An innovative approach for using non-noble metals as an alternative initiator for electroless copper plating of non-conductive materials

In the present study, a new approach to inducing the electroless copper deposition reaction was established utilising non-noble metals (zinc (Zn) and cobalt (Co)) as more sustainable, inexpensive, alternative initiators for electroless copper deposition with particular applicability to the coating of non-conductive materials. This work presents an innovative approach to replace critical raw materials (CRMs) like palladium (Pd) with more sustainable metals, addressing the growing risks of supply disruptions that threaten the progress of modern technologies, particularly in catalytic applications. The investigation involved the analysis of precipitates and electroless copper deposits using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and electrochemical analysis employing cyclic voltammetry (CV), impedance spectroscopy (EIS) and Tafel plots. The study clearly demonstrated that zinc (Zn) and cobalt (Co) particles are capable of initiating the electroless copper deposition process despite the fact that cyclic voltammetry (CV) analysis indicated no detectable oxidation of the reducing agent on either Zn or Co. Such results provide compelling evidence for a non-catalytic, indirect initiation mechanism for electroless copper deposition on these metals. Complementary X-ray photoelectron spectroscopy (XPS) analysis confirmed the deposition of copper on the surfaces of Zn and Co particles, even in the absence of the reducing agent. For the first time, a mechanism for the indirect initiation of electroless copper deposition by non-noble metals (Zn and Co) has been elucidated. The key step involves a displacement (or galvanic exchange) reaction that facilitates the initial deposition of copper onto the non-noble metal surface. Subsequent copper deposition proceeds via the conventional electroless process, catalysed by the oxidation of formaldehyde on this preliminary copper layer. This indirect initiation mechanism contrasts with the well-known ‘direct’ Pd initiation process, whereby the first layer of copper is formed by the catalytic oxidation of formaldehyde on the Pd particles.