18 research outputs found
Effect of doped substrate on GaAs/AlGaAs interfacial workfunction IR detector response through cavity enhancement
NRC publication: Ye
Dendritic Assembly of Gold Nanoparticles during Fuel-Forming Electrocatalysis
We observe the dendritic assembly of alkanethiol-capped gold nanoparticles on a glassy carbon support during electrochemical reduction of protons and CO2. We find that the primary mechanism by which surfactant-ligated gold nanoparticles lose surface area is by taking a random walk along the support, colliding with their neighbors, and fusing to form dendrites, a type of fractal aggregate. A random walk model reproduces the fractal dimensionality of the dendrites observed experimentally. The rate at which the dendrites form is strongly dependent on the solubility of the surfactant in the electrochemical double layer under the conditions of electrolysis. Since alkanethiolate surfactants reductively desorb at potentials close to the onset of CO2 reduction, they do not poison the catalytic activity of the gold nanoparticles. Although catalyst mobility is typically thought to be limited for room-temperature electrochemistry, our results demonstrate that nanoparticle mobility is significant under conditions at which they electrochemically catalyze gas evolution, even in the presence of a high surface area carbon and binder. A careful understanding of the electrolyte- and polarization-dependent nanoparticle aggregation kinetics informs strategies for maintaining catalyst dispersion during fuel-forming electrocatalysis
Space station biomining experiment demonstrates rare earth element extraction in microgravity and Mars gravity
Microorganisms are employed to mine economically important elements from rocks,
including the rare earth elements (REEs), used in electronic industries and alloy production.
We carried out a mining experiment on the International Space Station to test hypotheses on
the bioleaching of REEs from basaltic rock in microgravity and simulated Mars and Earth
gravities using three microorganisms and a purposely designed biomining reactor. Sphingomonas desiccabilis enhanced mean leached concentrations of REEs compared to non-biological
controls in all gravity conditions. No significant difference in final yields was observed
between gravity conditions, showing the efficacy of the process under different gravity
regimens. Bacillus subtilis exhibited a reduction in bioleaching efficacy and Cupriavidus
metallidurans showed no difference compared to non-biological controls, showing the
microbial specificity of the process, as on Earth. These data demonstrate the potential for
space biomining and the principles of a reactor to advance human industry and mining
beyond Earth