In this work we report the growth and characterisation of InAs nanostructures as a platform to understand the macroscopic electrochemically mediated growth of III-V semiconductors. We use Raman spectroscopy as means to probe the crystal quality and grain size as a function of deposition potential. We find that the average InAs grain size systematically decreases with increasing the cathodic voltage (from ~30 to ~10 nm), particularly after a certain critical potential. We explain our findings by the interplay between self-diffusion in the solidstate reaction rate, the voltage-dependent deposition rate and activation of spurious electrochemical reactions. This finding opens up the possibility to control the crystal grain size with potential to optimize the optoelectronic properties for specific applications. Even though we have used InAs as platform, our results can be used as guideline for the optimization of other III-V bimetallic compounds.