Unveiling the coordination and adsorption mechanisms of DMH and NA as composite complexing agents for cyanide-free silver electrodeposition: a combined DFT and electrochemical study

This work systematically investigates the intrinsic molecular properties of DMH and NA, their coordination ability with silver ions, their adsorption behaviour on silver surfaces, and the nucleation mechanism of silver electrodeposition through DFT calculations and electrochemical analysis. Analysis of frontier molecular orbitals, ESP and ALIE shows that DMH has a higher HOMO level and a more negative minimum ESP value, with its imine nitrogen atom being the preferred coordination site; while NA has a slightly lower minimum ALIE value, indicating a slightly stronger local electron-donating ability. Coordination energy calculations show that the total energy of [Ag(DMH)2]+ is significantly lower than that of [Ag(NA)2]+, and the N-Ag bond energy of the DMH system is higher than that of the NA system, proving that DMH is a superior master complexing agent. UV-Vis absorption spectroscopy further confirms that Ag+ preferentially coordinates with DMH in the composite system. Adsorption energy calculations indicate that NA has a stronger adsorption energy on the silver surface than DMH, while [Ag(DMH)2]+ has the most negative adsorption energy, exhibiting extremely strong surface affinity. LSV confirm that the electroreduction of the silver complex is an irreversible diffusion-controlled process, with a diffusion coefficient of 1.60 × 10−7 cm2/s. CA and fitting with the SH model show that the electro-crystallization of silver follows a diffusion-controlled transient nucleation mechanism.