Nickel electroplating solutions usually contain boric acid as a buffer to prevent fluctuations in pH during the plating process and thereby elimate the deposition of nickel oxides. What is the nickel electrolyte you are using? Is it a Watts bath?

Yes sir, it is Watts bath solution

The pH of the bath is set by the Boric acid buffer. What pH do you want the bath to be?

Thank you very much for your kind reply.

Actually i want know that why usually 3-4 pH is used in electrochemical deposition of nanocomposite coatings ? what is the reason?

Is it helpful for depositing the nanocomposite coating ?

The pH is governed by the formulation of the plating bath. The Watts bath dates back to 1916 and works at a pH of 3.5 - 4.5. If you want to plate nickel this is the formulation most people use. Most metal plating solutions will be acidic otherwise you will form oxide or hydroxide precipitates. You can use a chelating agent to prevent this and there are probably some different pH nickel plating formulations on the web. However, I must admit I’m not sure how changes in pH will help your incorporation of CNTs - will their zeta potential change? Might be worth looking at different pH formulations and see what happens.

Thank you very much dear sir for your time and informative answer !