MoS₂ and MoSe₂ in the stable semiconducting 2H form show negligible photocatalytic activity for the hydrogen evolution reaction (HER). By linking the layers of the dichalcogenide with layers of other 2D materials such as carbon-rich borocarbonitride (BC₇N), one can enhance the photochemical HER activitysignificantly. Interestingly, such nanocomposites, MoSe₂–MoSe₂ and MoSe₂–BCN show high photocatalytic activity even though the dichalcogenide itself is in the 2H form. This study shows the important role played by covalent cross-linking of layered compounds. Photocatalytic activity of covalently cross-linked layer of 2H-MoSe₂ is higher than that of 2H-MoS₂. Unlike the 2H forms, the metallic 1T forms of MoS₂ and MoSe₂ prepared by lithium intercalation followed by exfoliation, exhibit high photocatalytic HER activity. Unfortunately, materials prepared by lithium intercalation are unstable. The 1T forms of MoSe₂ and MoS₂ prepared by solvothermal or hydrothermal methods are, however, quite stable and exhibit good photochemical activity for HER. The 1T forms are generally superior to the covalently linked 2H forms. The present study shows how MoSe₂ and MoS₂ in both 2H and 1T forms can be exploited for photochemical HER activity by appropriate chemical manipulation.