Tailoring Oxygen Vacancy of Co₃O₄ Microcubes by Annealing Co₃[Co(CN)₆]₂ Template in Air for Ultrasensitive Humidity Mapping

Improving sensitivity under low humidity is highly desirable for the applications of humidity sensors in robotics, intelligent prosthetics, and human–machine interfaces, etc. Herein, by using K₃[Co(CN)₆] as a single‐source precursor, the Co₃[Co(CN)₆]₂ microcubes were synthesized, which can keep the morphology in temperature range of 380–880 °C as annealed in air. Benefited from the ultrahigh structural stability of the Co₃[Co(CN)₆]₂, the oxygen vacancy in the derived Co₃O₄ products can be controllably fabricated through altering calcination temperature. The oxygen vacancy‐abundant Co₃O₄ products displayed significantly enhanced response under low humidity (0–6%RH), and thus were applied in scanning a series of water areas to map the humidity distribution. This work presents a promising strategy on rationally designing humidity sensing materials via oxygen defect engineering and provides more possibilities for the application of low‐cost humidity sensors in some emerging fields.