Abstract
This article aims to address the formation and the structural disordering/ordering phenomena of PtNi nanoalloys supported on hollow graphitic spheres (HGSs) using pair distribution function (PDF) analysis under ex situ/in situ data collection conditions. Starting from small nanoparticles (10-15 Å in diameter) embedded in HGSs, structural changes were monitored during stepwise heating and cooling of the sample using in situ PDF analysis. In order to evaluate the conventional synthesis route for the production of PtNi nanoalloys supported on HGSs, ex situ PDF experiments were performed before and after heat treatment in a furnace. The studies demonstrate that the local structure of the in situ synthesised PtNi nanoalloy differs from its ex situ synthesised counterpart. A partially ordered PtNi nanoalloy was obtained during the stepwise in situ cooling of the precursor, whereas the conventional ex situ synthesis route did not lead to the formation of an ordered crystal structure. In this study we could show that rapid heating and cooling results in a disordered PtNi alloy whereas slow heating and cooling leads to disorder-order transitions in PtNi.
Highlights
Proton exchange membrane fuel cells (PEMFCs) are alternative hydrogen fuelled devices for clean energy conversion
In order to overcome this issue, the main research is focused on the design of cost-effective alternative catalysts that are competitive to Pt nanoparticles (Pt/C), exhibiting comparable or even higher electrocatalytic activities
In this paper we aim to reveal the formation and disordering/ordering phenomena of PtNi nanoalloys supported on hollow graphitic spheres (HGSs) using in situ X-ray pair distribution function (PDF) analysis in combination with conventional X-ray powder diffraction (XRPD)
Summary
Proton exchange membrane fuel cells (PEMFCs) are alternative hydrogen fuelled devices for clean energy conversion. Commercialisation and long-term viability of PEMFCs rely on the cost and the performance of electrocatalysts employed.[1,2,3,4,5,6,7] Carbon supported Pt nanoparticles (Pt/C) served as the commercial state-of-the-art electrocatalysts over years.[8,9] high cost and durability of electrocatalysts is a great challenge for the PEMFC technology.[5,10] In order to overcome this issue, the main research is focused on the design of cost-effective alternative catalysts that are competitive to Pt/C, exhibiting comparable or even higher electrocatalytic activities. It is well-known that alloying of Pt with 3d transition metals is a very convenient approach to improve the intrinsic activity towards the oxygen reduction reaction (ORR).[11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]
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