New nitrogen based supercapacitors have triple the energy capacity of the best previous supercapacitors. They do not store as much energy as lithium-ion batteries, which achieve 70 to 250 watt-hours per kilogram. However, the researchers say their supercapacitor beats them on power. The nitrogen supercapacitor can crank out 26 kilowatts per kilogram, while lithium-ion batteries are only capable of 0.2 to 1 kilowatts per kilogram.
Their devices could store 41 watt-hours per kilogram, comparable to lead-acid batteries.
A bus could run for 25 kilometers before a 30 second recharge, instead of an 8 kilometers before recharging.
Currently there are electric buses like the Proterra. New supercapacitors would vastly increase the deployment of electric buses
Carbon-based supercapacitors can provide high electrical power, but they do not have sufficient energy density to directly compete with batteries. We found that a nitrogen-doped ordered mesoporous few-layer carbon has a capacitance of 855 farads per gram in aqueous electrolytes and can be bipolarly charged or discharged at a fast, carbon-like speed. The improvement mostly stems from robust redox reactions at nitrogen-associated defects that transform inert graphene-like layered carbon into an electrochemically active substance without affecting its electric conductivity. These bipolar aqueous-electrolyte electrochemical cells offer power densities and lifetimes similar to those of carbon-based supercapacitors and can store a specific energy of 41 watt-hours per kilogram (19.5 watt-hours per liter).
Researchers fabricated a porous carbon material that was then doped with nitrogen. This raised the energy density of the carbon more than threefold—an increase that was retained in full capacitors, without losing their ability to deliver power quickly.