Ph.D Thesis


Ph.D StudentFarber Eliyahu
SubjectPore Design in Carbon Materials: Towards Tunability and
Connectivity
DepartmentDepartment of Energy
Supervisor DR. David Eisenberg
Full Thesis textFull thesis text - English Version


Abstract

Electrochemical devices play a crucial role in the transition to a world of cleaner energy. Electrochemical devices operate using electrodes, and in many cases these electrodes are made out of porous carbons. Carbons are especially useful electrode materials, as they combine many desired properties: conductivity, high surface area, lighter than metals, low cost, and most importantly- porosity. The more porous the carbon, the more surface area is exposed, the more the active sites are available, the more electric current can be drawn from the electrode, and the more power generated from the device. However, porosity is hard to control, and is generated through serendipitous processes. Increasing our ability to direct and guide the evolving porous structure is critical for improving electrochemical devices.

In my work, I expanded the tool-box of the self-templating method, as part of the effort to make pores more tunable. I did this by preparing porous carbons from metal organic coordination polymers (MOCPs) using different alkali earth metals, and investigating how they direct the formation of different porous structures. I utilized electron microscopy, nitrogen porosimetry, surface spectroscopy and more to investigate the materials. I observed that different templating inorganic phases form from the different metals, each with their own shape, dimensions and internal structure. These differences in the templates are then transferred to differences in the porous structures. I investigated the underlying processes directing the porosity, and tested how they affect the electrocatalytic behavior towards the oxygen reduction reaction.

The research was furthered by an in-depth investigation into how inorganic phases develop throughout the pyrolysis process. A barium-based MOCP was prepared in various temperatures, and different barium-phases were formed, thus changing the porous structure. I probed these changes using the investigative tools at my disposal, and measured how the differences affected the electrocatalytic hydrazine oxidation reaction

I further combined the self-templating method with “active site imprinting” in order to prepare a novel carbon which has all 3 of the following characteristics: scalable, hierarchically porous, and supporting atomically dispersed catalysts. This is a much sought after combination which may open the way to many investigations into atomically dispersed catalysts.

Finally, I developed a system for fine-tuning macro-templates, and used it to investigate macro-porosity. Using this system, I discovered that the pore connectivity behaves in a sigmoidal-like fashion when described as a function of the porosity, a discovery which has deep implications on any process that uses hard-templating to generate porosity.