Key role of anions in the 2D–3D electrochemical deposition of Rh on Ag electrodes

•Rh deposition over Ag substrates was studied in the presence of sulphate and chloride ions.•Rh deposition follows a 3D nucleation and growth mechanism in the presence of sulphate ions.•In the presence of chloride ions, Rh shows a 2D mechanism, followed by a 3D one.•DFT calculations were employed in order to explain the observed phenomena.•Chloride ions stabilize the Rh deposition, favouring a 2D mechanism at low overpotentials.