A Humidity‐Induced Large Electronic Conductivity Change of 10⁷ on a Metal‐Organic Framework for Highly Sensitive Water Detection

Abstract The electronic conductivity (EC) of metal–organic frameworks (MOFs) is sensitive to strongly oxidizing guest molecules. Water is a relatively mild species, however, the effect of H 2 O on the EC of MOFs is rarely reported. We explored the effect of H 2 O on the EC in the MOFs (NH 2 ) 2 ‐MIL‐125 and its derivatives with experimental and theoretical investigations. Unexpectedly, a large EC increase of 10 7 on H 2 SO 4 @(NH 2 ) 2 ‐MIL‐125 by H 2 O was observed. Brønsted acid–base pairs formed with the −NH 2 groups, and H 2 SO 4 played an important role in promoting the charge transfer from H 2 O to the MOF. Based on H 2 SO 4 @(NH 2 ) 2 ‐MIL‐125, a high‐performance chemiresistive humidity sensor was developed with the highest sensitivity, broadest detection range, and lowest limit of detection amongst all reported sensing materials to date. This work not only demonstrated that H 2 O can remarkably influence the EC of MOFs, but it also revealed that post‐modification of the structure of MOFs could enhance the influence of the guest molecule on their EC to design high‐performance sensing materials.