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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

The effect of SC on the morphology of copper electrodeposits grown in 100 mM CuSO4/100 mM H3BO3 solution after −1.8 V is applied for 5 min.SEM images of irregular nanowires generated in (a) bare AAO and (b) AAO(+). (c) SEM image of nanotubes grown in AAO(−), driven by SC as in (d).
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f5: The effect of SC on the morphology of copper electrodeposits grown in 100 mM CuSO4/100 mM H3BO3 solution after −1.8 V is applied for 5 min.SEM images of irregular nanowires generated in (a) bare AAO and (b) AAO(+). (c) SEM image of nanotubes grown in AAO(−), driven by SC as in (d).

Mentions: Figure 5 shows the dependence of the electrodeposit morphology on the nanopore surface charge, far above the limiting current. The bare AAO and AAO(+) have irregular nanowires (Figures 5A–B). Note that the surface of bare AAO is slightly positive since the isoelectric point (pI) of aluminum oxide is around 8. The irregular dendritic growth, penetrating past the blockage demonstrated in Figure 4D, may result from electroconvection in the depleted region at this high voltage. On the other hand, AAO(−) at the same voltage shows well-defined copper nanotubes of uniform height (Figure 5C and Figure S9), whose wall thickness is less than 20 nm (Figure S10). This is consistent with SC control (Figure 5D) rather than previously proposed mechanisms that are independent of the surface charge, such as chemical affinity71, vertical current by high current or potential21, and morphology of sputtered metal20.


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

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

The effect of SC on the morphology of copper electrodeposits grown in 100 mM CuSO4/100 mM H3BO3 solution after −1.8 V is applied for 5 min.SEM images of irregular nanowires generated in (a) bare AAO and (b) AAO(+). (c) SEM image of nanotubes grown in AAO(−), driven by SC as in (d).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: The effect of SC on the morphology of copper electrodeposits grown in 100 mM CuSO4/100 mM H3BO3 solution after −1.8 V is applied for 5 min.SEM images of irregular nanowires generated in (a) bare AAO and (b) AAO(+). (c) SEM image of nanotubes grown in AAO(−), driven by SC as in (d).
Mentions: Figure 5 shows the dependence of the electrodeposit morphology on the nanopore surface charge, far above the limiting current. The bare AAO and AAO(+) have irregular nanowires (Figures 5A–B). Note that the surface of bare AAO is slightly positive since the isoelectric point (pI) of aluminum oxide is around 8. The irregular dendritic growth, penetrating past the blockage demonstrated in Figure 4D, may result from electroconvection in the depleted region at this high voltage. On the other hand, AAO(−) at the same voltage shows well-defined copper nanotubes of uniform height (Figure 5C and Figure S9), whose wall thickness is less than 20 nm (Figure S10). This is consistent with SC control (Figure 5D) rather than previously proposed mechanisms that are independent of the surface charge, such as chemical affinity71, vertical current by high current or potential21, and morphology of sputtered metal20.

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