No abstract

Development of electrical double layer capacitors using vertically oriented graphene nanosheets with fast response continues. The inherent open morphology of the nanosheets allows efficient access to charge storage surfaces, making them suitable for AC line filtering. However, since the overall surface area is only about a factor of ∼310x over the geometric area, the specific capacitance available remains limited. This work presents utilization of the conventional growth of vertically oriented graphene nanosheets on Ni substrates as the underlying architecture for coating with high surface area carbon black to substantially increase the specific capacitance while retaining the open morphology to allow good frequency response at 120 Hz. The carbon black coating was deposited on ∼1.2 μm and ∼2.5 μm high nanosheets using an aerosol spray method. Deposition times from 0-8 s, in 1 s intervals, provided coatings which translated into a specific capacitance of 2.3 mF/cm 2 at 120 Hz (8 s coating) and a volumetric capacitance of 4.6 F/cc (energy storage elements). Improvements in the uniformity of the carbon black coatings suggest that much higher specific capacitances are possible. COMSOL models of high density VOGN grown to 10 μm high and covered uniformly with 100 nm of carbon black coating suggest a capacitance of ∼42 mF/cm 2 with acceptable frequency response at 120 Hz can be achieved.

A six Torr CO2 glow discharge in combination with a heated W mesh‐reinforced ultrathin Ag membrane is used to generate molecular oxygen. The Ag membrane is a commercially available 25‐μm‐thick Ag foil backed by a 25‐μm‐thick W electroformed mesh. The permeation flux is inversely dependent on the membrane thickness and exponentially dependent on the membrane temperature. Calculations show that a pressure differential of 1 atmosphere can be supported by the W mesh/Ag foil membrane at temperatures up to 350 °C. In this work, a glow discharge for pressures between 2 and 15 Torr CO2 and temperatures up to 500 °C were reported. The DC glow discharge was produced initially with a solid Ag rod cathode, 2 mm in diameter, and then with a 7‐mm‐diameter Ag rod machined into a hollow cathode, located 5 mm from, and normal to, the Ag membrane anode. The voltage was varied from 440 to 620 VDC with currents up to 41 mA. A stable flux of 1.61 × 1015 O2 molecules·cm−2·s−1 is observed for a membrane temperature of 450 °C and a CO2 pressure of 6 Torr. With ~4‐m2 surface area, this approach is competitive with the present mission qualified Mars Oxygen In‐Situ Resource Utilization Experiment (MOXIE) system planned by National Aeronautics and Space Administration (NASA) for the 2020 Mars rover mission which generates ≈12 g/hr O2. The proof of concept technique presented herein can be substantially improved by further reduction of the membrane thickness, refinement of the cathode, and glow discharge plasma.