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

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 R_ct 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.