Covalently modified nanocellulose materials: Enhanced performance and stability for self-powered and impedance humidity sensors

Real-time environmental and physiological humidity monitoring requires humidity sensors made of stable and reusable humidity-sensitive materials. Here, bacterial cellulose (BC) easily modified with phytic acid (PA) was shown to be useful for self-powered and impedance-based humidity sensors. Due to the strong covalent bonding between PA molecules and BC effectively enhancing water molecule adsorption and charge transfer, the modified self-powered humidity sensor exhibited high output voltage (0.53 V) and low hysteresis (ΔH = 2.8 %), whereas the impedance-based humidity sensor possessed a high response value (1831) and a fast response time (6.9 s). The sensor maintains excellent sensing performance after 50 cycles and even after immersion in various environments such as acids, alkalis, and salts. In addition, this synthetic material shows good application prospects in respiratory rate monitoring, non-contact measurement, and smart diaper humidity detection. Notably, the self-powered sensor incorporates advanced wireless transmission capabilities, thereby augmenting its portability and practicality.