The thickness of the slurry coating on the nickel foam for a three-electrode setup can indeed influence the electrochemical measurements. When you change the thickness of the electrode coating, you change the amount of active material, which can alter the electrochemical performance.

There isn't a definitive "right" thickness for the coating as it depends on various factors, including:

• The type of electrochemical measurements you're taking
• The performance characteristics you're interested in (e.g., energy density, power density)
• The specific properties of your active material (e.g., Ti3C2Tx)
• The porosity of your nickel foam substrate
• The consistency and composition of your slurry

Generally, a common range for the thickness of the coating in battery research is from tens of micrometres to a few hundred micrometres.

If the coating is too thin, it may not fully cover the substrate or provide enough active material for the reactions. On the other hand, if the coating is too thick, it might not allow for efficient transport of ions and electrons, reducing performance.

You may need to do some trial and error to find the best coating thickness for your specific situation. Consider starting with a moderate thickness (e.g., around 100-200 µm), then adjust as necessary based on your experimental results.

Lastly, be sure to control and measure the thickness accurately. The doctor blade technique you're using is a good method for this, as it allows for precise control over the coating thickness.