Fig. 1

Additional feed-layer enhanced hygroelectric generator. Schematic of previous hygroelectric generator (HEG) composed of single gradient reduced graphene oxide (rGO) (a) and well-designed HEG (b) developed with heterogeneous graphene oxide (h-GO) and well-matched electrodes. a Movable hydrated ions dissociate in gradient rGO with concentration difference and diffuse from high-concentration side to low-concentration side. Induced free electrons in electrodes flow through both the external circuit and inner gradient rGO layer to balance the built-in electric potential. b Feed-layer with additional graphene oxide (GO) supplies the depletion of ions in gradient rGO, and special electrode/h-GO interface can form a well-matched space charge zone, which acts as a “gate” to block free electrons through h-GO and regulates its flow direction, largely promoting the electric output