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) Experimental (solid line) and numerical current (dash line) versus voltage data for positively (+) and negatively (−) charged AAO membranes in 10 mM CuSO4 at a scan rate of 1 mV/s. (b) Physical picture of surface conduction effects at high voltage, driven by the large electric field in the depleted region. In AAO(+), the SO42− ions (blue) migrate toward the anode, reducing the net flux of Cu2+ in order to maintain neutrality. In AAO(−), the active Cu2+ ions (red) circumvent the depleted region by SC and contribute to OLC.
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f2: (a) Experimental (solid line) and numerical current (dash line) versus voltage data for positively (+) and negatively (−) charged AAO membranes in 10 mM CuSO4 at a scan rate of 1 mV/s. (b) Physical picture of surface conduction effects at high voltage, driven by the large electric field in the depleted region. In AAO(+), the SO42− ions (blue) migrate toward the anode, reducing the net flux of Cu2+ in order to maintain neutrality. In AAO(−), the active Cu2+ ions (red) circumvent the depleted region by SC and contribute to OLC.

Mentions: Figure 2A shows experimental current-voltage curves (solid lines) of AAO(+,−) in 10 mM CuSO4 for a linear voltage sweep at 1 mV/s, close to steady state. At low voltage below -0.1 V, the two curves overlap, indicating that the surface charge plays no role, consistent with the classical theory. Unlike ion-exchange membranes363945, a positive curvature is also observed at low voltage, due to the activated kinetics of charge transfer and nucleation. As expected, the onset potential of Cu reduction does not depend on the AAO surface charge.


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) Experimental (solid line) and numerical current (dash line) versus voltage data for positively (+) and negatively (−) charged AAO membranes in 10 mM CuSO4 at a scan rate of 1 mV/s. (b) Physical picture of surface conduction effects at high voltage, driven by the large electric field in the depleted region. In AAO(+), the SO42− ions (blue) migrate toward the anode, reducing the net flux of Cu2+ in order to maintain neutrality. In AAO(−), the active Cu2+ ions (red) circumvent the depleted region by SC and contribute to OLC.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: (a) Experimental (solid line) and numerical current (dash line) versus voltage data for positively (+) and negatively (−) charged AAO membranes in 10 mM CuSO4 at a scan rate of 1 mV/s. (b) Physical picture of surface conduction effects at high voltage, driven by the large electric field in the depleted region. In AAO(+), the SO42− ions (blue) migrate toward the anode, reducing the net flux of Cu2+ in order to maintain neutrality. In AAO(−), the active Cu2+ ions (red) circumvent the depleted region by SC and contribute to OLC.
Mentions: Figure 2A shows experimental current-voltage curves (solid lines) of AAO(+,−) in 10 mM CuSO4 for a linear voltage sweep at 1 mV/s, close to steady state. At low voltage below -0.1 V, the two curves overlap, indicating that the surface charge plays no role, consistent with the classical theory. Unlike ion-exchange membranes363945, a positive curvature is also observed at low voltage, due to the activated kinetics of charge transfer and nucleation. As expected, the onset potential of Cu reduction does not depend on the AAO surface charge.

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