Protocole de Montréal | EPFL Graph Search

Le protocole de Montréal est un accord multilatéral international sur l'environnement qui fait suite à la convention de Vienne sur la protection de la couche d'ozone adoptée le . Il a pour objectif de réduire et à terme d'éliminer complètement les substances qui réduisent la couche d'ozone. Il a été signé par 24 pays et par la Communauté économique européenne le dans la ville de Montréal, au Canada, et est entré en vigueur le . Les deux traités sur l'ozone ont été ratifiés par ( et l'Union européenne), ce qui en fait les premiers traités universellement ratifiés dans l'histoire des Nations unies. Genèse Problème de l'amincissement de la couche d'ozone En 1928, l'industrie chimique découvre les chlorofluorocarbures (CFC) via les travaux menés par General Motors, Du Pont et Frigidaire. Le Freon-11 (CFC-11) est alors un produit très utilisé dans l'industrie du froid. Quarante-cinq ans plus tard, dans un article publié dans le Canadian Journal of Chemistry , les

A Hierarchical 3D TiO2/Ni Nanostructure as an Efficient Hole-Extraction and Protection Layer for GaAs Photoanodes

Peer Fischer, Michael Graetzel, Hyeonho Jeong

Photoelectrochemical (PEC) water splitting is a promising clean route to hydrogen fuel. The best-performing materials (III/V semiconductors) require surface passivation, as they are liable to corrosion, and a surface co-catalyst to facilitate water splitting. At present, optimal design combining photoelectrodes with oxygen evolution catalysts remains a significant materials challenge. Here, we demonstrate that nickel-coated amorphous three-dimensional (3D) TiO(2)core-shell nanorods on a TiO(2)thin film function as an efficient hole-extraction layer and serve as a protection layer for the GaAs photoanode. Transient-absorption spectroscopy (TAS) demonstrated the role of nickel-coated (3D) TiO(2)core-shell nanorods in prolonging photogenerated charge lifetimes in GaAs, resulting in a higher catalytic activity. This strategy may open the potential of utilizing this low-cost (3D) nanostructured catalyst for decorating narrow-band-gap semiconductor photoanodes for PEC water splitting devices.

2020

Establishing Stability in Organic Semiconductor Photocathodes for Solar Hydrogen Production

Florent Alexandre Boudoire, Han-Hee Cho, Nestor Guijarro Carratala, Florian Le Formal, Yongpeng Liu, Arvindh Sekar, Kevin Sivula, Rebekah Anne Wells, Liang Yao, Jun Ho Yum

As organic semiconductors attract increasing attention to application in the fields of bioelectronics and artificial photosynthesis, understanding the factors that determine their robust operation in direct contact with aqueous electrolytes becomes a critical task. Herein we uncover critical factors that influence the operational stability of donor:acceptor bulk heterojunction photocathodes for solar hydrogen production and significantly advance their performance under operational conditions. First, using the direct photoelectrochemical reduction of aqueous Eu's and impedance spectroscopy, we determine that replacing the commonly used fullerene-based electron acceptor with a perylene diimide-based polymer drastically increases operational stability and identify that limiting the photogenerated electron accumulation at the organic/water interface to values of ca. 100 nC cm(-2) is required for stable operation (>12 h). These insights are extended to solar-driven hydrogen production using MoS3, MoP, or RuO2 water reduction catalyst overlayers where it is found that the catalyst morphology strongly affects performance due to differences in charge extraction. Optimized performance of bulk heterojunction photocathodes coated with a MoS3:MoP composite gave 1 Sun photocurrent density up to 8.7 mA cm(-2) at 0 V vs RHE (pH 1). However, increased stability was gained with RuO2 where initial photocurrent density (>8 mA cm(-2)) deceased only 15% or 33% during continuous operation for 8 or 20 h, respectively, thus demonstrating unprecedented robustness without a protection layer. This performance represents a new benchmark for organic semiconductor photocathodes for solar fuel production and advances the understanding of stability criteria for organic semiconductor/water-junction-based devices.

AMER CHEMICAL SOC2020

Dissipative-coupling-assisted laser cooling: Limitations and perspectives

Alexander Tagantsev

The recently identified possibility of ground-state cooling of a mechanical oscillator in the unresolved sideband regime by combination of the dissipative and dispersive optomechanical coupling under the red sideband excitation [Phys. Rev. A 88, 023850 (2013)] is currently viewed as a remarkable finding. We present a comprehensive analysis of this protocol, which reveals its very high sensitivity to small imperfections such as an additional dissipation, the inaccuracy of the optimized experimental settings, and the inaccuracy of the theoretical framework adopted. The impact of these imperfections on the cooling limit is quantitatively assessed. A very strong effect on the cooling limit is found from the internal cavity decay rate which, even being small compared with the detection rate, may drastically push that limit up, questioning the possibility of the ground-state cooling. Specifically, the internal loss can only be neglected if the ratio of the internal decay rate to the detection rate is much smaller than the ratio of the cooling limit predicted by the protocol to the common dispersive-coupling assisted sideband cooling limit. Moreover, we establish that the condition of applicability of theory of that protocol is the requirement that the latter ratio is much smaller than one. A detailed comparison of the cooling protocol in question with the dispersive-coupling-assisted protocols which use the red sideband excitation or feedback is presented.

AMER PHYSICAL SOC2020

Establishing Stability in Organic Semiconductor Photocathodes for Solar Hydrogen Production

Florent Alexandre Boudoire, Han-Hee Cho, Nestor Guijarro Carratala, Florian Le Formal, Yongpeng Liu, Arvindh Sekar, Kevin Sivula, Rebekah Anne Wells, Liang Yao, Jun Ho Yum

AMER CHEMICAL SOC2020