The purpose of this study is to explore a new synthesis way for the production of iron nanoparticles exploiting the nanometric structure of long ramified iron branches formed by electrodeposition in a Hele-Shaw cell. After the growth, these branches are fragmented by the action of a vibrating element (piezoelectric disk) integrated into the cell. The emphasis is put on the growth of the ramified iron branches which is performed by galvanostatic electrodeposition in a stagnant electrolyte (FeCl2) inside the Hele-Shaw cell (50 mu m deep). The competition between the co-formation of H-2 bubbles (H+ reduction) and the growth of ramified iron branches (Fe-II reduction) is analyzed by varying both the applied current density j and the FeCl2 concentration. Two regimes, depending mainly on j, are highlighted: below a threshold current density of 8 mA/cm(2) only H-2 bubbles are formed, while above this threshold, iron branches grow accompanied by the formation of H-2 bubbles which nucleate and grow at the top of the branches during their formation. The H-2 bubbles influence the branches growth especially at low j (<24 mA/cm(2)) when the growth velocity of the branches is low compared to the growth rate of the bubbles. At higher j (>24 mA/cm(2)), the branches follow a columnar growth with a constant front velocity, well predicted by the theory. Scanning Electron Microscopy (SEM) of the iron branches shows a dendritic structure constituted of nanometric crystallites, whose size depends on the local growth velocity: increasing the growth velocity from 3.6 mu m/s to 40 mm/s leads to a decrease in the crystallites size, from similar to 1 mu m to similar to 10 nm. Using the acoustic vibrations (4 kHz) of the piezoelectric disk, these fragile branches are successfully fragmented into submicrometric fragments of dendrites exhibiting high specific surfaces S/V (equivalent to the S/V of nanoparticles of 30 nm diameter). Advantages/Drawbacks compared to other synthesis ways as well as the optimization of the proposed synthesis are discussed. (C) 2017 Elsevier Ltd. All rights reserved.