Ruthenium-Decorated Cobalt Selenide Nanocrystals for Hydrogen Evolution

We report the synthesis of CoSe nanocrystals (NCs) decorated with Ru clusters which are employed as an electrocatalyst for the hydrogen evolution reaction in acid media. We show that this Ru-CoSe system undergoes chemical and structural transformations under hydrogen evolution conditions: CoSe NCs, which initially exhibit a hexagonal crystal structure, are converted into CoSe2 NCs having a cubic structure. The Co that is extracted during this process forms a Co oxide/hydroxide layer; the Ru clusters aggregate and form Ru NCs. Such modifications result in a final Ru-CoOx/Co(OH)(x) CoSe2 nanocomposite that exhibits an enhanced hydrogen evolution activity. Our work highlights the importance of studying the chemical transformations that occur in both the catalyst and the support during hydrogen evolution reactions.