Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 3E5, Canada.
Nanoscale. 2018 Mar 8;10(10):4904-4912. doi: 10.1039/c7nr08206a.
Nanoporous gold (NPG) is usually made by electrochemical dealloying of Ag from binary AgAu alloys. The resulting nanoscale ligaments are not very stable, and tend to coarsen with time by surface self-diffusion, especially in electrolyte, which may lead to inferior electrocatalytic properties. Addition of a small amount of Pt to the precursor alloy is known to refine and stabilize the nanoporous product (NPG-Pt). However, the mechanisms by which Pt serves to refine the microstructure remain poorly understood. The present study aims to expand our knowledge of the role of Pt by examining NPG-Pt at atomic resolution with Atom Probe Tomography (APT), as well as by aberration-corrected Transmission Electron Microscopy. Atomic level observation of Pt enrichment on ligament surfaces sheds light on the underlying mechanisms that give rise to Pt's refining effect. Owing to improved Ag retention with higher Pt content, NPG-Pt (made by dealloying AgAuPt) was shown to have the highest surface area-to-volume ratio, compared to NPG-Pt (made by dealloying AgAuPt). Quantitative estimates reveal up to 5-fold enrichment of Pt at nanoligament surfaces, compared to the precursor content, in NPG-Pt. The interface between the dealloyed layer and the substrate was captured by APT, for the first time. The findings of this investigation add insight into the functionality of NPG-Pt and its prospective catalytic performance.
纳米多孔金（NPG）通常通过电化学从二元 AgAu 合金中脱合金化 Ag 来制备。得到的纳米级线不太稳定，并且由于表面自扩散，特别是在电解质中，随着时间的推移往往会变粗，这可能导致较差的电催化性能。向前驱体合金中添加少量的 Pt 已知可以细化和稳定纳米多孔产物（NPG-Pt）。然而，Pt 细化微观结构的机制仍知之甚少。本研究旨在通过原子探针断层扫描（APT）以及像差校正透射电子显微镜（aberration-corrected Transmission Electron Microscopy）以原子分辨率检查 NPG-Pt，来扩展我们对 Pt 作用的认识。观察到在 Ligament 表面上 Pt 的富集，揭示了导致 Pt 细化效果的潜在机制。由于较高 Pt 含量下 Ag 的保留率提高，与 NPG-Pt（通过脱合金化 AgAuPt 制备）相比，NPG-Pt（通过脱合金化 AgAuPt 制备）具有更高的表面积与体积比。定量估计显示，与前驱体含量相比，在 NPG-Pt 中，Pt 在纳米 Ligament 表面的富集高达 5 倍。首次通过 APT 捕获了脱合金层与衬底之间的界面。这项研究的结果深入了解了 NPG-Pt 的功能及其潜在的催化性能。
