Scientists Produce a Ceramic Paper Consisting of Conductive Nanofibers

Nanostructure Renders a Wafer Thin Paper

Layered ceramic paper: Scanning electron micrographs show the stacked layers of vanadium pentoxide and water in the composite. The material is so elastic and tough that it can be bent (bottom image). Credit: Advanced Materials/Stuttgart University

Scientists have developed an electrically conductive paper-like material from a vanadium pentoxide ceramic that is as hard as copper, yet flexible enough to be rolled up or folded.




The fibers assemble themselves into a transparent orange paper

First, the scientists synthesized nanofibers of vanadium pentoxide using water-soluble vanadium salt according to the procedure known for over 20 years. The rather unusual feature of this ceramic is that the fibers conduct electricity. This is possible because the metal oxide chains contain weakly bound electrons which can hop along them.

The conductive fibers assembled into an elastic and strong paper – once the Stuttgart-based scientists had created the necessary conditions. They distributed the nanofibers suspended in water very thinly on a substrate, and afterwards let the aqueous film dry for several hours at room temperature, and then a few more hours at 40°C, slowly reducing the humidity in the climate chamber. This slow process allowed the fibres to assemble themselves into precisely parallel patterns. Finally, they annealed the film at 100 and 150°C, thus producing a transparent, orange paper whose thickness could be modified by changing the amount of nanofiber solution used (between 0.5 and 2.5 micrometers).




A cross-section shows a structure much like a brick wall

Scientists Produce a Paper Like Material from a Vanadium Pentoxide Ceramic

The nanostructure is what makes the material tough and elastic: The nanofibers layer themselves in slabs which are stacked in staggered formations on top of one another. In the cross-section, the material’s structure therefore resembles a brick wall, in which the ceramic slabs are held together by the water.

The structure begins with the assembly of the nanofibers, which was known prior to the Stuttgart project. The fibers consist of two vanadium pentoxide layers with a layer of water in between. Several fibers stack on top of one another laterally, forming slabs. The slabs also stack laterally, but staggered, on top of each other, so that the structure of the layered material will likely resemble a brick wall in a cross-section, where the vanadium pentoxide slabs make up the bricks embedded in a water layer that surrounds them like mortar.

It is this combination of hard ceramic and soft water in the special nanostructure that makes the paper hard, strong and pliable. It also results in high conductivity in the paper plane and low out-of-plane conductivity. However, the electricity is not only transported by the electrons that move along the nanofibers, but also by ions in the water layers between the ceramic.

Both the electrical properties and the mechanical properties of the paper therefore vary according to the water content. By drying and annealing the material, the scientists mainly remove weakly bound water to make the ceramic fibers form a denser structure. Since this also reinforces the bonds between the nanofibers, it makes the paper harder and more rigid.

Potential applications: batteries, gas sensors and artificial muscles




Publication: Zaklina Burghard, Andreas Leineweber, Peter A. van Aken, Thomas Dufaux, Marko Burghard and Joachim Bill, “Hydrogen-bond reinforced vanadia nanofiber paper of high stiffness,” Advanced Materials, 7 March 2013; DOI: 10.1002/adma.201300135

Source: Max Planck Institute

Image: Advanced Materials/Stuttgart University

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