Études de composés triarylboranes pour l’utilisation dans des batteries à flux

L’augmentation constante de la population cause une demande de plus en plus grande en énergie. Toutefois, un des problèmes principaux avec les énergies renouvelables est que la plupart sont intermittentes. Il faut donc pallier la dichotomie de la production et de l’utilisation d’énergie de ces sources grâce à l’entreposage sur de longues périodes de temps. Les batteries à flux (« Redox-Flow ») sont une solution intéressante pour ces applications. Elles sont conçues pour entreposer de grandes quantités d’énergie, en entreposant celles-ci dans des matériaux électro-actifs dans de larges réservoirs. Ces réservoirs peuvent aussi être facilement mis à l’échelle. Les batteries à flux à base de métaux ont toutefois plusieurs problèmes, comme le coût et la faible disponibilité des métaux utilisés. C’est ce problème que nous tentons de résoudre avec les travaux présentés ici. Les triarylboranes sont connus pour stabiliser les radicaux et le trimésityl borane montre la réduction réversible d’un électron avec un potentiel de -2,6 V (vs ferrocène). En se basant sur ce composé comme modèle de départ, nous avons étudié différents triarylboranes pour l’utilisation dans une batterie à flux organique. Dans ce mémoire, nous allons donc traiter des avenues de synthèses envisagées et empruntées pour obtenir les différents composés triarylboranes visés et les analyses de caractérisation effectuées sur ceux-ci. Les études électrochimiques seront aussi considérées et l’analyse des résultats de ces études sera aussi effectuée

Nunataryuk field campaigns: understanding the origin and fate of terrestrial organic matter in the coastal waters of the Mackenzie Delta region

Climate warming and related drivers of soil thermal change in the Arctic are expected to modify the distribution and dynamics of carbon contained in perennially frozen grounds. Thawing of permafrost in the Mackenzie River watershed of northwestern Canada, coupled with increases in river discharge and coastal erosion, triggers the release of terrestrial organic matter (OMt) from the largest Arctic drainage basin in North America into the Arctic Ocean. While this process is ongoing and its rate is accelerating, the fate of the newly mobilized organic matter as it transits from the watershed through the delta and into the marine system remains poorly understood. In the framework of the European Horizon 2020 Nunataryuk programme, and as part of the Work Package 4 (WP4) Coastal Waters theme, four field expeditions were conducted in the Mackenzie Delta region and southern Beaufort Sea from April to September 2019. The temporal sampling design allowed the survey of ambient conditions in the coastal waters under full ice cover prior to the spring freshet, during ice breakup in summer, and anterior to the freeze-up period in fall. To capture the fluvial–marine transition zone, and with distinct challenges related to shallow waters and changing seasonal and meteorological conditions, the field sampling was conducted in close partnership with members of the communities of Aklavik, Inuvik and Tuktoyaktuk, using several platforms, namely helicopters, snowmobiles, and small boats. Water column profiles of physical and optical variables were measured in situ, while surface water, groundwater, and sediment samples were collected and preserved for the determination of the composition and sources of OMt, including particulate and dissolved organic carbon (POC and DOC), and colored dissolved organic matter (CDOM), as well as a suite of physical, chemical, and biological variables. Here we present an overview of the standardized datasets, including hydrographic profiles, remote sensing reflectance, temperature and salinity, particle absorption, nutrients, dissolved organic carbon, particulate organic carbon, particulate organic nitrogen, CDOM absorption, fluorescent dissolved organic matter intensity, suspended particulate matter, total particulate carbon, total particulate nitrogen, stable water isotopes, radon in water, bacterial abundance, and a string of phytoplankton pigments including total chlorophyll. Datasets and related metadata can be found in Juhls et al. (2021) (https://doi.org/10.1594/PANGAEA.937587).</p

Tracing the footprint of permafrost carbon supply to the Canadian Beaufort Sea

The Canadian Beaufort Sea receives large quantities of sediment, organic carbon and nutrients from rapid coastal erosion and permafrost degradation. In addition, the Mackenzie River, the largest North American Arctic river, discharges great amounts of freshwater, dissolved solids and suspended sediments to the Beaufort Sea. Current changes in these fluxes in response to the warming climate have uncertain consequences for the carbon budget on the shelf and in the deep ocean. To investigate the movement and transformation of organic matter along the land-ocean continuum, we collected water and surface sediment samples along five major transects across the Beaufort Sea during the 2021 expedition of the Canadian Coast Guard Ship Amundsen. Sampling locations span from shallow, coastal, sites with water depths ≤ 20 m, to shelf-break and deep-water settings on the continental slope (water depths of ≥1000 m). For this study, we use stable and radiocarbon isotopic (δ13C and Δ14C) analyses of dissolved inorganic (DIC), dissolved organic (DOC) and particulate organic carbon (POC) for surface and bottom waters, as well as surface sediments, in order to compare, contrast and constrain the relative source contributions and ages of these different forms of carbon. Our results will help to better understand the fate of permafrost organic matter in the marine environment and to ultimately improve assessments of the Canadian Beaufort Sea shelf as a carbon source or sink and its potential trajectory with ongoing environmental changes

Colored dissolved organic matter absorption (aCDOM) and spectal slopes (S) in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Measurement of CDOM absorption was conducted from a water sample within 12 hours of collection using an UltraPath liquid waveguide system (World Precision Instruments, Inc.) over the wavelengths ranging from 200 to 722 nm (see also Matsuoka et al. (2012; doi:10.5194/bg-9-925-2012) for details). To minimize temperature effects, both the sample and the reference water were kept at 4 °C for at least 30 minutes prior to analysis. We followed the International Ocean Colour Coordinating Group (IOCCG) Ocean Optics and Biogeochemistry CDOM protocols (Mannino et al., 2019 (see further details)) with a few modifications: 1) reference water with salinity ±2 relative to the sample was prepared on site a few hours before sample analysis to minimize the effect of difference in refractive index between sample and reference; 2) aCDOM(λ) was measured in flow mode, meaning, a measurement was made while water was running using a peristaltic pump (Lefering et al., 2017; doi:10.1364/AO.56.006357). While the use of a long optical cell provides a good better signal particularly withinin the visible spectral domain essential to SOCRS, it necessarily suffers from light saturation in the UV domain. To overcome this issue, an optimal length of a cell (i.e. 10 cm or 200 cm) was selected following an empirical relationship between optical density observed at 350 and 443 nm based on Matsuoka et al. (2012; doi:10.5194/bg-9-925-2012). For each sample, measurements were done in triplicates of which each was visually inspected for quality control. CDOM measurements were fitted using following equation: a_CDOM (λ)=a_CDOM (λ_0 )*e^(-S(λ-λ_0)), where S is the spectral slope of aCDOM(λ) between 350 and 500 nm (Babin et al., 2003; doi:10.1029/2001JC000882 and Matsuoka et al., 2012; doi:10.5194/bg-9-925-2012)

Particle absorption (aP) in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Absorbance of particles retained on GF/F (0.7 µm) filters was measured using a Varian Cary 100 spectrophotometer equipped with an integrated sphere. Absorbance and reflectance spectra were measured by placing a sample filter in front and back of an integrating sphere, respectively (so-called Transmittance-Reflectance or T-R method; Tassan & Ferrari 1995; doi:10.4319/lo.1995.40.8.1358). An appropriate beta factor specific to the geometry of the instrument was used to calculate absorption coefficients of particles (Tassan & Ferrari 2002; doi:10.1093/plankt/24.8.757)

Stable water isotopes (δ18O, δD, d-excess) in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Water samples for stable isotopes were collected untreated in 10 mL HDPE vials, sealed tightly, stored in the dark at 4°C. Measurements were conducted at the laboratory facility for stable isotopes at AWI Potsdam using a Finnigan MAT Delta-S mass spectrometer equipped with equilibration units for the online determination of hydrogen and oxygen isotopic composition. The data is given as δD and δ18O values, which is the per mille difference to standard V-SMOW. The deuterium excess (d-excess) is calculated by: d-excess=δD-8.*δ18O. The measurement accuracy for hydrogen and oxygen isotopes was better than ±0.8%¸ and ±0.1%, respectively (Meyer et al., 2000; doi:10.1080/10256010008032939)

Bacteria cells in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Samples for bacterial abundance (1.5 mL) were preserved with glutaraldehyde (1% final concentration) and stored at -80°C. Samples were stained with SYBRTM Green I (Thermofisher Scientific) and analyzed on a flow cytometer (FACSCanto, BD Biosciences) as previously described (Gasol & Del Giorgio, 2000; doi:10.3989/scimar.2000.64n2197)

Particulate organic carbon (POC) and particulate organic nitrogen (PON) concentrations in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Particulate organic carbon (POC) and particulate organic nitrogen (PON) concentrations were obtained from water samples filtered on precombusted (450°C for >5 hours) 47mm Whatmann GF/F (0.7 µm) filters. The filters were dried overnight at 60°C and vacuum-sealed for storage in aluminum foil kept at -20°C until analysis. To determine POC and PON concentrations, the filters were acidified with 200-350 µl HCl 2N to remove carbonates, dried at 60°C overnight and then burned on a pre-calibrated CHN analyzer (Perkin Elmer, combustion at 925°C) for determination of the CO2 produced (Doxaran et al. 2012; doi:10.5194/bg-9-3213-2012)