Richly Ionized 2D HOF Membranes Enable Efficient Humidity Sensing

Abstract Current humidity sensors often underperform due to the limited availability of moisture‐sensitive active sites within their material substrates, as well as ineffective ion transport properties. Here, a new approach is presented using richly ionized 2D hydrogen‐bonded organic frameworks (HOFs) membranes, which feature a high density of pores and a wide network of continuous binding sites for water molecules. To significantly enhance humidity sensing performance, a cationic nanoconfined strategy is employed. This approach involves nanoscale cationic doping, which modifies the interlayer spacing of HOFs, thereby revealing more hydrophilic sites and providing additional ions to improve conductivity. Based on these advancements, a highly adjustable and flexible humidity sensor equipped with asymmetrical MXene electrodes is developed. This sensor demonstrates rapid response/recovery times of 0.42/0.62 s, an ultra‐high on/off ratio of 3.5 × 10 4 , and remarkable stability over more than 200 cycles. The electrical performance of the system is driven by the potential difference between the asymmetrical electrodes, rather than the electrode materials themselves, allowing for increased versatility and scalability. This development offers a new pathway for humidity sensors featuring enhanced ionic conductivity and improved non‐contact sensing capabilities.