Sequential Chemistry Toward Core–Shell Structured Metal Sulfides as Stable and Highly Efficient Visible‐Light Photocatalysts

A universal sequential synthesis strategy in aqueous solution is presented for highly uniform core–shell structured photocatalysts, which consist of a metal sulfide light absorber core and a metal sulfide co‐catalyst shell. We show that the sequential chemistry can drive the formation of unique core–shell structures controlled by the constant of solubility product of metal sulfides. A variety of metal sulfide core–shell structures have been demonstrated, including CdS@CoS x , CdS@MnS x , CdS@NiS x , CdS@ZnS x , CuS@CdS, and more complexed CdS@ZnS x @CoS x . The obtained strawberry‐like CdS@CoS x core–shell structures exhibit a high photocatalytic H 2 production activity of 3.92 mmol h −1 and an impressive apparent quantum efficiency of 67.3 % at 420 nm, which is much better than that of pure CdS nanoballs (0.28 mmol h −1 ), CdS/CoS x composites (0.57 mmol h −1 ), and 5 %wt Pt‐loaded CdS photocatalysts (1.84 mmol h −1 ).