Oleylamine Aging of PtNi Nanoparticles Giving Enhanced Functionality for the Oxygen Reduction Reaction

Abstract

We report a rapid solution-phase strategy to synthesize alloyed PtNi nanoparticles which demonstrate outstanding functionality for the oxygen reduction reaction (ORR). This one-pot coreduction colloidal synthesis results in a monodisperse population of single-crystal nanoparticles of rhombic dodecahedral morphology with Pt-enriched edges and compositions close to Pt 1 Ni 2 . We use nanoscale 3D compositional analysis to reveal for the first time that oleylamine (OAm)-aging of the rhombic dodecahedral Pt 1 Ni 2 particles results in Ni leaching from surface facets, producing aged particles with concave faceting, an exceptionally high surface area, and a composition of Pt 2 Ni 1 . We show that the modified atomic nanostructures catalytically outperform the original PtNi rhombic dodecahedral particles by more than two-fold and also yield improved cycling durability. Their functionality for the ORR far exceeds commercially available Pt/C nanoparticle electrocatalysts, both in terms of mass-specific activities (up to a 25-fold increase) and intrinsic area-specific activities (up to a 27-fold increase).

Recent Progress on Revealing 3D Structure of Electrocatalysts Using Advanced 3D Electron Tomography: A Mini Review

“…Nanostructures’s 3D morphology, in both terms of the particle size and shape, can be better studied by 3D electron tomography. A number of electrocatalysts with different morphology have been investigated, including nanoporous and nanodendrites ( Mourdikoudis et al, 2013 ; Geboes et al, 2016 ; Mourdikoudis et al, 2019 ; Pappert et al, 2019 ; Yu et al, 2019 ), nano platelets ( Kong et al, 2013 ; Toth et al, 2016 ; González-Jiménez et al, 2018 ), nanoframes and nanocages ( Becknell et al, 2017 ; Zhang et al, 2019a ; Gong, 2021a ), nanowires ( Bu et al, 2016 ; Liu et al, 2020 ), and the most widely studied nanoparticles ( Liu et al, 2012 ; Lu et al, 2014 ; Mourdikoudis et al, 2015 ; Londono-Calderon et al, 2017 ; Kang et al, 2018 ; Gong, 2021b ; Frank et al, 2021 ; Leteba et al, 2021 ).…”

“…The 3D study showed that the structure resembled a highly concave particles that nearly only skeleton remained, providing high surface area. Recently, Leteba et al reported that rhombic dodecahedral Pt-Ni nanoparticles after oleylamine aging showed enhanced ORR activity ( Leteba et al, 2021 ). By comparing the 3D morphology of Pt-Ni nanoparticles before and after aging, concave facets with exceptionally high surface area were revealed.…”

Formation of Pt-Based Alloy Nanoparticles Assisted by Molybdenum Hexacarbonyl

“…The most successful NPs reported to date, formed by the dilution of costly Pt with less-expensive 3d-transition metals, show good catalytic performance [ 2 , 7 , 8 , 9 ], but further improvement is sought. Optimising the functionality of alloy NP electrocatalysts, particularly for the ORR, requires an understanding of the solution-phase (wet-chemical) synthetic process [ 3 , 6 , 10 , 11 ]. Solution-phase synthesis of NPs for industrial applications should ideally result in NP structures with a high degree of crystallinity, narrow particle size distribution, uniform morphology and excellent dispersability in organic solvents [ 6 , 7 , 11 , 12 , 13 , 14 ].…”

“…Optimising the functionality of alloy NP electrocatalysts, particularly for the ORR, requires an understanding of the solution-phase (wet-chemical) synthetic process [ 3 , 6 , 10 , 11 ]. Solution-phase synthesis of NPs for industrial applications should ideally result in NP structures with a high degree of crystallinity, narrow particle size distribution, uniform morphology and excellent dispersability in organic solvents [ 6 , 7 , 11 , 12 , 13 , 14 ]. However, the reduction of two or more different metal precursors in solution-based media often leads to the creation of core-shell, hetero-structured, or segregated NPs, rather than homogenous nanoalloys, due to differences in the standard reduction potentials of the metal precursors [ 12 , 15 ].…”

Solvothermal Synthesis of Nanostructured PtnNi Tetrahedrons with Enhanced Platinum Utilization and Activity toward Oxygen Reduction Electrocatalysis

“…Extensive investigations have shown that Pt alloying with transition metals (Ni, Co, Fe, etc.) would be effective for creating the said nanostructures with significantly enhanced Pt activity toward ORR, due to transitional metal-induced alternations in the electronic structure of the topmost Pt atoms for weakening the adsorption of oxygenated species .…”