Hierarchical porous birnessite-MnO2-based nanostructure composite materials were prepared on a nickel foam substrate by a successive ionic layer adsorption and reaction method (SILAR). Following composition with reduced graphene oxide (rGO) and multiwall carbon nanotubes (MWCNTs), the as-obtained MnO2, MnO2/rGO and MnO2/rGO-MWCNT materials exhibited pore size distributions of 2–8 nm, 5–15 nm and 2–75 nm, respectively. For the MnO2/rGO-MWCNT material in particular, the addition of MWCNT and rGO enhanced the superb distribution of micropores, mesopores and macropores and greatly improved the electrochemical performance. The as-obtained MnO2/rGO-MWCNT/NF electrode showed a specific capacitance that reached as high as 416 F·g−1 at 1 A·g−1 in 1 M Na2SO4 aqueous electrolyte and also an excellent rate capability and high cycling stability, with a capacitance retention of 85.6% after 10,000 cycles. Electrochemical impedance spectroscopy (EIS) analyses showed a low resistance charge transfer resistance for the as-prepared MnO2/rGO-MWCNT/NF nanostructures. Therefore, MnO2/rGO-MWCNT/NF composites were successfully synthesized and displayed enhanced electrochemical performance as potential electrode materials for supercapacitors.

Controlling the cation to anion (Mn2+/MnO4−) molar ratios of the precursors was used to obtain a highly performance capacitive properties of nanostructural MnO2 hybridized carbon-based materials on nickel foam (NF) through successive ionic layer adsorption and reaction technology. SEM, XRD, BET, and XPS analyses are utilized to investigate the influence of cation/anion molar ratios of precursors on the as-obtained MnO2 electrode materials. At a lower molar ratio of cation/anion of 1, the prepared manganese oxide deposited on the NF with obvious δ-MnO2 phase. The average pore size distribution of BET analysis of the as-obtained δ-MnO2 is about 4.6 nm, the specific surface area is 155.7 m2 g−1, exhibiting a mesoporous structure. However, when the molar ratio of cation/anion is higher than 5, the deposited film produced by the reaction exhibits a γ-MnO2 crystal phase. The capacitance of δ-MnO2/NF electrode is 280 F g−1 at 1 A g−1 in a 1 M Na2SO4 aqueous electrolyte solution. In addition, reduced graphene oxide (rGO) mixed with multi-wall carbon nanotube (MWCNT) was added to synthesize γ-MnO2/rGO-MWCNT/NF electrode, which has a high capacitance of 377.4 F g−1 under the charge/discharge current density at 1 A g−1.