Supercapacitors Made From Hemp

Graphene could be a valuable material for use in commercial electronics, but it’s expensive to make. A research team has now developed a low-cost chemical process that can turn plant waste into graphenelike nanomaterials (ACS Nano 2013, DOI: 10.1021/nn400731g). The team, led by David Mitlin of the University of Alberta, used the carbon nanomaterials to make devices called supercapacitors, which provide quick bursts of electrical energy. Commercial supercapacitors, sometimes used in vehicle braking systems, have electrodes made from activated carbon. But experimental devices made with graphene can store more energy, Mitlin says. His group transformed inexpensive fibrous waste from the hemp plant (Cannabis sativa) into a carbon nanomaterial that has properties similar to those of graphene. The researchers heated a barklike layer of the plant at 180 °C for 24 hours. They then treated the resulting carbonized material with potassium hydroxide and cranked up the temperature to between 700 and 800 °C, causing the material to exfoliate into nanosheets. A supercapacitor they made with these nanosheets as electrodes discharged 49 kW of power per kg of material. Commercial electrodes supply 17 kW/kg.