title: Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies.
abstract: Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.
authors.affiliation: Department of Physics, Central Michigan University, Mt. Pleasant, Michigan 48858, USA. petko1vg@cmich.edu.
authors.forename: Valeri
authors.initials: V
authors.lastname: Petkov
authors.affiliation: Department of Physics, Central Michigan University, Mt. Pleasant, Michigan 48858, USA. petko1vg@cmich.edu.
authors.forename: Binay
authors.initials: B
authors.lastname: Prasai
authors.affiliation: Department of Chemistry, State University of New York at Binghamton, New York 13902, USA. cjzhong@binghamton.edu.
authors.forename: Shiyao
authors.initials: S
authors.lastname: Shan
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Ren
authors.affiliation: Department of Chemistry, State University of New York at Binghamton, New York 13902, USA. cjzhong@binghamton.edu.
authors.forename: Jinfang
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Chemistry, State University of New York at Binghamton, New York 13902, USA. cjzhong@binghamton.edu.
authors.forename: Hannah
authors.initials: H
authors.lastname: Cronk
authors.affiliation: Department of Chemistry, State University of New York at Binghamton, New York 13902, USA. cjzhong@binghamton.edu.
authors.forename: Jin
authors.initials: J
authors.lastname: Luo
authors.affiliation: Department of Chemistry, State University of New York at Binghamton, New York 13902, USA. cjzhong@binghamton.edu.
authors.forename: Chuan-Jian
authors.initials: CJ
authors.lastname: Zhong