The influence of platinum on the performance of silver–platinum anti-bacterial coatings

Anti-bacterial silver coatings were deposited on thermally sensitive polymeric substrates using a combination of magnetron sputtering and neutral atom beam (Saddle Field) plasma sources. The anti-bacterial activity of silver is dependent on the release of Ag+ ions, which act by displacing other essential metal ions such as Ca2+ or Zn2+. This study reports some initial electrochemical experiments intended to evaluate the use of platinum to enhance the release of silver ions from the silver coating. In the galvanic series in seawater silver is more active than platinum and therefore probably enhances Ag+ ion formation through galvanic action when the two metals are in electrical contact. In order to evaluate this several electrochemical methods were employed using magnetron target samples as working electrodes. Cyclic voltammetric, open circuit potential measurements and potential step (chronoamperometric) experiments were performed on several silver–platinum alloys containing from 0.5% to 3.0% Pt and on a pure silver target electrode. In the case of the chronoamperometric measurements, the resulting current–time curves demonstrated that Ag+ formation was enhanced with platinum addition by up to 100%. Results of this preliminary work are discussed with reference to various reactions that can occur on the surface of silver in chloride-containing environments.