Fig. 1: Ionic diode–type hybrid membrane device and the electric performance.

a Schematic diagram of solar photovoltaic power generation with PN junction, illustration of hydrovoltaic power generation principle inspired by photovoltaic effect. b Schematic diagram of the working principle for HEEG, the darker the color, the greater the humidity. c Explosion view of the HEEG. The SEM images of CNT top electrode (d), AAO from the top view (e) and AAO from the lateral view (f). g The SEM image of the contact interface between CNT and AAO. h, i The HEEG continuously work over 700 h for voltage and current respectively in 93% RH, 25 °C condition, indicating the robust and stable continuous output performance.