researchers at north carolina state university have discovered that a material with atomically think layers of water was capable of storing and delivering energy much quicker than the same material without layers of water, which could hold important clues about future energy storage technologies, according to a report on the school website.
low temperature high resolution transmission electron microscope image of a platelet
of tungsten oxide dihydrate; the "stripes" are individual layers of atoms separated
by water layers. (north carolina state university)
the scientists created a crystalline tungsten oxide and a layered, crystalline tungsten oxide hydrate, which had a thin layer of water between two layers of tungsten oxide. when charged for 10 minutes, the tungsten oxide had stored more energy than the hydrate, but when charged for only 12 seconds then the hydrate stored more than the regular material.
the researchers were intrigued by the hydrate’s ability to store energy more efficiently, with less wasted heat. the scientists argue that the water acts as a “pathway” for the transfer of ions through the material.
while this is a proof-of-concept study, the researchers are excited about the potential for this to allow increased energy storage per unit of volume, faster diffusion of ions through the material, and faster charge transfer. all of that would be a significant boost to the energy storage industry.
the research was recently published in chemistry of materials. the abstract read:
“the kinetics of energy storage in transition metal oxides are usually limited by solid-state diffusion, and the strategy most often utilized to improve their rate capability is to reduce ion diffusion distances by utilizing nanostructured materials.
“here, another strategy for improving the kinetics of layered transition metal oxides by the presence of structural water is proposed. to investigate this strategy, the electrochemical energy storage behavior of a model hydrated layered oxide, wo3·2h2o, is compared with that of anhydrous wo3 in an acidic electrolyte.
“it is found that the presence of structural water leads to a transition from battery-like behavior in the anhydrous wo3 to ideally pseudocapacitive behavior in wo3·2h2o. as a result, wo3·2h2o exhibits significantly improved capacity retention and energy efficiency for proton storage over wo3 at sweep rates as fast as 200 mv s–1, corresponding to charge/discharge times of just a few seconds.
“importantly, the energy storage of wo3·2h2o at such rates is nearly 100% efficient, unlike in the case of anhydrous wo3. pseudocapacitance in wo3·2h2o allows for high-mass loading electrodes (>3 mg cm–2) and high areal capacitances (>0.25 f cm–2 at 200 mv s–1) with simple slurry-cast electrodes.
“these results demonstrate a new approach for developing pseudocapacitance in layered transition metal oxides for high-power energy storage, as well as the importance of energy efficiency as a metric of performance of pseudocapacitive materials.”