In-Situ Single Particle Reconstruction Reveals 3D Evolution of PtNi Nanocatalysts During Heating

Tailoring nanoparticles’ composition and morphology is of particular interest for improving their performance for catalysis. A challenge of this approach is that the nanoparticles’ optimized initial structure often changes during use. Visualizing the three dimensional (3D) structural transformation in-situ is therefore critical, but often prohibitively difficult experimentally. Although electron tomography provides opportunities for 3D imaging, restrictions in the tilt range of in-situ holders together with electron dose considerations limit the possibilities for in-situ electron tomography studies. Here, we present an in-situ 3D imaging methodology using single particle reconstruction (SPR) that allows 3D reconstruction of nanoparticles with controlled electron dose and without tilting the microscope stage. This in-situ SPR methodology was employed to investigate the restructuring and elemental redistribution within a population of PtNi nanoparticles at elevated temperatures. We further examined the atomic structure of PtNi and found a heat-induced transition from a disordered to an ordered phase. Changes in structure and elemental distribution were linked to a loss of catalytic activity in the oxygen reduction reaction. The in-situ SPR methodology employed here could be extended to a wide range of in-situ studies employing not only heating, but gaseous, aqueous or electrochemical environments to reveal inoperando nanoparticle evolution in 3D.