Fabricating Flexibly Resistive Humidity Sensors with Ultra‐high Sensitivity Using Carbonized Lignin and Sodium Alginate

Abstract Lignin, an abundant and environmentally friendly renewable polymer, was used to attain the carbonized lignin in current study. Then, a highly humidity sensitive composite composite film was prepared by carbonized lignin (CL) applied as the conductive particles and sodium alginate (SA). The repeatability, hysteresis, stability and response‐recovery of the CL/SA composite film sensor were investigated in the range of 11 to 97 % relative humidity at room temperature. The results showed the maximum responsivity of CL/SA composite film is 502,895.40 % under 97 % relative humidity. In addition, CL/SA composite film can be used as humidity sensors with ultrahigh sensitivity, low hysteresis, and stable repeatability in a wide relative humidity range of 11–97 %. Finally, the humidity mechanism of the CL/SA sensor and its monitoring application in human respiration were analyzed. The research revealed that CL/SA composite is an excellent humidity sensitive material.