Morphology-dependent pseudocapacitive kinetics of MnO₂ nanoparticles and nanorods in neutral Na₂SO₄ electrolyte

Manganese dioxide (MnO2) is widely studied as a pseudocapacitive material due to its high theoretical capacitance, low cost, and environmental compatibility; however, its performance is strongly influenced by nanoscale morphology, particularly in neutral electrolytes relevant to practical applications. In this study, MnO2 nanoparticles (NPs) and nanorods (NRs) were synthesized via a controlled KMnO4-NH2OH redox route and characterized using FESEM and XRD. Their electrochemical behavior was evaluated in 1 M Na2SO4 using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) under identical conditions. MnO2 nanoparticles exhibit superior capacitive performance due to higher surface area and improved ion accessibility, whereas nanorods show stronger diffusion limitations. Dunn's analysis revealed capacitive contributions increasing from similar to 66 to similar to 85% for NPs, compared to similar to 28-54% for NRs. The corresponding b-values (0.681 and 0.744) confirm mixed charge-storage behavior, with nanoparticles maintaining higher surface-controlled contributions.