Improving Hydrogen Selectivity in Semiconductor Metal Oxide Gas Sensors with Cellulose Nanocrystal Membranes

As hydrogen (H₂) gains traction as a clean energy carrier, the need for reliable and selective gas sensors becomes increasingly urgent, particularly for detecting H₂ leaks amidst complex gas environments. While semiconducting metal oxide (SMOX)-based sensors are attractive due to their low cost and high sensitivity, their poor selectivity remains a major limitation. In this work, we address this challenge by integrating a gas-selective membrane into the sensor packaging, without altering the sensing material itself. The membrane is produced in situ by drop-casting a suspension of cellulose nanocrystals (CNCs) within the sensor housing. The CNCs self-assemble into a thin, gas-permeable barrier upon solvent evaporation. This simple addition significantly reduces cross-sensitivity to common interfering gases, suppressing the response to 30 ppm of ethanol (EtOH), acetone, ammonia (NH₃), nitrogen dioxide (NO₂), and carbon monoxide (CO) by factors of approximately 160, 1500, 370, 90, and 20, respectively, while reducing the H₂ signal by only a factor of 6. The result is a substantial improvement in H₂ selectivity using a low-cost, scalable approach that preserves the original sensor architecture. This method offers a practical path to enhanced performance in SMOX-based gas sensors for safety and energy applications.