Narrow Results

The sodium ion pre-intercalation manganese dioxide (Na${}_x$MnO${}_2)$ is supported on titanium nitride (TiN) substrate to form electroactive Na${}_x$MnO₂/TiN electrode through an electrodeposition process in Mn(CH₃COOH)₂/Na₂SO₄ precursors with high Mn/Na ratio. MnO₂ has a tiled leaf-like structure with a wrinkling morphology. Na${}_x$MnO₂ has a cross-linking nanorod structure with a nanoporous morphology, which is beneficial for electrolyte ion diffusion. The density functional theory (DFT) calculation results indicate that Na${}_x$MnO₂ reveals the enhanced density of states (DOS) and the lowered band gap than MnO₂, which is consistent with higher cyclic voltammetry current response due to superior electroactivity of Na${}_x$MnO₂. The Faradaic process involves Na${}^{+}$ adsorption/desorption on the surface of MnO₂ by contributing to electrochemical capacitance and Na${}^{+}$ intercalation/deintercalation on the deep interlayer of pre-intercalation Na${}_x$MnO₂ by contributing to pseudocapacitance. Concerning the electrolyte ion size effect, both MnO₂/TiN and Na${}_x$MnO₂/TiN electrodes have higher capacitive performance in Li₂SO₄ electrolyte than that in Na₂SO₄ and K₂SO₄ electrolyte due to more feasible Li${}^{+}$ diffusion. When MnO₂ is converted into Na${}_x$MnO₂, the capacitance at 2.5 mA cm${}^{-2}$ increases from 351.3 mF cm${}^{-2}$ to 405.6 mF cm${}^{-2}$ in Na₂SO₄ electrolyte and from 376.3 mF cm${}^{-2}$ to 465.1 mF cm${}^{-2}$ in Li₂SO₄ electrolyte. The conductive TiN substrate leads to high rate capacity retention ratio of 50.7% for MnO₂/TiN and 49.5% for Na${}_x$MnO₂/TiN when current density increases from 0.5 mA cm${}^{-2}$ to 5 mA cm${}^{-2}$. So, Na${}_x$MnO₂/TiN with sodium ion pre-intercalation exhibits the improved capacitive performance in Li₂SO4 electrolyte to act well as the promising supercapacitor electrode.