Fabricating random arrays of boron doped diamond nano-disc electrodes: Towards achieving maximum Faradaic current with minimum capacitive charging

We report the first construction of a random array of boron doped diamond (BDD) nano-disc electrodes (RAN BDD), formed by a simple three-step method. First molybdenum(IV) dioxide nanoparticles are electrodeposited onto a BDD substrate. Second the electrode surface is covered in an insulating polymer film by the electropolymerization of a 4-nitrophenyldiazonium salt. Third the molybdenum dioxide nanoparticles are dissolved from the BDD surface (removing the polymer layer directly above them only) using dilute hydrochloric acid to expose nano-discs of BDD, ca. 20 ± 10 nm in diameter surrounded by a polymer insulating the remainder of the BDD. This method produces up to 650 ± 25 million BDD nano-disc electrodes per cm2. Various RAN BDD electrodes were produced using this method with a similar distribution of nano-disc size and number density, confirming that this is a reliable and reproducible method of manufacturing such nanoelectrode arrays. At modest scan rates the RAN BDD array was found to produce peak currents approaching that of the Randles–Ševcík limit for the equivalent geometric electrode area despite the fact that most of the surface was insulated by the polymer as shown by voltammetry and atomic force microscopy. The experimental results are compared with simulations of both ordered and random arrays of nano-disc electrodes, the results of which demonstrate that the maximum current obtainable at such arrays is that predicted by the Randles–Ševcík equation. The array of BDD nano-discs shows a significantly reduced capacitive background current compared to the bare BDD electrode, suggesting that such devices may offer improved signal resolution in electroanalytical measurements.