Why should transition metal chalcogenides be investigated as water splitting precatalysts even though they transform into (oxyhydr)oxides?

The extensive investigation of 3d transition metal chalcogenide (sulphides, selenides, tellurides) precatalysts has shown that they transform into (oxyhydr)oxides during the oxygen evolution reaction (OER) and likely during industrial hydrogen evolution reaction (HER) conditions, as predicted by their Pourbaix diagrams. The phases formed from chalcogenide precatalysts are often more active, due to anion leaching induced effects. But are chalcogenides suitable to be used sacrificially, are they abundant, cheap, and non-toxic enough? Is their unique chemical nature really required? This review answers these questions by discussing the role of chalcogenides in the reconstruction/transformation process. Furthermore, it examines the role of remaining traces of chalcogenates (sulphate, selenate) that were recently shown to improve the OER activity and can break the ∗OH/∗OOH scaling relations.