A major challenge in electrocatalysis is to understand the effect of electrochemical processes on the physicochemical properties of nanoparticle or nanocluster (NC) ensembles, especially for complex processes, such as the oxygen reduction reaction (ORR) considered herein. We describe an approach whereby electrocatalysis at a small number of well-defined mass-selected Pt NCs (Pt_923±37, diameter, d ≈ 3 nm), deposited from a cluster beam source on carbon-coated transmission electron microscopy (TEM) grids, can be measured by a scanning electrochemical cell microscopy (SECCM) setup, in tandem with a range of complementary microscopy and spectroscopy techniques. The SECCM setup delivers high mass transport rates and allows the effects of transient reactive intermediates to be elucidated for different Pt surface coverages (NC spacing). A major observation is that the ORR activity decreases during successive electrochemical (voltammetric) measurements. This is shown to be due to poisoning of the Pt NCs by carbon-/oxygen-containing moieties that are produced by the reaction of reactive oxygen intermediates (RIs), generated by the ORR, with the carbon support. The effect is most prominent when the Pt surface coverage on the carbon support is low (<6%). Furthermore, the NC deposition impact energy drastically affects the resulting Pt NC stability during electrochemistry. For lower impact energy, Pt NCs migrate as a consequence of the ORR and are rearranged into characteristic groups on the support. This previously unseen effect is caused by an uneven flux distribution around individual NCs within the ensemble and has important consequences for understanding the stability and activity of NC and nanoparticle arrays.

中文翻译：

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大量选择的铂纳米团簇在氧还原反应过程中的移动性和中毒

电催化的主要挑战是了解电化学过程对纳米颗粒或纳米簇（NC）团簇的物理化学性质的影响，尤其是对于复杂过程，例如本文考虑的氧还原反应（ORR）。我们描述了一种方法，通过该方法，在少量定义明确的质量选择的Pt NCs（Pt _923±37，直径，d从簇束源沉积在碳涂层的透射电子显微镜（TEM）网格上的≈3 nm左右）可以通过扫描电化学池显微镜（SECCM）设置与一系列互补的显微镜和光谱技术一起进行测量。SECCM装置可提供较高的质量传输速率，并可以针对不同的Pt表面覆盖范围（NC间距）阐明瞬态反应性中间体的影响。一个主要的观察结果是，在连续的电化学（伏安）测量过程中，ORR活性降低。结果表明，这是由于Pt NCs被ORR生成的活性氧中间体（RIs）与碳载体反应生成的含碳/氧部分中毒所致。当碳载体上的铂表面覆盖率低（<6％）时，效果最显着。此外，在电化学过程中，NC沉积的冲击能量会极大地影响所得的Pt NC稳定性。对于较低的冲击能量，Pt NC由于ORR而迁移，并在支座上重新排列为特征组。这种先前看不见的效果是由整体内各个NC周围的通量分布不均引起的，对于理解NC和纳米颗粒阵列的稳定性和活性具有重要的意义。