Bulk electricity storage in 1-nm water channels

Nanometer-scale solid-state confinement has been shown to change water's structure and dynamics, offering new horizons in energy storage. However, most current materials operate at the micrometer scale, missing the interfacial effects that occur at three orders of magnitude smaller dimensions. Here, we report a scalable energy storage device that uses ultraconfined water as its sole electrolyte, unlocking the advantages of nanoscale confinement. We use the polarizability and proton 'superconductivity' of water confined in few-molecular-diameters clay channels to build an all-water supercapacitor. The device fabricated from reconstructed clay, graphene, and water by a sustainable self-assembly process, operates at voltages up to 1.65 V, has competitive power and energy density, and maintains near 100% Coulombic efficiency over 60,000 charge-discharge cycles. These results demonstrate the application of unique properties of ultraconfined water for sustainable energy storage and provide a benchmark for a class of novel ultraconfined water energy systems, or 'blue devices'.
Comment: Main text: 14 pages, 5 figures, 39 references. Supplementary: 28 pages, 28 figures, 3 tables, 4 references