R. W. Pekala

Carbon aerogels for electrochemical applications

A major advantage of highly crosslinked, organic aerogels is the ability to transform many of these materials into electrically conductive carbon aerogels. Carbon aerogels have been formed as monoliths, microspheres, irregularly-shaped powders, and thin film composites. In all cases, the carbon aerogels retain their high surface area (400–800 m2/g) and ultrafine cell/pore size (<100 nm). Carbon aerogels are being examined as electrodes for double layer capacitors, pseudocapacitors, and capacitive deionization units. This paper examines the synthesis, structure–property relationships, and performance of carbon aerogel electrodes used in electrochemical applications.

Capacitive Deionization of NaCl and NaNO3 Solutions with Carbon Aerogel Electrodes

A process for the capacitive deionization of water with a stack of carbon aerogel electrodes has been developed by Lawrence Livermore National Laboratory. Unlike ion exchange, one of the more conventional deionization processes, no chemicals are required for regeneration of the system. Electricity is used instead. Water with various anions and cations is pumped through the electrochemical cell. After polarization, ions are electrostatically removed from the water and held in the electric double layers formed at the surfaces of electrodes. The water leaving the cell is purified, as desired. The effects of cell voltage and cycling on the electrosorption capacities for NaCl and NaNO 3 have been investigated and are reported here.

The Aerocapacitor: An Electrochemical Double‐Layer Energy‐Storage Device

The authors have applied unique types of carbon foams developed at Lawrence Livermore National Laboratory (LLNL) to make an {open_quotes}aerocapacitor{close_quotes}. The aerocapacitor is a high power-density, high energy-density, electrochemical double-layer capacitor which uses carbon aerogels as electrodes. These electrodes possess very high surface area per unit volume and are electrically continuous in both the carbon and electrolyte phase on a 10 nm scale. Aerogel surface areas range from 100 to 700 m{sup 2}/cc (as measured by BET analysis), with bulk densities of 0.3 to 1.0 g/cc. This morphology permits stored energy to be released rapidly, resulting in high power densities (7.5 kW/kg). Materials parameterization has been performed, and device capacitances of several tens of Farads per gram and per cm{sup 3} of aerogel have been achieved.

Deposition of Ruthenium Nanoparticles on Carbon Aerogels for High Energy Density Supercapacitor Electrodes

Abstract : The preparation and characterization of high surface area ruthenium/carbon aerogel composite electrodes for use in electrochemical capacitors is reported. These new materials have been prepared by the chemical vapor impregnation of ruthenium into carbon aerogels to produce a uniform distribution of adherent approx. 2 nm nanoparticles on the aerogel surface. The electrochemically oxidized ruthenium particles contribute a pseudocapacitance to the electrode and dramatically improve the energy storage characteristics of the aerogel. These composites have demonstrated specific capacitances in excess of 200 F/g, in comparison to 95 F/g for the untreated aerogel.

Capacitive deionization of NH4ClO4 solutions with carbon aerogel electrodes

A process for the capacitive deionization of water with a stack of carbon aerogel electrodes has been developed by Lawrence Livermore National Laboratory (LLNL). Unlike ion exchange, one of the more conventional deionization processes, no chemicals are required for regeneration of the system. Electricity is used instead. An aqueous solution of NH4ClO4 is pumped through the electrochemical cell. After polarization, NHin4su+and ClOin4su−ions are removed from the water by the imposed electric field and trapped in the extensive cathodic and anodic double layers. This process produces one stream of purified water and a second stream of concentrate. The effects of cell voltage, salt concentration, and cycling on electrosorption capacity have been studied in detail.

Rate effect on lithium-ion graphite electrode performance

The electrochemical performance of lithium-ion graphite electrodes with particle diameter in the range of 6–44 µm was evaluated at different discharge (intercalation)/charge (deintercalation) rates (C to C/60). The electrode capacity depends on both the average particle size and rate. With a simple rate programme, the electrode performance is dependent on the cycling rate. The capacity of small graphite particles (6 µm) at C/2 rate was 80% of that achieved at C/24 rate (∼372 mAh g−1). The capacity of large graphite particles (44 µm) obtained at fast rates (C/2) was only 25% of that obtained under near-equilibrium conditions (C/24). The electrode capacity, however, is nearly independent of the charge rate when the electrode is fully intercalated using a modified rate programme containing a constant-voltage hold at 0.005 V (vs Li+/Li) for several hours. The electrochemical behaviour is related to the physicochemical properties of the graphite particles.

Carbon Aerogels: An Update on Structure, Properties, and Applications

Aerogels are unique porous materials whose composition, structure, and properties can be controlled at the nanometer scale. This paper examines the synthesis of organic aerogels and their carbonized derivatives. Carbon aerogels have low electrical resistivity, high surface area, and a tunable pore size. These materials are finding applications as electrodes in double layer capacitors.

The use of capacitive deionization with carbon aerogel electrodes to remove inorganic contaminants from water

The capacitive deionization of water with a stack of carbon aerogel electrodes has been successfully demonstrated for the first time. Unlike ion exchange, one of the more conventional deionization processes, no chemicals were required for regeneration of the system. Electricity was used instead. Water with various anions and cations was pumped through the electrochemical cell. After polarization, ions were electrostatically removed from the water and held in the electric double layers formed at electrode surfaces. The water leaving the cell was purified, as desired.