Annealing Behaviour of Pt and PtNi Nanowires for Proton Exchange Membrane Fuel Cells

Abstract

PtNi alloy and hybrid structures have shown impressive catalytic activities toward the cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, such promise does not often translate into improved electrode performances in PEMFC devices. In this contribution, a Ni impregnation and subsequent annealing method, translatable to vertically aligned nanowire gas diffusion electrodes (GDEs), is shown in thin-film rotating disk electrode measurements (TFRDE) to enhance the ORR mass activity of Pt nanowires (NWs) supported on carbon (Pt NWs/C) by around 1.78 times. Physical characterisation results indicate that this improvement can be attributed to a combination of Ni alloying of the nanowires with retention of the morphology, while demonstrating that Ni can also help improve the thermal stability of Pt NWs. These catalysts are then tested in single PEMFCs. Lower power performances are achieved for PtNi NWs/C than Pt NWs/C. A further investigation confirms the different surface behaviour between Pt NWs and PtNi NWs when in contact with electrolyte ionomer in the electrodes in PEMFC operation. Indications are that this interaction exacerbates reactant mass transport limitations not seen with TFRDE measurements.

Comparative Study of PtNi Nanowire Array Electrodes toward Oxygen Reduction Reaction by Half-Cell Measurement and PEMFC Test

“…Figure 5c shows Pt (111) peaks for the Pt NW array and PtNi NW array GDEs annealed at the different temperatures, including those that have undergone acid leaching. A progressive positive peak shift can be observed with the increase of the annealing temperature, indicating lattice contraction through the surface segregation of Pt and alloying of the smaller Ni atoms into the Pt fcc lattice, coinciding with our previous study 25 . This peak shift is lower than those of PtNi alloy nanostructures reported in literature due to the low annealing temperature used here for retaining NW morphology and the low Ni content in the final NW structures 31,35,36 .…”

“…These enhancements are thought to be due to the high aspect ratio of crystalline facets in the NWs as well as lattice-strain effects additionally presented in the PtNi NW arrays, as supported by previously published data recorded in half-cell measurement using the rotating disk electrode method 16,25 . The Tafel plots also demonstrate a larger absolute current for the Pt/C GDE in the region above 0.9 V in comparison to the NW array GDEs (in the 16 cm 2 MEA), and this can be ascribed to the much larger ECSA presented.…”

“…Inspired by promising catalytic activities of PtNi alloys, a method of fabricating PtNi NWs via the postsynthetic reduction and annealing of Ni onto the Pt NW structure was demonstrated on a carbon nanosphere support. 25 With this simple process, the mass activity of the Pt NW/C catalyst was boosted by 1.78-fold (using half-cell electrochemical measurement in a liquid electrolyte). However, the single-cell test in PEMFCs showed very poor power performance as a consequence of surface Ni hydroxide species.…”

Facile Synthesis of Co3O4@CoO@Co Gradient Core@Shell Nanoparticles and Their Applications for Oxygen Evolution and Reduction in Alkaline Electrolytes

“…However, due to the expensive nature of Pt, it is rather critical to explore low-cost alternatives that could still deliver similar ORR performances. A straightforward solution is the formation of alloyed nanoparticles with binary (Pt-Ni, Pt-Fe, and Pt-Co) and tertiary (Pt-Fe-Co, Pt-Cu-Ni, and Pt-Fe-Ni) constituents [21][22][23][24][25][26]. On many occasions, these alloyed electrocatalysts not only reduce the Pt utilization but also demonstrate even stronger ORR activities [27][28][29][30].…”

Modulating Catalytic Activity and Durability of PtFe Alloy Catalysts for Oxygen Reduction Reaction Through Controlled Carbon Shell Formation

“…Besides the durability issues, the catalytic activity needs to be greatly enhanced since the use of expensive Pt needs to be reduced. Therefore, various approaches have been extensively developed, which include alloying Pt with 3 d transition metals (M = Fe, Co, and Ni) [7,8,9,10,11,12,13,14,15], core-shell nanostructures [16], and modification of support materials [17,18].…”