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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - STEM (Structural energy harvesting composite materials)

Teaser

Summary

This project deals with the fabrication and study of new materials that combine structural mechanical properties, with the ability to harvest energy from the environment. It bears close relation with current technological trends in transport, not just with respect to continuous efforts to the reduction of emissions, but for the emerging interest in multifunctional materials for de-centralised power management and in general in mechanically-augmented electronics.
The materials studied in the project consist of a strong, highly-conducting fabric of carbon nanotubes, which provides most of the mechanical reinforcement and charge collection. It is used as a scaffold to support a thin layer of an inorganic material that can convert external energy (e.g. light) into electrical energy.
Key for successful realization of both mechanical and energy-harvesting properties is the controlled assembly of the carbon and inorganic building blocks. We perform studies detailed studies on the structure of these hybrid materials, particularly on interfacial stress and charge transfer processes, and which help us identify routes for improvement in multifunctional properties.

Work performed

The first part of the work so far has focused on the development of strategies to fabricate and large-area (i.e. 10 cm2) hybrid materials based on fabrics of carbon nanotubes and semiconducting metal oxides. We have developed a general process combining gas-phase and electrochemical methods, which produces highly-crystalline hybrids with good adhesion between the two phases. The method has been successfully applied to produce a wide range of hybrids.

The other major area of development in the project has been the study of the structure and properties of these hybrids. They are slightly unusual in that they are large samples but made up of a myriad of nanoscaled elements, and that their properties are strongly affected by processes occurring at their surface or at the interface between carbon nanotubes and the inorganic phase.

An important result of the project has been the demonstration that the proposed hybrid architecture leads to a low resistance to the flow of charge across the material. This has been demonstrated for hybrids with metal oxides ranging from TiO2, a semiconductor, to SiO2, a dielectric, and applied to improve processes ranging from photodetection to electrostatic water purification. More specifically related to STEM, it has been demonstrated that these flexible, free-standing hybrids are capable of conducting conversion of light and mechanical vibration into electricity, albeit currently producing low power.

Final results

The progress beyond state of the art has been mainly in the development of materials combining mechanical toughness and flexibility, with a low resistance to transport charge generated from energy harvested. En route to this objective, the group has made contributions to: the synthesis of hybrid materials based on carbon nanotube fibres using new gas-phase and electrochemical methodologies, understanding chemistry and electronic properties of large-area carbon nanotube/semiconductor interfaces, and development of models to relate nanoscale descriptors to bulk mechanical and electrochemical properties.

The work conducted so far has aimed at developing the various tools required to address the challenge of simultaneously realizing structural properties and energy harvesting. The second part of the project will apply these tools to a new form of nanostructured ensembles currently under development in the group, and will demonstrate a large-area structural composite with potential to harvest energy with output power an order above the state of the art. A methodologie to evaluate multifunctional performance and potential weight reduction of components will also be introduced.