Size & shape controlled synthesis of metal nanoparticles are of high
importance in catalysis. Colloidal techniques offer fine tunings in
synthesis process as it involve multiple steps and reaction parameters.
An efficient way of producing morphology controlled palladium
nanostructures viz. palladium nanocubes (Pd-nc), palladium
nanoicosahedrons (Pd-nico) supported on reduced graphene oxide (rGO) and
its application in electro-catalysis is reported here. These Pd
nano-shapes were achieved via sequential chemical reduction of Pd metal
precursor and graphene oxide in the presence of reductant, ethylene
glycol (EG) and stabilizer (capping agent), polyvinylpyrrolidone (PVP).
Potassium bromide (KBr) and ascorbic acid (AA) were used as structure
directing and secondary reducing agents respectively, to tune the
geometry of Pd nanoparticles (Pd NPs). The preparation steps were
optimized to yield cube shaped Pd nanoparticles (Pd-nc) with mean
diameter of 4 nm in the presence of KBr/AA; while in their absence, icosahedron shaped Pd nanoparticles (Pd-nico) with mean diameter of 3.1 nm
were formed and then homogeneously distributed over rGO sheets as
evidenced by SEM-EDX and TEM. Further, Pd-nc/rGO and Pd-nico/rGO hybrid
composite materials were used to investigate the electrochemical
oxidation of oxalic acid (OA) in acidic medium. The results reveal that,
these optimal size ranged nanostructures exhibit enhanced
electro-catalytic activity when compared to bare glassy carbon electrode
(GCE), towards OA oxidation. Among the two, Pd-nico/rGO showed enhanced
activity than Pd-nc/rGO. The activity difference was justified based on
the particle size distribution and no of surface exposed sites. The
synthesis approach provides a versatile route for morphology (shape and
size) controlled synthesis of metal nanostructures immobilized on
support materials aiming towards fabrication of low cost composites in
electro-catalysis and potential sensor applications.