Sara Cavaliere

Mesoporous Nanostructured Nb-Doped Titanium Dioxide Microsphere Catalyst Supports for PEM Fuel Cell Electrodes

Crystalline microspheres of Nb-doped TiO(2) with a high specific surface area were synthesized using a templating method exploiting ionic interactions between nascent inorganic components and an ionomer template. The microspheres exhibit a porosity gradient, with a meso-macroporous kernel, and a mesoporous shell. The material has been investigated as cathode electrocatalyst support for polymer electrolyte membrane (PEM) fuel cells. A uniform dispersion of Pt particles on the Nb-doped TiO(2) support was obtained using a microwave method, and the electrochemical properties assessed by cyclic voltammetry. Nb-TiO(2) supported Pt demonstrated very high stability, as after 1000 voltammetric cycles, 85% of the electroactive Pt area remained compared to 47% in the case of commercial Pt on carbon. For the oxygen reduction reaction (ORR), which takes place at the cathode, the highest stability was again obtained with the Nb-doped titania-based material even though the mass activity calculated at 0.9 V vs RHE was slightly lower. The microspherical structured and mesoporous Nb-doped TiO(2) is an alternative support to carbon for PEM fuel cells.

Single step elaboration of size-tuned Pt loaded titania nanofibres

Conductive titania nanofibres supporting Pt nanoparticles were synthesised in a one-pot method based on the electrospinning technique. The dimensions of both the oxide fibres and platinum particles were tuneable, leading to versatile nanomaterials with possible applications as electrodes for energy conversion devices.

Electrospun nanofibre composite polymer electrolyte fuel cell and electrolysis membranes

Large-scale commercialisation of Proton Exchange Membrane Fuel Cell (PEMFC) technology for automotive and stationary applications demands the development of a robust, durable and cost-effective materials. In this regard, ionomer membranes being present at the core of PEMFCs are required to maintain elevated proton conductivity, high mechanical strength and low gas permeability during the lifespan of the fuel cell. These challenges are addressed by investigating novel nano-structured membrane materials possessing long-range spatial organisation of ionic and hydrophobic domains at the micro-and nano-scales. Electrospinning, a versatile and easily up-scalable tool for the preparation of nanofibrous polymers and ceramics with targeted architectures, is being extensively applied for the development of nanostructured electrolyte membranes. This review describes the most important advances in the use of electrospun materials for the preparation of new generation fuel cell proton conducting membranes. It also highlights the challenges to be overcome and the new directions and future application fields of composite nanofibre-based membranes in the broader context of energy materials.

ALD SnO2 protective decoration enhances the durability of a Pt based electrocatalyst

Electrospinning and atomic layer deposition (ALD) have been coupled to prepare functional hetero-structures with potential application in fuel cells. Electrocatalysts comprising platinum (Pt) nanoparticles dispersed onto electrospun carbon fibers were selectively decorated with tin dioxide (SnO2) using ALD. The presence of SnO2 led to a considerable enhancement of the catalyst durability during voltage cycling.

1,2,3-Triazole-Functionalized Polysulfone Synthesis through Microwave-Assisted Copper-Catalyzed Click Chemistry: A Highly Proton Conducting High Temperature Membrane

Microwave heating holds all the aces regarding development of effective and environmentally friendly methods to perform chemical transformations. Coupling the benefits of microwave-enhanced chemistry with highly reliable copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry paves the way for a rapid and efficient synthesis procedure to afford high performance thermoplastic materials. We describe herein fast and high yielding synthesis of 1,2,3-triazole-functionalized polysulfone through microwave-assisted CuAAC as well as explore their potential as phosphoric acid doped polymer electrolyte membranes (PEM) for high temperature PEM fuel cells. Polymers with various degrees of substitution of the side-chain functionality of 1,4-substituted 1,2,3-triazole with alkyl and aryl pendant structures are prepared by sequential chloromethylation, azidation, and microwave-assisted CuAAC using a range of alkynes (1-pentyne, 1-nonyne, and phenylacetylene). The completeness of reaction at each step and the purity of the clicked polymers were confirmed by (1)H-(13)C NMR, DOSY-NMR and FTIR-ATR spectroscopies. The thermal and thermochemical properties of the modified polymers were characterized by differential scanning calorimetry and thermogravimetric analysis coupled with mass spectroscopy (TG-MS), respectively. TG-MS analysis demonstrated that the commencement of the thermal degradation takes place with the decomposition of the triazole ring while its substituents have critical influence on the initiation temperature. Polysulfone functionalized with 4-phenyl-1,2,3-triazole demonstrates significantly higher Tg, Td, and elastic modulus than the ones bearing 4-propyl-1,2,3-triazole and 4-heptyl-1,2,3-triazole groups. After doping with phosphoric acid, the functionalized polymers with acid doping level of 5 show promising performance with high proton conductivity in anhydrous conditions (in the range of 27-35 mS/cm) and satisfactorily high elastic modulus (in the range of 332-349 MPa).

A new fabrication method of an intermediate temperature proton exchange membrane by the electrospinning of CsH2PO4

A novel method for the fabrication of an intermediate temperature proton conducting composite membrane was developed. Cesium dihydrogen phosphate, CsH2PO4 (CDP), was electrospun to obtain a highly interconnected proton conducting fibre mat. CsH2PO4 was heat treated above its dehydration temperature (Tdehy ∼ 230 °C) in order to induce a partial polymerisation. The partially polymerised material produced a viscous aqueous solution which could be electrospun in the absence of a carrier polymer, thus leading to pure inorganic fibres. The electrospun fibre mats were characterised in terms of composition, structure and morphology by XRD, MAS NMR and SEM and their proton conductivity determined by electrochemical impedance spectroscopy. The electrospun fibres (CDPf) showed a maximum proton conductivity of 8 × 10−3 S cm−1 at 250 °C.

Reactive coaxial electrospinning of ZrP/ZrO2 nanofibres

Zirconium phosphate/zirconium oxide nanofibres have been fabricated using a novel, reactive coaxial electrospinning approach. In this approach, a zirconium precursor and a phosphorus source are spun together from separate solutions, using a coaxial needle, in order to delay formation of zirconium phosphate gel. The reaction between the zirconium and phosphorus sources is considered to initiate at the interface region in the coaxial fibres. The resultant nanofibres are calcined and further treated with H3PO4. The formation of ZrP/ZrO2 nanofibres was confirmed using 31P MAS NMR. Electron microscopy shows that the fibre morphology depends on solution parameters, and the X-ray amorphous fibres exhibit compositional homogeneity. Incorporation of the nanofibres into the short-side-chain perfluorosulfonic acid ionomer Aquivion™ yields membranes having significantly increased mechanical properties with greater elastic modulus and yield point as well as increased proton conductivity compared to both cast and commercial Aquivion™ membranes.

Pt Nanoparticles Supported on Niobium-Doped Tin Dioxide: Impact of the Support Morphology on Pt Utilization and Electrocatalytic Activity

AbstractTwo synthesis routes were used to design high surface area niobium-doped tin dioxide (Nb-doped SnO2, NTO) nanostructures with either loose-tube (fibre-in-tube) morphology using electrospinning or aerogel morphology using a sol-gel process. A higher specific surface area but a lower apparent electrical conductivity was obtained on the NTO aerogel compared to the loose tubes. The NTO aerogels and loose tubes and two reference materials (undoped SnO2 aerogel and Vulcan XC72) were platinized with a single colloidal suspension and tested as oxygen reduction reaction (ORR) electrocatalysts for proton-exchange membrane fuel cell (PEMFC) applications. The specific surface area of the supports strongly influenced the mass fraction of deposited Pt nanoparticles (NPs) and their degree of agglomeration. The apparent electrical conductivity of the supports determined the electrochemically active surface area (ECSA) and the catalytic activity of the Pt NPs for the ORR. Based on these findings, electrospinning appears to be the preferred route to synthesize NTO supports for PEMFC cathode application. Graphical AbstractOn top : SEM images of the synthesized supports : 5.0 at.% Nb-doped SnO2 aerogel (NTO-AG) and loose tubes (NTO-LT) - At the bottom : specific activity (SA0.90) and mass activity (MA0.90) of the synthesized electrocatalysts for the oxygen reduction reaction (ORR) determined at E = 0.90 V vs. RHE as a function of the conductivity of the supports

Towards ultrathin Pt films on nanofibres by surface-limited electrodeposition for electrocatalytic applications

Novel fuel cell nanofibrous electrodes (NFEs) with a higher degree of platinum exploitation and higher durability compared to commercial standards are produced, based on self-standing electrospun carbon nanofibre webs covered by platinum ultrathin nanoislands deposited by high overpotential pulsed electrodeposition.

Nickel Based Electrospun Materials with Tuned Morphology and Composition

Nickel is set to play a crucial role to substitute the less-abundant platinum in clean electrochemical energy conversion and storage devices and catalysis. The controlled design of Ni nanomaterials is essential to fine-tune their properties to match these applications. A systematic study of electrospinning and thermal post-treatment parameters has been performed to synthesize Ni materials and tune their morphology (fibers, ribbons, and sponge-like structures) and composition (metallic Ni, NiO, Ni/C, Ni3N and their combinations). The obtained Ni-based spun materials have been characterized by scanning and transmission electron microscopy, X-ray diffraction and thermogravimetric analysis. The possibility of upscaling and the versatility of electrospinning open the way to large-scale production of Ni nanostructures, as well as bi- and multi-metal systems for widened applications.