Effect of Surface Roughness on Electrochemical Adsorption/Desorption of Dopamine by Carbonaceous Electrodes

Electrochemical adsorption/desorption of dopamine by carbonaceous electrodes upon voltage variation is the key process of neurotransmitter detection through fast scan cyclic voltammetry. In the present study, ab initio molecular dynamics simulation empowered by image-charge method was applied to calculate the adsorption/desorption free energy profile of dopamine and dopamine o-quinone at fixed electrode potentials using our newly developed open-source CP2K simulation package. It was found that the activation barriers for both adsorption and desorption were substantially reduced with increasing surface roughness of the carbonaceous electrodes. For example, on the flat graphene electrode, the activation barrier for dopamine adsorption at V0=−0.4V is 1.34 kcal/mol, while its counterpart on the curved nanotube electrode drops to 0.82 kcal/mol. Moreover, the diffusion coefficient of dopamine decreases by approximately 60% when it is moving close to the graphene electrode, while its diffusion is accelerated by up to 100% when the nanotube electrode is adopted. The faster diffusion alongside the reduced activation barrier greatly facilitates the electrochemically driven adsorption/desorption of dopamine by nanotube electrodes, in consistent with experimental findings that a rougher carbonaceous surface is critical for fast scan cyclic voltammetry.