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.