| Description |
This dissertation focuses on the fundamental properties of nanoscale electrochemistry. It includes investigations on the relationship between size and electrocatalytic activity of single nanoparticles. Chapter 1 overviews the importance of single nanoparticle electrochemical measurements and provides a brief introduction to the resistive-pulse analysis of individual nanoparticles, the stochastic single nanoparticle collision amperometry method, and electrochemical scanning probe microscopy measurements of single nanoparticles. Chapter 2 describes a multipass resistive-pulse method that measures the rotational tumbling of individual nanorods during their translocations through a nanopipette. Multiple peaks in individual resistive-pulse current blockades are observed and can be related to an average rotation of approximately 90° of a nanorod along the rod's long axis. Through analytical expressions, the average time between the local maxima and minima in current can be used to compute the rotational diffusion coefficient and length of individual nanorods. Finite element simulation modeling results show good agreement with the experimental data. Chapter 3 reports measurements of electrocatalytic oxygen reduction at single Pt nanoparticles through their collisions with an inert Au microelectrode. A pressurized electrochemical cell is developed to elevate the dissolved O2 concentration and significantly enhance the signal-to-noise ratio, allowing measurement of the oxygen iv reduction activity at single Pt nanoparticles with radii down to 2-3 nm. Based on potential-activity analysis, the heterogeneous kinetics of oxygen reduction at single Pt nanoparticles is evaluated. An increase in the catalytic activity with decreasing nanoparticle size is observed. Chapter 4 describes a single-particle injection system with electronic feedback, and combines the resistive-pulse sensing method and the nanoparticle collision method together. A nanopipette is employed as a scanning probe in this experiment, which is able to deliver nanoparticles to selected areas of an electrochemical interface. The size of individual nanoparticle can be measured when a nanoparticle passes through the orifice of the nanopipette and generates a resistive pulse, while the electrocatalytic activity of individual nanoparticle can be simultaneously measured when a nanoparticle collides on the electrode surface and results in a redox transient current. This technique provides a means to measure the relationship between the size and catalytic activity of single nanoparticles. |
