Multifunctional Carbazole-Based Materials as Electrochemical Water Splitting and Photoredox Catalysis

Abstract

The combustion of fossil fuels releases carbon dioxide and other harmful greenhouse gases into our living atmosphere, which traps heating and causes global warming. Renewable energy, however, can help solve the problem above by producing far fewer greenhouse gases. Renewable energy is a general term for any form of naturally replenishable energy, such as sunlight, wind, waves, or heat of the earth. Converting sunlight or electricity into chemical bond energy has several advantages. One of these benefits is the ability to store clean energy for later use. Another merit is the ability to convert chemicals into more valuable products. This dissertation includes synthesis, characterization, usage, and explanation of catalysts or electrodes for water oxidation, and photoreaction. The second part of the thesis describes that the electrolysis of water to form hydrogen and oxygen is a promising method to store renewable energy. This method requires electrodes that convert water into protons, electrons, and oxygen. We report a multifunctional polymer that conducts electrons, ions, and may co-react with the metal ions in an oxygen evolution reaction (OER). The electrodes were prepared in two steps from off-the-shelf reagents. They operate with low loadings of abundant catalysts, and are among the most active (100 mA cm-2 at 1.43 V vs. RHE (1.41 V, iR corrected), and stable reported to date under harsh conditions (85 °C, 6 M KOH, 120 h (0.69 % loss over the first 14.5 h, then 0.61 % loss over 105.5 h). Control experiments on glassy carbon electrodes showed that the polycarbazole system significantly outperformed a Nafion system of the same catalyst loading. This simple strategy can be applied to other types of electrodes. The next part of the thesis reports the study of the first direct electropolymerization of a dicyanobenzene-carbazole dye functionalized with an imidazole group to prepare redox- and photoactive porous organic polymer (POP) films with a controlled amount. The POP films were grown on indium-doped tin oxide (ITO) and carbon surfaces using a new monomer, 1-imidazole-2,4,6-tri(carbazol-9-yl)-3,5-dicyanobenzene (3CzImIPN), through a simple one-step process. The structure and activities of the POP films were investigated as photoelectrodes for electrooxidations, as heterogeneous photocatalysts for photosynthetic olefin isomerizations, and their solid-state photoluminescence behavior tunable by lithium-ion concentrations in solution. The results demonstrate that the photoredox-POPs can be used as efficient photocatalysts and have potential applications in sensing.