Alginate Biopolymer Effect on the Electrodeposition of Manganese Dioxide on Electrodes for Supercapacitors

Electrolytic manganese dioxide (EMD) synthesized from different electrolytic baths with varying biopolymer additive concentrations has been investigated for application as an electrochemical supercapacitor. Alginic acid, also termed "alginate", is a widely used biopolymer for various biological applications due to its physicochemical properties. Here, the EMD material synthesized with alginate crosslinking was introduced in the field of electrochemistry for supercapacitors. Different EMD and alginate composites were characterized to find the trade-off between the biopolymer content in the bath and the energy storage capability. Compared to the pristine EMD, the EMD composites at all of the alginate concentrations influenced both the physical and the electrochemical storage properties of the materials. The presence of alginate in the solution at higher concentrations altered the morphology from spindle-shaped to cactus-shaped with flutes. Rearranged morphology and enhanced particle size are attributed to the ability of the alginate to act as a template for binding the Mn2+ ions on the substrate in a relatively ordered and widely distributed manner. The EMD composite delivered 5 times higher capacitance (487 F g–1) than the pristine EMD at a current density of 1 mA cm–2 in a three-electrode system using a 2 M NaOH aqueous electrolyte. When the EMD composite was coupled with activated carbon, the asymmetric device exhibited 52 F g–1 capacitance at a current density of 2 mA cm–2 while giving excellent capacitance retention (94%) over 5000 cycles. The molecular dynamics simulation model supported the influence of alginate on ion–polymer interactions in the electrolytic bath. The simulations showed that the alginate provides a template for binding Mn2+ ions in a relatively ordered manner. It could assist the EMD/Alg composite growth in a more favorable condition for energy storage applications.