1] Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] [3].
Nat Mater. 2013 Oct;12(10):905-12. doi: 10.1038/nmat3716. Epub 2013 Aug 4.
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.
对纳米晶体相转变的定量理解将能够实现更高效的能量转换和催化，但由于难以直接监测反应环境中具有良好特性的纳米尺度系统，这一目标受到了阻碍。我们提出了一种新的基于原位发光的探针，可直接定量纳米晶体的相转变，在此应用于钯纳米晶体的氢化转变。我们的方法揭示了纳米晶体相转变的内在动力学和热力学，消除了衬底应变、配体效应和外部信号转换器的复杂性。在长期被认为具有块状行为的纳米晶体中，出现了明显的尺寸依赖性趋势。统计力学模拟表明，这些趋势是热驱动的一级相变的纳米限制的结果：在相变边界附近，新相的临界核的尺寸与纳米晶体本身相当。因此，转变速率不可避免地受到纳米晶体尺寸的控制。我们的结果为理解纳米限制如何从根本上影响与储氢、催化、电池和燃料电池相关的广泛的热驱动固态相转变提供了一个通用框架。
