Proton-Conduction-Mediated High-Performance Ethanol Sensing in a Ni3(HHTP)2/Nafion Composite at Room Temperature

Conductive metal-organic frameworks (c-MOFs) are promising chemiresistive sensing materials for selective gas detection; however, their practical deployment is hindered by insufficient selectivity and humidity-induced performance degradation, both of which stem from poorly understood molecular-level conduction mechanisms. Here, we address this gap by engineering a Nafion-functionalized Ni3(HHTP)2 composite that enables a mechanistic shift from electron-dominant to synergistic electron-proton conduction. Through systematic in situ fourier transform infrared spectroscopy (FTIR)/X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS), we elucidate that the sensing process depends on competitive adsorption between ethanol molecules and prehydrated hydronium ions at the composite interface, disrupting the hydrogen-bond network. The conductive Ni3(HHTP)2 framework ensures efficient electron transport, while Nafion's microphase-separated structure confers dual molecular sieving and preconcentration effects for ethanol. The resulting sensor delivers a high response of 729% to 30 ppm ethanol at RT and 40% RH, exhibits remarkable selectivity, as evidenced by linear discriminant analysis (LDA) with a classification accuracy of 90.91%, and shows rapid kinetics and strong discrimination against common interferents. This work established a fundamental mechanistic framework for proton-electron co-conduction in c-MOFs, supported by in situ spectroscopy and electrochemical analysis. It presents a generalizable interface-modulation strategy for selective volatile organic compound (VOC) sensing under ambient conditions, showing promise for breath analysis applications and industrial safety monitoring.