Crystal Facet-Engineered Indium Sulfide Ultrathin Nanosheets for Photocatalytic Hydrogen Evolution

Two types of ultrathin In₂S₃ nanosheets with thicknesses of 3–5 nm, terminated with (100) and (110) crystal facets, were successfully synthesized. The introduction of an excess sulfur precursor enables selective adsorption of released S^2– ions onto the (100) surface, suppressing its growth and promoting the growth and exposure of the (110) crystal facets (denoted as IS-(100) and IS-(110), respectively). IS-(100) is of a narrower bandgap compared to IS-(110), enhancing its light absorption range. Water adsorption and dissociation were found to be more favorable on the IS-(100) surface, as indicated by the hydrogen reaction Gibbs free energy diagram. Furthermore, kinetic analysis demonstrates that IS-(100) has superior charge separation and transfer capabilities and reduced carrier recombination, relative to IS-(110), as evidenced by photoelectrochemical tests and photoluminescence measurements. In addition, IS-(100) has a more negative conduction band position than IS-(110). Consequently, IS-(100) exhibited a higher hydrogen evolution efficiency, achieving a value 1.67 times greater than that of IS-(110).