Sung Chul Yi

Octahedral PtNi nanoparticles with controlled surface structure and composition for oxygen reduction reaction

Controlling the surface structure and composition at the atomic level is an effective way to tune the catalytic properties of bimetallic catalysts. Herein, we demonstrate a generalized strategy to synthesize highly monodisperse, surfactant-free octahedral PtxNi1−x nanoparticles with tunable surface structure and composition. With increasing the Ni content in the bulk composition, the degree of concaveness of the octahedral PtxNi1−x nanoparticles increases. We systematically studied the correlation between their surface structure/composition and their observed oxygen reduction activity. Electrochemical studies have shown that all the octahedral PtxNi1−x nanoparticles exhibit enhanced oxygen reduction activity relative to the state-of-the-art commercial Pt/C catalyst. More importantly, we find that the surface structure and composition of the octahedral PtxNi1−x nanoparticles have significant effect on their oxygen reduction activity. Among the studied PtxNi1−x nanoparticles, the octahedral Pt1Ni1 nanoparticles with slight concaveness in its (111) facet show the highest activity. At 0.90 V vs. RHE, the Pt mass and specific activity of the octahedral Pt1Ni1 nanoparticles are 7.0 and 7.5-fold higher than that of commercial Pt/C catalyst, respectively. The present work not only provides a generalized strategy to synthesize highly monodisperse, surfactant-free octahedral PtxNi1−x nanoparticles with tunable surface structure and composition, but also provides insights to the structure-activity correlation.摘要双金属催化材料的催化性质可以通过在原子水平下控制材料的表面结构和组成进行有效调节. 本文发展了一种普适性的方法合成 具有高度分散性、洁净表面和可调的表面结构和组成的PtxNi1−x八面体纳米粒子. 研究发现在反应过程中, 通过增加Ni前驱体的含量, 合成 的PtxNi1−x八面体纳米粒子的(111)晶面的凹陷程度逐渐加大. 我们系统研究了PtxNi1−x八面体纳米粒子的表面结构或组成与其氧还原电催化 活性之间的相互关系. 电化学研究结果表明所有的PtxNi1−x八面体纳米粒子均表现出比标准商业Pt/C催化剂更高的氧还原活性. 更重要的 是, 我们发现PtxNi1−x八面体纳米粒子的表面结构和组成对其氧还原电催化活性具有很大的影响. 研究发现, 具有轻微(111)晶面凹陷程度的 Pt1Ni1八面体纳米粒子显示出最高的氧还原电催化活性. 在0.9 V(相对于标准氢电极)电势条件下, Pt1Ni1八面体纳米粒子的氧还原质量活性 和面积活性分别为标准商业Pt/C催化剂的7.0和7.5倍. 该研究不仅提供了一种普适性的方法合成具有高度分散性、洁净表面和可调的表面 结构和组成的PtxNi1−x八面体纳米粒子, 同时可为理解催化材料的结构-性质相互关系规律提供指导.

Molybdenum Sulphoselenophosphide Spheroids as an Effective Catalyst for Hydrogen Evolution Reaction

Electrocatalytic splitting of water is the most convincing and straight forward path to extract hydrogen, but the efficiency of this process relies heavily on the catalyst employed. Here, molybdenum sulphoselenophosphide (MoS45.1 Se11.7 P6.1 ) spheroids are reported as an active catalyst for the hydrogen evolution reaction (HER) and this is the first attempt to study on ternary anion based molybdenum chalcogenides. As-prepared MoSx Sey Pz catalyst reveals a unique morphology of microspheroids capped by stretched-out nanoflakes that exhibits excellent electrocatalytic activity (   j-10 mA cm-2 @ 93 mV, Tafel slope of 50.1 mV dec-1 , TOF-0.40 s-1 ) fairly closer to the performance of platinum (Pt) and predominant to those of the pre-existing Mo-chalcogenides and phosphides. Such an increase in performance stems from the copious amount of active edge sites, the presence of nanoflakes, and high circumferential area exposed by the spheroids. Besides, the electrode with MoS45.1 Se11.7 P6.1 displays excellent stability in acidic medium over 10 h of continuous operation. This work paves way for improving the catalytic activity of existing Mo-chalcogenide compounds by doping suitable mixed anions and also reveals the integral role of anions as well as their synergetic effects on the surface physiochemical properties and the HER catalysis.