An environmental consequence of the COVID pandemic is the mountain of medical waste that requires disposal. Incineration of used personal protective equipment, such as masks, and pharmaceutical blister packs is a source of toxic gas emissions. An international research effort may have forged an ecological disposal route by repurposing such waste into the raw materials needed to assemble solid state supercapacitors.

Discarded masks are disinfected with ultrasound, then dipped in ink made of graphene, which saturates the mask. The material is pressed under pressure and heated to 140° C, far below the 1,000° C to 1,300° C range required for the pyrolysis-carbonation of conventional supercapacitor batteries. A separator composed of mask material with insulating properties is then placed between the two electrodes made of the new material. The device is saturated with a special electrolyte and then encased in a protective shell derived from medical blister pack material.

An energy density of 99.7 Wh/kg was documented for the produced supercapacitors, not far behind that of lithium-ion batteries. The addition of calcium-cobalt oxide perovskite nanoparticles to the electrodes more than doubled the energy density to 208 Wh/kg. The best-performing version of the battery retained 82% of its capacity after 1,500 cycles, and could deliver energy for more than 10 hours at a voltage up to 0.54 V.

Researchers from CONACYT (National Council of Science and Technology, Mexico), National Polytechnic Institute Saltillo (Mexico), Unidad Mérida (Mexico), University of Texas at Dallas and National University of Science and Technology (Russia) contributed to this development, which is described in the Journal of Energy Storage.