Activated Biochar Supercapacitors Fabricated Using Scalable Roll Coating

Supercapacitors have the potential to replace batteries as energy storage devices due to their rapid charge/discharge ability and high specific capacitance. The most commonly used materials for supercapacitors include carbon nanotubes, graphene and activated carbon which are expensive materials and require sophisticated processing. Yellow pine biochar is readily available, low-cost waste material that possess properties of an ideal supercapacitor material. High specific capacitance has been achieved from biochar by efficient plasma activation method, however, the conventional hydraulic press method used for fabrication is time consuming and not repeatable. However, there is a need for low cost, less time consuming and environmentally safe method for biochar activation. The objective of this research was to find the optimum milling time for biochar and a method to easily control the mass of material on electrodes to obtain high specific capacitance. In this research both conventional hydraulic press and roll coating methods were used for electrode fabrication and specific capacitances were compared. All the plasma treatments were done in capacitively coupled plasma using oxygen plasma (10 % O2 in Ar). One hour was found to be the optimum milling time. Two minutes of oxygen plasma treatment resulted in the highest specific capacitances of 101 F/g and 124 F/g for hydraulic press and roll coating methods. Plasma treated biochar (100 W) with acetylene black provided the highest specific capacitance of 161 F/g. High power plasma xii treatment resulted in increased wettability of electrodes by 50%. This is the first report of increasing surface energy, wettability and capacitance using oxygen plasma treatment of yellow pine biochar. This is also the first report of roll coating method for supercapacitor electrode fabrication using plasma activated yellow pine biochar. It provides a low cost, low temperature, nontoxic method to fabricate state of the art supercapacitors in which mass of material being deposited can be controlled. Effects of other plasma gases and other electrolytes on specific capacitance and lifetime of the device should be studied