Gigantic Thermal Shielding in 2D Oxide Nanosheets.

Thermal shielding materials that can block near-infrared (NIR) light from the sunlight while maintaining visible transparency have become increasingly important from an energy-saving perspective. Here, we demonstrate a gigantic NIR shielding by an engineered plasmonic material based on a two-dimensional (2D) polytungstate (Cs _{4- x} W ₁₁ O _{35- d} ). Starting from a charge-neutral polytungstate (Cs ₄ W ₁₁ O ₃₅ ), we synthesize charge-imbalanced 2D nanosheets (Cs _{4- x} W ₁₁ O _{35- d} ) that undergo an unusual structural change with the semiconductor-to-metal transition in a reduced atmosphere. Layer-by-layer engineering of the 2D nanosheets enables a plasmon-induced enhancement of the NIR reflectance (>53%) with a high visible transparency (>71%), realizing high-performance thermal shielding. Our approach offers a solution for future thermal management technology.