A novel asymmetric electrochemical capacitor (AEC) with high energy and power densities has been
developed using a graphene oxide/cobalt(II)tetrapyrazinoporphyrazine composite (GO/CoTPyzPz) as the
positive electrode and graphene oxide/carbon black (GO/CB) as the negative electrode in a neutral
aqueous Na2SO4 electrolyte. The excellent specific capacitance, energy and power densities ( 500 F g 1,
44 W h kg 1 and 31 kW kg 1) coupled with long cycle life, excellent short response time, and low
equivalent series resistance clearly indicate that this new material has great potential for the
development of low-cost and ‘green’ aqueous AECs that operate at high energy and power densities.
Interestingly, the energy density of the GO/CoTPyzPz//GOCB based AEC falls within the range usually
observed for nickel metal hydride (NiMH) batteries (30–100 W h kg 1), but more importantly, shows
better power performance than NiMH batteries (0.25–1 kW kg 1) widely used in hybrid vehicles such as
Toyota Prius and Honda Insight.