Ambient Surfactantless Synthesis, Growth Mechanism, and Size-Dependent Electrocatalytic Behavior of High-Quality, Single Crystalline Palladium Nanowires

Abstract

In this report, we utilize the U-tube double diffusion device as a reliable, environmentally friendly method for the size-controlled synthesis of high-quality, single crystalline Pd nanowires. The nanowires grown in 200 and 15 nm polycarbonate template pores maintain diameters of 270 ± 45 nm and 45 ± 9 nm, respectively, and could be isolated either as individual nanowires or as ordered free-standing arrays. The growth mechanism of these nanowires has been extensively explored, and we have carried out characterization of the isolated nanowires, free-standing nanowire arrays, and cross sections of the filled template in order to determine that a unique two-step growth process predominates within the template pores. Moreover, as-prepared submicrometer and nanosized wires were studied by comparison with ultrathin 2 nm Pd nanowires in order to elucidate the size-dependent trend in oxygen reduction reaction (ORR) electrocatalysis. Subsequently, the desired platinum monolayer overcoating was reliably deposited onto the surface of the Pd nanowires by Cu underpotential deposition (UPD) followed by galvanic displacement of the Cu adatoms. The specific and platinum mass activity of the core-shell catalysts was found to increase from 0.40 mA/cm(2) and 1.01 A/mg to 0.74 mA/cm(2) and 1.74 A/mg as the diameter was decreased from the submicrometer size regime to the ultrathin nanometer range.

Ambient synthesis, characterization, and electrochemical activity of LiFePO4 nanomaterials derived from iron phosphate intermediates

“…Specifically, we have exchanged the 200 nm pore size PC template, previously used in the synthetic setup, with a 50 nm pore size PC template to produce NWs that have a significantly smaller diameter. Although the reduction in pore size may impact the diffusion of the precursors into the pores with adverse effects upon the resulting length and crystallinity of the NWs [31,39], we found that our initial experimental parameters, such as reaction time and precursor concentration, also produced high-quality amorphous NWs under the 50 nm pore size conditions.…”

“…Within our group, we have typically prepared NWs from templates with pore diameters as small as 15 nm and as large as 200 nm [25,29,31,32,39,[40][41][42]. It has also been shown that arrays of 1-D nanomaterials can be obtained by selectively etching the template during the isolation process [29,31,38].…”

PdNi Hollow Nanoparticles for Improved Electrocatalytic Oxygen Reduction in Alkaline Environments

“…7,[11][12][13][14] Pd alloyed with transition metals (Pd-TMs), such as Pd-Ni, [15][16] Pd-Cu, [17][18][19][20] 27 while the ORR performance was not improved, mainly because the larger lattice constant of silver would subject the Pd to a tensile strain effect, decreasing the electroactivity of Pd towards the ORR. 36 Pd-Co 37 and Pd-Cu 38 hollow nanostructures were also reported with large particle size (> 50 nm) but their ORR properties were not extensively studied due to the large particle size, which may decrease the active surface area.…”

An Overview of One-Dimensional Metal Nanostructures for Electrocatalysis

“…The Pd/ Fe bimetallic nanotube-PC membrane electrode was used as electrocatalysts of ascorbic acid, showing the substantially low overpotential, high selectivity and very good working and storage stability [69]. As seedless and surfactantless synthesis method at the ambient environment, Wong and co-workers developed the U-tube double diffusion technique for one-dimensional metal nanowires with controllable morphology, shape, size, and composition [70][71][72][73]. The crystalline nanowires were prepared using a commercial PC membrane, whose pores were filled with a precursor and a reducing agent held in separate half cells by means of double diffusion.…”

“…Pt, Ag, and Au nanowires prepared by this method exhibited high oxygen reduction reaction activity [70]. Later, they employed the same method to prepare high-quality, single crystalline, submicrometer (270 nm) or nanosized (45 nm) Pd nanowires to explore the size-dependent electrochemical performance of both Pd nanowires, which revealed a distinctive size-dependent oxygen reduction activity enhancement as the wire diameter was decreased [71]. Recently, the morphology-and composition-dependent performance of PtPd nanowires and PdAu nanowires prepared using this method was examined by the same group on the basis of methanol and formic acid oxidation and oxygen reduction behavior [72,73].…”