High-performance humidity sensor: Ternary Cu(II)/SnO2/MOF-303 nanocomposites for wide-range and fast response

To develop a high-performance humidity sensor, MOF-303, possessing both micro- and mesoporous structures, was selected as the host material for the sensor. SnO 2 nanoparticles were introduced via wet impregnation, and Cu(II) ions were anchored onto uncoordinated nitrogen sites of MOF-303, forming a ternary Cu(II)/SnO 2 /MOF-303 nanocomposites. The optimal sample denoted as 1-2CuSnM (with a molar ratio of Cu(II) to SnO 2 /MOF-303 of 1:2) achieved a response value of 116.98 over 11-98% RH, with response/recovery times of 16.2/6.3 s, low hysteresis (2.48% RH), and excellent 30-day stability (SD < 0.01) at room temperature. The synergy between Cu(II) and SnO 2 introduces abundant oxygen vacancies for water adsorption, while uncoordinated N sites enable proton hopping (Grotthuss mechanism) and Cu(II) dissociation enhances ionic conductivity, collectively reducing impedance. This ternary strategy is novel in combining protonic and ionic conduction pathways within a MOF framework, enabling a humidity sensor with wide range, fast response, and low hysteresis, key advancements over conventional materials.