Surfactant-mediated electrodeposition of a pseudocapacitive manganese dioxide a twofer

Abstract

Electrochemical energy storage is one of the most promising ways of storing energy from intermittent, renewable sources. To meet the needs, the development of scalable, earth-abundant, chemically stable, and environmentally friendly electrode materials is crucial. This work presents four cationic surfactant-mediated manganese sulfate electrolytic solutions used for the synthesis of electrolytic manganese dioxide (EMD) to produce scalable material that satisfies the pre-requisites desired for supercapacitor applications. The influence of the surfactant molecular structure, its concentration, and its interaction in the electrolytic sulfate bath was studied, which opens up new possibilities for the fabrication of the supercapacitor electrode. The performance of three surfactants (Tetradecyltrimethylammonium bromide, Didodecyldimethylammonium bromide, Benzyldodecyldimethylammonium bromide) was benchmarked against the widely used Cetyltrimethylammonium bromide under identical conditions. The surfactants were chosen based on their different head groups and hydrocarbon chains. Benzyldodecyldimethylammonium bromide-assisted EMD (EMD/B-AB) in a single-electrode device showed improved capacitance of 602 F g−1 (at 1 mA cm−2) over the other surfactant-mediated samples. The molecular dynamics simulations indicated that the electrodeposition of manganese dioxide is highly influenced by B-AB, as it adsorbs with the aryl group planar to the Pb surface. The appropriate concentration of B-AB surfactant in the bulk solution appears to be incorporated into the EMD deposit due to their hydrophobic nature and controlled nucleation and established improved pseudocapacitive performance to score a twofer. The asymmetric capacitor of EMD/B-AB30 vs. porous activated carbon exhibited a high specific capacitance of 91 F g−1, with an energy density of 32.4 Wh kg−1 for a corresponding power density of 971 W kg−1.