Electrochemical metal nucleation and growth mechanism from metal nitrate-L-serine deep eutectic solvent

Electrodeposited nickel, cobalt, and their alloys are critical for applications including energy storage, electrocatalysis and magnetic devices. Traditional aqueous electrodeposition suffers from hydrogen evolution, causing embrittlement, while deep eutectic solvents (DES) offer a promising alternative owing to their low water activity. Here, amino acid-metal nitrate DES (Ni(NO₃)₂ and/or Co(NO₃)₂-L‑serine) are introduced, and the electrochemical nucleation and growth mechanisms of Ni, Co, and their alloys are investigated. Cyclic voltammetry and potentiostatic transient analyses reveal potential-dependent nucleation and growth behavior. Electrodeposition of Ni from Ni(NO₃)₂/L‑serine DES exhibits a two-stage nucleation and growth behavior. The electrodeposition of Co from Co(NO₃)₂/L‑serine DES follows a three-dimensional progressive nucleation mechanism. New models integrating proton reduction and adsorption with Scharifker-Mostany model for monometallic deposition and with Scharifker model for alloy deposition are proposed to interpret potentiostatic current transient behavior. The deposits are characterized by X-ray diffraction and scanning electron microscopy and the crystalline metal phases are confirmed.