High-performance self-powered sensors based on direct-printing Ag/Al asymmetric electrodes and graphene oxide composites for non-contact humidity monitoring

Non-contact sensing is crucial for human-machine interaction and healthcare. However, its advancement is often constrained by limitations in device fabrication and integration. This study reports a high-performance, self-powered humidity sensor based on direct-printing Ag/Al asymmetric electrodes and graphene oxide (GO) composites, enabling rapid and sensitive non-contact detection of humidity. Through material optimization, GO/polyvinyl alcohol (PVA), GO/hyaluronic acid (HA), and GO/NaCl composite sensing materials are prepared, which optimized the sensor's recovery time (as short as 4.18 s), output voltage (up to 978.38 mV), and output current (up to 8.46 μA). Additionally, an electrochemically active Ag/Al hybrid ink was developed, and asymmetric electrodes were successfully fabricated using a direct printing process. Sensors fabricated with this technique served as effective non-contact switches, showing high sensitivity (ΔV/V₀=180.33 at 85% RH) and a distinct distance-dependent response. Furthermore, a serially connected sensor array was integrated into a mask and achieved an output voltage of up to 2.77 V, which demonstrated stable, real-time tracking of breathing patterns, with response/recovery speeds exceeding 400 mV/s. This study provides an effective solution for the design, printing fabrication, and system integration of high-performance, integrable humidity sensors for the advanced non-contact monitoring.