Remarkable photochemical HER activity of semiconducting 2H $$\hbox {MoSe}_{{2}}$$ MoSe 2 and $$\hbox {MoS}_{{2}}$$ MoS 2 covalently linked to layers of 2D structures and of the stable metallic 1T phases prepared solvo- or hydro-thermally $$^{\S }$$ §

Abstract

$$\hbox {MoS}_{{2}}$$ and $$\hbox {MoSe}_{{2}}$$ 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 ( $$\hbox {BC}_{{7}}\hbox {N}$$ ), one can enhance the photochemical HER activity significantly. Interestingly, such nanocomposites, $$\hbox {MoSe}_{{2}}$$ – $$\hbox {MoSe}_{{2}}$$ and $$\hbox {MoSe}_{{2}}$$ –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- $$\hbox {MoSe}_{{2}}$$ is higher than that of 2H- $$\hbox {MoS}_{{2}}$$ . Unlike the 2H forms, the metallic 1T forms of $$\hbox {MoS}_{{2}}$$ and $$\hbox {MoSe}_{{2}}$$ prepared by lithium intercalation followed by exfoliation, exhibit high photocatalytic HER activity. Unfortunately, materials prepared by lithium intercalation are unstable. The 1T forms of $$\hbox {MoSe}_{2}$$ and $$\hbox {MoS}_{{2}}$$ 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 $$\hbox {MoSe}_{{2}}$$ and $$\hbox {MoS}_{{2}}$$ in both 2H and 1T forms can be exploited for photochemical HER activity by appropriate chemical manipulation. SYNOPSIS Photocatalytic HER activity of 2H- $$\hbox {MoSe}_{{2}}$$ covalently linked with other 2D layered materials is superior to that of the pristine sheets. 1T-forms of $$\hbox {MoSe}_{2}$$ and $$\hbox {MoS}_{{2}}$$ grown by solvothermal or hydrothermal method show good photochemical activity. The present study shows that both $$\hbox {MoSe}_{{2}}$$ and $$\hbox {MoS}_{{2}}$$ in either 2H or 1T form can be exploited for photochemical HER activity by suitable chemical and physical manipulation.