  Recently the successful formation of PEO coatings on zinc in a phosphate
aluminate electrolyte was shown. The produced composite coatings contain
various mixtures of ZnO and ZnAl$_2$O$_4$. In frame of the current study, the
properties of the formed coatings including adhesion/cohesion, wear, corrosion
and photocatalytic activity were analysed to identify possible applications.
However, the coatings show internal porosity and a sponge-like structure. Thus
the cohesion within the coating is quite low. Pull-off tests have demonstrated
clear rupture within the PEO layer at strength values as low as 1 MPa. The
photocatalytic activity is limited, in spite of the formation of a higher
amount of ZnO at shorter treatment times. Interestingly, the composite coatings
of ZnO and higher amounts of ZnAl$_2$O$_4$ spinel showed a higher activity, but
not sufficient for fast and effective catalytic cleaning applications.
