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A new technique termed Supercritical Ion Exchange (SCIE) was developed and used to synthesize Cu-mordenite (Cu-MORS). The ion exchange takes place between the Cu complex (Copper(II)trifluoroacetylacetonate) dissolved in supercritical CO2 (scCO2) and the extraframework protons in mordenite zeolite without requiring an aqueous phase. The occurrence of the ion exchange reaction was demonstrated by using 1H NMR analysis of the high-pressure fluid phase samples and by visual inspection of the fluid phase color change during the synthesis. SCIE resulted in selective ion-exchange inferred by the equilibrium isotherm. The prepared catalysts were used for the stepwise direct methane to methanol (sDMTM) process and results showed that methanol productivity increased linearly with increasing Cu loading up to a certain Cu wt%. Cu-MORS displayed 16% higher methanol productivity as compared to Cu-MORA (prepared by aqueous ion exchange) with the same Cu loading. The results demonstrated the importance of site selective ion-exchange for zeolite catalysis.

Supercritical deposition (SCD) is used to prepare carbon-supported Pt nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Dimethyl(1,5-cyclooctadiene)platinum(II) (Pt(cod)me 2 ) is adsorbed from supercritical carbon dioxide (scCO 2 ) solutions onto Vulcan VX-72 at 13.2 MPa and 50 °C. The adsorbed metal precursor is converted to its metal form via three different routes: thermal conversion in N 2 at ambient pressure (route 1), thermal conversion in scCO 2 (route 2), or chemical conversion in H 2 at ambient pressure (route 3). Sequential SCD is used in routes 1 and 3. The mean diameters of the synthesized Pt nanoparticles are smallest for route 1 and largest for route 3. Nano-scale morphology of the electrocatalysts is characterized using transmission electron microscopy (TEM), revealing narrower Pt particle size distributions for the catalyst prepared via route 1 than for those synthesized by routes 2 and 3. Electrocatalyst prepared using route 1 showed the best performance both in specific activity (measured via cyclic voltammetry) and in PEMFC tests among electrocatalysts prepared using different routes.

Supercritical deposition is an alternative technique to incorporate metals on supports. It has been used to deposit a wide variety of single or multi-metallic morphologies such as highly dispersed species, nanoparticles, nanorods and conformal films on high surface area supports, polymers and crystalline substrates. Preparation consists of three main stages which are the dissolution of a metal complex in a supercritical fluid, adsorption or sorption of the metal complex onto support and the conversion of the adsorbed complex to metal species. Studies associated with each of these stages were described along with a thorough summary of recent studies on the preparation of the aforementioned materials. Perspectives for future studies were presented at the end of each section.

Optofluidic components enable flexible routing and transformations of light beams in integrated lab-on-a-chip systems with the use of carefully shaped fluid parcels. For structural integrity reasons, the working fluid is typically contained within a solid-material chip. One of the outstanding challenges in optofluidics is the preparation and processing of optofluidic waveguides. These require solid cladding materials that are sufficiently strong to contain the fluid while possessing optical properties that allow efficient confinement of light within fluidic channels. Here, we report on a new technique to obtain liquid-core optofluidic waveguides based on total internal reflection of light in three-dimensional water-filled channels embedded in hydrophobic silica aerogel. To form the channels, we employ a fiber made of cage-like silicon-oxygen compound – trifluoropropyl polyhedral oligomeric silsesquioxane (trifluoropropyl POSS) – which has high solubility in supercritical CO 2 (scCO 2 ). A U-shaped fiber made of trifluoropropyl POSS is obtained by melt/freeze processing of POSS powder and subsequently placed in a silicate sol. After gelation of the sol and aging of the gel, scCO 2 extraction is used to dry the wet gel and extract the POSS fiber, yielding a dry silica aerogel with a U-shaped empty channel inside it. Finally, the silanol groups at the surface of the aerogel are reacted with hexamethyldisilazane (HMDS) in the presence of scCO 2 to render the aerogel surface hydrophobic and the channel is filled with water. We demonstrate efficient waveguiding by coupling light into the water-filled channel and monitoring the channel output. The presented procedure opens up new possibilities for creating complex three-dimensional networks of liquid channels in aerogels for optofluidic applications.

Carbon aerogel (CA)–nickel nanocomposites were synthesized by impregnating the CAs with nickel(II) acetylacetonate (Ni(acac) 2 ) from supercritical carbon dioxide at 30 MPa and 60 °C followed by thermal or chemical treatment using H 2 at atmospheric pressure. The CA–Ni(acac) 2 –CO 2 adsorption isotherm was measured at the impregnation condition and found to be linear. The decomposition of Ni(acac) 2 on the CA surface was investigated using thermo-gravimetry and mass-spectroscopy. Propane was found in the gaseous decomposition products. CA–Ni composites were characterized using Infrared (IR) Spectroscopy and characteristic Ni(acac) 2 peaks were found to disappear after thermal or chemical treatments. X-ray diffraction (XRD) data confirmed that after H 2 treatments nickel nanocrystals were present in the CA. Transmission electron microscopy (TEM) revealed the presence of nickel nanostructures dispersed homogeneously on the surface of the CA. In the samples treated with H 2 at 170 °C, the average Ni nanoparticle size increased from 4.9 to 12.9 nm when the Ni loading increased from 3 to 6.5 wt.%. The H 2 treatment at 200 °C resulted in Ni nanorods with diameters of 7–11 nm and lengths of 25–50 nm dispersed throughout the CA surface.

Fuel cells (FCs) are emerging as devices for electricity generation in a new economic era where energy is increasingly obtained from renewable sources. FCs operate with relatively higher efficiencies as compared to internal combustion engines due to the direct conversion of chemical energy to electricity by electrochemical reactions. However, there exist a number of obstacles for their widespread acceptance and integration in our daily lives. These obstacles can be summarized as the high cost of FCs due to the high costs of materials, the need to process fuels to very high-purity levels, the unacceptable declines in performance with time as well as the absence of a H2 infrastructure. Applications of supercritical fluids (SCFs) in synthesis of novel materials and development of new processing techniques offer a wide range of opportunities that can help commercialization of FCs. These include the preparation of micro or nanoarchitectured materials in a highly controllable manner for electrolyte-electrode assemblies of a wide variety of FCs including proton exchange membrane FCs (PEMFCs) and solid oxide FCs (SOFCs). In this extent, materials synthesized using SCFs are (at least) comparable or superior in performance as compared to their conventional counterparts. The synthesis and processing of novel materials necessary for efficient hydrogen storage/processing and design of novel processes for H2 production may also benefit from the use of SCFs.