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Bilirubin oxidase encapsulated within a silica sol-gel/carbon nanotube composite electrode effectively catalyzed the reduction of molecular oxygen into water through direct electron transfer at the carbon nanotube electrode surface. In this nanocomposite approach, the silica matrix is designed to be sufficiently porous for substrate molecules to have access to the enzyme and yet provides a protective cage for immobilization without affecting biological activity. The incorporation of carbon nanotubes adds electrical connectivity and increases active electrode surface area. The standard surface electron transfer rate constant was calculated to be 59 s(-1) which indicates that the carbon nanotube side walls are primarily responsible for electron transfer. The use of direct electron transfer processes simplifies biofuel cell fabrication by eliminating the need for redox mediator and ion-conducting separators.

Progress in the miniaturization of batteries has lagged well behind that of microelectronics. Although lithium‐ion (Li‐ion) battery technology has been vital in advancing portable consumer electronics, it is not clear whether future generations of microscale devices can be powered using traditional battery designs. In this paper, we report on the fabrication and properties of battery electrodes comprised of arrays of vertically aligned carbon rods. The electrodes exhibit good reversibility and represent the first carbon arrays to achieve areal capacities greater than 5 mAh cm−2 at relatively large current densities, although the capacity does fade with cycling. The 3D battery designs based on these architectures offer the promise of achieving high energy densities within small footprint areas.

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