“Power sources commensurate in size with the electronic devices are in great demand,” Alok Singh told nanotechweb.org. “We wanted to develop a battery small enough to fit into nanoscopic devices by using environmentally benign materials and a simple and straightforward methodology.”

Singh and colleagues created their batteries by encapsulating oxidant and reductant chemicals inside separate polymerized phospholipid membranes. The resulting vesicles were around 45 nm in size. The scientists attached the vesicles to gold films using a disulphide functionalized phospholipid tether. They linked oxidant-containing cathodic vesicles to one substrate and anodic vesicles, which contained reductants, to another. Then they joined these electrodes using a salt bridge consisting of filter paper impregnated with potassium chloride solution.

“We found that the content of such tethered vesicles can be reduced/oxidized by the electrode in a controlled manner,” said Singh. “Once we had incorporated fuel in one kind of vesicle and the oxidant in separate vesicles, we had all the relevant constituents of a battery.”

The cathodic vesicles contained the oxidants ferricyanide (K3[Fe(CN)6]) inside the vesicle core and benzoquinone (BQ) in the bilayer membrane. The anodic vesicles incorporated the reductants ferrocyanide (K4[Fe(CN)6]) within the vesicle and hydroquinone (H2Q) in the membrane. Benzoquinone is the oxidized form of H2Q.

The team found they could tune the charge capacities and drain rates of the batteries by altering parameters such as the concentration of BQ, H2Q and [Fe(CN)6]3-/4-. The maximum charge capacity they produced was 17.6 aC and the maximum current per vesicle pair was 0.2 aA. This gave power outputs of the order of sub-nanowatts per square centimetre. The batteries also proved to be rechargeable over three consecutive discharge-recharge cycles.

“We can power loads at the atto to femto watt level, which is probably a future challenge to the community involved in developing low-power detectors and autonomous devices,” said Singh. “We envision that these vesicle batteries can serve as a rechargeable power source for distributed autonomous systems that may be of interest to the military and medical communities.”

Now the researchers plan to design more robust vesicles and to encapsulate other redox couples to improve the efficiency of the system. “We are also looking for other collaborators to transform this capability into viable commercial products,” said Singh.

The researchers reported their work in Advanced Materials.