Optimising sequential electrodeposition to control structure and pseudocapacitive performance in PEDOT/MnOx electrodes

This work systematically investigates how PEDOT and MnOx deposition parameters affect the electrochemical performance of sequentially electrodeposited composites by independently varying the growth potential and synthesis charge of each layer. The PEDOT underlayer transformed the heterogeneous deposition of MnOx into a finer, uniform particle distribution, thereby improving electronic contact and access to oxide active sites. Increasing the deposition potential and charge of both layers enhanced the capacitance. The composite, obtained by depositing PEDOT at 1.0 V for 300 mC followed by MnOx at 1.0 V for 500 mC, delivered an areal capacitance of 47 mF cm −2 at 0.13 mA cm −2 and retained 68% of this value at 2 mA cm −2 . It also exhibited an approximately 60% lower charge-transfer resistance than pristine MnOx. EQCM analysis showed that the composite exhibits a mass profile that varies with contributions from both layers but is dominated by Na + intercalation/deintercalation in the MnOx layer, with a higher outer capacitance, while the charge contribution analysis indicated that 60.8% of the stored charge originated from readily accessible outer regions. The enhanced electrochemical response is attributed to the combined effect of PEDOT-assisted MnOx nucleation, efficient interfacial electron transport and improved utilisation of the oxide redox sites.