Abstract
Developing sustainable energy conversion systems with highly efficient and robust
electrocatalysts is essential for addressing global warming and the energy crisis. Direct alcohol
fuel cells (DAFCs) have evolved into highly efficient energy conversion technologies that
significantly reduce the energy crisis and environmental pollution due to their high energy density
and minimal environmental risks. Recently, heterostructures incorporating multi-interfaces for
noble metals have been recognized as an effective strategy to enhance the performance and
commercialization of fuel cells. In this regard, metal-organic frameworks (MOFs) have garnered
significant study interest as potential catalyst support materials owing to their elevated surface area
and porosity, which augment activity by expanding the electrocatalyst's surface area. Furthermore,
MOFs provide a superior option by anchoring metals in their porous structure with a robust carbon
framework combined with other supports. Hence, this study aimed to elucidate the essential effect
of introducing MOFs as a secondary support material for palladium nanoparticles (Pd NPs) and
carbon nanotubes (CNTs) electrocatalyst system.
Initially, MIL-101 and Pd/CNTs were prepared using the hydrothermal and microwave-assisted
synthesis methods, respectively. Thereafter, the obtained novel composite hybrid of monometallic
Pd/CNTs@MIL-101 nanomaterial exhibited a high surface area of 174.29 m2/g from BET
analysis, with diffraction peaks (111), (002) and (311) confirming the successful synthesis of
Pd/CNTs@MIL-101 together with the crystalline nature of Pd and symmetry of Mil-101.
Pd/CNTs@MIL-101 displayed an ECSA of 433.54 m2/g and significantly greater mass activity of
926.49 mA mgPd
-1for ethylene glycol (EG) oxidation than the commercial Pd/C (142.10 mA mgPd
-
1). Furthermore, Pd/CNTs@MIL-101 retained a mass activity of 738.85 mA mgPd
-1 after the 24-
hour stability and durability test, rendering it a suitable stable and active electrocatalyst for longterm
fuel cell utilization. The improved performance of Pd/CNTs@MIL-101 is attributed to the
high surface area of the combined CNTs@MIL-101 double support material, the high electrical
conductivity of CNTs, and strong metal-support interactions between Pd NPs, CNTs, and MIL-
101.
Inspired by the above outcome, further research was conducted to evaluate the effect of supporting
the Pd-Ni NPs (alloy) on the CNTs@ZIF-8 double support material. The binary triple-junction
vi
interface nanomaterial recorded a BET surface area of 93.98 m2/g. Its XRD spectra revealed the
presence of (111), (002), (101), and (011), confirming the Pd-Ni alloy formation. The binary metalbased
Pd/NiO-CNTs@ZIF-8 electrocatalyst exhibited improved catalytic activity for glycerol
oxidation in an alkaline environment, achieving a high current density of 4202.81 mA mgPd
-1, the
most negative onset potential, good reaction kinetics, and long-term stability. Furthermore, the
composite electrocatalyst exhibited good resistance to CO poisoning after 24 hours of long-term
stability and durability test with a retained mass activity of 1578.10 mA mgPd
-1. This remarkable
activity performance is attributed to the high surface area brought by the double support materials
(CNTs and ZIF-8), the bifunctional mechanisms of the triple-junction interfaces, synergistic effect
(Pd-Ni), and strong metal-support interactions between Pd, NiO, CNTs, and ZIF-8.