Abstract The ease by which hydrogen is absorbed into a metal can be either advantageous or deleterious, depending on the material and application in question. For instance, in metals such as palladium (Pd), rapid absorption kinetics are seen as a beneficial property for hydrogen purification and storage applications, whereas the contrary is true for structural metals such as steel, which are susceptible to mechanical degradation in a process known as hydrogen embrittlement. It follows that understanding how the microstructure of metals (i.e., grains and grain boundaries) influences adsorption and absorption kinetics would be extremely powerful to rationally design materials (e.g., alloys) with either a high affinity for hydrogen or resistance to hydrogen embrittlement. To this end, scanning electrochemical cell microscopy (SECCM) is deployed herein to study surface structure-dependent electrochemical hydrogen absorption across the surface of flame annealed polycrystalline Pd in aqueous sulfuric acid (considered to be a model system for the study of hydrogen absorption). Correlating spatially-resolved cyclic voltammetric data from SECCM with co-located structural information from electron backscatter diffraction (EBSD) reveals a clear relationship between the crystal orientation and the rate of hydrogen adsorption-absorption. Grains that are closest to the low-index orientations [i.e., the {100}, {101}, and {111} facets, face-centered cubic (fcc) system] facilitate the lowest rates of hydrogen absorption, whereas grains of high-index orientation (e.g., {411}) promote higher rates. Apparently enhanced kinetics are also seen at grain boundaries, which are thought to arise from physical deformation of the Pd surface adjacent to the boundary, resulting from the flame annealing and quenching process. As voltammetric measurements are made across a wide potential range, these studies also reveal palladium oxide formation and stripping to be surface structure-dependent processes, and further highlight the power of combined SECCM-EBSD for structure-activity measurements in electrochemical science.

中文翻译：

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多晶钯电化学吸氢的表面微结构控制

摘要 氢被金属吸收的难易可能是有利的，也可能是有害的，这取决于所讨论的材料和应用。例如，在钯 (Pd) 等金属中，快速吸收动力学被视为有利于氢气净化和储存应用的特性，而钢等结构金属则相反，它们在已知过程中易于机械降解如氢脆。因此，了解金属的微观结构（即晶粒和晶界）如何影响吸附和吸收动力学对于合理设计对氢具有高亲和力或抗氢脆性的材料（例如合金）将非常有效。为此，本文采用扫描电化学电池显微镜 (SECCM) 来研究火焰退火多晶 Pd 在硫酸水溶液中表面结构依赖的电化学吸氢（被认为是研究吸氢的模型系统）。将来自 SECCM 的空间分辨循环伏安数据与来自电子背散射衍射 (EBSD) 的共位结构信息相关联，揭示了晶体取向与氢吸附-吸收速率之间的明确关系。最接近低指数取向的晶粒 [即 {100}、{101} 和 {111} 面，面心立方 (fcc) 系统] 有助于最低的氢吸收率，而高-指数取向（例如，{411}）促进更高的比率。在晶界处也观察到明显增强的动力学，这被认为是由邻近边界的 Pd 表面的物理变形引起的，由火焰退火和淬火过程引起。由于伏安测量是在很宽的电位范围内进行的，这些研究还揭示了氧化钯的形成和剥离是依赖于表面结构的过程，并进一步突出了 SECCM-EBSD 组合在电化学科学中进行结构-活性测量的能力。