Main Text: Hydrogen gas (H2) sensors play a critical role in the hydrogen economy due to the safety concerns associated with the production, distribution, and utilization of flammable H2. The United States Department of Energy (DOE) has set targets for H2 sensors, in terms of concentration range (0.1-10%), operating temperature (-30 to 80 °C), response time (<1.0 s), gas environment (ambient air; 10-98% humidity), and lifetime (>10 years). In addition to these metrics, H2 sensors should be resistant to poisoning gases (e.g., hydrocarbons, CO, NO2, H2S, SOx), inexpensive (< $40 per unit),(4) miniaturized, and power-efficient (< 1 W), to ensure their effectiveness in various applications. There have been enormous efforts to develop highperformance and efficient H2 sensors; however, it is incredibly challenging to meet all the target metrics. Typical commercially available H2 sensors are of four types: electrochemical, catalytic, metaloxide-semiconductor, and thermal conductivity, claiming over 90% of the H2 sensor market. Among the four sensor types, catalytic sensors were found to be the most accurate and robust sensor type because they show little to no dependence of sensor output on the ambient parameters such as temperature, pressure, and humidity. Catalytic sensors detect H2 based on the exothermic oxidation reaction of H2 with air on a catalyst surface (typically, Pt), which generates heat to change the electrical resistance of the catalyst for determining the H2 concentration. However, due to the low activity of Pt catalysts in conventional catalytic H2 sensors, a high operating temperature of ~500°C is often required (achieved by external heating), causing high power consumption (~0.5-3.0 W) and severe cross-sensitivity to other combustible gases, such as hydrocarbons, CO, etc. In addition, the performance of catalytic H2 sensors is also affected following exposure to poisoning gases, such as H2S and SO2 (even at ppm level), which adsorb onto the Pt catalyst more strongly than H2, thereby reducing the number of sites available to catalyze H2 oxidation. To overcome the limitations of catalytic H2 sensors, prior efforts were focused on the miniaturization of the sensors, resulting in lower power consumption and faster response times. (14-19) However, the cross-sensitivity to combustible gases and susceptibility to catalyst poisoning is still not addressed.