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Enhanced electrochemical performance of MnO2 nanoparticles: graphene aerogels as conductive substrates and capacitance contributors.

An N-doped graphene aerogel (NGA) is used as a reactive container for growing MnO2 nanoparticles via a soaking-hydrothermal strategy. MnO2 nanoparticles pile up on the surface of reduced graphene oxide sheets with crosslinked structures serving as electrical conductors. Importantly, the NGA generates extra capacitance during the electrochemical process, which accomplishes a satisfactory compensation in the physical-chemical properties of MnO2. As a cathodic electrode for Zn-ion batteries, the MnO2/NGA exhibits a specific capacity of 275.8 mA h g-1 and pre-eminent cycling stability with a retention of 93.6% at 3 A g-1 after 1000 cycles. Meanwhile, the proposed electrode also shows a relatively high specific capacitance of 341 F g-1 for a supercapacitor in 1 M Na2SO4. Meanwhile, the long-term cycling stability shows only a slight decrease by 5.1% of the initial capacitance after 5000 continuous cycles at 3 A g-1, which indicates its superior electrochemical stability. Additionally, the assembled asymmetric supercapacitor also shows good electrochemical performance. This work highlights the extensive function of an N-doped graphene aerogel as a promising substrate for enhancing the electrochemical performance of MnO2, which opens the gate for wide potential applications of graphene aerogel composites emphasizing their complementary effects.