepare Fe-N/CNN electrocatalysts. The oxygen reduction reaction (ORR) activity was evaluated by rotating disk electrode measurements. Interestingly, the highest ORR activity belonged to the catalyst with the highest iron and cobalt content. The most promising catalyst was investigated as the cathode material in a polymer electrolyte membrane fuel cell (PEMFC) and a direct methanol fuel cell (DMFC). The maximum recorded power densities were 121 mW cm −2 for PEMFC and 15 mW cm −2 for DMFC, respectively. These values are superior or comparable to the best state of the art for similar materials. The durability to potential cycling was tested in half-cell studies and an activity loss around 10% was found after 1000 cycles, which is not significantly different from what is reported in the literature. The relatively simple synthesis approach and the cheap precursor materials make this electrocatalyst promising for low-temperature fuel cell applications.

Starting from metal nitrates and glycine, 2% Pd/BaCeO 3 ∙2ZrO 2 catalyst was prepared by solution combustion synthesis and tested towards the total oxidation of methane. The catalyst underwent heavy sulphur-hydrothermal treatment at 800 °C up to 450 h. The catalyst was fully characterized (XRD, BET, SEM, O 2 -TPD, FTIR analyses and catalytic activity via CH 4 -TPC) every 150 h. With ageing, catalytic activity tests demonstrated that the catalyst was heavily poisoned after 150 h; then it recovered the catalytic activity after 300 h, with a resulting performance better than the one reached in the fresh status. At the end of the sulphur-hydrothermal treatment, after 450 h, the catalyst resulted heavily poisoned again. On the fresh catalyst surface, IR analysis of CO adsorption evidenced the formation of highly dispersed Pd metal clusters and Pd ions. After 300 h of sulphur hydrothermal ageing, the increased catalytic activity towards methane combustion was probably supported by the segregation of ZrO 2 and CeO 2 . Moreover, subsurface and bulk sulphate formation was detected with ageing and Pd metal species were not anymore available for CO coordination, probably because hindered by sulphate deposits. Prevailing ageing mechanisms resulted in the oxidation of the surface Pd metal particles and surface-bulk sulphates formation, the latter destroying the starting crystallographic structure, leading thus to the final catalytic activity decay.

Two catalysts are synthesized by wet impregnation of multi walled carbon nanotubes (MWCNT) with a complex formed between Co(II) ions and the nitrogen-containing molecule 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ), followed by one or two identical heat treatments in N 2 atmosphere at 800 °C for 3 h. Catalysts are fully characterized by FESEM, EDX, BET, XRD, FTIR, TGA, XPS analyses, and electrochemical techniques. The electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalysts in acid conditions is assessed by means of a rotating disk electrode (RDE) apparatus and a specific type of cell equipped with a gas diffusion working electrode (GDE). In both testing approaches, the catalyst heat-treated twice (Co-N/MWCNT-2) exhibits higher electroactivity than the catalyst heat-treated once (Co-N/MWCNT-1). Chronoamperometries both in RDE and GDE cell are also performed, showing less electroactivity decay and better current performance for the catalyst heat-treated twice.

The solution combustion method (SCS) is demonstrated as an easy and fast alternative method allowing the synthesis of mixed oxides with thermally sensitive metals, still keeping a good control on their stoichiometry and phase composition. Bismuth molybdates with different theoretical Bi/Mo atomic ratios, namely α-Bi2Mo3O12, β-Bi2Mo2O9, and γ-Bi2MoO6 were synthesized by the SCS, fully characterized by XRD, Raman, SEM/EDX, BET and XPS analyses, and tested in the partial oxidation of propene to acrolein. The SCS method allowed obtaining crystalline catalysts with Bi/Mo atomic ratios close to the theoretical values and very good catalytic properties namely high propene conversion (from 13.4 to 23.4%) and acrolein selectivity (from 71.5 to 80.0%) at 425 °C. A high purity of the SCS prepared bismuth molybdates was obtained by means of a subsequent calcination treatment. Such treatment did not alter the high catalytic activity of the catalysts, which slightly increased (from 12.3 to 25.5%), but induced a marked loss of acrolein selectivity (from 66.2 to 48.4%) at 425 °C. This effect is due to a strong increase of the oxidation states of Mo and Bi and reduction of the specific surface area during the calcination.

Pharmaceuticals have low biodegradability and can retain their chemical structure for long periods of time leading to an accumulation in the environment causing irreversible changes. Electrochemical oxidation has been proved to be an environmentally friendly and economically viable solution for bio-refractory of organic molecules as well as for the disinfection of wastewaters. This paper aims to evaluate the performance of specific energy consumption for a given reduction of toxic organic compound loads in a continuous flow bipolar packed-bed electrochemical reactor and compare this with a classical parallel plate reactor. The energy cost for both the parallel plate and bipolar electrochemical reactors are similar (around 1.6 kWh m-3) lower than other advanced oxidation process reported in literature. However, the bipolar configuration is particularly suitable for low conductivity waste water and/or for avoiding the formation of organochloride compounds in a chloride rich wastewater.

In this paper, the reduced graphene oxide (rGO) is synthesized from graphite oxide (GO) via microwave exfoliation method, and used to support non-noble metal Fe–NX based electrocatalysts (Fe–NX/rGO) for the oxygen reduction reaction (ORR). Tripyridyl triazine (TPTZ) is used as a ligand for Fe–NX catalyst preparation. The obtained catalyst presents a high content of pyridinic (N1) and pyrrolic (N2) nitrogen types on the catalyst surface (40.0% and 52.3% atomic concentrations, respectively) with Fe atomic content of 0.7%. A catalyst loading of 0.5 mg cm−2 with a ionomer-to-carbon (ITC) mass ratio of 0.2 deposited on the glassy carbon electrode allows the highest ORR activity with the specific current of −0.35 mA mg−1 at a cell voltage of 0.8 V (vs. RHE). The overall electron transfer number obtained is of 3.98. Stability tests in acidic solution for this catalyst are also performed.

Three types of iron-nitrogen-containing non-noble metal catalysts, supported on an ultrasonic spray pyrolysis mesoporous carbon (USPMC), a hollow core mesoporous shell carbon (HCMSC), and a standard carbon (Ketjen Black CJ600, KB), respectively, are synthesized using a wet-impregnation method. The morphologies and structure as well as composition of the synthesized carbon supports and their corresponding supported Fe-N X catalysts (namely Fe-N X /USPMC, Fe-N X /HCMSC, and Fe-N X /KB, respectively) are physically characterized using EDX, SEM, FESEM, and BET analysis, respectively. The catalytic activities of these three electrocatalysts toward oxygen reduction reaction (ORR) are measured using rotating disk electrode technique in O2-saturated 0.5 M H2SO4 solution. The catalyzed ORR exchange current densities are also obtained using the Tafel method based on the measured data. Among these three electrocatalysts, Fe-N X /HCMSC can give the best ORR performance, which is correlated to its higher nitrogen, mesopore, and micropore contents, compared to the other electrocatalysts. It is rationalized that the performance improvement of these electrocatalysts may be achieved as long as an optimal relationship among mesopores, micropores, and even macropores for increasing both ORR kinetics and reactant gases accessibility to the active sites can be found.