• Energy Research

Capacitive desalination (CD) is a promising desalination technique as, relative to reverse osmosis (RO), it requires no membrane components, can operate at low (sub-osmotic) pressures, and can potentially utilize less energy for brackish water desalination. In a typical CD cell, the feed water flows through the separator layer between two electrically charged, nanoporous carbon electrodes. This architecture results in significant performance limitations, including an inability to easily (in a single charge) desalinate moderate brackish water feeds and slow, diffusion-limited desalination. We here describe an alternative architecture, where the feed flows directly through electrodes along the primary electric field direction, which we term flow-through electrode (FTE) capacitive desalination. Using macroscopic porous electrode theory, we show that FTE CD enables significant reductions in desalination time and can desalinate higher salinity feeds per charge. We then demonstrate these benefits using a custom-built FTE CD cell containing novel hierarchical carbon aerogel monoliths as an electrode material. The pore structure of our electrodes includes both micron-scale and sub-10 nm pores, allowing our electrodes to exhibit both low flow resistance and very high specific capacitance (>100 F g−1). Our cell demonstrates feed concentration reductions of up to 70 mM NaCl per charge and a mean sorption rate of nearly 1 mg NaCl per g aerogel per min, 4 to 10 times higher than that demonstrated by the typical CD cell architecture. We also show that, as predicted by our model, our cell desalinates the feed at the cell's RC timescale rather than the significantly longer diffusive timescale characteristic of typical CD cells.

Capacitive desalination (CD) is a promising desalination technique as, relative to reverse osmosis (RO), it requires no membrane components, can operate at low (sub-osmotic) pressures, and can potentially utilize less energy for brackish water desalination. In a typical CD cell, the feed water flows through the separator layer between two electrically charged, nanoporous carbon electrodes. This architecture results in significant performance limitations, including an inability to easily (in a single charge) desalinate moderate brackish water feeds and slow, diffusion-limited desalination. We here describe an alternative architecture, where the feed flows directly through electrodes along the primary electric field direction, which we term flow-through electrode (FTE) capacitive desalination. Using macroscopic porous electrode theory, we show that FTE CD enables significant reductions in desalination time and can desalinate higher salinity feeds per charge. We then demonstrate these benefits using a custom-built FTE CD cell containing novel hierarchical carbon aerogel monoliths as an electrode material. The pore structure of our electrodes includes both micron-scale and sub-10 nm pores, allowing our electrodes to exhibit both low flow resistance and very high specific capacitance (>100 F g−1). Our cell demonstrates feed concentration reductions of up to 70 mM NaCl per charge and a mean sorption rate of nearly 1 mg NaCl per g aerogel per min, 4 to 10 times higher than that demonstrated by the typical CD cell architecture. We also show that, as predicted by our model, our cell desalinates the feed at the cell's RC timescale rather than the significantly longer diffusive timescale characteristic of typical CD cells.

Nanoporous metals have many technologically promising applications, but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only 1 nm thick oxide films can stabilize the nanoscale morphology of np-Au up to 1,000°C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO(2) ALD coatings. Our results open the door to high-temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

Nanoporous metals have many technologically promising applications, but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only 1 nm thick oxide films can stabilize the nanoscale morphology of np-Au up to 1,000°C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO(2) ALD coatings. Our results open the door to high-temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl3·6H2O or Al(NO3)3·9H2O, followed by drying with supercritical CO2. This technique affords low-density (60−130 kg/m3), high-surface-area (600−700 m2/g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, high-resolution transmission electron microscopy, powder X-ray diffraction, solid-state NMR, acoustic measurements, and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl3 in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2−5 nm in diameter and of varying lengths, whereas the aerogels prepared from hydrated Al(NO3)3 in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5−15 nm ra...

Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl3·6H2O or Al(NO3)3·9H2O, followed by drying with supercritical CO2. This technique affords low-density (60−130 kg/m3), high-surface-area (600−700 m2/g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, high-resolution transmission electron microscopy, powder X-ray diffraction, solid-state NMR, acoustic measurements, and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl3 in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2−5 nm in diameter and of varying lengths, whereas the aerogels prepared from hydrated Al(NO3)3 in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5−15 nm ra...

Carbon aerogels are a unique class of high-surface-area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility and chemical inertness make them very promising materials for many energy related applications, specifically in view of recent developments in controlling their morphology. In this perspective we will review the synthesis of monolithic resorcinol–formaldehyde based carbon aerogels with hierarchical porosities for energy applications, including carbon nanotube and graphene composite carbon aerogels, as well as their functionalization by surface engineering. Applications that we will discuss include hydrogen and electrical energy storage, desalination and catalysis.

Carbon aerogels are a unique class of high-surface-area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility and chemical inertness make them very promising materials for many energy related applications, specifically in view of recent developments in controlling their morphology. In this perspective we will review the synthesis of monolithic resorcinol–formaldehyde based carbon aerogels with hierarchical porosities for energy applications, including carbon nanotube and graphene composite carbon aerogels, as well as their functionalization by surface engineering. Applications that we will discuss include hydrogen and electrical energy storage, desalination and catalysis.

We report the synthesis and characterization for the first example of a low-density nanocrystalline thoria aerogel. The monolithic aerogels were prepared through the solgel polymerization of hydrated thorium nitrate in ethanol using ammonium hydroxide and propylene oxide as gelation initiators. The dried ThO{sub 2} aerogel was characterized by high-resolution transmission electron microscopy (HRTEM) and nitrogen adsorption/desorption analyses. The aerogel network was determined to be composed of spherical primary particles with features in the 5-20 nm range. These particles were also determined to be highly crystalline as evidenced by the higher magnification TEM examination. The thoria aerogel possesses high surface area (120 m{sup 2}/g) and pore diameters in the micro- and mesoporous range.