Palladium (Pd) has recently emerged as a stable and active
yet
cheaper alternative electrocatalyst to costly platinum for the formic
acid oxidation reaction (FAOR). Crystal engineering, wherein particle
morphologies, defects, and facets are selectively altered, can enhance
the electrocatalytic activities of Pd nanostructures. Herein, we have
demonstrated that a combination of crystal engineering and supporting
the nanostructures on a conductive catalyst support (few-layered
graphene (FLG)) leads to highly enhanced catalytic activities. FLG
was prepared by using liquid-phase exfoliation in aqueous solution
of a surfactant. Swollen liquid crystals promoted the nanostructuring
of Pd as well as nanocomposite formation as they acted as “soft”
templates. Spherical nanoparticles (Pd0D), nanowires (Pd1D), and nanosheets (Pd2D) of Pd were formed and
preferentially deposited on graphene sheets on the exposure of mesophases
containing graphene along with Pd2(dba)3 to
hydrazine vapor, H2, and CO, respectively. The Pd1D/FLG nanocomposite exhibited an exceptional electrocatalytic activity
for FAOR. It had many folds higher electrocatalytically active surface
area (ECSA), current density, and stability than the other nanocomposites
as well as other Pd-based catalysts reported in the literature. Increased
presence of more active Pd(100) facets was identified as the major
reason for the enhanced catalytic activity of Pd1D. Supporting
the Pd nanostructures on graphene led to enhanced electrocatalytic
activities owing to the preserved surface sites of Pd nanoparticles,
enhancement in electronic conductivities, and mass transfer and charge
transfer from graphene to Pd.