Self-Terminated Electrodeposition of Ni, Co, and Fe Ultrathin Films

Abstract

Self-terminated Fe-group metal (Ni, Co, Fe) electrodeposition occurs at potentials negative of the onset of water reduction where OH– generation leads to the formation of a blocking hydroxide monolayer. Quenching of metal deposition is accompanied by an increase in dissipative energy loss in microbalance experiments attributed to increased hydrogen bonding to the adjacent double layer. Pulse deposition at −1.5 VSSCE in 5 mmol/L (NiCl2, CoCl2, FeSO4) – 0.1 mol/L NaCl pH 3.0 electrolytes yields fully coalesced ultrathin films of Ni, Co, Fe, or alloys thereof, on Au. The film thickness is controlled by the nucleation, growth, and termination dynamics constrained by the electrochemical cell time constant. Precipitation of bulk Ni(OH)2 and related phases is minimized by using short deposition times and dilute metal cation concentrations to limit supersaturation. The rapid deposition of smooth, compact ultrathin Fe, Co, and Ni films should facilitate mechanistic and durability studies of Fe-group metal catalysi...