Fast electrochemical triple-interface processes at boron-doped diamond electrodes

Two important mechanisms for electron transfer processes at boron-doped dia mond electrodes involving the oxidation of tetramethylphenylenediamine (TMP D) dissolved in aqueous solution and the oxidation of tetrahexylphenylenedi amine (THPD) deposited in the form of microdroplets and immersed into aqueo us eletrolyte solution are reported. For TMPD, the first oxidation step in aqueous solution follows the equation: TMPDaqueous reversible arrow TMPDaqueous+ + e(-) Remarkably slow heterogeneous kinetics at a H-plasma-treated boron-doped di amond electrode are observed. consistent with a process following a pathway more complex than outer-sphere electron transfer. At the same boron-doped diamond electrode surface a deposit of THPD undergoes facile oxidation foll owing the equation: THPDorganic + SCNaqueous- reversible arrow [THPD+SCN-](organic) + e(-) This oxidation and re-reduction of the deposited liquid material occurs at the triple interface organic droplet/diamond/aqueous electrolyte and is the refore an example of a facile high-current-density process at boron-doped d iamond electrodes due to good electrical contact between the deposit and th e diamond surface.