The fuel cell industry is the most promising industry in terms of the advancement of clean and safe technologies for sustainable energy generation. The polymer electrolyte membrane fuel cell is divided into two parts: anion exchange membrane fuel cells (AEMFCs) and proton exchange membrane fuel cells (PEMFCs). In the case of PEMFCs, high-power density was secured and research and development for commercialization have made significant progress. However, there are technical limitations and high-cost issues for the use of precious metal catalysts including Pt, the durability of catalysts, bipolar plates, and membranes, and the use of hydrogen to ensure system stability. On the contrary, AEMFCs have been used as low-platinum or non-platinum catalysts and have a low activation energy of oxygen reduction reaction, so many studies have been conducted to find alternatives to overcome the problems of PEMFCs in the last decade. At the core of ensuring the power density of AEMFCs is the anion exchange membrane (AEM) which is less durable and less conductive than the cation exchange membrane. AEMFCs are a promising technology that can solve the high-cost problem of PEMFCs that have reached technological saturation and overcome technical limitations. This review focuses on the various aspects of AEMs for AEMFCs application.

Au-decorated WO₃ cross-linked nanodomes are fabricated using soft templates composed of highly ordered polystyrene beads and self-agglomeration of Au. The distribution and size of Au nanoparticles on the surface of WO₃ cross-linked nanodomes are controlled by varying the thickness of the initial Au film. The responses of Au-decorated WO₃ cross-linked nanodomes to various gases such as NO₂, CH₃COCH₃, C₂H₅OH, NH₃ , CO, H₂, and C₆H₆ are at least 5 times higher than those of bare WO₃ cross-linked nanodomes. The response enhancement by Au decoration is dependent on the target gas, which is attributed to an interplay between electronic and chemical sensitizations. In particular, the Au-decorated WO₃ cross-linked nanodomes exhibit extremely high sensitivities and selectivities, and ppt-level detection limits to NO₂ and C₂H₅OH at 250 °C and 450 °C, respectively. These results suggest that Au-decorated WO₃ cross-linked nanodomes are very promising for use in breath analysers to diagnose both asthma and lung cancer from exhaled human breath.

Few studies have investigated the gas-sensing properties of graphene oxide/titanium dioxide (GO/TiO₂) composite combined with photocatalytic effect. Room temperature gas-sensing properties of the GO/TiO₂ composite were investigated towards various reducing gases. The composite sensor showed an enhanced gas response and a faster recovery time than a pure GO sensor due to the synergistic effect of the hybridization, such as creation of a hetero-junction at the interface and modulation of charge carrier density. However, the issue of long-term stability at room temperature still remains unsolved even after construction of a composite structure. To address this issue, the surface and hetero-junction of the GO/TiO₂ composite were engineered via a UV process. A photocatalytic effect of TiO₂ induced the reduction of the GO phase in the composite solution. The comparison of gas-sensing properties before and after the UV process clearly showed the transition from n-type to p-type gas-sensing behavior toward reducing gases. This transition revealed that the dominant sensing material is GO, and TiO₂ enhanced the gas reaction by providing more reactive sites. With a UV-treated composite sensor, the function of identifying target gas was maintained over a one-month period, showing strong resistance to humidity.