Tuning parallel manganese dioxide to hollow parallel hydroxyl oxidize iron replicas for high-performance asymmetric supercapacitors.

A novel and facile strategy is developed to tune parallel manganese dioxide (MnO2) to hollow parallel hydroxyl oxidize iron (FeOOH) replicas, which can exactly keep its original morphology. The key factors leading to the morphology-preserved transformation are the low-temperature and dropwise strategy via a serial of controlled experiments. Benefiting from the characteristics of parallel and hollow structures, the FeOOH replica delivers remarkable specific capacitance of 186.8F g-1 at 0.5 A g-1. The electrochemical performances delivered by the asymmetric supercapacitor (parallel MnO2//hollow parallel FeOOH) are much superior to those where conventional activated graphene or FeOOH nanoneedles are used as negative electrode materials. This can be attributed to the advantages of parallel nanostructure and high electrochemical matching effect of positive and negative electrode materials. The energy density is recorded up to 46.8 Wh kg-1 at the power density of 0.5 kW kg-1, while it still remains 20.7 Wh kg-1 with the maximum power density of 10 kW kg-1. Furthermore, this strategy shows great universality and can be broadened to almost all MnO2 related researches to synthesize ideal negative electrode materials with high structural and electrochemical matching effect, thus further enhances the electrochemical performances of as-prepared asymmetric supercapacitor devices.