Boosted Na⁺-MnO₂ supercapacitor performance via strong metal support interaction

MnO₂ is widely utilized as an electrode material in supercapacitors. However, overcoming challenges such as sluggish ion migration, aggregate tendency, and low conductivity is imperative for optimizing MnO₂-based supercapacitors. Herein, NaMnO₄ was employed as the Mn precursor to introducing a higher concentration of small Na⁺ ions into the layer structure of δ-MnO₂. This elevated Na concentration fosters efficient ion migration within the MnO₂ lattice. Moreover, Na⁺-MnO₂ was deposited onto Cu/graphene (Cu/G) composites. Leveraging the strong metal-support interactions (SMSI) between Cu and graphene, the resulting composite demonstrates enhanced conductivity and reduced aggregation. Combining MnO₂ with Cu/G resulted in a conductivity of 5.78 × 10^-3 S cm^-1, which is significantly better than that of MnO₂. The composite material exhibits an exceptional electrochemical performance, boasting a specific capacitance of 655 F g^-1 at 1 A g^-1 and impressive long-term stability, retaining 95 % of its capacitance after 4000 cycles at 10 A g^-1. Additionally, a 1.6 V asymmetric supercapacitor was assembled, featuring carbon as the anode, Cu/G/MnO₂ as the cathode, and 1 M KOH as the electrolyte, achieving a superior specific capacitance of 75 F g^-1 at 1 A g^-1. Cu/G/MnO₂//carbon demonstrates a maximum energy density of 27 Wh kg^-1 at a power density of 0.8 W kg^-1. This study underscores a facile strategy to enhance MnO₂-based supercapacitors by leveraging the SMSI effect for boosted performance.