Voltage

Composite number

Engineering

Materials science

Nanosensor

Relative humidity

Humidity

Carbon fibers

Respiratory monitoring

Nanodot

Physics

Nanotechnology

Triboelectric effect

Electronic engineering

Internal medicine

Composite material

Sensitivity (control systems)

Respiratory system

Medicine

Piezoelectricity

Meteorology

Nanogenerator

Optoelectronics

Electrical engineering

Nano Energy

Developing low-cost, portable, and high-performance humidity sensors for respiratory monitoring has received considerable attention in recent years. Herein, humidity sensors have been fabricated based on carbon nanodots (CDs), which exhibit high sensitivity (5318%) at 94% relative humidity (RH) and excellent long-time stability under the RH range of 11% to 94%. The high sensitivity can be attributed to the adsorption of the water molecules by the massive hydrophilic functional groups on the surface of CDs. By introducing a breath-driven triboelectric nanogenerator (TENG), the self-powered humidity sensor is developed for the first time, exhibiting a wide sensing range (11–94% RH) and excellent stability. The maximum output voltage of the TENG is up to 200 V and the maximum short-circuit current is about 9.2 μA. Furthermore, the self-powered humidity sensor further demonstrates the potential ability for real-time respiration monitoring, which can detect different breathing statuses. This work provides a convenient and low-cost strategy for constructing sensitive CDs-based humidity sensors, and prospects their applications in respiratory monitoring systems.

Carbon nanodot-based humidity sensor for self-powered respiratory monitoring