High-performance aqueous asymmetric electrochemical capacitors based on graphene oxide/cobalt(ii)-tetrapyrazinoporphyrazine hybrids

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.