Review of Noble Metal and Metal-Oxide-Semiconductor Based Chemiresitive Hydrogen Sensors

Hydrogen (H2) gas stands at the forefront of next-generation energy, offering unparalleled combustion efficiency with minimal carbon emissions. H2 is also an important marker of many H2-related physiochemical processes in industries or medical practices (e.g., H2 release in the thermal runaway of lithium-ion battery and the biodegradation of magnesium (Mg) implants in human body). The development of high-performance H2 sensors is paramount for not only ensuring safety across various stages of H2 production, storage, transportation, and utilization, and also monitoring many critical steps in industrial or medical processes. Among the multitude of sensing technologies, chemiresistive sensors, particularly those utilizing noble metals such as Pd and Pt, or metal-oxide-semiconductor (MOS) materials like SnO2 and ZnO, have emerged as promising candidates, because these sensing materials can specifically and sensitively react with H2 to result in their conductivity change allowing for the detection of H2 gas. These materials offer not only exceptional performance metrics, but also cost-effectiveness, compact design, low power consumption, and ease of operation. In our review, for each type of chemiresistive sensors (noble-metal-based or MOS-based), we reviewed the fundamental sensing principles, and then summarized representative strategies that researchers developed in the last few years to improve specific aspects of sensing performance (e.g., sensitivity, selectivity, humidity tolerance, response time, hysteresis, etc.). In the summarization of each catalog of representative strategies, we emphasized why such strategies can improve specific sensing performance parameters. We hope that this review can help researchers gain valuable insights into this field and motivate them to explore and further advance the development of H2 sensors for broader applications.