Size and Composition Dependence of Oxygen Reduction Reaction Catalytic Activities of Mo-Doped PtNi/C Octahedral Nanocrystals

Abstract

A variety of synthesis protocols for octahedral PtNi nanocatalysts have led to remarkable improvements in platinum mass and specific activities for the oxygen reduction reaction. Nevertheless, the values achieved are still only one tenth of the activity measured from Pt 3 Ni single-crystal (111) surfaces. These particles lose activity during potential cycling, primarily because of Ni leaching and subsequent loss of shape. Here, we present the syntheses and high catalytic oxygen reduction reaction activities of molybdenum-doped PtNi octahedral catalysts with different sizes (6−14 nm) and compositions. We show that the Mo-doped, Nirich, PtNi octahedral catalysts exhibit enhanced stability over their undoped counterpart. Scanning transmission electron microscopy with energy-dispersive Xray analysis reveals the particular elemental distribution for the size and composition of the different catalysts. By combining high-resolution compositional analysis with electrochemical measurements and online inductively coupled plasma mass spectrometry, it was possible to correlate the size, morphology, and composition with the oxygen reduction reaction activities before and after accelerated stress tests. The octahedral catalysts show high electrochemical surface areas and increasing specific activity with increasing surface area of the (111) facets and Ni content, leading to high mass activities. These results demonstrate the advantages of increasing the (111) surface area and Ni content of PtNi nano-octahedral catalysts to improve the performance and stability for the oxygen reduction reaction.

Seed-Mediated, Shape-Controlled Synthesis Methods for Platinum-Based Electrocatalysts for the Oxygen Reduction Reaction—A Mini Review

“…PtNi-6 had an ECSA of 33.5 m 2 g Pt −1 , a specific activity of 0.5 mA cm −2 and a mass activity of 0.32 A mg Pt −1 , whereas PtNi(Mo)-14 had an ECSA of 56.6 m 2 g PT −1 , a specific activity of 5.84 mA cm −2 , and a mass activity of 1.95 A mg Pt −1 . After accelerated stress testing the undoped PtNi-6 specific and mass activities improved but still did not reach the values of PtNi(Mo)-14 (Figure 2B) (Polani et al, 2021) Zhu et al found that alloying Pt with Ir to produce Pd@Pt-Ir core-shell nanocrystals resulted in better performance and stability compared to Pd@Pt/C materials. Pt and Ir were simultaneously deposited in thin layers over cubic, octahedral, and icosahedral Pd seeds with {100} and {111} facets.…”

Gram-Scale Synthesis of Carbon-Supported Sub-5 nm PtNi Nanocrystals for Efficient Oxygen Reduction

“…Second, alloying Pt with a less expensive 3d transition metal (Ni, Co, Cu, etc.) is a feasible method to improve the ORR intrinsic activity [16][17][18][19][20]. For example, Tian et al reported that 1D bunched PtNi alloy nanocages with a Pt-skin structure displayed a high activity and durability for ORR [21].…”

Stabilization of Co oxide during oxygen evolution in alkaline media by the introduction of Mn oxide

“…measured by cyclic voltammetry. [25][26][27] Yet, the discussion of stability requires additional measurements to determine dissolved cations, [28,29] as well as changes in the catalyst composition, [20,30] morphology [31][32][33] and structure. [34,35] Co-based ATMO have attracted particular attention due to their high catalytic activity.…”