Effective use of biomass ash as an ultra-high humidity sensor

The paper reports a facile, green, cost-effective, and sustainable track to fabricate humidity sensors with superior performance. This frugal way make use of biomass ashes, left by combustion and annealing of natural wood pulp paper, that can emerge as an alternative source of sensing materials. In comparison to other humidity sensors, the optimized humidity sensor based on annealed tissue ash exhibited ultra-high sensitivity of six orders of magnitude (∼10⁶), excellent selectivity (against H₂, CO, CH₄) and good stability (1–8 weeks) in the range of 15–90% RH at room temperature. Further characterization was carried out to elucidate the sensing mechanism, which includes chemical composition, functional group, crystal structure, surface morphology and elemental composition of the ashes by XRF, FT-IR, XRD, SEM and EDS analysis, respectively. The proposed strategy and fabricated sensors also enable the real-time humidity monitoring in human breath, which demonstrates the feasibility of its practical application ability as a flexible and wearable humidity sensor.