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Morphology and porosity are crucial aspects for designing electrodes with facile transport of electrons, ions and matter, which is a key parameter for electrochemical energy storage and conversion. Carbon nanofibers (CNFs) prepared by electrospinning are attractive for their high aspect ratio, inter-fiber macroporosity and their use as self-standing electrodes. The present work compares several strategies to induce intra-fiber micro-mesoporosity in self-standing CNF webs prepared by electrospinning polyacrylonitrile (PAN). Two main strategies were investigated, namely i) a templating method based on the addition of a porogen (polymethyl methacrylate, polyvinylpyrrolidone, Nafion&reg, or ZnCl2) in the electrospinning solution of PAN, or ii) the activation in ammonia of previously formed CNF webs. The key result of this study is that open intra-fiber porosity could be achieved only when the strategies i) and ii) were combined. When each approach was applied separately, only closed intra-fiber porosity or no intra-fiber porosity was observed. In contrast, when both strategies were used in combination all CNF webs showed high mass-specific areas in the range of 325 to 1083 m2&middot, g&minus, 1. Selected webs were also characterized for their carbon structure and electrical conductivity. The best compromise between high porosity and high electrical conductivity was identified as the fibrous web electrospun from PAN and polyvinylpyrrolidone.

Galvanic displacement is widely used for material preparation in high-tech and electronics industries, and in the last years has also found application for preparation of advanced electrocatalysts. Herein, the use of microwave irradiation is developed as an alternative means of energy delivery to increase galvanic exchange kinetics and significantly reduce the reaction time. By this means, Ni@Pt core@shell nanofibres with controlled platinum shell thickness and the Pt/Ni ratio are synthesised by an extremely fast and reproducible route. The reaction time is reduced 200-fold compared to the conventional thermal galvanic reaction. Furthermore, using microwave-assisted exchange, Pt forms a shell cleanly separated from the Ni core allowing their direct use as an electrocatalyst.

We discuss the electrodeposition of two-dimensional (2D) Pt-nanostructures on Highly Oriented Pyrolytic Graphite (HOPG) achieved under constant applied potential versus a Pt counter electrode (Eappl = ca. &minus, 2.2 V vs. NHE, normal hydrogen electrode). The deposition conditions are discussed in terms of the electrochemical behavior of the electrodeposition precursor (H2PtCl6). We performed cyclic voltammetry (CV) of the electrochemical Pt deposit on HOPG and on Pt substrates to study the relevant phenomena that affect the morphology of Pt deposition. Under conditions where the Pt deposition occurs and H2 evolution is occurring at the diffusion-limited rate (&minus, 0.3 V vs. NHE), Pt forms larger structures on the surface of HOPG, and the electrodeposition of Pt is not limited by diffusion. This indicates the need for large overpotentials to direct the 2D growth of Pt. Investigation of the possible effect of Cl&minus, showed that Cl&minus, deposits on the surface of Pt at low overpotentials, but strips from the surface at potentials more positive than the electrodeposition potential. The CV of Pt on HOPG is a strong function of the nature of the surface. We propose that during immersion of HOPG in the electrodeposition solution (3 mM H2PtCl6, 0.5 M NaCl, pH 2.3) Pt islands are formed spontaneously, and these islands drive the growth of the 2D nanostructures. The reducing agents for the spontaneous deposition of Pt from solution are proposed as step edges that get oxidized in the solution. We discuss the possible oxidation reactions for the edge sites.

Niobium carbide/carbon nanotubular porous structures have been prepared using electrospinning and used as electrocatalyst supports for proton exchange membrane fuel cells. They were functionalised with 3.1 nm Pt particles synthesised by a microwave-assisted polyol method and characterised for their electrochemical properties. The novel NbC-based electrocatalyst demonstrated electroactivity towards the oxygen reduction reaction as well as greater stability over high potential cycling than a commercial carbon-based electrocatalyst. Pt/NbC/C was integrated at the cathode of a membrane electrode assembly and characterised in a single fuel cell showing promising activity and power density.

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

International audience; Continuous thin platinum nanoplatelet networks and thin films were obtained on the flat surface of highly ordered pyrolytic graphite (HOPG) by high overpotential electrodeposition. By increasing the deposition time, the morphology of the Pt deposits can be progressively tuned from isolated nanoplatelets, interconnected nanostructures, and thin large flat islands. The deposition is surface-limited and the thickness of the deposits, equivalent to 5 to 12 Pt monolayers, is not time dependent. The presence of Pt (111) facets is confirmed by High Resolution Transmission Electron Microscopy (HRTEM) and evidence for the early formation of a platinum monolayer is provided by Scanning Transmission Electron Microscopy and Energy Dispersive X-rays Spectroscopy (STEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) analysis. The electroactivity towards the oxygen reduction reaction of the 2D deposits is also assessed, demonstrating their great potential in energy conversion devices where ultra-low loading of Pt via extended surfaces is a reliable strategy.

International audience; 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, Ni 3 N 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.

International audience; High durability and activity for the oxygen reduction reaction (ORR) was demonstrated for oxide-supported platinum catalysts. The supports were antimony doped SnO2 (ATO) fibres-in-tubes obtained by electrospinning and subsequent calcination. The doping with antimony instead of the already reported niobium, allowed the preparation of tin oxide with electrical conductivity similar to carbon, as well as an increased electrocatalyst loading. Platinum nanoparticles supported on electrospun ATO demonstrated higher electrochemical stability and comparable mass activity to commercial Pt/C during ex situ potential cycling. The in situ fuel cell tests also revealed an improved corrosion resistance with no noticeable degradation of the oxide based membrane electrode assembly (MEA), but a slightly lower performance compared to the MEA with carbon-supported catalysts.

A thriving market for emerging and established mobile devices, operating on electrical energy is pushing the research and the market demands towards continuous sustainable and clean sources of energy. In particular key operators of the automotive industry are seeking a leading market position introducing hybrid and electric vehicles. Proton exchange membrane fuel cells (PEMFC) provide clean and long lasting electrical energy while being portable and operated at relatively low temperatures and would be the obvious power source for those applications. However a reduction of the fabrication costs and an improved durability are pivotal to a successful market introduction of this technology. A more effective utilisation of the highly priced Pt catalyst and the use of more durable materials for the catalyst supports are the core of the development of novel, market ready PEMFC. A paradigm shift from Pt nanoparticles supported on carbon to thin layers of platinum deposited on metals, metal oxides or carbon could be achieved adopting electrochemical Pt deposition techniques like the galvanostatic displacement of Ni and Cu ions with Pt 1 , self-terminated Pt electrodeposition 2 or electrochemical atomic layer deposition 1. This novel morphologies could push the boundary of Pt exploitation further and vastly increase the stability of the electrodes, therefore the sought after reduction of fabrication costs and increased stability are within the reach of current researches. Electrospinning is a proven technique and is reliable and scalable for the production of nanowires made of several metals 3, metal oxides 4 or carbon 5. The capability to finely control the diameter and composition of the nanowires makes this technique appealing in the search of novel catalyst support materials and morphologies. Our research group is actively testing different Pt deposition techniques on electrospun carbon, metal oxide nanowires, pristine and doped, as well as metallic nanowires. 1. Adzic, R. R. et al. Platinum Monolayer Fuel Cell Electrocatalysts. Top. Catal. 46,249–262 (2007). 2. Liu, Y., Gokcen, D., Bertocci, U. & Moffat, T. P. Self-terminating growth of platinum films by electrochemical deposition. Science 338,1327–30 (2012). 3. Wu, H. et al. Electrospun metal nanofiber webs as high-performance transparent electrode. Nano Lett. 10,4242–8 (2010). 4. Cavaliere, S., Subianto, S., Savych, I., Jones, D. J. & Rozière, J. Electrospinning: designed architectures for energy conversion and storage devices. Energy Environ. Sci.(2011). 5. Qiu, Y. et al. Nitrogen-doped ultrathin carbon nanofibers derived from electrospinning: Large-scale production, unique structure, and application as electrocatalysts for oxygen reduction. J. Power Sources 196, 9862–9867 (2011).