Doctor of Philosophy (PhD), Ohio University, 2020, Chemical Engineering (Engineering and Technology)

Growing renewable energy technologies is not only essential to reduce carbon emissions and mitigate climate change, but also critical to boost global energy security and support a sustainable basis for economic development. Prioritizing new technologies that promote the transition from fossil fuels to renewable energy technologies is critical to address future global energy demands and prevent global warming. Lignin is a major renewable and non-fossil source of aromatic compounds that can be used to generate sustainable fuels, fine chemicals, additives, and resins. The application of lignin, however, as a source of aromatic compounds has been largely undeveloped due to the lack of an efficient depolymerization process. Among various methods that have been developed so far for lignin depolymerization, electrochemical conversion is a promising approach for industrial application because it occurs at room temperature and ambient pressure. Nickel-based and lead dioxide-based materials are among the most common electrocatalysts for lignin oxidation, as both are inexpensive and stable in highly alkaline electrolytes, and possess high catalytic activities for lignin oxidation. In this Ph.D. project, several nickel-based alloys were developed through co-electrodeposition of nickel and cobalt; and nickel and tin, to enhance the properties of the nickel catalysts for lignin depolymerization. Incorporation of cobalt to nickel reduces the onset potential for lignin oxidation due to the enhanced properties resulting from doping cobalt to nickel. Electrochemical oxidation of lignin on nickel-cobalt alloys with a higher cobalt content leads to lower energy requirements for lignin depolymerization and higher rates of formation of the functionalized aromatic compounds. Nickel-tin alloys provide higher surface areas and better stabilities for long term lignin oxidation. Lignin depolymerization is the dominant reaction at the low cell voltages when the oxygen evolution faradaic effici (open full item for complete abstract)

Committee: John Staser (Advisor); Rebecca Barlag (Committee Member); Sarah Davis (Committee Member); Kevin Crist (Committee Member); Marc Singer (Committee Member) Subjects: Chemical Engineering

Master of Science (MS), Ohio University, 2019, Chemical Engineering (Engineering and Technology)

The aim of this study is to first develop a non-precious metal oxide electrocatalyst for selective electrochemical oxidation of lignin. Next, the metal oxide electrocatalyst along with a modified metal electrocatalyst, previously developed in our research group are studied for the lignin electrolysis process in an anion exchange membrane (AEM) electrolysis cell. To that aim, four β-PbO2/MWNTs nanocomposites were developed via a wet-chemistry procedure and studied in a three electrode cell configuration. Product stream analysis was conducted by gas chromatography-mass spectroscopy (GS-MS). In addition, cyclic voltammetry (CV), linear sweep voltammetry (LSV) and potentiostatic measurements were carried out to evaluate electrocatalyst performance. The 33.3 wt% β-PbO2 nanocomposite possessed the highest electro-catalytic activity and stability for oxidation of lignin. Also, GC-MS results revealed that the β-PbO2/MWNTs nanocomposite is likely a selective electrocatalyst for conversion of lignin into low molecular weight aromatic (LMWA) compounds. The 33.3 wt% β-PbO2 nanocomposite and a modified bimetallic Ni-Co supported on TiO2 were used as the anodic catalyst in an AEM system to quantify H2 production and energy consumption rates of this system and compare them with recent efforts for water and lignin electrolysis in the literature. From the results, it was demonstrated that the β-PbO2/MWNTs nanocomposite is a stable and active electrocatalyst that can fasten the anodic lignin oxidation rate and therefore increase the cathodic reaction rate which is H2 evolution. At the end, our results showed that using β-PbO2/MWNTs as the anodic catalyst can lead to high hydrogen evolution rates (~45.6 mL/h) and increase energy efficiency by 20%, compared to a well-established and commercial alkaline water electrolyzer.

Committee: John A. Staser (Advisor); Kevin Crist (Committee Member); Marc Singer (Committee Member); Marcia Kieliszewski (Committee Member) Subjects: Chemical Engineering; Chemistry

Doctor of Philosophy (PhD), Ohio University, 2020, Chemical Engineering (Engineering and Technology)

Lignin is one of the main byproducts of pulp and paper industry and biorefineries. Depolymerization of lignin can lead to producing valuable low molecular weight compounds with different functional groups, which are mainly achieved from crude oil sources. Lignin electrolysis could address issues of other lignin depolymerization methods such as complexity, lignin combustion, and low selectivity. On the other hand, lignin electrolysis can occur at significantly lower overpotentials than those required for water electrolysis, which leads to lower-voltage electrolyzer operation and as a result lower energy consumption for hydrogen production. This study includes research and experimental works on developing a continuous electrochemical process for both lignin electrolysis and hydrogen production in an electrolyzer. At the first step of this project, high surface area TiO2 or carbon-supported NiCo electrocatalysts were synthesized and applied for lignin depolymerization at room temperature and pressure. The electrocatalysts were characterized by Brunauer-Emmett-Teller (BET), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS) techniques. In addition, a three-electrode rotating disc electrode (RDE) system was used to test the performance and durability of 6 electrocatalysts individually and among them 1:3NiCo/TiO2 was selected as the most effective catalyst for lignin depolymerization. In the second step, a continuous electrochemical cell with 10 cm2 electrodes, separated by an anion exchange membrane (AEM), was applied for lignin electrolysis in the anode and hydrogen generation in the cathode. The effects of temperature, lignin concentration, cell voltage, and electrolysis time on hydrogen production, oxygen evolution, lignin conversion, products with different functional groups, and energy efficiency of the electrochemical reactor were investigated. Although applying high cell voltages increases the rate of electr (open full item for complete abstract)

Committee: John Staser (Advisor) Subjects: Chemical Engineering; Chemistry; Engineering; Environmental Engineering; Wood Sciences

Master of Science (MS), Ohio University, 2019, Chemical Engineering (Engineering and Technology)

The aim of this study is to first develop a non-precious metal oxide electrocatalyst for selective electrochemical oxidation of lignin. Next, the metal oxide electrocatalyst along with a modified metal electrocatalyst, previously developed in our research group are studied for the lignin electrolysis process in an anion exchange membrane (AEM) electrolysis cell. To that aim, four β-PbO2/MWNTs nanocomposites were developed via a wet-chemistry procedure and studied in a three electrode cell configuration. Product stream analysis was conducted by gas chromatography-mass spectroscopy (GS-MS). In addition, cyclic voltammetry (CV), linear sweep voltammetry (LSV) and potentiostatic measurements were carried out to evaluate electrocatalyst performance. The 33.3 wt% β-PbO2 nanocomposite possessed the highest electro-catalytic activity and stability for oxidation of lignin. Also, GC-MS results revealed that the β-PbO2/MWNTs nanocomposite is likely a selective electrocatalyst for conversion of lignin into low molecular weight aromatic (LMWA) compounds. The 33.3 wt% β-PbO2 nanocomposite and a modified bimetallic Ni-Co supported on TiO2 were used as the anodic catalyst in an AEM system to quantify H2 production and energy consumption rates of this system and compare them with recent efforts for water and lignin electrolysis in the literature. From the results, it was demonstrated that the β-PbO2/MWNTs nanocomposite is a stable and active electrocatalyst that can fasten the anodic lignin oxidation rate and therefore increase the cathodic reaction rate which is H2 evolution. At the end, our results showed that using β-PbO2/MWNTs as the anodic catalyst can lead to high hydrogen evolution rates (~45.6 mL/h) and increase energy efficiency by 20%, compared to a well-established and commercial alkaline water electrolyzer.

Committee: John A. Staser (Advisor); Kevin Crist (Committee Member); Marc Singer (Committee Member); Marcia Kieliszewski (Committee Member) Subjects: Chemical Engineering; Chemistry