Structural and electrochemical properties of MnO2-Carbon based supercapacitor electrodes

Abstract

We present results of an approach to incorporate redox-active manganese oxide into the 3-dimensional porous structure of carbon xerogels under self-limiting electroless conditions. By varying the structure of the carbon backbone, we found that deposition of manganese oxide preferably takes place on the external surface area of the carbon xerogels. From our detailed analysis we conclude that 3-dimensional carbon xerogels with particle and pore sizes ranging from 10 to 20 nm and low manganese oxide precursor concentration combined with long deposition times are beneficial for fast operating pseudocapacitance electrodes with high capacitance and effective use of the redox active component.

Electroless Preparation and ASAXS Microstructural Analysis of Pseudocapacitive Carbon Manganese Oxide Supercapacitor Electrodes

“…The mass uptake exhibits a linear correlation with the infiltration time; however, there is an additional offset for infiltration times shorter than 4 h. Indeed, earlier investigations showed a change in the slope of the mass uptake at short impregnation times, hinting for two different deposition mechanisms. 8 In agreement with other studies, we assume that, in an early stage, the deposition coats the carbon surface with a homogeneous layer. 29 However, the deposition does not cease after completion of a homogeneous cover layer in the vicinity of the carbon scaffold, as it becomes evident by the thicker layers detected by SEM cross section scans (Figure 4).…”

“…The respective contributions to the composition were identified in a complementary XPS study. 8 The slight decline in the effective density ρ x is therefore likely to be caused by dilution of the precursor solution.…”

“…In order to vary the external surface area of the xerogel, monolithic carbon xerogels with different primary particle sizes of about 50 nm (sample series CX S) and 300 nm (sample series CX L), yet similar apparent density (ρ ≈ 0.48 g/cm 3 ), were prepared from a sol-gel process based on resorcinol and formaldehyde, as described previously. 8,19 In detail, resorcinol (R) was dissolved in formaldehyde (F) with a molar ratio R:F = 1:2. The molar ratio of resorcinol to catalyst (C, sodium carbonate) accounted for R/C = 4000 and R/C = 6000 for sample series CX S and CX L, respectively.…”

“…The MnO 2 deposition was performed via immersion of the discs of each series in 0.05 M aqueous solutions of NaMnO 4 for 4, 16, 24, 30, and 48 h, according to the procedure described in the literature. 8,20 The samples are labeled such that the abbreviation for the carbon particle size is followed by the MnO 2 impregnation time, e.g., CXMn S 48 is the carbon xerogel sample with small carbon particles, impregnated for 48 hours. After thoroughly washing out the remaining NaMnO 4 solution, the composite was dried in air at 50 °C.…”