Electrochemical and in situ optical characterization of single micrometer-size particles of spherical nickel oxide in alkaline aqueous electrolytes

A method is herein described for the micromanipulation and subsequent in situ, real-time optical and spectroscopic characterization of individual micrometer-size particles of electrochemically active materials under potential control. This novel approach relies on the use of a micropipette to capture, by suction, single particles, which are then attached to the surface of a glass-encased microelectrode placed inside an empty, shallow Petri dish, and held in position by a small glass rod in the form of truncated cone. This configuration allows for particles to be placed directly beneath the microscope objective enabling visual and spectroscopic monitoring during electrochemical measurements by simply filling the dish with sufficient electrolyte to completely cover the particle and make electrolytic contact with a reference and a counter electrode. Illustrations are provided for particles of spherical Ni hydroxide, S-Ni(OH)₂, in alkaline solutions, which following activation at fairly positive potentials, yielded an electrochemical response characteristic of Ni(OH)₂ in more conventional electrode configurations. The much darker appearance of NiOOH compared to the virtually translucent character of virgin S-Ni(OH)₂ allowed for the spatial and temporal evolution of charge flow within the microparticle to be monitored in real time during the first scan in the positive direction using computer-controlled video imaging.