SYNTHESIS AND CHARACTERIZATION OF Cu-BASED NANOMATERIALS WITH EMPHASIS ON INTERFACIAL STUDIES

Abstract

With the objective to produce stable Cu nanoparticles (NPs) of size ≤10 nm for their multi- facet applications particularly as an electrocatalyst for the CO 2 reduction, various synthesis routes have been systematically applied. Otherwise quite reactive towards atmosphere, the desired Cu NPs were stabilized by incorporating the metal in inert matrix of Au to produce Au x Cu 1-x NPs (x=0 to 1). For the purpose both single- and two-phase wet chemical routes having various combinations of stabilizers, reductants and reaction media were employed and the NPs were characterized by various pertinent techniques such as UV-visible and FTIR spectroscopy, TEM, HRTEM, STEM, elemental analysis, XPS and XRD. The NPs synthesized using alkyl amines, acting as both phase transfer agents and stabilizers, were not only in the desired size range but also exhibited adequate stability. However, the most interesting feature of amine-capped bimetallic NPs, confirmed using HRTEM, STEM and XPS measurements, was the surface segregation of Cu. From the temperature dependent XRD studies higher crystallinity in the cores of Au x Cu 1-x NPs has been established. As for the pure Cu nanostructures, they were produced on glassy carbon electrode (GCE) from acidified SO 42− and Cl − media using chronoamperometry (CA), cyclic voltammetry (CV) and linear sweep voltammetry on rotating GCE (RDE); the techniques also provided useful information such as optimal conditions to be applied for the CO 2 reduction reaction (CRR) on in-situ produced Cu nanostructures. Regarding the Cu nucleation, CV study provided various relevant parameters and CA data fitted to the Scharifker-Hills models furnished information on kinetics and mechanism while RDE experiments were utilized to find out kinetic current density (j k ) and rate constant (k f ) of the process. FESEM coupled with EDX clearly demonstrated formation of Cu nano-dendrites. Differential electrochemical mass spectrometry (DEMS) has been used to establish products of the CRR. From the above mentioned electrochemical techniques it has been demonstrated that instead of using bulk Cu, addition of just few mM Cu(II) in the reaction mixture produces more efficient and durable in-situ catalyst for the CRR. Compared to SO 42− it is better to use Cl − medium which renders stability to Cu(I) centers that have additional role towards higher catalytic activity of the in- situ Cu. An interesting phenomenon observed for the CO 2 -saturated solutions is the splitting of Cu anodic peak with the Cl − concentration; a mechanism has been proposed which could very well be substantiated by additional CV experiments carried out in the presence of Cu(I) and CO. DEMS experiments employed for online characterization of the CRR products have provided evidence for the formation of CH 3 OH and CH 4 which being products of interest in the area of alternate fuels.