Boron-doped diamond electrodes: The role of surface termination in the oxidation of dopamine and ascorbic acid

Due to the lack of strong adsorption of reactants, intermediates or products on the boron-doped diamond electrode surface, the electrochemical behavior can be simulated based on a model involving only electron transfer, chemical reactions and solution mass transport (DigiSim). The electrochemical behavior of several different biogenic redox-active species, dopamine, ascorbic acid, uric acid and 3,4-dihydroxyphenylacetic acid, was compared experimentally at as-deposited (hydrogen-terminated) and anodically oxidized (oxygen-terminated) boron-doped diamond surfaces, and molecular orbital theory was used to help explain the results. Using semi-empirical calculations, we find that, for dopamine, which is protonated in acid solution, the interaction of the positively charged quaternary ammonium group with the surface is relatively strong and nearly equal for both hydrogen- and oxygen-terminated surfaces, which explains the lack of sensitivity of the cyclic voltammetry to the surface termination. For ascorbic acid, the interaction of the neutral compound with the hydrogen-terminated surface is weaker, while that with the oxygen-terminated surface is very weak, consistent with the highly inhibited electron transfer.