Combination of porous structure and MnO2 modification for improving capacitance of planar BDD electrode

Abstract

Wearable electronic devices have become a preferred choice for health monitoring, but suffer from low capacitance of planar electrodes. This work aims to improve the capacitive performance through the combination of porous boron-doped diamond (BDD) and MnO2 modification. BDD film was deposited on the substrate of titanium foam using hot-filament chemical vapor deposition (HFCVD). Constant-voltage deposition was then employed to deposit MnO2 on the BDD, and the deposition time was adjusted to evaluate the influence of MnO2 modification on the electrode capacitance. Porous structure formed by titanium foam enables BDD electrode to exhibit larger specific surface area, and reach a capacitance of 67.9 mF/cm2. Porous BDD/MnO2 film (MnO2 deposited for 1500 s) shows pea-like morphology and has optimal capacitive performance. BDD/MnO2-1500 s electrode displays a maximum capacitance of 1383.6 mF/cm2 at a current density of 2 mA/cm2, which is about 195 times that of the planar BDD electrode (7.1 mF/cm2 at a current density of 2 mA/cm2) along with a minimum Rct value of 2 Ω. This allows us to see the fact that improvement mechanism of combining porous structure and MnO2 modification may result from common effect of three following aspects: (1) Porous structure gives BDD superior specific surface area and favorable ion transport channels than planar electrode; (2) Pseudocapacitance effect of MnO2 increases the capacitance density; (3) Pea structure of MnO2 may markedly increase the specific surface area of the film and shorten ion/electronic diffusion distances.