Bimetallic Conductive Co/Fe-HITP for Sensitive H₂S Detection at Low Temperature

The metal nodes in conductive metal-organic (c-MOFs) play a crucial role in determining surface chemical activity. Tuning the metal sites of Co₃(HITP)₂ is expected to enhance its low-temperature gas sensing performance. Here, a series of bimetallic Co/Fe-HITP materials are synthesized by partially substituting Co with Fe ions at varying Fe/Co ratios. Gas sensing tests reveal that the Fe incorporation not only improves the response of H₂S at low temperature but also reduces the fluctuations caused by low temperatures. The optimal Co_1.5Fe_1.5-HITP_9.5 sensor delivers a response of 10.05 toward 20 ppm H₂S at room temperature (25°C) and 9.69 at a refrigerating temperature (0°C), with corresponding LODs of 18.9 ppb and 16.8 ppb, respectively. Density functional theory (DFT) calculations on Co-HITP, Co₂Fe₁-HITP_9.5, and Co₁Fe₂-HITP_9.5 show that increasing the Fe content leads to a larger absolute adsorption energy, rationalizing the enhanced low-temperature sensing performance. Furthermore, band structure analysis elucidates the origin of the higher surface catalytic activity upon Fe substitution. This work establishes bimetallic Co/Fe-HITP as a promising platform for sensitive, low-temperature H₂S detection.