Chemical Engineering Program, School of Energy, Environmental, Biomedical, and Medical Engineering, University of Cincinnati, Cincinnati, Ohio 45221, United States.
Langmuir. 2011 May 17;27(10):5781-91. doi: 10.1021/la1049953. Epub 2011 Apr 15.
Monodisperse Pt nanoparticles with atomic structures that span the cluster to crystal transition have recently been synthesized in electrostatically stabilized, aqueous-based suspensions. In the present study, the anionic charge from the stabilizing SnCl(2) sheath adsorbed on the surface of these particles is used for the first time to assemble Pt directly onto porous carbon supports via electrostatic assembly. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals that these assemblies have substantially higher Pt-C dispersions than obtained from precipitation methods commonly used for commercial electrocatalyst systems. Energy dispersive spectroscopy (EDS) and inductively coupled plasma-mass spectrometry (ICP-MS) are used to determine that loadings of 10-30% by weight Pt (particle packing fractions from 0.05 to 0.25) are obtained through a single electrostatic application of these particles on Vulcan carbon, depending on particle size. The highest average oxygen reduction reaction (ORR) mass activity obtained using this approach is 90.4 A/g(Pt) at 0.9 V vs RHE in 0.1 M perchloric acid is with 1-2 nm particles that exhibit a transitional atomic structure. This activity compares to an average value of 74.0 A/g(Pt) obtained from densely packed electrostatic layer-by-layer (LbL) assemblies of unsupported particles and 36.7 A/g(Pt) commercial Vulcan electrocatalyst from Tanaka Kikinzoku Kogyo (TKK). Enhanced activity is observed with electrostatic assembly of any particle size on Vulcan relative to unsupported or commercial electrocatalyst with comparable durability. Such enhanced activity is attributed to improved reactant accessibility to the catalyst surface due to the increase in particle dispersion. An extinction coefficient of 7.41 m(2)/g at 352 nm is obtained across the entire cluster to crystal transition from 20 atom clusters to 2.9 nm single crystal nanoparticles, indicating that observed variation in ORR activity with particle size may be associated primarily with changes in atomic surface structure as opposed to the metallic character of the nanoparticles as assessed by UV-vis spectroscopy.
最近，在静电稳定的水基悬浮液中合成了具有跨越团簇到晶体转变的原子结构的单分散 Pt 纳米粒子。在本研究中，首次利用吸附在这些粒子表面的稳定化 SnCl2 壳层的阴离子电荷，通过静电组装将 Pt 直接组装到多孔碳载体上。高角度环形暗场扫描透射电子显微镜（HAADF-STEM）显示，与商业电催化剂系统中常用的沉淀方法相比，这些组装体具有更高的 Pt-C 分散度。能量色散光谱（EDS）和电感耦合等离子体质谱（ICP-MS）用于确定，通过将这些粒子在 Vulcan 碳上进行单次静电应用，可以获得 10-30wt%的 Pt 负载量（颗粒堆积分数为 0.05 至 0.25），具体取决于颗粒尺寸。通过这种方法获得的最高平均氧还原反应（ORR）质量活性是在 0.1 M 高氯酸中在 0.9 V 相对于 RHE 下，对于 1-2nm 颗粒，其具有过渡原子结构，为 90.4 A/g(Pt)。与未负载的颗粒的紧密堆积静电层层（LbL）组装相比，该活性与来自 Tanaka Kikinzoku Kogyo（TKK）的商业 Vulcan 电催化剂相比，具有 74.0 A/g(Pt)的平均值相比有所提高。与未负载或商业电催化剂相比，在 Vulcan 上通过静电组装任何颗粒尺寸都可以观察到增强的活性，并且具有类似的耐久性。这种增强的活性归因于催化剂表面反应物的可及性提高，这是由于颗粒分散度的增加所致。在从 20 原子团簇到 2.9nm 单晶纳米颗粒的整个团簇到晶体转变过程中，在 352nm 处获得了 7.41m2/g 的消光系数，表明观察到的 ORR 活性随颗粒尺寸的变化可能主要与原子表面结构的变化有关，而不是与由紫外可见光谱评估的纳米颗粒的金属性质有关。
