Electrodeposition

Electroplating/ Electrodeposition Wei Yan ABC’s of Electrochemistry 03/22/2012

OUTLINE • Introduction • Electroplating Setup • Importance of Electrodeposition

• Electrochemistry Fundamentals • Factors affecting the Electrodeposits Ohio - Avionics Engineering Center • University Conclusions

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Introduction Definition Electroplating? Electrodeposition? Electrolytic deposition? • Electroplating is often also called "electrodeposition,” a short version of “electrolytic deposition,” and the two terms are used interchangeably. • It’s a process using electrical current to reduce cations of a desired material from a solution and to coat the material as a thin film onto a conductive substrate surface. Reference: http://electrochem.cwru.edu/encycl/art-e01-electroplat.htm

Center for Electrochemical Engineering Research, Ohio University

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Electroplating Setup Electrolytic Cell

1. Is the core part of the electroplating. 2. Cathode: the object to be plated 3. Anode: (1)dissolvable anode (2) inert anode 4. Electrolyte/plating bath Reference: http://electrochem.cwru.edu/encycl/art-e01-electroplat.htm Center for Electrochemical Engineering Research, Ohio University

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Table =The metals can be plated

Part of Periodic Table. Metals inside the frame can be electrodeposited from aqueous solutions Center for Electrochemical Engineering Research, Ohio University

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Importance of Electrodeposition Applications • 1. Decoration: Coating a more expensive metal onto a base metal surface in order to improve the appearance. Such as jewelry, furniture fitting • 2. Protection: Corrosion-resistant coatings such as chromium plating of automobile parts • 3. Electroforming: Manufacture of sieves, screens, dry shaver heads and dies.

• 4. Enhancement: coatings with improved electrical and thermal conductivity, reflectivity etc. In CEER,

Electrodeposition of Metals in Catalyst Synthesis


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Electrochemistry Fundamentals A typical electroplating setup for plating copper one mistake?

Anode Anode

Cathode Cathode

Reference: http://chem1.eng.wayne.edu/~yhuang/Papers/Book_Plating_ECHP Center for Electrochemical Engineering Research, Ohio University

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Electrochemistry Fundamentals Anode and Cathode • Cathode:

Cathode •

Reduction reaction

Anode:

Anode

Oxidation reaction


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Electrochemistry Fundamentals Faraday’s Laws of Electrolysis According to the Faraday’s first law and second law of electrolysis, the amount of material deposited on an electrode is proportional to the amount of electricity used. m is the number of moles of the metals reduced by charge Q; F is Faraday constant Mw is the atomic weight W is the weight of deposit


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Electrochemistry Fundamentals Current Efficiency, and Current Distribution • Current efficiency = 100 * WAct/WTheo Wact is the weight of metal deposited or dissolved WTheo is the corresponding weight to be expected from Faraday’s laws if there is no side reaction.

Cathode efficiency

Anode efficiency

Current distribution Center for Electrochemical Engineering Research, Ohio University

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Electrochemistry Fundamentals Overpotential and overvoltage • Overpotential is the difference in the electrode potential of an electrode between its equilibrium potential and its operating potential when a current is flowing. • It represents the extra energy needed to force the electrode reaction to proceed at a required rate. • A slow reaction will require a larger overpotential for a given current density than a fast reaction.

Reference : http://chem1.eng.wayne.edu/~yhuang/Papers/Book_Plating_ECHP


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Electrochemistry Fundamentals Overpotential and overvoltage • Overvoltage is the difference between cell voltage and the open circuit voltage (OCP) when a current is flowing. • It represents the extra energy needed to force the cell reaction to proceed at a required rate. • The overvoltage is the sum of the overpotentials of the two electrodes of the cell and the ohmic loss of the cell. Unfortunately, the terms overvoltage and overpotential are sometimes used interchangeably. .


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Electrochemistry Fundamentals How to determine the potential of deposition

Fig. Typical voltammogram for a single-metal deposition Reference:

http://electrochem.cwru.edu/encycl/art-e01-electroplat.htm


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Electrochemistry Fundamentals • How to determine the potential of deposition for two metals codeposition ? Key point- the onset of the reduction peaks in CV

(1) If the two reduction peaks of metals are not separated, both of metals can be reduced when operating potential is more negative than the onset potential. (2) If the two reduction peaks of metals are clearly separated, both of metals can be reduced (codeposition) at a more negative potential than onset potential of the less noble metal


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Electrochemistry Fundamentals How to determine the potential of deposition E < -0.75 V, cathodic deposition -0.75V -0.3V anodic dissolution

Fig. CV for Ni-Co codeposition in the plating bath containing 0.06M NiCl2 and 0.06M CoCl2 at 25C. Reference: Chi-chang Hu and Allen Bai, J.Electrochem.Soc. 149(615) 2002 Center for Electrochemical Engineering Research, Ohio University

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Electrochemistry Fundamentals How to determine the potential of deposition E < -1.00V Fe and Ni codeposition -1.00V