Limits...
Over-limiting current and control of dendritic growth by surface conduction in nanopores.

Han JH, Khoo E, Bai P, Bazant MZ - Sci Rep (2014)

Bottom Line: Copper electrodeposits are grown in anodized aluminum oxide membranes with polyelectrolyte coatings to modify the surface charge.At low currents, uniform electroplating occurs, unaffected by surface modification due to thin electric double layers, but the morphology changes dramatically above the limiting current.With positive surface charge, dendrites avoid the surfaces and are either guided along the nanopore centers or blocked from penetrating the membrane.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

ABSTRACT
Understanding over-limiting current (faster than diffusion) is a long-standing challenge in electrochemistry with applications in desalination and energy storage. Known mechanisms involve either chemical or hydrodynamic instabilities in unconfined electrolytes. Here, it is shown that over-limiting current can be sustained by surface conduction in nanopores, without any such instabilities, and used to control dendritic growth during electrodeposition. Copper electrodeposits are grown in anodized aluminum oxide membranes with polyelectrolyte coatings to modify the surface charge. At low currents, uniform electroplating occurs, unaffected by surface modification due to thin electric double layers, but the morphology changes dramatically above the limiting current. With negative surface charge, growth is enhanced along the nanopore surfaces, forming surface dendrites and nanotubes behind a deionization shock. With positive surface charge, dendrites avoid the surfaces and are either guided along the nanopore centers or blocked from penetrating the membrane.

No MeSH data available.


Related in: MedlinePlus

(a) Cell configuration in CuSO4 solution: Cu cathode/polyelectrolyte-coated AAO/Cu anode. (b) Nanopore EDL structure. The ions in EDL contributing to surface conductivity are displayed as larger circles than the bulk ions.
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f1: (a) Cell configuration in CuSO4 solution: Cu cathode/polyelectrolyte-coated AAO/Cu anode. (b) Nanopore EDL structure. The ions in EDL contributing to surface conductivity are displayed as larger circles than the bulk ions.

Mentions: In our experiments, the AAO membrane is clamped between two copper disk electrodes under constant pressure, as shown in Figure 1A. Electrochemical transient signals are measured in CuSO4 solutions of varying salt concentrations, where the dominant Faradaic reactions are copper electrodeposition at the cathode and copper dissolution at the anode. Although the more common method of fabricating the cathodes is to sputter gold or copper onto one side of the AAO membrane, the clamping procedure we use more closely resembles the electrode/separator/electrode sandwich structure in a battery and removes the initial distribution of the sputtered metal as a confounding variable that could affect the current and the morphology of the electrodeposits20. We confirmed that there are no cracks on the AAO membrane when the cell is disassembled after electrochemical measurements. In order to prevent the evaporation of the binary electrolyte solution inside the AAO membrane, the electrochemical cell is immersed in a beaker containing the same electrolyte.


Over-limiting current and control of dendritic growth by surface conduction in nanopores.

Han JH, Khoo E, Bai P, Bazant MZ - Sci Rep (2014)

(a) Cell configuration in CuSO4 solution: Cu cathode/polyelectrolyte-coated AAO/Cu anode. (b) Nanopore EDL structure. The ions in EDL contributing to surface conductivity are displayed as larger circles than the bulk ions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4231330&req=5

f1: (a) Cell configuration in CuSO4 solution: Cu cathode/polyelectrolyte-coated AAO/Cu anode. (b) Nanopore EDL structure. The ions in EDL contributing to surface conductivity are displayed as larger circles than the bulk ions.
Mentions: In our experiments, the AAO membrane is clamped between two copper disk electrodes under constant pressure, as shown in Figure 1A. Electrochemical transient signals are measured in CuSO4 solutions of varying salt concentrations, where the dominant Faradaic reactions are copper electrodeposition at the cathode and copper dissolution at the anode. Although the more common method of fabricating the cathodes is to sputter gold or copper onto one side of the AAO membrane, the clamping procedure we use more closely resembles the electrode/separator/electrode sandwich structure in a battery and removes the initial distribution of the sputtered metal as a confounding variable that could affect the current and the morphology of the electrodeposits20. We confirmed that there are no cracks on the AAO membrane when the cell is disassembled after electrochemical measurements. In order to prevent the evaporation of the binary electrolyte solution inside the AAO membrane, the electrochemical cell is immersed in a beaker containing the same electrolyte.

Bottom Line: Copper electrodeposits are grown in anodized aluminum oxide membranes with polyelectrolyte coatings to modify the surface charge.At low currents, uniform electroplating occurs, unaffected by surface modification due to thin electric double layers, but the morphology changes dramatically above the limiting current.With positive surface charge, dendrites avoid the surfaces and are either guided along the nanopore centers or blocked from penetrating the membrane.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

ABSTRACT
Understanding over-limiting current (faster than diffusion) is a long-standing challenge in electrochemistry with applications in desalination and energy storage. Known mechanisms involve either chemical or hydrodynamic instabilities in unconfined electrolytes. Here, it is shown that over-limiting current can be sustained by surface conduction in nanopores, without any such instabilities, and used to control dendritic growth during electrodeposition. Copper electrodeposits are grown in anodized aluminum oxide membranes with polyelectrolyte coatings to modify the surface charge. At low currents, uniform electroplating occurs, unaffected by surface modification due to thin electric double layers, but the morphology changes dramatically above the limiting current. With negative surface charge, growth is enhanced along the nanopore surfaces, forming surface dendrites and nanotubes behind a deionization shock. With positive surface charge, dendrites avoid the surfaces and are either guided along the nanopore centers or blocked from penetrating the membrane.

No MeSH data available.


Related in: MedlinePlus