Single-Layer PtI2: A Multifunctional Material with Promising Photocatalysis toward the Oxygen Evolution Reaction and Negative Poisson's Ratio.

Exploring novel two-dimensional multifunctional materials with distinguished properties lies at the core of materials innovation. Here, we identify a hitherto-neglected single-layer PtI2, which can readily be exfoliated from its bulk experimentally, with appealing multifunctional properties through first-principles calculations. Single-layer PtI2 is an indirect-gap semiconductor with a band gap of 2.56 eV, and its band gap is extremely robust against external strain. We find that it is a promising two-dimensional photocatalyst, exhibiting outstanding catalytic performances toward oxygen evolution reactions, with the water oxidation reaction occurring spontaneously under light irradiation. Moreover, we unveil that single-layer PtI2 is a long-sought auxetic material with a negative Poisson's ratio of -0.54, arising from its particular puckered hinge crystal. Our findings highlight single-layer PtI2 as a promising multifunctional material for nanoscale mechanical and photocatalytic applications.