Filière hydrogène | EPFL Graph Search

La filière hydrogène regroupe la production et le stockage de l'hydrogène, puis son utilisation notamment dans le secteur des transports. Elle apparaît comme un moyen de favoriser la transition énergétique. Les composés d’hydrogène évoqués dans cet article sont l’essence et le gas-oil, le méthane, l'hydrogène lui-même, l’ammoniac et l’hydrure de magnésium. La densité énergétique très élevée de l’essence ou du gas-oil a permis le développement de véhicules propulsés par des moteurs thermiques de toutes tailles, aussi bien pour les camions, les bateaux, que pour les véhicules particuliers. Certains préconisent déjà la fin des moteurs thermiques et la fermeture des gisements pétroliers ou gaziers. Pourtant, d’autres voies de recherche portent sur des véhicules fonctionnant à l’hydrogène ou à l’ammoniac, par l’intermédiaire de piles à combustibles ou de moteurs thermiques. vignette|redresse=1.3| Production d'hydrogène Production d'hydrogène Hydrogène par électrolyse

Analysis and comparison of hydrogen routes for automotive use

Peter Loveday

The goal of this project would be to analyze and compare systematically the different existing and emerging processes producing hydrogen from fossil and renewable resources. As the perspective would be the replacement of fossil fuels with hydrogen in the transportation sector, the comparison of the different processes will essentially be based on the environmental impacts.

2009

Coupling of electrocatalysts to photoabsorbers for solar fuels production

Carlos Gilberto Morales Guio

The direct transformation of sunlight into fuels and chemicals has attracted considerable attention for the potential impact on the storage of solar energies at large scales and the reduction of CO2 emissions. More than 80% of our current global energy consumption comes from the burning of non-renewable fossil fuels which produces enormous quantities of CO2 and contributes to global warming. We believe today that the key to reduce our dependence on exhaustible natural resources and limit the emission of greenhouse gases is the transition to CO2-free renewable energy sources. However, harvesting of energy from renewable sources (i.e. solar, wind, tidal) is intermittent and the deployment of devices for their transformation into useful forms of energy (i.e. electricity, chemicals, fuels, biomass) in a global scale is conditioned upon the improvement in efficiency of the energy storage mechanisms. A promising approach to store energy is the use of sunlight to drive the production of hydrogen fuel from water. Hydrogen produced from water and sunlight can be transformed back to electricity on demand or be used to generate mechanical energy in cars to power the transportation industry. The oxidation of hydrogen generates useable energy and at the same time exhaust clean, carbon-free water as the only product. Therefore, the production of hydrogen using a renewable energy source in an efficient and inexpensive device has the potential to discourage the continued use of fossil fuels and improve our environment. The viability of any mechanism for the storage of sunlight as fuel will depend on the reduction of energy penalties during the transformation process. Electrocatalysts are advanced materials that bring into one active site electrons and molecules in the appropriate orientation to lower activation energy barriers, accelerate rate of transformations and improve overall efficiencies for chemical reactions. The best catalysts for water splitting are precious metals such as Pt, Ir and Ru, which show superior rates of reaction at low overpotentials. However, these noble metals are too expensive and scarce for large scale applications. This thesis summarizes our recent research in the preparation, characterization, and application of Earth-abundant electrocatalysts for solar water splitting. Although in the last decade a great number of efficient and inexpensive electrocatalysts have been reported, methods for the deposition of these materials on the surface of photoabsorbers are rarely reported. This work shows various simple and scalable techniques for the deposition of hydrogen and oxygen evolving electrocatalysts on the surface of photocathodes and photoanodes, respectively. Surface-protected photocahodes were activated for solar hydrogen production in alkaline conditions with MoS2+x, Ni-Mo and Mo2C. A novel method for the deposition of an optically transparent amorphous iron nickel oxide oxygen evolution electrocatalyst is also reported. The catalyst was deposited on both thin film and high-aspect ratio nanostructured hematite photoanodes. The low catalyst loading combined with its high activity at low overpotential results in significant improvement on the onset potential for photoelectrochemical water oxidation. This transparent catalyst further enables the preparation of a stable hematite/perovskite solar cell tandem device, which performs unassisted water splitting.

EPFL2016

Stability profiles of transition metal oxides in the oxygen evolution reaction in alkaline medium

Xile Hu, Aliki Moysiadou

The electrochemical water splitting reaction can convert renewable electricity into clean hydrogen fuel. The efficiency of water splitting is limited to a large extent by the sluggish oxygen evolution reaction (OER). Numerous transition metal oxides have been developed as electrocatalysts for the OER in alkaline medium. However, in-depth studies of the stability of these catalysts have rarely been performed. Here we report a systematic investigation of the stability profiles of five archetypical OER catalysts including CoOx, CoFeOx, CoFeNiOx, NiOx, and NiFeOx. We combine measurements of electrochemical activity, electrochemical quartz crystal microbalance (eQCM), inductively coupled plasma optical emission spectrometry (ICP-OES), and electrochemical impedance spectroscopy (EIS). We find that the eQCM analysis gives incorrect information about the mass change during the OER due to a non-ideal response, and confirms that activity is not a valid descriptor of stability. Of the five oxides, CoOx and CoFeOx lose some mass during the initial period of the OER while CoFeNiOx, NiOx, and NiFeOx maintain their mass. However, all five catalysts undergo noticeable compositional changes due to a dynamic exchange of metal ions with the electrolyte solutions. Partial dissolution of CoOx and incorporation of Fe ions are the main processes of this exchange. The dynamic exchange reaches equilibrium after 6 h, and the catalysts are stable afterwards.

ROYAL SOC CHEMISTRY2019

Coupling of electrocatalysts to photoabsorbers for solar fuels production

Carlos Gilberto Morales Guio

EPFL2016