Instant‐in‐Air Liquid Metal Printed Ultrathin Tin Oxide for High‐Performance Ammonia Sensors

Liquid metal‐based printing techniques are emerging as an exemplary platform for harvesting non‐layered 2D materials with a thickness down to a few nanometres, leading to an ultra‐large surface‐area‐to‐volume ratio that is ideal for sensing applications. In this work, the synthesis of 2D tin dioxide (SnO 2 ) by exfoliating the surface oxide of molten tin is reported which highlights the enhanced sensing capability of the obtained materials to ammonia (NH 3 ) gas is reported. It is demonstrated that amperometric gas sensors based on liquid metal‐derived 2D SnO 2 nanosheets can achieve excellent NH 3 sensing performance at low temperature (150 °C) with and without UV light assistance. Detection over a wide range of NH 3 concentrations (5–500 ppm) is observed, revealing a limit of detection at the parts per billion (ppb) level. The 2D SnO 2 nanosheets also feature excellent cross‐interference performance toward different organic and inorganic gas species, showcasing a high selectivity. Further, ab initio DFT calculations reveal the NH 3 adsorption mechanism is dominated by chemisorption with a charge transfer into 2D SnO 2 nanosheets. In addition, a proof of concept for prototype flexible ammonia sensors is demonstrated by depositing 2D SnO 2 on a polyimide substrate, signifying the high potential of employing liquid metal printed SnO 2 for realizing wearable gas sensors.