Influence of the Ligands in Cu(II) Complexes on the Oscillatory Electrodeposition of Cu/Cu₂O

Abstract

Oscillatory electrodeposition reactions have been utilized to create nanostructured materials under the microscale and nanoscale. This alternative method of synthesis, when compared to the traditional step-by-step synthesis procedure, takes advantage of the self-organizing processes that do not require any external control or template-based support, resulting in materials with higher complexity in terms of structure and composition. Nanolayers made of Cu and semiconductor composites, such as Cu/Cu2O, can be finely tuned by controlling ordinary period-one oscillations in the cathodic deposition. As the reaction media is alkaline, a complexing agent is commonly added in the solution to prevent the precipitation of the copper ions as hydroxides. Lactate and tartrate molecules are two α-hydroxy carboxylate organic ligands extensively used for this aim. Although some studies have shown the electrochemical synthesis of Cu/Cu2O nanolayers, no grounded discussion about the influence of the chemical nature of the ligands on the oscillatory reaction has been investigated so far. Here, we provide a well-detailed and rigorous study of the effect of both ligands in the electrodeposition of Cu/Cu2O under galvanostatic control, accurately mapping differences in the oscillation period and amplitude. On the basis of recent advances on the understanding of the copper complex structures, we attributed a distorted tetrahedral structure with four monodentate lactate ligands linked to the Cu2+ central ion ([Cu­(Lac)4]2–) and a distorted square-planar coordination of the tartrate’s deprotonated alkoxide groups, forming a chelate ([Cu­(TartH–2)2]6–), as the species that have a buffering effect on the oscillatory mechanism and, consequently, can control the extension of the oscillation period and amplitude. In this matter, the tartrate complex should have a higher buffering capacity to prolong the period and decrease the amplitude. More importantly, we unequivocally show that a surface blocking effect due to the adsorption reactions cannot be neglected in the mechanism description. The adsorption of the tartrate anions and its complexes has, also as an outcome, period enlargement and amplitude shrinkage, as compared to that of the lactate. Hence, both mechanisms seem to operate in the adjustment of the dynamic characteristics of the oscillatory electrodeposition of Cu/Cu2O.

In Situ Regeneration of Copper-Coated Gas Diffusion Electrodes for Electroreduction of CO2 to Ethylene

“…Among all carboxylate complexes, copper lactate and tartrate should be the most stable of the studied electrolytes. Out of these two, lactate seems to be the ligand of choice, as it should give copper depositing of the most porous structures (i.e., compatible with the surface of GDE) due to its tendency to induce electrochemical oscillations [35].…”

Additive-Assisted Electrodeposition of Cu on Gas Diffusion Electrodes Enables Selective CO2 Reduction to Multicarbon Products

“…Hence, there is a pressing need to conduct comprehensive studies on the levers, such as additives, temperatures, pHs, etc., that can control the electrodeposition of Cu-based catalysts directly on GDEs that afford exceptional CO 2 R performance. Furthermore, some additives, such as lactic acid, acetic acid, and citrate, can be used as complexing agents to prevent the precipitation of Cu in alkaline and/or acidic environments and to afford more diverse Cu surfaces, i.e., Cu/Cu 2 O, for applications of photovoltaic or photoelectric. , These diverse Cu surfaces are worth exploring for CO 2 R as well due to the fact that diverse Cu active sites/defects may be resulted from these materials . Overall, conducting comprehensive studies on these parameters will help us uncover the underlying mechanisms of electrodeposition and optimize the synthesis of Cu-based catalysts for CO 2 R with desired performance for future applications.…”

Potential Oscillations During Cobalt–Nickel Electrodeposition in the Presence of Butynediol

“…Electrochemical oscillation is a unique phenomenon observed during electrodeposition, − electrodissolution, − and electrocatalytic processes, − where complex surface chemical and electrochemical processes are expected to take place. Electrodeposition of metals and alloys has been shown to possess negative differential resistances (NDRs) or hidden-NDRs with electrochemical oscillation. − This provides a vista to control the microstructure and thickness of the deposited layers. , Widely studied oscillatory systems involve (electro-)­chemical processes coupled with the diffusion of the solution species to the interface, e.g., oscillatory systems involving adsorption/desorption of metal–ligand complexes and the dissolution of the passive hydroxide layer . We recently reported a new type of oscillatory system during the electrodeposition of cobalt involving adsorbed hydrogen and its chemical scavenging by hydrogenation of organic additives and the dissolution of passive cobalt hydroxide layers under diffusion control .…”