Department of Chemistry, University of Utah , Salt Lake City, Utah 84112, United States.
College of Chemistry and Molecular Sciences, Wuhan University , Wuhan, 430072, China.
J Am Chem Soc. 2017 Nov 22;139(46):16923-16931. doi: 10.1021/jacs.7b09842. Epub 2017 Nov 9.
Recent high-bandwidth recordings of the oxidation and dissolution of 35 nm radius Ag nanoparticles at a Au microelectrode show that these nanoparticles undergo multiple collisions with the electrode, generating multiple electrochemical current peaks. In the time interval between observed current peaks, the nanoparticles diffuse in the solution near the electrolyte/electrode interface. Here, we demonstrate that simulations of random nanoparticle motion, coupled with electrochemical kinetic parameters, quantitatively reproduce the experimentally observed multicurrent peak behavior. Simulations of particle diffusion are based on the nanoparticle-mass-based thermal nanoparticle velocity and the Einstein diffusion relations, while the electron-transfer rate is informed by the literature exchange current density for the Ag/Ag redox system. Simulations indicate that tens to thousands of particle-electrode collisions, each lasting ∼6 ns or less (currently unobservable on accessible experimental time scales), contribute to each experimentally observed current peak. The simulation provides a means to estimate the instantaneous current density during a collision (∼500-1000 A/cm), from which we estimate a rate constant between ∼5 and 10 cm/s for the electron transfer between Ag nanoparticles and the Au electrode. This extracted rate constant is approximately equal to the thermal collisional velocity of the Ag nanoparticle (4.6 cm/s), the latter defining the theoretical upper limit of the electron-transfer rate constant. Our results suggest that only ∼1% of the surface atoms on the Ag nanoparticles are oxidized per instantaneous collision. The combined simulated and experimental results underscore the roles of Brownian motion and collision frequency in the interpretation of heterogeneous electron-transfer reactions involving nanoparticles.
最近在金微电极上对 35nm 半径的 Ag 纳米颗粒的氧化和溶解进行了高带宽记录，结果表明这些纳米颗粒与电极发生多次碰撞，产生多个电化学电流峰。在观察到的电流峰之间的时间间隔内，纳米颗粒在靠近电解质/电极界面的溶液中扩散。在这里，我们证明了随机纳米颗粒运动的模拟，结合电化学动力学参数，可以定量再现实验观察到的多电流峰行为。颗粒扩散的模拟基于纳米颗粒质量的热纳米颗粒速度和爱因斯坦扩散关系，而电子转移率则由 Ag/Ag 氧化还原体系的文献交换电流密度提供。模拟表明，每个实验观察到的电流峰都由数十到数千个颗粒-电极碰撞贡献，每个碰撞持续约 6ns 或更短（目前在可访问的实验时间尺度上不可观察）。模拟提供了一种估计碰撞过程中瞬时电流密度（约 500-1000A/cm）的方法，据此我们估计 Ag 纳米颗粒和 Au 电极之间的电子转移速率常数在 5 到 10cm/s 之间。该提取的速率常数约等于 Ag 纳米颗粒的热碰撞速度（4.6cm/s），后者定义了电子转移速率常数的理论上限。我们的结果表明，每个瞬时碰撞只有约 1%的 Ag 纳米颗粒表面原子被氧化。模拟和实验结果的综合表明，布朗运动和碰撞频率在解释涉及纳米颗粒的非均相电子转移反应中起着重要作用。
