Tofik, volume is not the priority. Concentration is the more important factor and understand that what is deposited is the Celsium salt. This can help you figure out where to start off from.

You may want to understand the overall mechanism of your electrodeposition and function of each individual component. If you look at these reactants here, Ce(NO3)3 seems to be the precursor salt (something that gives you your Ce in CeO2), NH4Cl is going to be your complexing agent (which is going to form complexes with Ce and control/stabilize its concentration). KCl is the supporting electrolyte. Glancing at your system, I can say that the electrodepositon is going to proceed trough cathodic reduction of Ce^3+ (in Ce(NO3)3) to Ce2+ (which is what you ultimately need for CeO2). The electrode surface may have Ce(OH)2 at the end of your reaction (im sure you are running this in aqueous media), which will ultimately convert to CeO2 upon annealing or drying (depending on your phase etc). You may also need to control pH here so that you do not end up forming Ce(OH)3 or other undesirable stuff. This is the basic mechanism. I would assume (looking at your system) the concentration of your precursor and supporting electrolyte is pretty low (around 0.05-0.1 M).NH4Cl may be a bit higher (may be around 0.5 M). Specific to Nanowires, you may want to look into  agents for morphology control, electrodeposition potentials, heat treatment temperatures, pH etc. So, you may want to just understand the role of each component and then look into literature for approximate conditions, from which you can optimize the perfect conditions specific to your application.