A lead-free K2CuBr3 microwires-based humidity sensor realized via QCM for real-time breath monitoring

Halide perovskites have recently emerged as potential humidity-detection materials due to their excellent chemical and physical properties. However, the toxicity of Pb and environmental instability of the lead halide perovskites restrict the application in humidity detection. Herein, a lead-free K 2 CuBr 3 microwires-based quartz crystal microbalance (QCM) humidity sensor was investigated, and the application in human respiratory monitoring was developed. Coupling the high humidity sensitivity of K 2 CuBr 3 with the high mass change sensitivity of QCM, the lead-free K 2 CuBr 3 coated QCM humidity sensor exhibited excellent logarithmic linearity response (R 2 = 0.98626, 11–95% RH). In addition, the sensor demonstrated excellent repeatability, fast response/recover time (10.63 s/4.31 s), and considerable stability. Moreover, the Fourier transform infrared spectra (FTIR) and Langmuir adsorption model were applied to reveal the corresponding humidity sensing mechanism. The results indicate the lead-free K 2 CuBr 3 -based QCM sensor reported in this work could be a promising candidate for real-time breath monitoring. • Lead-free K 2 CuBr 3 microwires were synthesized successfully. • Humidity sensors based on QCM and K 2 CuBr 3 microwires were fabricated. • The sensor demonstrated a fast response/recover time (10.63 s/4.31 s). • The application in human respiratory monitoring was developed.