Two-Dimensional Nanofluidic Gradient Graphene Oxide Membranes as Portable Power Sources

With traditional fossil energy sources and energy storagetechnologiesgradually unable to meet the needs of future portable flexible electronicdevices, there is a growing interest in research of power sourceswith small sizes, high energy density, and durability. Here, inspiredby the cell membrane potential in living species, we demonstrate atwo-dimensional nanofluidic gradient structure (TNGS) by integratinga series of graphene oxide (GO) and reduced GO (rGO) in the orderof the size of interlayer spacing along the horizontal direction.Through asymmetric adsorption of hygroscopic CaCl2 salt,a sustained built-in hygroscopic gradient is constructed in the TNGS.Driven by the built-in hygroscopic gradient, the TNGS not only offersa proton concentration gradient but promotes selective migration ofCa(2+). Under the synergistic effect of the TNGS and redoxreaction, the directional Ca2+ and proton transport isconverted into electrical energy on electrodes. Under ambient humidity,such a solid-state power source (0.9 cm(2) x 10 & mu;m)can output a voltage of & SIM;1.35 V for over 100 h and a volumetricpower density of & SIM;515 & mu;W cm(-3). Thisfinding opens a universal avenue for harvesting hygro-ionic electricityand offers a constructive insight into designing portable, easy-preparation,and cost-effective self-powered devices.