All-water supercapacitor enabled by 1-nm clay channels

TL;DR

This paper presents a scalable, sustainable supercapacitor using nanoconfined water in clay channels as the electrolyte, achieving high stability and efficiency in energy storage.

Contribution

It introduces a novel all-water supercapacitor design utilizing 1-nm clay channels, demonstrating practical electrochemical performance with natural materials.

Findings

Achieves specific capacitance of up to 40 F/g

Operates stably up to 1.6 V and over 60,000 cycles

Confirms nanoconfined water as effective electrolyte

Abstract

Water confined to channels one nanometer thick exhibits electrochemical behavior distinct from bulk water, including enhanced protonic conductivity and large dielectric anisotropy. Here, we exploit these characteristics to design a scalable electrochemical energy-storage system ("blue capacitor") constructed entirely from naturally abundant materials. By assembling layered clays and conductive graphene, we produce 1-nm-thick channels in which confined water acts as the sole electrolyte. We systematically study different clay types, the electrode composition, and separator thickness using complementary physicochemical and electrochemical techniques. The device operates stably up to 1.6 V, achieves specific capacitances of up to 40 F/g, nearly 100% coulombic efficiency, and stable performance over more than 60,000 charge-discharge cycles. Structural and dynamic analyses validate the device architecture, water purity, and proton transport in the nanopores. These results demonstrate that nanoconfined water can function as an electrolyte in a macroscopic electrochemical device, providing a platform for exploring sustainable aqueous energy-storage systems.