High throughput electrochemical screening and dissolution monitoring of Mg-Zn material libraries

A combinatorial study on Mg-Zn material libraries obtained by thermal evaporation is performed in order to investigate the effect of alloying magnesium on the electrochemical behaviour and dissolution rate of zinc in borate buffer of pH 7.4. The surface morphology of the graded samples is complex and subject to a detailed discussion, whereas the crystal composition revealed Mg, MgZn2 and Zn exclusively. Open circuit potential measurements and potential sweeps along the graded samples are combined with downstream zinc detection and revealed several strongly non linear dependencies between electrochemical features and magnesium content. While the chemical dissolution rate of zinc by the electrolyte was found to reflect the film stoichiometry except in the regions of high surface roughness, the open circuit potential revealed a local minimum around 20 at. % magnesium accompanied by a maximum in the current plateau during the anodic sweep and a high thickness of the native oxides present prior to electrochemical experiments. All compositions showed passive like behaviour during anodic sweeps with high plateau current densities (200-350 μA cm−2) originating from slow but constant oxide dissolution as supported by XPS analysis of the surface before and after contact with the electrolyte.