We report the electrocatalytic reduction of CO 2 to the highly reduced C 2 products, ethylene and ethane, as well as to the fully reduced C 1 product, methane, on three different phases of nickel−gallium (NiGa, Ni 3 Ga, and Ni 5 Ga 3 ) films prepared by drop-casting. In aqueous bicarbonate electrolytes at neutral pH, the onset potential for methane, ethylene, and ethane production on all three phases was found to be −0.48 V versus the reversible hydrogen electrode (RHE), among the lowest onset potentials reported to date for the production of C 2 products from CO 2 . Similar product distributions and onset potentials were observed for all three nickel− gallium stoichiometries tested. The onset potential for the reduction of CO 2 to C 2 products at low current densities catalyzed by nickel−gallium was >250 mV more positive than that of polycrystalline copper, and approximately equal to that of single crystals of copper, which have some of the lowest overpotentials to date for the reduction of CO 2 to C 2 products and methane. The nickel−gallium films also reduced CO to ethylene, ethane, and methane, consistent with a CO 2 reduction mechanism that first involves the reduction of CO 2 to CO. Isotopic labeling experiments with 13 CO 2 confirmed that the detected products were produced exclusively by the reduction of CO 2 .

Abstract. Geodetic surveys suggest that ocean tides can modulate the motion of Antarctic ice streams, even at stations many tens of kilometers inland from the grounding line. These surveys suggest that ocean tidal stresses can perturb ice stream motion at distances about an order of magnitude farther inland than tidal flexure of the ice stream alone. Recent models exploring the role of tidal perturbations in basal shear stress are primarily one-or two-dimensional, with the impact of the ice stream margins either ignored or parameterized. Here, we use two-and three-dimensional finiteelement modeling to investigate transmission of tidal stresses in ice streams and the impact of considering more realistic, three-dimensional ice stream geometries. Using Rutford Ice Stream as a real-world comparison, we demonstrate that the assumption that elastic tidal stresses in ice streams propagate large distances inland fails for channelized glaciers due to an intrinsic, exponential decay in the stress caused by resistance at the ice stream margins. This behavior is independent of basal conditions beneath the ice stream and cannot be fit to observations using either elastic or nonlinear viscoelastic rheologies without nearly complete decoupling of the ice stream from its lateral margins. Our results suggest that a mechanism external to the ice stream is necessary to explain the tidal modulation of stresses far upstream of the grounding line for narrow ice streams. We propose a hydrologic model based on time-dependent variability in till strength to explain transmission of tidal stresses inland of the grounding line. This conceptual model can reproduce observations from Rutford Ice Stream.

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Abstract:In this study, the influence of metals (Mg, Al, and Ca) and reaction conditions (time, temperature, and metal grain size) on the metallothermic reduction of Stöber silica nanoparticles (NPs) to form porous Si was explored. Mg metal was found to be an effective reducing agent even at temperatures below its melting point; however, it also induced a high degree of structural damage and morphology change. Al was effective at reducing silica NPs only at its melting point and higher temperatures, but the resulting particles retained a higher degree of structural morphology as compared to those reduced using Mg. Ca was found to be ineffective in reducing silica. A new reductant, a mixture of 70% Mg and 30% Al, was found to induce the least amount of morphology change, and the reactions proceeded at temperatures (450 °C) lower than those required by Mg or Al individually. Furthermore, porous Si-NPs obtained using Mg, Al, and the mixture of 70% Mg and 30% Al as reductants were investigated as carriers for ibuprofen loading and release. Porous Si obtained from Mg and Mg/Al mixture reductions showed higher drug loading and a sustained drug release profile whereas porous Si obtained from Al reduction had lower loading and showed a conventional release profile over 24 hours.