Confinement-controlled Water Engenders High Energy Density Electrochemical-double-layer Capacitance

The renewable energy sector critically needs low-cost and environmentally neutral energy storage solutions throughout the entire device life cycle. However, the limited performance of standard water-based electrochemical systems prevents their use in certain applications. Meanwhile, recent fundamental studies revealed dielectric anomalies of water near solid-liquid interfaces of carbon-based nanomaterials. In contrast to the bulk water properties, these anomalies of water under nano-confinement and in the presence of electric fields have not yet been understood and used. Here, we experimentally study the ability of the interfacial water layer to engender and store charge in electrochemical double-layer capacitance. We demonstrate the first prototype of a water-only membrane-electrode assembly. The prototype exhibits characteristics comparable to existing batteries and supercapacitors without using electrolytes as ionic carriers. The results provide the impetus for the development of high-energy-density electrochemical double-layer capacitors and open up other avenues for ecologically-neutral batteries, fuel cells, and nanofluidic devices

Confinement-Controlled Water Engenders Unusually High Electrochemical Capacitance

The electrodynamics of nanoconfined water have been shown to change dramatically compared to bulk water, opening room for safe electrochemical systems. We demonstrate a nanofluidic “water-only” battery that exploits anomalously high electrolytic properties of pure water at firm confinement. The device consists of a membrane electrode assembly of carbon-based nanomaterials, forming continuously interconnected water-filled nanochannels between the separator and electrodes. The efficiency of the cell in the 1–100 nm pore size range shows a maximum energy density at 3 nm, challenging the region of the current metal-ion batteries. Our results establish the electrodynamic fundamentals of nanoconfined water and pave the way for low-cost and inherently safe energy storage solutions that are much needed in the renewable energy sector

Ionic logic with highly asymmetric nanofluidic memristive switches

While most neuromorphic systems are based on nanoscale electronic devices, nature relies on ions for energy-efficient information processing. Therefore, finding memristive nanofluidic devices is a milestone toward realizing electrolytic computers mimicking the brain down to its basic principles of operations. Here, we present a nanofluidic device designed for circuit scale in-memory processing that combines single-digit nanometric confinement and large entrance asymmetry. Our fabrication process is scalable while the device operates at the second timescale with a twenty-fold conductance ratio. It displays a switching threshold due to the dynamics of an extended space charge. The combination of these features permits assembling logic circuits composed of two interactive nanofluidic devices and an ohmic resistor. These results open the way to design multi-component ionic machinery, such as nanofluidic neural networks, and implementing brain-inspired ionic computations

Ionization differences between weak and strong electrolytes: the role of protonic quantum effects as perturbed by dielectric relaxation spectroscopy

Revealing the microscopic dynamics, including protonic quantum effects, in aqueous electrolyte solutions has been a challenge for modern experimental methods and molecular dynamics simulations of the past decade. These properties are out of the scope of the standard electrolytic dissociation model and leave a gap between theory and experiment due to the lack of details of the fast molecular dynamics during solvation. We report a dielectric-spectroscopy study (1Hz to 20 GHz), which unambiguously demonstrates a net difference in the dynamic structures of weak and strong electrolytes, shedding new light on the mechanism of solvation via proton exchange reactions. Based on these data, we suggest an extension of Arrhenius’ seminal model, providing a more accurate description of the electrical properties of electrolytes over a wide range of concentrations (10$^{-7}$ to 10 M). We show that dissolved species of weak electrolytes more likely interact with each other than with the solvent, preventing dissociation and explaining a sharp difference between weak and strong electrolytes. These results extend our understanding of the molecular dynamics of aqueous electrolyte solutions in biology, electrochemical systems, and nanofluidics

Anomalously High Proton Conduction of Interfacial Water

Water at the solid-liquid interface exhibits an anomalous ionic conductivity and dielectric constant compared to bulk water. Both phenomena still lack a detailed understanding. Here, we report radiofrequency measurements and analyses of the electrodynamic properties of interfacial water confined in nano-porous matrices formed by diamond grains of various sizes, ranging from 5 nm to 0.5 μm in diameter. Contrary to bulk water, the charge-carrying protons/holes in interfacial water are not mutually screened allowing for higher mobility in the external electric field. Thus, the protonic conductivity reaches a maximum value, which can be five orders of magnitude higher than that of bulk water. Our results aid in the understanding of physical and chemical properties of water confined in porous materials, and pave the way to the development of new type of highly-efficient proton-conductive materials for applications in electrochemical energy systems, membrane separations science and nano-fluidics

Nanofluidic logic with mechano-ionic memristive switches.

Neuromorphic systems are typically based on nanoscale electronic devices, but nature relies on ions for energy-efficient information processing. Nanofluidic memristive devices could thus potentially be used to construct electrolytic computers that mimic the brain down to its basic principles of operation. Here we report a nanofluidic device that is designed for circuit-scale in-memory processing. The device, which is fabricated using a scalable process, combines single-digit nanometric confinement and large entrance asymmetry and operates on the second timescale with a conductance ratio in the range of 9 to 60. In operando optical microscopy shows that the memory capabilities are due to the reversible formation of liquid blisters that modulate the conductance of the device. We use these mechano-ionic memristive switches to assemble logic circuits composed of two interactive devices and an ohmic resistor

Confinement-Controlled Water Engenders Unusually High Electrochemical Capacitance

The electrodynamics of nanoconfined water have been shown to change dramatically compared to bulk water, opening room for safe electrochemical systems. We demonstrate a nanofluidic “water-only” battery that exploits anomalously high electrolytic properties of pure water at firm confinement. The device consists of a membrane electrode assembly of carbon-based nanomaterials, forming continuously interconnected water-filled nanochannels between the separator and electrodes. The efficiency of the cell in the 1–100 nm pore size range shows a maximum energy density at 3 nm, challenging the region of the current metal-ion batteries. Our results establish the electrodynamic fundamentals of nanoconfined water and pave the way for low-cost and inherently safe energy storage solutions that are much needed in the renewable energy sector