Flammability reduction in a pressurised water electrolyser based on a thin polymer electrolyte membrane through a Pt-alloy catalytic approach

Various Pt-based materials (unsupported Pt, PtRu, PtCo) were investigated as catalysts for recombining hydrogen and oxygen back into water. The recombination performance correlated well with the surface Pt metallic state. Alloying cobalt to platinum was observed to produce an electron transfer favouring the occurrence of a large fraction of the Pt metallic state on the catalyst surface. Unsupported PtCo showed both excellent recombination performance and dynamic behaviour. In a packed bed catalytic reactor, when hydrogen was fed at 4% vol. in the oxygen stream (flammability limit), 99.5% of the total H 2 content was immediately converted to water in the presence of PtCo thus avoiding safety issues. The PtCo catalyst was thus integrated in the anode of the membrane-electrode assembly of a polymer electrolyte membrane electrolysis cell. This catalyst showed good capability to reduce the concentration of hydrogen in the oxygen stream under differential pressure operation (1-20 bar), in the presence of a thin (90 µm) Aquivion® membrane. The modified system showed lower hydrogen concentration in the oxygen flow than electrolysis cells based on state-of-the-art thick polymer electrolyte membranes and allowed to expand the minimum current density load down to 0.15 A cm -2 . The electrolysis cell equipped with a dual layer PtCo/IrRuOx oxidation catalyst achieved a high operating current density (3 A cm -2 ) as requested to decrease the system capital costs, under high efficiency conditions (about 77% efficiency at 55°C and 20 bar). Moreover, the electrolysis system showed reduced probability to reach the flammability limit under both high differential pressure (20 bar) and partial load operation (5%), as needed to properly address grid-balancing service

Dry Hydrogen Production in a Tandem Critical Raw Material-Free Water Photoelectrolysis Cell Using a Hydrophobic Gas-Diffusion Backing Layer

A photoelectrochemical tandem cell (PEC) based on a cathodic hydrophobic gas-diffusion backing layer was developed to produce dry hydrogen from solar driven water splitting. The cell consisted of low cost and non-critical raw materials (CRMs). A relatively high-energy gap (2.1 eV) hematite-based photoanode and a low energy gap (1.2 eV) cupric oxide photocathode were deposited on a fluorine-doped tin oxide glass (FTO) and a hydrophobic carbonaceous substrate, respectively. The cell was illuminated from the anode. The electrolyte separator consisted of a transparent hydrophilic anionic solid polymer membrane allowing higher wavelengths not absorbed by the photoanode to be transmitted to the photocathode. To enhance the oxygen evolution rate, a NiFeOX surface promoter was deposited on the anodic semiconductor surface. To investigate the role of the cathodic backing layer, waterproofing and electrical conductivity properties were studied. Two different porous carbonaceous gas diffusion layers were tested (Spectracarb® and Sigracet®). These were also subjected to additional hydrophobisation procedures. The Sigracet 35BC® showed appropriate ex-situ properties for various wettability grades and it was selected as a cathodic substrate for the PEC. The enthalpic and throughput efficiency characteristics were determined, and the results compared to a conventional FTO glass-based cathode substrate. A throughput efficiency of 2% was achieved for the cell based on the hydrophobic backing layer, under a voltage bias of about 0.6 V, compared to 1% for the conventional cell. For the best configuration, an endurance test was carried out under operative conditions. The cells were electrochemically characterised by linear polarisation tests and impedance spectroscopy measurements. X-Ray Diffraction (XRD) patterns and Scanning Electron Microscopy (SEM) micrographs were analysed to assess the structure and morphology of the investigated materials.Authors gratefully acknowledge funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 760930 (FotoH2 project)

Optimizing the synthesis of carbon nanofiber based electrocatalysts for fuel cells

7 páginas, 2 tablas, 7 figuras.This work deals with an optimization of the platinum dispersion on low surface area carbon nanofibers (CNFs) by using different synthesis procedures and its electrocatalytic activity towards oxygen reduction. The selected CNFs were characterized by a BET surface area of ca. 100 m2 g-1 and were in-house synthesized by the decomposition of CH4 at 700ºC. Pt nanoparticles were deposited by using four different synthesis routes. A metal concentration of 20 wt% was confirmed by EDX and TGA. Two classical impregnation routes were employed, one using NaBH4 as reducing agent at 15ºC and the second one using formic acid at 80ºC. Two alternative processes consisted in a microemulsion procedure followed by reduction with NaBH4 and a colloidal route by using the sulphite complex method followed by reduction with hydrogen. The main differences regarded the platinum crystal size varying from 2.5 nm for the colloidal route to 8.1 nm for the impregnation route (formic acid). The classical impregnation procedures did not result appropriate to obtain a small particle size in the presence of this support, whereas microemulsion and colloidal methods fit the requirements for the cathodic oxygen reduction reaction in polymer electrolyte fuel cells, despite the low surface area of CNFs. The catalysts were subjected to an accelerated degradation test by continuous potential cycling. Although the initial activity was the highest for the microemulsion based catalyst, after the accelerated degradation test the colloidal based catalyst experienced a relatively lower loss of performance.The authors wish to thank FEDER and the Spanish MEC for financial support to project CTQ2011-28913-C02-01. The authors also acknowledge the support of bilateral CNR (Italy) -CSIC (Spain) joint agreement 2011-2012 (project Baglio/Lazaro 2010IT0026).Peer reviewe

Enhanced Photoelectrochemical Water Splitting at Hematite Photoanodes by Effect of a NiFe-Oxide co-Catalyst

Tandem photoelectrochemical cells (PECs), made up of a solid electrolyte membrane between two low-cost photoelectrodes, were investigated to produce “green” hydrogen by exploiting renewable solar energy. The assembly of the PEC consisted of an anionic solid polymer electrolyte membrane (gas separator) clamped between an n-type Fe2O3 photoanode and a p-type CuO photocathode. The semiconductors were deposited on fluorine-doped tin oxide (FTO) transparent substrates and the cell was investigated with the hematite surface directly exposed to a solar simulator. Ionomer dispersions obtained from the dissolution of commercial polymers in the appropriate solvents were employed as an ionic interface with the photoelectrodes. Thus, the overall photoelectrochemical water splitting occurred in two membrane-separated compartments, i.e., the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. A cost-effective NiFeOx co-catalyst was deposited on the hematite photoanode surface and investigated as a surface catalytic enhancer in order to improve the OER kinetics, this reaction being the rate-determining step of the entire process. The co-catalyst was compared with other well-known OER electrocatalysts such as La0.6Sr0.4Fe0.8CoO3 (LSFCO) perovskite and IrRuOx. The Ni-Fe oxide was the most promising co-catalyst for the oxygen evolution in the anionic environment in terms of an enhanced PEC photocurrent and efficiency. The materials were physico-chemically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM).Authors gratefully acknowledge funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 760930 (FotoH2 project)

Frequency and type of domestic injuries among children during COVID-19 lockdown: what changes from the past? An Italian multicentre cohort study

: Accidents are the main cause of injury in children, more than half events happen at home. Aims of this study were to assess if SARS-CoV-2 lockdown influence emergency department (ED) visits due to children domestic accident (DAs) and to identify factors associated with hospitalization. This was a multicentre, observational, and retrospective cohort study involving 16 EDs in Italy and enrolling children (3-13 years) receiving a visit in ED during March-June 2019 and March-June 2020. Risk factors for hospitalization were identified by logistic regression models. In total, 8860 ED visits due to domestic accidents in children occurred before (4380) and during (4480) lockdown, with a mean incidence of DA of 5.6% in 2019 and 17.9% in 2020 (p < 0.001) (IRR: 3.16; p < 0.001). The risk of hospitalization was influenced by the type of occurred accident, with fourfold higher for poisoning and twofold lower risk for stab-wound ones. In addition, a higher risk was reported for lockdown period vs 2019 (OR: 1.9; p < 0.001), males (OR: 1.4; p < 0.001), and it increased with age (OR: 1.1; p < 0.001).    Conclusions: The main limitation of this study is the retrospective collection of data, available only for patients who presented at the hospital. This does highlight possible differences in the total number of incidents that truly occurred. In any case, the COVID-19 lockdown had a high impact on the frequency of DAs and on hospitalization. A public health campaign aimed at caregivers would be necessary to minimize possible risks at home. What is Known: • In Italy, domestic accidents are the second leading cause of paediatric mortality after cancer. • During the first SARS-CoV-2 lockdown in 2020, a sharp decrease in the total number of Emergency Departments visits for all causes was observed, both in children and in adults. What is New: • During the first SARS-CoV-2 lockdown in 2020, domestic accidents involving children increased threefold from the previous year. • Higher risk of hospitalization was showed in minors accessing during 2020 vs 2019, in males than in females and it increased with advancing age. Considering the type of injury, a significant higher risk of hospitalization for poisoning was observed

Application of Low-Cost Me-N-C (Me = Fe or Co) Electrocatalysts Derived from EDTA in Direct Methanol Fuel Cells (DMFCs)

Co-N-C and Fe-N-C electrocatalysts have been prepared by mixing Fe or Co precursors, ethylene diamine tetra acetic acid (EDTA) as a nitrogen source, and an oxidized carbon. These materials were thermally treated at 800 °C or 1000 °C under nitrogen flow to produce four samples, named CoNC8, CoNC10, FeNC8, and FeNC10. They have been physicochemically characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Direct methanol fuel cell (DMFC) analyses have been carried out to investigate the performance of the nonprecious cathode catalysts, using a low amount of Pt (0.7 mg/cm2) at the anode side. It appears that FeNC8 is the best performing low-cost cathode catalyst in terms of higher oxygen reduction reaction activity and methanol tolerance

Lanthanum Ferrites-Based Exsolved Perovskites as Fuel-Flexible Anode for Solid Oxide Fuel Cells

Exsolved perovskites can be obtained from lanthanum ferrites, such as La0.6Sr0.4Fe0.8Co0.2O3, as result of Ni doping and thermal treatments. Ni can be simply added to the perovskite by an incipient wetness method. Thermal treatments that favor the exsolution process include calcination in air (e.g., 500 °C) and subsequent reduction in diluted H2 at 800 °C. These processes allow producing a two-phase material consisting of a Ruddlesden–Popper-type structure and a solid oxide solution e.g., α-Fe100-y-zCoyNizOx oxide. The formed electrocatalyst shows sufficient electronic conductivity under reducing environment at the Solid Oxide Fuel Cell (SOFC) anode. Outstanding catalytic properties are observed for the direct oxidation of dry fuels in SOFCs, including H2, methane, syngas, methanol, glycerol, and propane. This anode electrocatalyst can be combined with a full density electrolyte based on Gadolinia-doped ceria or with La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) or BaCe0.9Y0.1O3-δ (BYCO) to form a complete perovskite structure-based cell. Moreover, the exsolved perovskite can be used as a coating layer or catalytic pre-layer of a conventional Ni-YSZ anode. Beside the excellent catalytic activity, this material also shows proper durability and tolerance to sulfur poisoning. Research challenges and future directions are discussed. A new approach combining an exsolved perovskite and an NiCu alloy to further enhance the fuel flexibility of the composite catalyst is also considered. In this review, the preparation methods, physicochemical characteristics, and surface properties of exsoluted fine nanoparticles encapsulated on the metal-depleted perovskite, electrochemical properties for the direct oxidation of dry fuels, and related electrooxidation mechanisms are examined and discussed

New Insights into Properties of Methanol Transport in Sulfonated Polysulfone Composite Membranes for Direct Methanol Fuel Cells

Methanol crossover through a polymer electrolyte membrane has numerous negative effects on direct methanol fuel cells (DMFCs) because it decreases the cell voltage due to a mixed potential (occurrence of both oxygen reduction and methanol oxidation reactions) at the cathode, lowers the overall fuel utilization and contributes to long-term membrane degradation. In this work, an investigation of methanol transport properties of composite membranes based on sulfonated polysulfone (sPSf) and modified silica filler is carried out using the PFG-NMR technique, mainly focusing on high methanol concentration (i.e., 5 M). The influence of methanol crossover on the performance of DMFCs equipped with low-cost sPSf-based membranes operating with 5 M methanol solution at the anode is studied, with particular emphasis on the composite membrane approach. Using a surface-modified-silica filler into composite membranes based on sPSf allows reducing methanol cross-over of 50% compared with the pristine membrane, making it a good candidate to be used as polymer electrolyte for high energy DMFCs

Carbon nanofiber-based counter electrodes for low cost dye-sensitized solar cells

8 páginas.- 5 tablas.- 11 figuras.Carbon materials represent an attractive alternative to platinum in dye-sensitized solar cells (DSSC) counter electrodes to contribute to an efficient conversion of solar energy into electricity. The use of highly graphitic carbon nanofibers (CNFs) is investigated by analyzing the effect of the filament diameter, surface area and graphitization degree on the DSSC cathode performance. To this purpose, transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and physisorption analysis are used to characterize the main properties of the CNFs. The behavior of CNFs as counter electrodes in DSSC is investigated by polarization experiments and electrochemical impedance spectroscopy. Among the different materials, the CNF characterized by the highest surface area (183 m2 g-1), thinnest filament size (24 nm) and highest density of surface defects shows the best performance in terms of efficiency, open circuit potential and short circuit current density. Further investigation of the electrode thickness together with series and charge transfer resistance cross-analysis evidences the key role played by the surface area and surface graphitization to obtain a suitable performance. Compared to literature, so-obtained CNFs represent an interesting alternative to manufacture low cost DSSC cathodes.CNR-ITAE authors acknowledge the financial support of the POR Project “Fotovoltaico di III generazione: sviluppo di celle solari senzibilizzate con coloranti estratti da prodotti vegetali siciliani (SAGRO)”. Authors also thank the financial support of the bilateral CNR (Italy) – CSIC (Spain) joint agreement 2011-2012 (project Baglio/Lazaro 2010IT0026).Peer reviewe