Bhalothia Dinesh, Chou Jyh-Pin, Yan Che, Hu Alice, Yang Ya-Tang, Chen Tsan-Yao
Institute of Electronics Engineering, Department of Engineering and System Science, and Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 30013, Taiwan.
Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong SAR 999077, China.
ACS Omega. 2018 Aug 7;3(8):8733-8744. doi: 10.1021/acsomega.8b01234. eCollection 2018 Aug 31.
Carbon nanotube supported ternary metallic nanocatalysts (NCs) comprising Ni-Pd structure and Pt atomic scale clusters in shell (namely, Ni@Pd/Pt) are synthesized by using wet chemical reduction method with reaction time control. Effects of Pt adsorption time and Pt/Pd composition ratios on atomic structure with respect to electrochemical performances of experimental NCs are systematically investigated. By cross-referencing results of high-resolution transmission electron microscopy, X-ray diffraction, X-ray absorption, density functional theoretical calculations, and electrochemical analysis, we demonstrate that oxygen reduction reaction (ORR) activity is dominated by depth and distribution of Pt clusters in a Ni@Pd/Pt NC. For the optimum case (Pt adsorption time = 2 h), specific activity of Ni@Pd/Pt is 0.732 mA cm in ORR. Such a value is 2.8-fold higher as compared to that of commercial J.M.-Pt/C at 0.85 V (vs reversible hydrogen electrode). Such improvement is attributed to the protection of defect sites from oxide reaction in the presence of Pt clusters in NC surface. When adsorption time is 10 s, Pt clusters tends to adsorb in the Ni@Pd surface. A substantially increased galvanic replacement between Pt ion and Pd/Ni metal is found to result in the formation of Ni@Pd shell with Pt cluster in the interface when adsorption time is 24 h. Both structures increase the surface defect density and delocalize charge density around Pt clusters, thereby suppressing the ORR activity of Ni@Pd/Pt NCs.
通过湿化学还原法并控制反应时间，合成了碳纳米管负载的三元金属纳米催化剂（NCs），其具有Ni-Pd结构且壳层含有原子尺度的Pt簇（即Ni@Pd/Pt）。系统研究了Pt吸附时间和Pt/Pd组成比相对于实验NCs电化学性能对原子结构的影响。通过交叉引用高分辨率透射电子显微镜、X射线衍射、X射线吸收、密度泛函理论计算和电化学分析的结果，我们证明氧还原反应（ORR）活性由Ni@Pd/Pt NC中Pt簇的深度和分布主导。对于最佳情况（Pt吸附时间 = 2 h），Ni@Pd/Pt在ORR中的比活性为0.732 mA cm。与商业J.M.-Pt/C在0.85 V（相对于可逆氢电极）时的值相比，该值高出2.8倍。这种改进归因于在NC表面存在Pt簇的情况下，缺陷位点受到保护而不发生氧化反应。当吸附时间为10 s时，Pt簇倾向于吸附在Ni@Pd表面。当吸附时间为24 h时，发现Pt离子与Pd/Ni金属之间的电化学生成置换大幅增加，导致在界面处形成带有Pt簇的Ni@Pd壳层。这两种结构都增加了表面缺陷密度并使Pt簇周围的电荷密度离域，从而抑制了Ni@Pd/Pt NCs的ORR活性。
