Rare Earth Ion-Doped α-MnO2Nanorods for an Asymmetric Supercapacitor

The limited electrical conductivity of manganese dioxide (MnO2) hinders its broad use as an electrode in all-solid-state supercapacitor devices (ASDs). To overcome this, trivalent gadolinium (Gd) and erbium (Er) ions are incorporated into MnO2, effectively addressing the issue. This involves synthesizing α-MnO2 nanorods infused with Gd and Er by using a modified chemical process. Through the creation of crystal defects, augmentation of electrical conductivity, and increased porosity, the electrochemical performance is significantly enhanced. Cyclic voltammetry and galvanostatic charge–discharge measurements within the range of −0.2 to +0.6 V unveil improved capacitance values of 798 and 647 F g−1 at 1 A g−1 current density for Gd- and Er-doped α-MnO2 respectively, maintaining 92.4% and 89.7% charge retention after 5000 cycles. Analysis reveals that both samples are primarily dominated by electric double-layer capacitance (EDLC). Furthermore, surface capacitance outweighs diffusion-controlled processes in the electrochemical storage mechanism. The Gd-doped α-MnO2 coated device depicts a peak energy density of 78.5 Wh kg–1 at 106.01 W kg–1 power density for 0.5 A g−1 and maximum power density of 498.1 W kg–1 at 9.13 Wh kg–1 energy density for 3 A g−1. Even a handcrafted 1 cm × 1 cm device achieves 2.252 V potential, effectively illuminating commercial LEDs.