Observing Mixed\nChemical Reactions at the Positive\nElectrode in the High-Performance Self-Powered Electrochemical Humidity\nSensor

Electrochemical\nhumidity (ECH) sensors that integrate\npower generation\nand humidity sensing have attracted great research attention in recent\nyears. However, the design of high-performance ECH sensors faces many\nchallenges. Namely, the working mechanism of the ECH sensors is still\ncontroversial, and related self-powered applications have not been\nwell implemented. To overcome these limitations, this study constructs\nan ECH sensor with high power-generation and humidity-sensing performance\nusing the KCl/carbon black/halloysite nanotubes (KCl/CB/HNTs) as a\nhumidity-sensing electrolyte. The proposed ECH sensor has a wide humidity-sensing\nresponse of 10.9%–91.5% relative humidity (RH), and a single\nECH sensor can output 1.46 V with a maximum power of 133.2 μW\nat 91.5% RH. Particularly, the unprecedented mixed chemical reactions\nat the positive electrode, including the hydrogen evolution reaction\nand oxygen reduction reaction, are analyzed using multiple characterization\nand testing techniques. The analysis results provide solid experimental\nevidence for the current controversial working mechanism of ECH sensors.\nDue to the advantage of high-power generation, the proposed ECH sensor\ncan be used for self-powered humidity detection. This study provides\na valuable reference for improving the power generation of ECH sensors\nand solid evidence for clarifying their working mechanism, which could\nbe beneficial for guiding the future development of ECH sensors.