Microwave-hydrothermal in situ fabrication of porous NiO@SnO2 heterostructures: synergistic effects of p-n junction and oxygen vacancies for ultrafast hydrogen sensing

A microwave-hydrothermal route was developed to fabricate porous NiO@SnO 2 heterostructures with SnO 2 nanoparticles embedded in NiO sheets. The optimized NiO@SnO 2 -2 (NiO:SnO 2 = 1:2) exhibits outstanding H 2 sensing performance at 300 °C, including a response time of 10 s (with an estimated uncertainty of ±1 s based on repeated measurements) to 9000 ppm H 2 , a high response of 90, excellent selectivity and stability. This enhanced performance stems from the synergistic effect of the p–n heterojunction and oxygen vacancies: the heterojunction enlarges the depletion layer while oxygen vacancies promote oxygen adsorption. Upon H 2 exposure, reduction of adsorbed oxygen releases electrons, modulating sensor resistance. This work provides an effective strategy for developing high-performance gas sensors via heterointerface engineering.