The electrochemical cell consisted of a Au(111) single crystal substrate with two gold wires for both the counter electrode and as a quasi-reference electrode (QRE). The STM tips were either Pt or Pt-Ir, and were coated with an insulating wax to decrease the exposed area and minimize parasitic Faradaic current along the length of the probe. All experiments were done in ambient conditions. Figure shows a cyclic voltammogram (CV) of the Au substrate in 500 mM CoSO4 in DMSO (blue curve). The reduction reaction with an onset at ~-900 mV is associated with the deposition of cobalt, as confirmed by in-situ STM imaging (not shown). The cobalt dissolution is connected to the oxidation wave starting at ~-400 mV, confirmed by the absence of this wave when stopping the scan at cathodic potentials >-900 mV (grey dashed curve). Importantly the reduction/oxidation of cobalt are separated in potential by a few hundred mV, which provides an electrochemical window where the substrate potential can be fixed as to prevent global deposition on the substrate to occur, while also preventing dissolution of the deposited structures .