A self-assembled array of MnO nanoparticles linked to an Au surface using 1.5 nm conducting organic chains. The array creates a new route to oxide supercapacitor electrodes, Li battery electrodes, and catalysts for Li-air batteries and is a step towards addressing many of the challenges currently faced in electrochemical energy storage.
A self-assembled array of MnO nanoparticles linked to an Au surface using 1.5 nm conducting organic chains. The array creates a new route to oxide supercapacitor electrodes, Li battery electrodes, and catalysts for Li-air batteries and is a step towards addressing many of the challenges currently faced in electrochemical energy storage.

Researchers from Sandia National Laboratories have devised electrodes consisting of nanoparticles tethered to the surface of a charge collector using short organic conductors that could revolutionize energy storage [Stevens et al., Scientific Reports (2017), doi: 10.1038/srep44191].

Electrochemical storage technologies like batteries and superconductors have taken great strides in recent years but neither quite satisfies the needs of users for high power and energy densities in a single device. These technologies are limited by the inclusion of electrically inactive material such as binders, poor charge transfer, and the degradation of electrode materials over many cycles of charging and discharging.

Todd C. Monson and his team believe that their approach, while it might not overcome all the obstacles facing energy storage, could provide an important step toward high energy and power density in a single, reliable device.

“Our primary motivation was to revolutionize how battery and electrochemical capacitor electrodes could be fabricated by increasing the active material by up to 99.9% by mass,” he explains.

The researchers devised a new synthesis route that creates an array of MnOx nanoparticles tethered to a surface by short, conductive organic linkers. The first step is to create MnOx nanoparticles with diameters of 10 nm that possess ligands terminated with bromine. Next the team formed a self-assembled monolayer (SAM) on the substrate of choice − in this case Au − which is terminated with amine groups. When the two are brought together, the bromine on the surface of the particles reacts with the SAM amine groups to create short linkages or tethers.

“The tethered nanoparticle approach dramatically reduces the amount of electrochemically inactive material, leading an electrode that is 99.9% active material by mass,” says Monson.

The practical approach could be applied to a wide range of nanoparticles and different surfaces, including curved or irregular shaped objects, leading to a broad range of applications in energy storage devices like supercapacitors and Li-ion batteries and as catalysts for Li-air batteries.

“Our findings could have huge implications on energy storage,” suggests Monson. “Battery and electrochemical capacitors fabricated with tethered nanoparticles would have increased energy density, charge/discharge rates, efficiency, cycle life, and affordability.”

The researchers are now hoping to evaluate the performance of the tethered nanoparticles as battery and capacitor electrodes.

This article was originally published in Nano Today (2017), doi: 10.1016/j.nantod.2017.04.004.