Molten Salt Synthesis and Electrochemical Evaluation of Na/Ag-Containing MnO Composites for Pseudocapacitor Applications.

Different composites of manganese oxides (MnO) containing sodium (Na) and silver (Ag) were synthesized by the molten salt method with various MnSO·HO/NaNO (M/N) molar ratios (between 0.3 and 1), and different AgNO and NaOH amounts, obtaining two groups of materials: without the addition of AgNO (labeled as M/N) and with AgNO (labeled as M/N-A). As for the M/N group, the system with the lowest M/N ratio yielded the highest specific capacitance (160.5 F g-1), attributed to the formation of MnO and sodium birnessite. In the M/N-A group, the 1 M/N-0.5A system, produced with M/N ratio of 1 and addition of 0.5 g of AgNO, exhibited the highest specific capacitance (229.1 F g-1), associated with the presence of MnO, silver hollandite, and metallic Ag. This enhancement is attributed to the synergistic effects of Na and Ag ions, which improve charge transfer kinetics and electrochemical performance. It was demonstrated that decreasing the MnSO·HO/NaNO ratio in the M/N group and increasing AgNO content in the M/N-A group enhances the electrochemically active surface area. Galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques confirmed that the 1 M/N-0.5A system exhibited the best performance, characterized by high energy retention, stable cycling behavior, and low capacitance dispersion, indicating its strong potential as an active material for pseudocapacitor applications.