title: Uncovering the intrinsic size dependence of hydriding phase transformations in nanocrystals.
abstract: A quantitative understanding of nanocrystal phase transformations would enable more efficient energy conversion and catalysis, but has been hindered by difficulties in directly monitoring well-characterized nanoscale systems in reactive environments. We present a new in situ luminescence-based probe enabling direct quantification of nanocrystal phase transformations, applied here to the hydriding transformation of palladium nanocrystals. Our approach reveals the intrinsic kinetics and thermodynamics of nanocrystal phase transformations, eliminating complications of substrate strain, ligand effects and external signal transducers. Clear size-dependent trends emerge in nanocrystals long accepted to be bulk-like in behaviour. Statistical mechanical simulations show these trends to be a consequence of nanoconfinement of a thermally driven, first-order phase transition: near the phase boundary, critical nuclei of the new phase are comparable in size to the nanocrystal itself. Transformation rates are then unavoidably governed by nanocrystal dimensions. Our results provide a general framework for understanding how nanoconfinement fundamentally impacts broad classes of thermally driven solid-state phase transformations relevant to hydrogen storage, catalysis, batteries and fuel cells.
authors.affiliation: 1] Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] [3].
authors.forename: Rizia
authors.initials: R
authors.lastname: Bardhan
authors.forename: Lester O
authors.initials: LO
authors.lastname: Hedges
authors.forename: Cary L
authors.initials: CL
authors.lastname: Pint
authors.forename: Ali
authors.initials: A
authors.lastname: Javey
authors.forename: Stephen
authors.initials: S
authors.lastname: Whitelam
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Urban
references.citation: Phys Rev Lett. 2010 Apr 2;104(13):135502
references.pmid: 20481892
references.citation: Science. 1997 Apr 18;276(5311):398-401
references.pmid: 9103194
references.citation: Science. 2001 Sep 21;293(5538):2227-31
references.pmid: 11567132
references.citation: ChemSusChem. 2010 Dec 17;3(12):1332-48
references.pmid: 21080405
references.citation: Nano Lett. 2007 Oct;7(10):3122-7
references.pmid: 17850168
references.citation: Nat Mater. 2011 Apr;10(4):286-90
references.pmid: 21399630
references.citation: Science. 2009 Nov 13;326(5955):980-4
references.pmid: 19965508
references.citation: Chemphyschem. 2009 Oct 19;10(15):2566-76
references.pmid: 19823997
references.citation: Nano Lett. 2010 Sep 8;10(9):3529-38
references.pmid: 20718400
references.citation: Nat Mater. 2011 May;10(5):361-6
references.pmid: 21478881
references.citation: Phys Rev Lett. 2009 Jun 5;102(22):226102
references.pmid: 19658880
references.citation: ACS Nano. 2010 Apr 27;4(4):1987-96
references.pmid: 20307089
references.citation: Nat Mater. 2011 May 15;10(8):631-6
references.pmid: 21572410
references.citation: Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics. 1994 Jun;49(6):5080-5090
references.pmid: 9961829