25 years ago, at the very beginning of my activities in industrial recovery/refining, I had to operate some Wohlwill cells the very first time, instructed by the engineer who planned and installed the whole chemical and electrochemical refining units. The racks to hold and contact anodes and cathodes were made of plain silver. The very first electrolysis-experiment rapidly showed up as a disaster, caused by heavy corrosion of the silver, leading to a rapid growing of the cell resistance and thus to rapidly sinking current flow. So the racks had to be replaced, and titanium was the material chosen. It worked successfully nearly endless, even without traces of corrosion.
Titanium as such is a very reactive metal, like aluminum, but covered with a very compact oxide layer on its surface, protecting it efficiently against attack with mineral acids, elemental halogens and strong bases. This very high chemical resistance leads to its industrial use as so called dimensionally stable anodes (DSA) in chlor-alcali-electrolysis and different electrochemical processes. In a DSA the original titaniumoxide surface layer, which is a very good electrical insulator, is replaced by a mixed oxide layer, for example a mixed titanium/ruthenium-dioxide layer, which conducts electrical current and is able to oxidize chloride to elemental chlorine at even lower potentials than a platinum- or a graphite-anode.
