Advanced development of metal oxide nanomaterials for H2 gas sensing applications

Hydrogen (H2) has been considered as one of the cleanest renewable energy sources. However, it is still challenging to use H2 due to its hazardous flammable and explosive properties under mild conditions in the event of leakage, and the difficulty to detect or sense it through human sensory organs because of its colorless and odorless nature. Traditional detection methods are usually complicated and the testing instruments are expensive. Thus, it is of significant importance to develop sensors for H2 detection with facile operation conditions, low costs, and excellent performance (i.e., sensitivity, selectivity, and stability). To overcome the problems and for practically detecting H2 gas, metal oxide (MOx) nanomaterials have become more crucial in such a gas sensor because of the simple preparation method, high surface area, high sensitivity, and low costs. This review will focus on the recent state-of-the-art advances in resistive H2 gas sensors based on MOx nanomaterials, starting from a brief introduction of resistive gas sensors. The following sections will focus on the synthesis of different structures and types of such MOx nanomaterials, including mono/binary/ternary/ternary or more complicated MOx nanomaterials. Meanwhile, we highlight some regulation methods such as surface or inner decoration by noble or non-noble metals to improve the performance as well as summarize and compare different structures (core–shell and heterojunction), and mechanisms in H2 sensing. Finally, the opportunities and challenges of MOx-based H2 gas sensors are proposed in detail.