Hydro-Québec

About: Hydro-Québec is a government organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Electric power system & Dielectric. The organization has 2596 authors who have published 4433 publications receiving 100878 citations.

Geopolymer mortars as sustainable repair material: A comprehensive review

Abstract: Environmentally sustainable repair materials with reduced carbon footprint have been in great demand by the construction industry worldwide. Gradual deterioration of concrete containing large quantities of Portland cement is inevitable, and requires repair or replacement. Numerous repair materials including cementitious mortars, polymer-modified cementitious mortars, resinous mortars, etc. have been utilized to rectify the problem. Cement-free geopolymer mortars prepared from waste materials with high content of silicate aluminum and alkaline activator solution are emerging as prominent sustainable repair materials. Geopolymer binders are preferred because they generate 70–80% less carbon dioxide with remarkably lesser greenhouse gas emissions than ordinary Portland cement. These new binders are highly sought-after due to their enhanced durability performance, sustainability, and environmental affability. This paper provides a comprehensive overview of state-of-the-art research on sustainable geopolymers for repairing deteriorated and damaged concrete structures as well as restoring their integrity. Present challenges and future prospects of various geopolymer mortars as repair materials are emphasized.

Tuning the surface Fermi level on p-type gallium nitride nanowires for efficient overall water splitting

Abstract: Solar water splitting is one of the key steps in artificial photosynthesis for future carbon-neutral, storable and sustainable source of energy. Here we show that one of the major obstacles for achieving efficient and stable overall water splitting over the emerging nanostructured photocatalyst is directly related to the uncontrolled surface charge properties. By tuning the Fermi level on the nonpolar surfaces of gallium nitride nanowire arrays, we demonstrate that the quantum efficiency can be enhanced by more than two orders of magnitude. The internal quantum efficiency and activity on p-type gallium nitride nanowires can reach ~51% and ~4.0 mol hydrogen h(-1) g(-1), respectively. The nanowires remain virtually unchanged after over 50,000 μmol gas (hydrogen and oxygen) is produced, which is more than 10,000 times the amount of photocatalyst itself (~4.6 μmol). The essential role of Fermi-level tuning in balancing redox reactions and in enhancing the efficiency and stability is also elucidated.

Differential Capacitance Study of Stress‐Annealed Pyrolytic Graphite Electrodes

Abstract: : The non-faradaic capacity of electrodes prepared from high pressure stress-annealed pyrolytic graphite has been examined in aqueous solutions using an a.c. impedance bridge. SUCH MATERIALS HAVE A ROCKING ANGLE (x-ray diffraction) as small as 0.4 degrees and the properties of surfaces oriented parallel to the basal plane approach rather closely those of single crystal graphite. The differential capacity measured on this surface has a near parabolic dependence on electrode potential with no evidence of a hump and a minimum of about 3 microfarads/sq. cm in 0.9 M NaF. This low value is explained on the basis that a substantial fraction of the potential change between the electrode bulk and the solution bulk occurs across a space charge layer within the graphite.