Non-uniform metal deposition and dendrite formation in high density energy storage devices reduces the efficiency, safety, and life of batteries with metal anodes. Superconcentrated ionic liquid (IL) electrolytes (e.g. 1:1 IL:alkali ion) coupled with anode preconditioning at more negative potentials can completely mitigate these issues, and therefore revolutionize high density energy storage devices. However, the mechanisms by which very high salt concentration and preconditioning potential enable uniform metal deposition and prevent dendrite formation at the metal anode during cycling are poorly understood, and therefore not optimized. Here, we use atomic-force microscopy and molecular dynamics simulations to unravel the influence of these factors on the interface chemistry in a sodium electrolyte, demonstrating how a molten salt like structure at the electrode surface results in dendrite free metal cycling at higher rates. Such a structure will support the formation of a more favorable solid electrolyte interphase (SEI) accepted as being a critical factor in stable battery cycling. This new understanding will enable engineering of efficient anode electrodes by tuning interfacial nanostructure via salt concentration and high voltage preconditioning. File list (2) download file view on ChemRxiv supplementary.pdf (5.03 MiB) download file view on ChemRxiv Manuscript-V1.pdf (2.06 MiB)

This study attempts to optimize the properties of the anode current collector of a polymer electrolyte membrane water electrolyzer at high temperatures, particularly at the boiling point of water. Different titanium meshes (4 commercial ones and 4 modified ones) with various properties are experimentally examined by operating a cell with each mesh under different conditions. The average pore diameter, thickness, and contact angle of the anode current collector are controlled in the ranges of 10-35 µm, 0.2-0.3 mm, and 0-120°, respectively. These results showed that increasing the temperature from the conventional temperature of 80°C to the boiling point could reduce both the open circuit voltage and the overvoltages to a large extent without notable dehydration of the membrane. These results also showed that decreasing the contact angle and the thickness suppresses the electrolysis overvoltage largely by decreasing the concentration overvoltage. The effect of the average pore diameter was not evident until the temperature reached the boiling point. Using operating conditions of 100°C and 2 A/cm 2 , the electrolysis voltage is minimized to 1.69 V with a hydrophilic titanium mesh with an average pore diameter of 21 µm and a thickness of 0.2 mm.

Ionic liquids (ILs) have become highly popular solvents over the last two decades in a range of fields, especially in electrochemistry. Their intrinsic properties include high chemical and thermal stability, wide electrochemical windows, good conductivity, high polarity, tunability, and good solvation properties, making them ideal as solvents for different electrochemical applications. At charged surfaces such as electrodes, an electrical double layer (EDL) forms when exposed to a fluid. IL ions form denser EDL structures compared to conventional solvent/electrolyte systems, which can cause differences in the behavior for electrochemical applications. This Perspective discusses some recent work (over the last three years) where the structure of the EDL in ILs has been examined and found to influence the behavior of supercapacitors, batteries, sensors, and lubrication systems that employ IL solvents. More fundamental work is expected to continue in this area, which will inform the design of solvents for use in these applications and beyond.

Effects of operating conditions of a high-temperature polymer electrolyte water electrolyzer (HT-PEWE) on the electrolysis voltage are evaluated, and the optimal conditions for a high performance are revealed. A HT-PEWE unit cell with a 4-cm 2 electrode consisting of Nafion117-based catalyst-coated membrane with IrO2 and Pt/C as the oxygen and hydrogen evolution catalysts is fabricated, and its electrolysis voltage and high-frequency resistance are assessed. The cell temperature and pressure are controlled at 80-130 °C and 0.1-0.5 MPa, respectively. It is observed that increasing the temperature at a constant pressure of 0.1 MPa does not increase the ohmic overvoltage of the cell; however, it does increase the concentration overvoltage. It is also found that the increase in the overvoltage resulting from the rise in the temperature can be suppressed by elevating the pressure. When operating the cell at a temperature of 100 °C, pressure greater than 0.1 MPa suppresses the overvoltage, and so does pressures greater than 0.3 MPa at 130°C. This behavior suggests that keeping the water in a liquid water phase by increasing the pressure is critical for operating PEWEs at high temperatures.

<div> <div> <div> <p>Non-uniform metal deposition and dendrite formation in high density energy storage devices reduces the efficiency, safety, and life of batteries with metal anodes. Superconcentrated ionic liquid (IL) electrolytes (e.g. 1:1 IL:alkali ion) coupled with anode preconditioning at more negative potentials can completely mitigate these issues, and therefore revolutionize high density energy storage devices. However, the mechanisms by which very high salt concentration and preconditioning potential enable uniform metal deposition and prevent dendrite formation at the metal anode during cycling are poorly understood, and therefore not optimized. Here, we use </p> </div> </div> </div> <div> <div> <div> <p>atomic-force microscopy and molecular dynamics simulations to unravel the influence of these factors on the interface chemistry in a sodium electrolyte, demonstrating how a molten salt like structure at the electrode surface results in dendrite free metal cycling at higher rates. Such a structure will support the formation of a more favorable solid electrolyte interphase (SEI) accepted as being a critical factor in stable battery cycling. This new understanding will enable engineering of efficient anode electrodes by tuning interfacial nanostructure via salt concentration and high voltage preconditioning. </p> </div> </div> </div>