Electric Field Effects on the Adsorption of Dopamine Species on Ag(111): DFT Investigation of Interaction Mechanism

Abstract

The study of interactions between dopamine (DA) and noble metal surfaces as Ag, is envisaged as a fundamental factor to attain more efficient electrochemical sensor materials. We describe, in the framework of Density Functional Theory, the adsorption of four dopamine species, neutral (NDA), zwitterionic (ZDA), protonated (PDA) and deprotonated (DPDA) species on Ag(111), upon the application of an external electric field (E), a fact of pertinence for electrochemistry tests. The ZDA and PDA species show relatively large binding energies of about 2.9 eV to 4.6 eV and suffer a significant flatting upon adsorption, compared with DPDA and NDA. The adsorbates binding energy is an increasing function of the applied E for ZDA and PDA species, showing a great change when the results for positive and negative E are compared. An electron transfer is produced from NDA, ZDA and PDA species to Ag, while in the case of DPDA an opposite behavior is obtained. As the sign of E is modified, an increase of charge values in all DA species is observed. The theoretical results obtained here show that ZDA and PDA species are the most affected DA species upon adsorption on Ag(111) and when non-zero electric fields are applied.