The characterization of electrocatalytic reactions at individual nanoparticles (NPs) is presently of considerable interest but very challenging. Herein, we demonstrate how simple-to-fabricate nanopipette probes with diameters of approximately 30 nm can be deployed in a scanning ion conductance microscopy (SICM) platform to simultaneously visualize electrochemical reactivity and topography with high spatial resolution at electrochemical interfaces. By employing a self-referencing hopping mode protocol, whereby the probe is brought from bulk solution to the near-surface at each pixel, and with potential-time control applied at the substrate, current measurements at the nanopipette can be made with high precision and resolution (30 nm resolution, 2600 pixels μm^–2, <0.3 s pixel⁻¹) to reveal a wealth of information on the substrate physicochemical properties. This methodology has been applied to image the electrocatalytic oxidation of borohydride at ensembles of AuNPs on a carbon fiber support in alkaline media, whereby the depletion of hydroxide ions and release of water during the reaction results in a detectable change in the ionic composition around the NPs. Through the use of finite element method simulations, these observations are validated and analyzed to reveal important information on heterogeneities in ion flux between the top of a NP and the gap at the NP-support contact, diffusional overlap and competition for reactant between neighboring NPs, and differences in NP activity. These studies highlight key issues that influence the behavior of NP assemblies at the single NP level and provide a platform for the use of SICM as an important tool for electrocatalysis studies.

中文翻译：

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同时在电催化纳米颗粒周围及其周围的形貌和反应通量图

目前，对单个纳米颗粒（NPs）上的电催化反应进行表征非常令人感兴趣，但具有很大的挑战性。在本文中，我们演示了如何在直径约30 nm的纳米吸管探针上进行简单的制造，以将其部署在扫描离子电导显微镜（SICM）平台上，同时在电化学界面上以高空间分辨率可视化电化学反应性和形貌。通过采用自参考跳跃模式协议，从而将探针从大体积溶液中带到每个像素的近表面，并通过在基板上施加电势时间控制，可以在纳米移液器上进行高精度的电流测量。分辨率（30 nm分辨率，2600像素μm ^–2，<0.3 s像素^-1）以揭示有关底物理化性质的大量信息。该方法已应用于在碱性介质中碳纤维载体上AuNPs团簇上硼氢化物的电催化氧化成像，从而反应过程中氢氧根离子的消耗和水的释放导致NPs周围离子组成的可检测变化。通过使用有限元方法模拟，对这些观察结果进行了验证和分析，以揭示关于NP顶部与NP-支撑接触间隙之间的离子通量异质性，扩散重叠以及相邻NP之间反应物竞争的重要信息，和NP活性的差异。