Uncovering the intrinsic size dependence of hydriding phase transformations in nanocrystals
Uncovering the intrinsic size dependence of hydriding phase transformations in nanocrystals
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DOI：
10.1038/nmat3716
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发表时间：
2013-10-01
期刊：
影响因子：
41.2
通讯作者：
Urban, Jeffrey J.
中科院分区：
文献类型：
--
作者：
Bardhan, Rizia;Hedges, Lester O.;Urban, Jeffrey J.
对纳米晶体相变的定量理解将实现更有效的能量转换和催化，但由于直接监测反应环境中特征良好的纳米级系统的困难而受到阻碍。我们提出了一种新的基于原位发光的探针，能够直接量化纳米晶体相变，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变的内在动力学和热力学，消除了基质应变、配体效应和外部信号传感器的复杂性。纳米晶体中出现了明显的尺寸依赖性趋势，长期以来人们认为纳米晶体的行为类似于块体。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：在相边界附近，新相的临界核的尺寸与纳米晶体本身相当。转化率不可避免地受到纳米晶体尺寸的控制。我们的研究结果为理解纳米限域如何从根本上影响与氢存储、催化、电池和燃料电池相关的广泛的热驱动固态相变提供了一个总体框架。
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.