By Michael Klein, The University of Texas at Austin, Electrochemical Energy Laboratory and MRS Student Chapter
In the November 5th issue of Advanced Materials, Zhibin Yang and coworkers from Professor Huisheng Peng’s group at Fudan University report the fabrication of a flexible microfiber integrating a dye-sensitized TiO2 photoelectric energy-converting shell surrounding a carbon nanotube electrochemical capacitor. After stable charging under AM1.5 simulated solar illumination, the full device discharged for over 40 seconds at a very respectable 100 mA/g rate. In verifying the functional flexibility of the integrated device, the microfibers was subjected to bending as well as stretching up to almost 30% with minimal degradation in photovoltage and discharge performance.
The intricately assembled architecture starts with two aligned CNT sheets separated by a gel electrolyte wrapped around an elastic fiber electrode. This electrochemical capacitor core is then inserted into a plastic tube coated with another aligned CNT sheet. Then, a helical Ti fiber with perpendicularly-grown N719 dye-sensitized TiO2 nanotubes is wrapped around this structure to act as the photoanode. Finally, this entire structure is inserted into another tube and filled with an I-/I3- electrolyte to serve as the redox couple for the solar cell.
While the complexity of this assembly process is daunting from a fabrication perspective, the applicability and promise of this scheme is undeniable. As the authors highlight, wearable electronics (as well as microscale bio-devices) are currently severely limited by the need for on-board energy storage. Integrated generation is key; but most existing solutions are neither as elegant nor as flexible as the scheme presented in this paper.