How can i understand which ions oxidize or reduze in which voltage. To make the topic more solid, lets go on the example of nickel coating i perform. I perform nickel coating in Watts Bath with platinum anode (insoluble anode). In my solution Ni++, H+, SO4--, Cl-, B(OH)4- exist.
How can i understand whether metalic nickel forms or hydrogen gas evolves in my cathode (of course there is metealic nickel formation but i want to predict it by comparison of voltage’s reduction of hydrogen and nickel ions).
In the anode, which ion will be oxidized? How much voltage should i apply to oxidize these ions?
Another point is; What kind of correlation does exist between “the voltage to reduce/oxidize these ions” and standart oxidation/reduction of these ions?
Probably the term which is called “overvoltage” must be induced to predict how much voltage should i apply to oxidize/reduze ions. What is the nature of overvoltage?
Thanks in advance
Frankly, to answer you properly and in detail, I would have to write a book chapter. Should you wish to go into the minute details, I would recommend "Physical Electrochemistry" by Eliezer Gileadi. As for the answers, I'll try to provide some brief explanations where possible:
While the standard redox potentials can be used to calculate, at what potentials and in which order your anions will undergo electrode reactions, this will be more or less an estimate, due to "imperfections" of the system, such as overpotential, which you mentioned.
As for finding out the overpotential (overvoltage is more commonly used in circuit theory, AFAIK), the two equations that will be helpful to you are the Tafel equation (using it, you can experimentally determine the overpotential value) and the Butler-Volmer equation (a more general form, of which the Tafel equation is a specific case).
In general, overpotential can be related to the activation energy of transferring an electron from a particular electrode to a species undergoing an electrochemical reaction, can be related to the depletion of charge carriers at the electrode surface or can be related to high-resistivity electrochemical cells (due to some exotic design, such as is the case in many spectroelectrochemical cells).
Frankly, to answer you properly and in detail, I would have to write a book chapter. Should you wish to go into the minute details, I would recommend "Physical Electrochemistry" by Eliezer Gileadi. As for the answers, I'll try to provide some brief explanations where possible:
While the standard redox potentials can be used to calculate, at what potentials and in which order your anions will undergo electrode reactions, this will be more or less an estimate, due to "imperfections" of the system, such as overpotential, which you mentioned.
As for finding out the overpotential (overvoltage is more commonly used in circuit theory, AFAIK), the two equations that will be helpful to you are the Tafel equation (using it, you can experimentally determine the overpotential value) and the Butler-Volmer equation (a more general form, of which the Tafel equation is a specific case).
In general, overpotential can be related to the activation energy of transferring an electron from a particular electrode to a species undergoing an electrochemical reaction, can be related to the depletion of charge carriers at the electrode surface or can be related to high-resistivity electrochemical cells (due to some exotic design, such as is the case in many spectroelectrochemical cells).
@ Tomasz Jarosz , thank you for your explanatory answer. It clarified many things in my mind.
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