PhD Oral Exam - Maniya Aghasibeig, Mechanical Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Alkaline water electrolysis is one of the most promising methods for producing high purity hydrogen to be used as a clean and renewable energy carrier. However, due to the high costs of the electrolysers in addition to high energy consumption of the electrolysis process, this method is still not used for large scale hydrogen production in industrial applications. The costs associated with the materials and energy loss of this technology can be reduced by decreasing the hydrogen evolution overpotentials by using durable and inexpensive electrocatalysts with high intrinsic activities and large active surface areas.
The main objective of this work is to manufacture cathode electrodes for the hydrogen evolution reaction (HER) with modified surface structures and large effective areas, using different thermal spray techniques. For this purpose, new methodologies for manufacturing the electrodes are introduced while the surface morphology of the electrodes is designed and engineered by the coating processes. Nickel is used as electrode material as it shows high electrocatalytic activity, has high stability in alkaline solutions and is relatively inexpensive compared to noble metals with the best activities. Suspension plasma spray (SPS), high velocity oxy-fuel (HVOF) and cold spray are introduced as novel methods for producing nickel electrodes for the HER. A combination of atmospheric and suspension plasma spray, with optimized parameters toward enhancement of the electrode surface area, is effectively used for development of multiscale electrode surface structures with micron and nanosized features. In addition, the surface texture of the electrodes is engineered by deposition of three-dimensional fin arrays by employing mesh screens when either the combined atmospheric and suspension plasma spray or HVOF processes were used. For these electrodes the surface area was mainly enhanced by deposition of the particles at normal and off-normal angles. The produced hierarchical multiscale electrode structures enhanced the electrocatalytic activity for the HER by increasing the accessibility of the electrode surface to the electrolyte besides facilitating the hydrogen bubble detachment. Finally, cold spray was used to manufacture the electrodes with large activities by peening of the electrode surface by the solid-state nickel particles during the deposition process. The activity of the electrodes was enhanced by increasing the surface defects and changing the electronic structure of the electrodes induced by the peening effect.