The development and characterization of a nickel/metal hydride microbattery for microfluidic applications
Microfabrication , Microbattery , Battery on Glass , Physical Vapor Deposition , Nickel Metal Hydride , Micro Power Supply , Microfluidics , Thin Film Electrode
Micro Electro Mechanical Systems as well as Microfluidics are versatile technologies which have been evolved due to the advantage of miniaturization over the last decades. However, the majority of microfluidic devices are still powered by macroscale power supplies. Here, interconnection problems, unwanted electronic interactions (noise), and difficulties in controlling the power delivered are some of the problems which can arise. One possible approach to ease such difficulties is through the use of integrated (embedded) power sources. This thesis is focused on the development and characterization of a nickel/metal hydride microbattery on a glass substrate which can be easily integrated during the regular microfabrication process of the microfluidic device. Glass or glass-like materials, such as silicon dioxide, are often used as substrates for microfluidic chips. Hence, we pursue a two-dimensional approach in that we fabricate thin films of electroactive materials on glass wafers using microfabrication techniques which are common in semiconductor (electronics) industries. A tailored polymeric layer is placed between the two electrodes to serve as an electrolyte reservoir and electrode separator in a sandwich-like structure which mimics a typical microfluidic chip design. The microfabricated electrodes are investigated in terms of material characterization and electrochemical performance. In detail, we use x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscope/energy dispersive spectroscopy, and profilometry to study the materials properties as well as the surface morphologies. Furthermore, cyclic voltammetry, charge-discharge characterization, and electrochemical impedance spectroscopy are performed to gain insights into the electrochemical performance of the single nickel electrode and of the single metal hydride electrode. This is also accompanied by a mathematical derivation and evaluation of electrolytic and gas sorption models of the metal hydride electrode. Finally, the performance of the microbattery is investigated using charge-discharge, voltage-current, and electrochemical impedance spectroscopy measurements.