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While most of the reports on NH 3 gas sensors are either based on metal oxide composites with other 2D materials, polymers or noble metals or involve multi-step-based synthesis routes, this work is the first report on a pristine ternary metal oxide, 2D NiCo 2 ZnO 4 nanoflake based room-temperature (RT) NH 3 gas sensor. The 2D NiCo 2 ZnO 4 nanoflakes were prepared by a one-step hydrothermal method. FESEM and TEM images displayed micro-flower like morphologies, containing vertically aligned interwoven porous 2D nanoflakes, whereas XPS and XRD data confirmed the successful growth of this ternary metal-oxide. This sensor revealed a good response, repeatability, linearity ( R 2 = 0.9976), a low detection limit of 3.024 ppb, and a response time of 74.84 s with excellent selectivity towards NH 3 over six other VOCs. This improved performance of the sensor is ascribed to its large specific surface area (127.647 m 2 g -1 ) resulting from the 2D nanoflake like structure, good electronic conductivity, variable valence states and abundant surface-active oxygen of NiCo 2 ZnO 4 . Thus, this highly selective 2D NiCo 2 ZnO 4 based RT NH 3 gas sensor can be an attractive solution for the fabrication of next-generation NH 3 gas sensors.