A simple and innovative prototype for biomass pyrolysis is presented, together with some experime... more A simple and innovative prototype for biomass pyrolysis is presented, together with some experimental results. The setup uses only the thermal solar energy provided by a system of reflecting mirrors (Linear Mirror II) to heat a selected agro-waste biomass, such as wheat straw. At the end of the pyrolysis process, solar carbon with a high energy density (around 24 - 28 MJ/kg) is produced from a biomass with an energy density of 16.9 MJ/kg. The perspectives for a future industrial application of this setup are also discussed.
High-temperature reduction/oxidation cycles promote the oxygen storage capacity of mesoporous cer... more High-temperature reduction/oxidation cycles promote the oxygen storage capacity of mesoporous ceria; this is associated with the formation during reduction of a hexagonal CeOx phase which on reoxidation gives amorphous ceria
erium Oxide (CeO2): Synthesis, Properties and Applications provides an updated and comprehensive ... more erium Oxide (CeO2): Synthesis, Properties and Applications provides an updated and comprehensive account of the research in the field of cerium oxide based materials. The book is divided into three main blocks that deal with its properties, synthesis and applications. Special attention is devoted to the growing number of applications of ceria based materials, including their usage in industrial and environmental catalysis and photocatalysis, energy production and storage, sensors, cosmetics, radioprotection, glass technology, pigments, stainless steel and toxicology. A brief historical introduction gives users background, and a final chapter addresses future perspectives and outlooks to stimulate future research
With the advent of green technologies, solar fuel has gained particular interest that helps in pr... more With the advent of green technologies, solar fuel has gained particular interest that helps in producing syngas which is the primary feedstock for many of the synthetic chemicals using emissions (CO2 and H2O). Thermochemical redox cycles use metal oxides as oxygen carriers that are capable of oxygen diffusion during continuous reduction and oxidation cycles. In the chapter, the focus has been derived in many aspects such as metal oxides and their evolution, reactor design and their scope of large-scale modularity, and lastly its application in fuel, chemicals and power plants. The chapter also highlights the system analysis for different chemicals, their techno-economic feasibility, and viability.
A multi-analytical approach (in situ X-ray diffractometry, XRD, temperature programmed reduction ... more A multi-analytical approach (in situ X-ray diffractometry, XRD, temperature programmed reduction TPR, thermogravimetry TGA) was used to deeply study the phase transition between the Pr0.5Ba0.5MnO3- δ (m-PBM) and the double layered perovskite PrBaMn2O5+ δ (l-PBM). m-PBM sample was prepared by an auto-combustion based citrate procedure and exposed to consecutive reduction and oxidation cycles at high temperature to understand the effect of oxidizing and reducing atmospheres on structural changes and stabilization of the layered double perovskite. XRD analysis showed the existence of a pseudo cubic structure (c-PBM), which is formed from the direct oxidation of l-PBM. TPR results confirmed the c-PBM to l-PBM reversibility to the redox processes, and the TGA characterization showed a fast transition between l-PBM to c-PBM. The oxidation of l-PBM to c-PBM seems pivotal for the stabilization of the layered reduced structure. The results are discussed in the perspective to develop versatil...
22 Tailoring active, durable and cost-effective electrocatalysts are crucial for hydrogen evoluti... more 22 Tailoring active, durable and cost-effective electrocatalysts are crucial for hydrogen evolution 23 (HER) and oxidation reaction (HOR) in alkaline medium. Herein, the synthesis, physicochemical 24 and electrochemical characterization of NiO-Ni nanostructures supported onto multi-walled carbon nanotubes (CNT), as well as its performance in a unitized regenerative alkaline micro-26 fluidic cell (URAμFC) as hydrogen bifunctional electrode is reported. The hydrogen electrode 27 reaction (HER/HOR) activity on NiO-Ni/CNT nanomaterial (0.36 mAcm-2) outperformed that of 28 commercial Pd/C (0.05 mAcm-2) and turned out to be competitive with commercial Pt/C (0.56 mA 29 cm-2). With NiO-Ni/CNT catalyst, a maximum power density (fuel cell mode) of ca. 40 mW cm-2 30 was obtained, whereas the electrocatalyst submitted to electrolyzer mode, consumed an electrical 31 power density of ca. 165 mW cm-2 , at 100 mA cm-2. 32 33 1. INTRODUCTION 34 Hydrogen (H 2) has been considered as a promising energy-carrier to replace fossil fuels, due to its 35 high energy density (143 kJ g-1). Its use in a fuel cell (FC) is not limited by the Carnot cycle 1 , and 36 the only oxidation product is water. Up-to-date, the alkaline hydrogen technology can offer the 37 great advantage to avoid the use of noble metals (Platinum group metals, PGMs), turning it up an 38 economically viable technology. Indeed, PGM-free based catalysts for the oxygen electrode 39 reaction (ORR/OER), with activity and stability similar or higher than that of Pt or IrO x , have been 40 developed. 2-3 The future of this technology relies on the efficient hydrogen evolution reaction 41 (HER), and hydrogen oxidation reaction (HOR), henceforth labeled as the hydrogen electrode 42 reaction (HER/HOR). Moreover, the HER/HOR kinetics in alkaline medium possesses higher 43 energy barriers with respect to that in acid medium, 4 and thus it is considered as a bottleneck for the alkaline hydrogen technology. The use of earth-abundant PGM-free catalysts is imperative to 45 inspire the above-mentioned technology. Some transition metals are able of catalyzing the slow 46 HER/HOR reaction, focusing primarily on Ni-based materials. 5-7 Nonetheless, the tuning of a highactive Ni-based catalyst for the alkaline HER/HOR still remains a challenge. Recently, some 48 strategies have been developed to improve the HER/HOR performance with Ni-based catalysts, 49 e.g., alloying Ni with another transition metal, 8-10 Ni sulfides and phosphides, 11 carbon-50 encapsulated Ni-based particles, 12 the interaction between Ni and carbon supports, 6, 13 or the use 51 of heterostructures (Ni 3 N, 14 Ni 3 N/Ni 15 or NiO-Ni 16-18). Among these strategies, NiO-Ni structures 52 do not require a complex synthesis protocol, and their reported activity is listed as a potential 53 option for HER 19-20 or HOR 16-18 electrocatalysts. However, in spite of the continuous efforts, their 54 electrocatalytic activity, described by the exchange current density, is still far from that of PGM-55 based catalysts, hampering their application in an electrolyzer (HER), or FC (HOR) or, in the best 56 case, in a unitized regenerative cell (URFC). On the other hand, the coupling between metal-based 57 nanostructures with multi-walled carbon nanotubes (hereafter simplified to CNT) is an strategy of 58 paramount potentiality to achieve advanced materials with exceptional properties for energy-59 conversion devices. 21 The so-called strong metal-support interaction (SMSI) modifies the local 60 surface, since the non-planar CNT structure can cause π-electron density to shift from the concave 61 to the convex CNT surface leading to electron potential difference between inner and outer walls 62 of CNTs, 21 which can bias the actual interactions. In addition, we exploited the synergy between 63 Ni and NiO phases, 16-19 and the SMSI effect, so that our engineered NiO-Ni/CNT nanostructures 64 were positively tested as an efficient alkaline HER/HOR electrode material. The role of the CNT Page 3 of 32 ACS Paragon Plus Environment ACS Applied Energy Materials 4 65 was elucidated by using Carbon Vulcan XC-72 for comparative purposes. A URFC system in an 66 alkaline microfluidic cell (URAμFC) has been adopted as a proof-of-concept of the NiO-Ni/CNT 67 electrocatalyst, to demonstrate its effectiveness in an energy-conversion device system. 68 69 2. EXPERIMENTAL SECTION 70 2.1 Materials synthesis 71 Multi-walled carbon nanotubes (CNTs) from Sigma-Aldrich (outer diameter 10-15 nm, internal 72 diameter 2-6 nm, and length 0.1-10 µm) and Carbon XC-72 Vulcan (C) from Cabot were used as 73 supports. The carbon-supported NiO-Ni hybrid catalysts were prepared using a modified two-steps synthesis procedure. 22 In short, 250 mg of carbon (C or CNT) support and 2.62 g of NiCl 2 •6H 2 O 75 were ultra-sonicated in 50 mL of deionized water for 30 min. The suspension was cooled down 76 (ice bath) at 4 °C and stirred for 1 h in N 2 atmosphere. Then, ice-cold NaBH 4 solution (186 mg 77 diluted in 20 mL of ethanol) was added dropwise. After 2 h, the suspension was transferred to a 78 Teflon-lined stainless-steel autoclave. NH 4 OH (5 mL) and mono-hydrated hydrazine (2 mL) were 79 added. The autoclave was sealed and subjected to a hydrothermal treatment at 150 °C for 12 h. 80 The final product was washed with deionized water and filtered at vacuum. The black solid powder 81 was dried at 60 °C overnight. 82 2.2 Physicochemical characterization 83 Raman spectroscopy: Raman spectra were obtained in a Horiba Jobin Yvon Spectrometer HR 800 84 with a 532 nm laser in the range of 100-3000 cm-1 .
Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for the distributed production o... more Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for the distributed production of energy require the cell to operate with both traditional hydrocarbon fuels (CH4 and LPG) and biomass-derived fuels (biogas, ethanol). Benefits in terms of lifetime and thermo-mechanical resistance are achieved by decreasing the operating temperature to 500-700°C (IT-SOFC). On the one hand, the use of hydrocarbons leads the traditional Ni-based anodes to deactivate due to coke formation; on the other hand, lower temperatures ask for electrolytes different from YSZ, for instance based on Ce oxides. Novel cells and materials are required, whose development must be closely accompanied by numerical model analysis, to rationalize chemical and physical phenomena. In this work, IT-SOFCs based on Samarium doped Ceria (SDC, Ce0.8Sm0.2O1.91) electrolytes and Cu/Pd/CZ80 anodes are investigated for applications with biogas mixtures (CO2/CH4) and syngas mixtures (H2/CO/H2O). Polarization curves and ...
Nowadays, dense ceramic membranes based on mixed ionic and electronic conductors are considered v... more Nowadays, dense ceramic membranes based on mixed ionic and electronic conductors are considered very promising materials for H2 separation at T > 600°C. Among these, BaCe0.65Zr0.2Y0.15O3-δ-Ce0.85Gd0.15O2-δ (BCZ20Y15-GDC15) composite combine an acceptable H2 flux and good chemical stability under CO2-and H2S-containing atmospheres. However, a clear understanding of its crystal structure, phase stability and mechanical stability under real working conditions could not yet be obtained. In this work, its structural evolution was investigated from room temperature to 800°C by in-situ synchrotron XRD analyses under dry and wet H2. No chemical interaction between the BCZ20Y15 and GDC15 phases occurred in the composite, thus evidencing its excellent chemical stability under operating conditions. However, some phase transitions were observed for the BCZ20Y15 phase, under both dry and wet H2: i.e., it showed an orthorhombic Imma structure from room temperature to 100°C, trigonal R-3c up to 700°C and cubic Pm-3m up to 800°C. On the other hand, the GDC15 phase did not display any phase transition, remaining in a cubic Fm-3m structure in all tested conditions. Moreover, a synergistic effect of the BCZ20Y15 and GDC15 phases in the volume expansion of the composite was revealed: indeed, BCZ20Y15 and GDC15 lattice
The development of a sustainable economy based on the use of renewable resources and the reductio... more The development of a sustainable economy based on the use of renewable resources and the reduction of greenhouse gases emissions is an important mandate in modern societies to minimize the global warming. The CO 2-reforming of methane through a conversion of CO 2 and CH 4 to syngas is a suitable process for this purpose and there is growing interest in the development of new catalysts for this process' application at an industrial scale. This study is the first to investigate methane dry reforming activity of nickel supported on CeO 2 and CeO 2-ZrO 2 solid solutions doped with neodymium. The supports were synthesized using a surfactant-assisted co-precipitation method and characterized through several analytical techniques to understand the role of synthesis parameters in the distribution of the dopant as well as in the properties of the supports. Co-doping with Zr and Nd resulted in an enhancement of dry reforming activity of ceria due to a higher dispersion of Ni and changes in the strength of basic sites. It was also shown that the addition of Nd helped to mitigate coking issues by increasing the mobility of surface oxygen in ceria and ceria-zirconia oxides and, accordingly, the rate of oxidation of carbonaceous deposits.
Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for distributed production of en... more Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for distributed production of energy require the cell to operate both with traditional hydrocarbons (CH4, LPG) and biomass-derived fuels (biogas). Several benefits in terms of lifetime and thermo-mechanical resistance are achieved by decreasing the operating temperature to 500-700°C (IT-SOFC). On the one hand, the use of hydrocarbons leads traditional Ni-based anodes to deactivate due to coke formation; on the other hand, lower temperatures ask for electrolytes different from YSZ, mostly based on Ce oxides. Novel cells and materials are then required. In this work, IT-SOFCs based on Samarium doped Ceria (Sm0.2Ce0.8O1.9, SDC) electrolytes and Cu/Pd/CZ80 anodes are investigated for applications with syngas mixtures and CO2/CH4 mixtures. A physically-based, numerical model of the IT-SOFC was applied to analyze the experimental results and kinetic equations were derived for the electro-chemical reactions: in the presence of syngas, the occurrence of a co-oxidation route is proved, wherein H2 and CO are electro-oxidized contemporarily. Materials and Methods SDC electrolyte-supported cells with 15 wt% Cu, 0.15 wt% Pd, 15 wt% CZ80 (CZ80 20 wt% CeO2, 80 wt% ZrO2) composite anodes and LSCF cathodes were prepared by die-pressing. SDC powders mixed with graphite were pressed with pure SDC. The bilayer was calcined in air (1400°C, 3 h) producing a porous SDC scaffold (150 μm) supported on a dense SDC electrolyte (380 μm). The porous scaffold was impregnated with Cu/Pd/CZ80-based solutions and then the cathode (40 μm) was deposited. Polarization and EIS measurements were collected between 600 and 700°C with syngas mixtures (2.3 – 0.4 H2/CO ratio), H2/N2 mixtures (from 97 to 30% H2 v/v), CO/CO2 mixtures (from 97 to 50% CO v/v) and synthetic biogas (75% CH4/25% CO2). The EIS tests were performed at the OCV. A model was applied to analyze both the EIS spectra and the polarization curves. The model is one-dimensional, charge-distributed, Dusty-Gas, dynamic and heterogeneous and allows to predict the cell voltage based on physically-sound conservation equations for mass, charge and energy. The model includes molecular kinetic schemes for the anodic catalytic reactions (CO2 reforming of CH4, WGS) and for the electrocatalytic reactions (H2 and CO electro-oxidation, O2 reduction). Appropriate correlations account for the presence of the electronic current leakage in the electrolyte. Results and Discussion The IT-SOFCs were first tested in syngas mixtures at varying the H2/CO ratio: no variation was found passing from 2.3 to 0.4 ratio (Fig. 1a). Analogous observations were done with the EIS spectra. These results suggested that both the H2 electro-oxidation and the CO electro-oxidation occurred simultaneously in the presence of syngas. A model analysis of the polarization and EIS curves was performed to prove the activation of the co-oxidative route for CO and H2. The IT-SOFCs were thus tested in H2/N2 mixtures at varying H2 concentration to derive a power-law kinetic rate equation for the electro-oxidation of H2. The polarization curves (Fig. 1b) showed a decrease of the extracted current at decreasing H2 partial pressure. As well, an increase of the polarization resistance at decreasing H2 content was observed in the EIS tests (Fig. 1c). Coherently with the use of SDC, which is a MIEC electrolyte and activates a leakage current, the measured OCVs were smaller than the Nernstian ones. Application of the charge distributed model revealed the axial variation of the leakage current in the electrolyte and in the electrodes. To complete the kinetic investigation, EIS and polarization tests with CO/CO2 mixtures were performed to derive a power-law rate for the CO electro-oxidation reaction. A picture similar to that of the H2/N2 tests was observed. The rate equations and their parameters (reaction orders, activation energies and rate constants) were derived based on the best simulation of the impedance spectra. Once these rates were extracted, the experiments with syngas mixtures were simulated on a fully predictive basis: the close match of the simulations confirmed that the co-oxidative scheme could rationalize the data. Simulations based on different reactive schemes (H2 oxidation + WGS, CO oxidation + RWGS) failed in achieving a satisfactory description, suggesting that the parallel oxidation of H2 and CO was the only adequate scheme. Conclusions By means of model analysis of experimental polarization and impedance curves, we show that, in the presence of syngas, the electro-oxidation of H2 and that of CO occur simultaneously in a novel, Ni-free, IT-SOFCs based on Samaria-doped Ceria. The activation of a co-oxidative route is a most distinguishing feature of Ce-based cells, compared to traditional SOFCs. Figure 1
The reactivity of a ceria-rich Ce0.85Zr0.15O2 solid solution towards the thermochemical water spl... more The reactivity of a ceria-rich Ce0.85Zr0.15O2 solid solution towards the thermochemical water splitting process (TWS) was studied over repeated H2/H2O redox cycles. The structural and surface modifications after treatment at high temperature under air or N2 atmospheres were characterized by High-Resolution Transmission Electron Microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray Photoemission Spectroscopy (XPS) and Positron Annihilation Lifetime Spectroscopy (PALS). Samples treated under nitrogen resulted more active due to phase segregation with formation of a zirconyl oxynitride phase in catalytic amount. Insertion of N 3into the structure contributes to increase the numbers of oxygen vacancies that preferably arrange in large clusters, and to stabilize Ce 3+ centers on the surface. In comparison, treatment under air resulted in a different arrangement of defects with less Ce 3+ and smaller and more numerous vacancy clusters. This affects charge transfer and H-coupling processes, that play an important role in boosting the rate of H2 production. The behavior is found to be only slightly dependent on the starting ceria-zirconia composition and it is related to the development of a similar surface hetero-structure configuration, characterized by the presence of at least a ceria-rich solid solution and a (cerium-doped) zirconyl oxynitride phase, which is supposed to act as a promoter for TWS reaction. The above findings confirm the importance of a multi-phase structure in the design of ceria-zirconia oxides for water splitting reaction and allow a step forward to find an optimal composition. Moreover, the results indicate that doping with nitrogen might be a novel approach for the design of robust, thermally resistant and redox active materials. All these findings suggest new approaches for the development and design of ceria based materials for the two-step water splitting reaction and highlight the importance of engineering the surface defect structure/configuration of the material to obtain an efficient catalyst. In this regard, the role and the impact of nitridation process need to be further investigated.
The study presented in this paper aims to evaluate the performance degradation of Polybenzimidazo... more The study presented in this paper aims to evaluate the performance degradation of Polybenzimidazole (PBI) based High Temperature PEM (HTPEM) fuel cells subjected to different ageing tests, according to a methodology already used by the authors. Three HTPEM Membrane Electrode Assemblies (MEAs) were characterized before and after different aging tests and performance compared. The three MEAs have been named MEA C, MEA D and MEA E. MEA C was subjected to 100,000 triangular sweep cycles between Open Circuit Voltage (OCV) and 0.5 A/cm 2 with 2 s of permanence at OCV at each cycle. MEA D and MEA E were subjected to 440 h of operation at constant load of 0.22 A/cm 2. In order to assess the cell performance, polarization curves, Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) were recorded during the ageing tests. Degradation rates have been obtained for MEA C (44 mV/h), for MEA D (30 mV/h) and for MEA E (29 mV/h). ECSA (Electrochemical Surface Area) has been calculated for the three MEAs showing a reduction of approximately 50% for MEA C and of approximately 30% for MEA D and MEA E. Polarization curves during aging tests confirm that load cycling is more detrimental. A comparison with data obtained by the authors in a previous research seems to confirm the repeatability of the test protocol used.
Ce0.8Zr0.2O2 and Ce0.8La0.5Nd0.2Zr0.13O2-x, were prepared with a surfactant assisted approach and... more Ce0.8Zr0.2O2 and Ce0.8La0.5Nd0.2Zr0.13O2-x, were prepared with a surfactant assisted approach and impregnated with different amounts of nickel. The catalysts were studied in the dry reforming reaction with the aim of using them in a biogas fuelled IT-SOFC anode. The oxidative dry reforming reaction was also investigated, finding that small amounts of oxygen in the biogas mixture reduce the effect of dry reforming side reactions. Catalysts containing Lanthanum and Neodymium showed an improved activity at 600 °C and 650 °C in terms of H2 selectivity and carbon resistance.
A simple and innovative prototype for biomass pyrolysis is presented, together with some experime... more A simple and innovative prototype for biomass pyrolysis is presented, together with some experimental results. The setup uses only the thermal solar energy provided by a system of reflecting mirrors (Linear Mirror II) to heat a selected agro-waste biomass, such as wheat straw. At the end of the pyrolysis process, solar carbon with a high energy density (around 24-28 MJ/kg) is produced from a biomass with an energy density of 16.9 MJ/kg. The perspectives for a future industrial application of this setup are also discussed.
A series of Pd/CeO 2 catalysts was prepared by solution combustion synthesis (SCS) using differen... more A series of Pd/CeO 2 catalysts was prepared by solution combustion synthesis (SCS) using different Pd precursors. The powders were characterized by complementary techniques such as BET surface area measurements, X-Ray diffraction analysis, X-Ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed oxidation, and high-resolution TEM. The results obtained evidenced the formation of a Pd-Ce solid solution on all SCS samples. This solid solution is in the form of an ordered supercell structure only in the SCS catalyst prepared from palladium nitrate. This was correlated to the heat of reaction between Pd(NO3)2 and the fuel. The samples were tested for methane catalytic combustion, and the reaction rates on all SCS samples were approximately twice that of the impregnated counterpart, irrespective of the precursor. This was attributed to the presence of the Pd-O-Ce solid solution, which gave rise to strong Pd-ceria interactions.
... Effect of Sulfur on the Oxygen Storage/release Capacity of Rh/CeO2 and Rh/CeO2-ZrO2 Model TWC... more ... Effect of Sulfur on the Oxygen Storage/release Capacity of Rh/CeO2 and Rh/CeO2-ZrO2 Model TWCs Marta Boaro, Carla de Leitenburg, Giuliano ... 15. G. Colon, M. Pijolat, F. Valdivieso, H. Vidal, J. Kaspar, E. Finocchio, M. Daturi, C. Binet, JC Lavalley, RT Baker, and S. Bernal, J ...
Porous Y 2 O 3-stabilized ZrO 2 (YSZ) samples were synthesized by preparing NiO/YSZ composites by... more Porous Y 2 O 3-stabilized ZrO 2 (YSZ) samples were synthesized by preparing NiO/YSZ composites by tape casting and calcining at 1800 K, reducing the NiO to nickel in H 2 at 973 K, and finally leaching the nickel out of the structure with 2.2M HNO 3 at 353 K. Porous YSZ was prepared from NiO/YSZ composites containing 0, 20, 40, and 50 wt% NiO. Complete removal of the nickel was demonstrated by XRD, weight changes, and porosity increases. Porosities >75% could be achieved without structural collapse of the YSZ phase. Finally, the method was applied to the fabrication of a solid oxide fuel cell with a copper-based anode operating on H 2 and n-butane. Comments
A simple and innovative prototype for biomass pyrolysis is presented, together with some experime... more A simple and innovative prototype for biomass pyrolysis is presented, together with some experimental results. The setup uses only the thermal solar energy provided by a system of reflecting mirrors (Linear Mirror II) to heat a selected agro-waste biomass, such as wheat straw. At the end of the pyrolysis process, solar carbon with a high energy density (around 24 - 28 MJ/kg) is produced from a biomass with an energy density of 16.9 MJ/kg. The perspectives for a future industrial application of this setup are also discussed.
High-temperature reduction/oxidation cycles promote the oxygen storage capacity of mesoporous cer... more High-temperature reduction/oxidation cycles promote the oxygen storage capacity of mesoporous ceria; this is associated with the formation during reduction of a hexagonal CeOx phase which on reoxidation gives amorphous ceria
erium Oxide (CeO2): Synthesis, Properties and Applications provides an updated and comprehensive ... more erium Oxide (CeO2): Synthesis, Properties and Applications provides an updated and comprehensive account of the research in the field of cerium oxide based materials. The book is divided into three main blocks that deal with its properties, synthesis and applications. Special attention is devoted to the growing number of applications of ceria based materials, including their usage in industrial and environmental catalysis and photocatalysis, energy production and storage, sensors, cosmetics, radioprotection, glass technology, pigments, stainless steel and toxicology. A brief historical introduction gives users background, and a final chapter addresses future perspectives and outlooks to stimulate future research
With the advent of green technologies, solar fuel has gained particular interest that helps in pr... more With the advent of green technologies, solar fuel has gained particular interest that helps in producing syngas which is the primary feedstock for many of the synthetic chemicals using emissions (CO2 and H2O). Thermochemical redox cycles use metal oxides as oxygen carriers that are capable of oxygen diffusion during continuous reduction and oxidation cycles. In the chapter, the focus has been derived in many aspects such as metal oxides and their evolution, reactor design and their scope of large-scale modularity, and lastly its application in fuel, chemicals and power plants. The chapter also highlights the system analysis for different chemicals, their techno-economic feasibility, and viability.
A multi-analytical approach (in situ X-ray diffractometry, XRD, temperature programmed reduction ... more A multi-analytical approach (in situ X-ray diffractometry, XRD, temperature programmed reduction TPR, thermogravimetry TGA) was used to deeply study the phase transition between the Pr0.5Ba0.5MnO3- δ (m-PBM) and the double layered perovskite PrBaMn2O5+ δ (l-PBM). m-PBM sample was prepared by an auto-combustion based citrate procedure and exposed to consecutive reduction and oxidation cycles at high temperature to understand the effect of oxidizing and reducing atmospheres on structural changes and stabilization of the layered double perovskite. XRD analysis showed the existence of a pseudo cubic structure (c-PBM), which is formed from the direct oxidation of l-PBM. TPR results confirmed the c-PBM to l-PBM reversibility to the redox processes, and the TGA characterization showed a fast transition between l-PBM to c-PBM. The oxidation of l-PBM to c-PBM seems pivotal for the stabilization of the layered reduced structure. The results are discussed in the perspective to develop versatil...
22 Tailoring active, durable and cost-effective electrocatalysts are crucial for hydrogen evoluti... more 22 Tailoring active, durable and cost-effective electrocatalysts are crucial for hydrogen evolution 23 (HER) and oxidation reaction (HOR) in alkaline medium. Herein, the synthesis, physicochemical 24 and electrochemical characterization of NiO-Ni nanostructures supported onto multi-walled carbon nanotubes (CNT), as well as its performance in a unitized regenerative alkaline micro-26 fluidic cell (URAμFC) as hydrogen bifunctional electrode is reported. The hydrogen electrode 27 reaction (HER/HOR) activity on NiO-Ni/CNT nanomaterial (0.36 mAcm-2) outperformed that of 28 commercial Pd/C (0.05 mAcm-2) and turned out to be competitive with commercial Pt/C (0.56 mA 29 cm-2). With NiO-Ni/CNT catalyst, a maximum power density (fuel cell mode) of ca. 40 mW cm-2 30 was obtained, whereas the electrocatalyst submitted to electrolyzer mode, consumed an electrical 31 power density of ca. 165 mW cm-2 , at 100 mA cm-2. 32 33 1. INTRODUCTION 34 Hydrogen (H 2) has been considered as a promising energy-carrier to replace fossil fuels, due to its 35 high energy density (143 kJ g-1). Its use in a fuel cell (FC) is not limited by the Carnot cycle 1 , and 36 the only oxidation product is water. Up-to-date, the alkaline hydrogen technology can offer the 37 great advantage to avoid the use of noble metals (Platinum group metals, PGMs), turning it up an 38 economically viable technology. Indeed, PGM-free based catalysts for the oxygen electrode 39 reaction (ORR/OER), with activity and stability similar or higher than that of Pt or IrO x , have been 40 developed. 2-3 The future of this technology relies on the efficient hydrogen evolution reaction 41 (HER), and hydrogen oxidation reaction (HOR), henceforth labeled as the hydrogen electrode 42 reaction (HER/HOR). Moreover, the HER/HOR kinetics in alkaline medium possesses higher 43 energy barriers with respect to that in acid medium, 4 and thus it is considered as a bottleneck for the alkaline hydrogen technology. The use of earth-abundant PGM-free catalysts is imperative to 45 inspire the above-mentioned technology. Some transition metals are able of catalyzing the slow 46 HER/HOR reaction, focusing primarily on Ni-based materials. 5-7 Nonetheless, the tuning of a highactive Ni-based catalyst for the alkaline HER/HOR still remains a challenge. Recently, some 48 strategies have been developed to improve the HER/HOR performance with Ni-based catalysts, 49 e.g., alloying Ni with another transition metal, 8-10 Ni sulfides and phosphides, 11 carbon-50 encapsulated Ni-based particles, 12 the interaction between Ni and carbon supports, 6, 13 or the use 51 of heterostructures (Ni 3 N, 14 Ni 3 N/Ni 15 or NiO-Ni 16-18). Among these strategies, NiO-Ni structures 52 do not require a complex synthesis protocol, and their reported activity is listed as a potential 53 option for HER 19-20 or HOR 16-18 electrocatalysts. However, in spite of the continuous efforts, their 54 electrocatalytic activity, described by the exchange current density, is still far from that of PGM-55 based catalysts, hampering their application in an electrolyzer (HER), or FC (HOR) or, in the best 56 case, in a unitized regenerative cell (URFC). On the other hand, the coupling between metal-based 57 nanostructures with multi-walled carbon nanotubes (hereafter simplified to CNT) is an strategy of 58 paramount potentiality to achieve advanced materials with exceptional properties for energy-59 conversion devices. 21 The so-called strong metal-support interaction (SMSI) modifies the local 60 surface, since the non-planar CNT structure can cause π-electron density to shift from the concave 61 to the convex CNT surface leading to electron potential difference between inner and outer walls 62 of CNTs, 21 which can bias the actual interactions. In addition, we exploited the synergy between 63 Ni and NiO phases, 16-19 and the SMSI effect, so that our engineered NiO-Ni/CNT nanostructures 64 were positively tested as an efficient alkaline HER/HOR electrode material. The role of the CNT Page 3 of 32 ACS Paragon Plus Environment ACS Applied Energy Materials 4 65 was elucidated by using Carbon Vulcan XC-72 for comparative purposes. A URFC system in an 66 alkaline microfluidic cell (URAμFC) has been adopted as a proof-of-concept of the NiO-Ni/CNT 67 electrocatalyst, to demonstrate its effectiveness in an energy-conversion device system. 68 69 2. EXPERIMENTAL SECTION 70 2.1 Materials synthesis 71 Multi-walled carbon nanotubes (CNTs) from Sigma-Aldrich (outer diameter 10-15 nm, internal 72 diameter 2-6 nm, and length 0.1-10 µm) and Carbon XC-72 Vulcan (C) from Cabot were used as 73 supports. The carbon-supported NiO-Ni hybrid catalysts were prepared using a modified two-steps synthesis procedure. 22 In short, 250 mg of carbon (C or CNT) support and 2.62 g of NiCl 2 •6H 2 O 75 were ultra-sonicated in 50 mL of deionized water for 30 min. The suspension was cooled down 76 (ice bath) at 4 °C and stirred for 1 h in N 2 atmosphere. Then, ice-cold NaBH 4 solution (186 mg 77 diluted in 20 mL of ethanol) was added dropwise. After 2 h, the suspension was transferred to a 78 Teflon-lined stainless-steel autoclave. NH 4 OH (5 mL) and mono-hydrated hydrazine (2 mL) were 79 added. The autoclave was sealed and subjected to a hydrothermal treatment at 150 °C for 12 h. 80 The final product was washed with deionized water and filtered at vacuum. The black solid powder 81 was dried at 60 °C overnight. 82 2.2 Physicochemical characterization 83 Raman spectroscopy: Raman spectra were obtained in a Horiba Jobin Yvon Spectrometer HR 800 84 with a 532 nm laser in the range of 100-3000 cm-1 .
Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for the distributed production o... more Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for the distributed production of energy require the cell to operate with both traditional hydrocarbon fuels (CH4 and LPG) and biomass-derived fuels (biogas, ethanol). Benefits in terms of lifetime and thermo-mechanical resistance are achieved by decreasing the operating temperature to 500-700°C (IT-SOFC). On the one hand, the use of hydrocarbons leads the traditional Ni-based anodes to deactivate due to coke formation; on the other hand, lower temperatures ask for electrolytes different from YSZ, for instance based on Ce oxides. Novel cells and materials are required, whose development must be closely accompanied by numerical model analysis, to rationalize chemical and physical phenomena. In this work, IT-SOFCs based on Samarium doped Ceria (SDC, Ce0.8Sm0.2O1.91) electrolytes and Cu/Pd/CZ80 anodes are investigated for applications with biogas mixtures (CO2/CH4) and syngas mixtures (H2/CO/H2O). Polarization curves and ...
Nowadays, dense ceramic membranes based on mixed ionic and electronic conductors are considered v... more Nowadays, dense ceramic membranes based on mixed ionic and electronic conductors are considered very promising materials for H2 separation at T > 600°C. Among these, BaCe0.65Zr0.2Y0.15O3-δ-Ce0.85Gd0.15O2-δ (BCZ20Y15-GDC15) composite combine an acceptable H2 flux and good chemical stability under CO2-and H2S-containing atmospheres. However, a clear understanding of its crystal structure, phase stability and mechanical stability under real working conditions could not yet be obtained. In this work, its structural evolution was investigated from room temperature to 800°C by in-situ synchrotron XRD analyses under dry and wet H2. No chemical interaction between the BCZ20Y15 and GDC15 phases occurred in the composite, thus evidencing its excellent chemical stability under operating conditions. However, some phase transitions were observed for the BCZ20Y15 phase, under both dry and wet H2: i.e., it showed an orthorhombic Imma structure from room temperature to 100°C, trigonal R-3c up to 700°C and cubic Pm-3m up to 800°C. On the other hand, the GDC15 phase did not display any phase transition, remaining in a cubic Fm-3m structure in all tested conditions. Moreover, a synergistic effect of the BCZ20Y15 and GDC15 phases in the volume expansion of the composite was revealed: indeed, BCZ20Y15 and GDC15 lattice
The development of a sustainable economy based on the use of renewable resources and the reductio... more The development of a sustainable economy based on the use of renewable resources and the reduction of greenhouse gases emissions is an important mandate in modern societies to minimize the global warming. The CO 2-reforming of methane through a conversion of CO 2 and CH 4 to syngas is a suitable process for this purpose and there is growing interest in the development of new catalysts for this process' application at an industrial scale. This study is the first to investigate methane dry reforming activity of nickel supported on CeO 2 and CeO 2-ZrO 2 solid solutions doped with neodymium. The supports were synthesized using a surfactant-assisted co-precipitation method and characterized through several analytical techniques to understand the role of synthesis parameters in the distribution of the dopant as well as in the properties of the supports. Co-doping with Zr and Nd resulted in an enhancement of dry reforming activity of ceria due to a higher dispersion of Ni and changes in the strength of basic sites. It was also shown that the addition of Nd helped to mitigate coking issues by increasing the mobility of surface oxygen in ceria and ceria-zirconia oxides and, accordingly, the rate of oxidation of carbonaceous deposits.
Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for distributed production of en... more Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for distributed production of energy require the cell to operate both with traditional hydrocarbons (CH4, LPG) and biomass-derived fuels (biogas). Several benefits in terms of lifetime and thermo-mechanical resistance are achieved by decreasing the operating temperature to 500-700°C (IT-SOFC). On the one hand, the use of hydrocarbons leads traditional Ni-based anodes to deactivate due to coke formation; on the other hand, lower temperatures ask for electrolytes different from YSZ, mostly based on Ce oxides. Novel cells and materials are then required. In this work, IT-SOFCs based on Samarium doped Ceria (Sm0.2Ce0.8O1.9, SDC) electrolytes and Cu/Pd/CZ80 anodes are investigated for applications with syngas mixtures and CO2/CH4 mixtures. A physically-based, numerical model of the IT-SOFC was applied to analyze the experimental results and kinetic equations were derived for the electro-chemical reactions: in the presence of syngas, the occurrence of a co-oxidation route is proved, wherein H2 and CO are electro-oxidized contemporarily. Materials and Methods SDC electrolyte-supported cells with 15 wt% Cu, 0.15 wt% Pd, 15 wt% CZ80 (CZ80 20 wt% CeO2, 80 wt% ZrO2) composite anodes and LSCF cathodes were prepared by die-pressing. SDC powders mixed with graphite were pressed with pure SDC. The bilayer was calcined in air (1400°C, 3 h) producing a porous SDC scaffold (150 μm) supported on a dense SDC electrolyte (380 μm). The porous scaffold was impregnated with Cu/Pd/CZ80-based solutions and then the cathode (40 μm) was deposited. Polarization and EIS measurements were collected between 600 and 700°C with syngas mixtures (2.3 – 0.4 H2/CO ratio), H2/N2 mixtures (from 97 to 30% H2 v/v), CO/CO2 mixtures (from 97 to 50% CO v/v) and synthetic biogas (75% CH4/25% CO2). The EIS tests were performed at the OCV. A model was applied to analyze both the EIS spectra and the polarization curves. The model is one-dimensional, charge-distributed, Dusty-Gas, dynamic and heterogeneous and allows to predict the cell voltage based on physically-sound conservation equations for mass, charge and energy. The model includes molecular kinetic schemes for the anodic catalytic reactions (CO2 reforming of CH4, WGS) and for the electrocatalytic reactions (H2 and CO electro-oxidation, O2 reduction). Appropriate correlations account for the presence of the electronic current leakage in the electrolyte. Results and Discussion The IT-SOFCs were first tested in syngas mixtures at varying the H2/CO ratio: no variation was found passing from 2.3 to 0.4 ratio (Fig. 1a). Analogous observations were done with the EIS spectra. These results suggested that both the H2 electro-oxidation and the CO electro-oxidation occurred simultaneously in the presence of syngas. A model analysis of the polarization and EIS curves was performed to prove the activation of the co-oxidative route for CO and H2. The IT-SOFCs were thus tested in H2/N2 mixtures at varying H2 concentration to derive a power-law kinetic rate equation for the electro-oxidation of H2. The polarization curves (Fig. 1b) showed a decrease of the extracted current at decreasing H2 partial pressure. As well, an increase of the polarization resistance at decreasing H2 content was observed in the EIS tests (Fig. 1c). Coherently with the use of SDC, which is a MIEC electrolyte and activates a leakage current, the measured OCVs were smaller than the Nernstian ones. Application of the charge distributed model revealed the axial variation of the leakage current in the electrolyte and in the electrodes. To complete the kinetic investigation, EIS and polarization tests with CO/CO2 mixtures were performed to derive a power-law rate for the CO electro-oxidation reaction. A picture similar to that of the H2/N2 tests was observed. The rate equations and their parameters (reaction orders, activation energies and rate constants) were derived based on the best simulation of the impedance spectra. Once these rates were extracted, the experiments with syngas mixtures were simulated on a fully predictive basis: the close match of the simulations confirmed that the co-oxidative scheme could rationalize the data. Simulations based on different reactive schemes (H2 oxidation + WGS, CO oxidation + RWGS) failed in achieving a satisfactory description, suggesting that the parallel oxidation of H2 and CO was the only adequate scheme. Conclusions By means of model analysis of experimental polarization and impedance curves, we show that, in the presence of syngas, the electro-oxidation of H2 and that of CO occur simultaneously in a novel, Ni-free, IT-SOFCs based on Samaria-doped Ceria. The activation of a co-oxidative route is a most distinguishing feature of Ce-based cells, compared to traditional SOFCs. Figure 1
The reactivity of a ceria-rich Ce0.85Zr0.15O2 solid solution towards the thermochemical water spl... more The reactivity of a ceria-rich Ce0.85Zr0.15O2 solid solution towards the thermochemical water splitting process (TWS) was studied over repeated H2/H2O redox cycles. The structural and surface modifications after treatment at high temperature under air or N2 atmospheres were characterized by High-Resolution Transmission Electron Microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray Photoemission Spectroscopy (XPS) and Positron Annihilation Lifetime Spectroscopy (PALS). Samples treated under nitrogen resulted more active due to phase segregation with formation of a zirconyl oxynitride phase in catalytic amount. Insertion of N 3into the structure contributes to increase the numbers of oxygen vacancies that preferably arrange in large clusters, and to stabilize Ce 3+ centers on the surface. In comparison, treatment under air resulted in a different arrangement of defects with less Ce 3+ and smaller and more numerous vacancy clusters. This affects charge transfer and H-coupling processes, that play an important role in boosting the rate of H2 production. The behavior is found to be only slightly dependent on the starting ceria-zirconia composition and it is related to the development of a similar surface hetero-structure configuration, characterized by the presence of at least a ceria-rich solid solution and a (cerium-doped) zirconyl oxynitride phase, which is supposed to act as a promoter for TWS reaction. The above findings confirm the importance of a multi-phase structure in the design of ceria-zirconia oxides for water splitting reaction and allow a step forward to find an optimal composition. Moreover, the results indicate that doping with nitrogen might be a novel approach for the design of robust, thermally resistant and redox active materials. All these findings suggest new approaches for the development and design of ceria based materials for the two-step water splitting reaction and highlight the importance of engineering the surface defect structure/configuration of the material to obtain an efficient catalyst. In this regard, the role and the impact of nitridation process need to be further investigated.
The study presented in this paper aims to evaluate the performance degradation of Polybenzimidazo... more The study presented in this paper aims to evaluate the performance degradation of Polybenzimidazole (PBI) based High Temperature PEM (HTPEM) fuel cells subjected to different ageing tests, according to a methodology already used by the authors. Three HTPEM Membrane Electrode Assemblies (MEAs) were characterized before and after different aging tests and performance compared. The three MEAs have been named MEA C, MEA D and MEA E. MEA C was subjected to 100,000 triangular sweep cycles between Open Circuit Voltage (OCV) and 0.5 A/cm 2 with 2 s of permanence at OCV at each cycle. MEA D and MEA E were subjected to 440 h of operation at constant load of 0.22 A/cm 2. In order to assess the cell performance, polarization curves, Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) were recorded during the ageing tests. Degradation rates have been obtained for MEA C (44 mV/h), for MEA D (30 mV/h) and for MEA E (29 mV/h). ECSA (Electrochemical Surface Area) has been calculated for the three MEAs showing a reduction of approximately 50% for MEA C and of approximately 30% for MEA D and MEA E. Polarization curves during aging tests confirm that load cycling is more detrimental. A comparison with data obtained by the authors in a previous research seems to confirm the repeatability of the test protocol used.
Ce0.8Zr0.2O2 and Ce0.8La0.5Nd0.2Zr0.13O2-x, were prepared with a surfactant assisted approach and... more Ce0.8Zr0.2O2 and Ce0.8La0.5Nd0.2Zr0.13O2-x, were prepared with a surfactant assisted approach and impregnated with different amounts of nickel. The catalysts were studied in the dry reforming reaction with the aim of using them in a biogas fuelled IT-SOFC anode. The oxidative dry reforming reaction was also investigated, finding that small amounts of oxygen in the biogas mixture reduce the effect of dry reforming side reactions. Catalysts containing Lanthanum and Neodymium showed an improved activity at 600 °C and 650 °C in terms of H2 selectivity and carbon resistance.
A simple and innovative prototype for biomass pyrolysis is presented, together with some experime... more A simple and innovative prototype for biomass pyrolysis is presented, together with some experimental results. The setup uses only the thermal solar energy provided by a system of reflecting mirrors (Linear Mirror II) to heat a selected agro-waste biomass, such as wheat straw. At the end of the pyrolysis process, solar carbon with a high energy density (around 24-28 MJ/kg) is produced from a biomass with an energy density of 16.9 MJ/kg. The perspectives for a future industrial application of this setup are also discussed.
A series of Pd/CeO 2 catalysts was prepared by solution combustion synthesis (SCS) using differen... more A series of Pd/CeO 2 catalysts was prepared by solution combustion synthesis (SCS) using different Pd precursors. The powders were characterized by complementary techniques such as BET surface area measurements, X-Ray diffraction analysis, X-Ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed oxidation, and high-resolution TEM. The results obtained evidenced the formation of a Pd-Ce solid solution on all SCS samples. This solid solution is in the form of an ordered supercell structure only in the SCS catalyst prepared from palladium nitrate. This was correlated to the heat of reaction between Pd(NO3)2 and the fuel. The samples were tested for methane catalytic combustion, and the reaction rates on all SCS samples were approximately twice that of the impregnated counterpart, irrespective of the precursor. This was attributed to the presence of the Pd-O-Ce solid solution, which gave rise to strong Pd-ceria interactions.
... Effect of Sulfur on the Oxygen Storage/release Capacity of Rh/CeO2 and Rh/CeO2-ZrO2 Model TWC... more ... Effect of Sulfur on the Oxygen Storage/release Capacity of Rh/CeO2 and Rh/CeO2-ZrO2 Model TWCs Marta Boaro, Carla de Leitenburg, Giuliano ... 15. G. Colon, M. Pijolat, F. Valdivieso, H. Vidal, J. Kaspar, E. Finocchio, M. Daturi, C. Binet, JC Lavalley, RT Baker, and S. Bernal, J ...
Porous Y 2 O 3-stabilized ZrO 2 (YSZ) samples were synthesized by preparing NiO/YSZ composites by... more Porous Y 2 O 3-stabilized ZrO 2 (YSZ) samples were synthesized by preparing NiO/YSZ composites by tape casting and calcining at 1800 K, reducing the NiO to nickel in H 2 at 973 K, and finally leaching the nickel out of the structure with 2.2M HNO 3 at 353 K. Porous YSZ was prepared from NiO/YSZ composites containing 0, 20, 40, and 50 wt% NiO. Complete removal of the nickel was demonstrated by XRD, weight changes, and porosity increases. Porosities >75% could be achieved without structural collapse of the YSZ phase. Finally, the method was applied to the fabrication of a solid oxide fuel cell with a copper-based anode operating on H 2 and n-butane. Comments
High-temperature reduction/oxidation cycles promote the oxygen storage capacity of mesoporous cer... more High-temperature reduction/oxidation cycles promote the oxygen storage capacity of mesoporous ceria; this is associated with the formation during reduction of a hexagonal CeO x phase which on reoxidation gives amorphous ceria.
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