Hydrochromic Visualization of a Keggin-Type Structure Triggered by Metallic Fluids for Liquid Displays, Reversible Writing, and Acidic Environment Detection

Hydrochromic visualization of a liquid interface shows vital potential applications in liquid displays, reversible writing, and acidic environmental detection, which offers a platform for detection and forewarning due to its intuitive and visual characteristics. Herein, we report a hydrochromic display due to the interfacial effect of liquid metal (LM)-triggered ammonium metatungstate (AMT) with instant dual-mode color switching. The double-electron-transfer reaction of the AMT on the surface of gallium-based LM caused the formation of heteropoly blue in the presence of acidic surroundings, resulting in a reversible color switching from being colorless to blue or blue to colorless. This visual interfacial discoloration phenomenon can be applied to the liquid display on diverse patterns of the LM surface. Furthermore, papers with a functional display were prepared, which can be used for writing up to eight times with dual-mode color switching. In addition, the reactive activity of acid triggering make it a potential candidate for use in visualizing an acidic environment with a detection range of pH = 1 to 0 (0.1–1.5 M). Briefly, this interfacial discoloration phenomenon enriches the interfacial engineering of LM and provides a unique prospective and wide-range platform for the application of LM.