Review of optical hydrogen sensors based on metal hydrides: Recent developments and challenges

• Seven types of optical hydrogen sensors based on metal hydrides are reviewed. • Strategies for the improvement of sensing materials are presented. • Existing challenges are discussed. • Future prospects in terms of sensing materials and device structures are proposed. As a clean and sustainable energy source, hydrogen gas is highly demanded in industrial and commercial fields. Accordingly, the swift and accurate detection of hydrogen gas is becoming increasingly important for the safe production and operation of hydrogen. This review presents recent advancements of optical hydrogen sensors based on metal hydrides, focusing on the sensing material, sensor structure, and sensing principles. Starting with an overview of the significance of hydrogen sensing, this paper lists the demands for ideal hydrogen sensors and addresses the practical advantages of optical hydrogen sensors. Secondly, seven types of optical hydrogen sensors based on the gasochromic effect, micro-mirror, fiber grating, interferometer, evanescent field, surface plasmon resonance and localized surface plasmon resonance are comprehensively discussed. Then the preparation methods, advantages and disadvantages of different metal hydrides for hydrogen sensing are summarized. Lastly, the practical challenges, possible solutions and future prospects are outlined.