|The development of miniaturized self-powered gas sensors to achieve the real-time respiratory monitoring and analyses has great clinic significance on early diagnosis. In this work, self-powered formaldehyde sensors based on triboelectric nanogenerator (TENG) are demonstrated. Two new interfacial layer materials, including 4,4'-bipyridine (bpy)-functionalized phosphomolybdic acid (bpy-PMA) as both triboelectric layer and active sensing layer, and phenothiazine (PTZ) as the seed layer for solution-processed Ag nanoparticles (NPs) electrode, are demonstrated. The resulting TENG manifests high instantaneous power density up to 8.93 W m-2 and outstanding stability with the open-circuit voltage nearly unchanged after 200,000 cycles of continuous operation in ambient conditions. Meanwhile, such TENG also delivers remarkable sensing properties for FA detection at room temperature. To the best of our knowledge, this the first demonstration of TENG-based self-powered FA sensors, and excellent gas sensor performance (selectivity = 130 and ultra-fast response time of ≈5 sec) to sub-ppm level achieved herein are superior to those of state-of-the-art FA sensors. More encouragingly, the integration of TENG with face mask for detecting FA concentration in exhaled breath is also demonstrated.