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.