Microbial electrolysis cell (MEC) system is a potential technology that could treat wastewater while simultaneously generating H2 (green energy). MEC's electroactive bacteria (EAB) are essential microbes responsible for oxidizing organic pollutants (such as acetate) in wastewater using an electrogenesis process. Since EABs comprise the core of MECs, they are essential for maintaining functional stability (Coulombic efficiency (CE), current density, and pollutant removal) of MECs. The cause of EAB becoming dominant at the anode of MECs fed with wastewater is still unclear. Furthermore, efficient EAB are typically not detected in wastewater, and when they are present their abundance is low, which affects their early colonization on the anode and subsequent growth into a mature biofilm. This study investigated bioaugmentation as a strategy to drive the assembly of functionally redundant anode EAB biofilms to improve MEC performance. Two bioaugmentation strategies (Conditions 2 and 3) with known EABs (G. sulfurreducens and D. acetexigens) were tested during the startup of MECs. Meanwhile, control MEC reactors (Condition 1) were operated with only wastewater as the sole source of inoculum to compare the anodic biofilm assembly and system performance with the bioaugmented reactors. Equal number of G. sulfurreducens and D. acetexigens cells were added to the wastewater-fed MEC (10% inoculum at 2.1E+07 live cells/mL). In Condition 3, anodic-biofilm colonized G. sulfurreducens and D. acetexigens was used as anode in wastewater fed MECs. Using single-chambered MEC reactors, the bioaugmented MECs (Condition 2 and 3) performed more efficiently than the non-bioaugmented (Condition 1) MECs. Current generation, CE and gas production were different between the three conditions tested (Condition 3 > Condition 2 > Condition 1). Analysis of 16S rRNA gene sequencing of anodic biofilm indicates revealed that the bacterial communities was not affected between the tested conditions. However, the relative abundance of EABs, mainly G. sulfurreducens and D. acetexigens, was markedly influenced by bioaugmentation compared to the control reactor. The highest peak current generation (~ 1500 mA/m2), CE (70.3 ± 9%), and gas production (0.04 m3/m3/day) was observed in Condition 3. Collectively, these results provide a framework for engineering the anode microbial communities in MECs for wastewater treatment.

The biodiesel industry produces millions of kilograms of low-value glycerol, which must be either stored or disposed of, creating environmental concerns. Even though glycerol is utilized as a raw material within various industries its supply is still superior to the demand. Upgrading this biodiesel by-product into value-added products using electrochemical technologies is a promising approach and will make biodiesel production more environmentally friendly with added financial benefits. Precious metals are the state-of-the-art electro-catalysts for the oxidation of organic compounds, and so are a logical choice for the electro-oxidation of glycerol. Two factors that hinder their use in this regard for commercial applications include their cost and susceptibility to poisoning by the carbonyl (CO) species formed during the electro-oxidation process. The use of inexpensive transition metals as the principal metals in a catalyst composite is thus appealing, leading to the selection of nickel (Ni). Furthermore, its high activity, anti-poison ability and long-term stability in alkaline solutions make it an attractive candidate for glycerol electrooxidation reaction (GEOR). The main thrust of this work is to develop a deeper understanding of the factors involved in controlling the selectivity of the product reaction without 3 carbon cleavage on non-precious metal surfaces. To overcome a trial-and-error approach, we took advantage of modern synthesis and characterization techniques for metal alloy nanoparticles and advances in rapid identifications and quantifications of products based on infrared spectroscopy. These tools were expected to provide the foundation for the detailed understanding of GEOR mechanism hence would pave the way for the rational design of catalysts to produce specific high value-added chemicals. We cared out extensive research to determine the effect of size, morphology, shape, support, experimental conditions and catalyst preparation methods on the catalytic performance of Ni. The thesis aims to demonstrate how the selectivity of unsupported Ni nanoparticles for GEOR can be improved via interaction of Ni with low noble and transition metals content. Enhanced selectivity towards C3 and C2 products such as glycerate, lactate, oxalate and tartronate, was achieved by simply adding less than 20 atomic percent of any of bismuth (Bi), Pd or Au onto Ni nanoparticles. Furthermore, the composition effect of carbon supported NiₓM₁₋ₓ (M = Bi, Pd and Au) nanomaterials were combined with Pt/C and commercial silver nanoparticles for cathodic hydrogen production and CO₂ electro-reduction, respectively. These rich-phase of Ni(OH)₂ catalysts were highly active and selective towards C-C bond breaking products leading to 100% selectivity of formate after 1 hr electrolysis and 100% conversion of glycerol after 24 hr at +1.55 V. Lastly, the first principles calculations based on the density functional theory (DFT) insights provided an explanation to understand the electronic structure, magnetism and reactivity of our catalysts. Core@shell (Mm@Nin) nanoparticles of 13-, 54- and 55-atoms with different elements concentrations matched the experimental results and assisted us with a better understanding of some of the microscopic phenomena involved with the reactivity of bimetallic nanoparticles.

Electricity-driven water splitting reaction achieved by electrochemical method to produce hydrogen and oxygen is utilized as an energy carrier in the form of highly pure hydrogen gas. However, the development of earth-abundant, durable, and highly effective electrocatlyst to overcome the high overpotentials of hydrogen, and oxygen evolution reaction (HER, OER) is extremely challenging. This dissertation presents firstly the catalytic properties of tungsten disulfide (WS2) as highly effective HER catalyst through direct growth of 2H-WS2 layered materials on a conductive substrate. Effect of various gaseous atmosphere and temperatures was studied and it was found that the amorphous structure of WS2 can be strongly affected under H2S environment which leads to the formation of bridging disulfide ligands S2 2- and apical S2- from WS3 phase, which is consequently contribute to the catalytic enhancement toward HER with extremely low overpotential (η10 = 184 mV). On the other hand, OER is the major bottleneck in water splitting reaction due to its poor kinetics originated from the complex four electrons transfer process. Chemical vapor deposition strategy is used here to enable stoichiometric tuning and phase engineering of CoP2 OER electrocatalyst followed by deposition of carbonaceous protection layer to overcome surface oxidation. Electrochemical studies indicate that C@CoP2/CC can achieve a remarkable activity (η10 = 234 mV), with minor decay from its initial current density after continuous operation of 80 hours. Lastly, electrolysis of alkaline water is the most common industrial method to produce H2; however, it is a formidable challenging to compete with Pt catalyst in base at industrial scale. For that, temperature-dependent phase evolution was studied in details and it is found that (Co(OH)2) precursor undergoes phase transition under a unique phosphidation system starting with partially phosphatized phase CoP-CoxOy, followed by phosphorus rich phase CoP2, and ultimately to pure CoP phase under elevated temperatures. Comprehensive analysis revealed that concerted composite CoP-CoxOy is the most active phase to produce H2 electrochemically from alkaline water which is contributed to the unique role of integrated phase and its ability to overcome the sluggish hydrogen kinetics in base.

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Linear Alpha Olefins (LAOs) are one of the most important commodities in the chemical industry, which are currently mainly produced via homogenous catalytic processes. Heterogeneous catalysts have always been desirable from an industrial viewpoint due to their advantages of low operation cost, ease of separation, and catalyst reusability. However, the development of highly active, selective, and stable heterogeneous catalysts for the production of LAOs has been a challenge throughout the last 60 years. In this dissertation, we designed and prepared a series of heterogeneous catalysts by incorporating structural moieties of homogenous benchmark catalysts into metal-organic-frameworks (MOFs), aiming to provide a feasible solution to this long-standing challenge. First, we reviewed the background and state of the art of this field and put forward the main objectives of our research. Then, we thoroughly discussed a novel heterogeneous catalyst (Ni-ZIF-8) that we developed for ethylene dimerization to produce 1-butene, focusing on its designed principle, detailed characterizations, catalytic performance evaluation, and reaction mechanisms. Ni-ZIF-8 exhibits an average ethylene turnover frequency greater than 1,000,000 h$^{-1}$ (1-butene selectivity >85%), far exceeding the activities of previously reported heterogeneous and many homogenous catalysts under similar conditions. Compared with homogenous nickel catalysts, Ni-ZIF-8 has significantly higher stability and showed constant activity during four hours of continuous reaction for at least two reaction cycles. The combination of isotopic labeling studies and Density Functional Theory calculations demonstrated that ethylene dimerization on Ni-ZIF-8 follows the Cossee-Arlman mechanism, and that the full exposure and square-planer coordination of the nickel sites account for the observed high activity. After that, we further optimized the Ni-ZIF-8 catalytic system from the perspective of practical applications. We achieved double productivity of 1-butene by optimizing the synthetic conditions and explored its usability and performances under solvent-free conditions. Then, we extended our catalyst design concept to prepare heterogeneous catalysts comprising other metals and MOFs, which provided a suitable platform for studying the effects of the metallic center and coordination environment on the catalytic production of LAOs. Finally, we gave our perspectives on the further development of heterogeneous catalysts for the production of LAOs.

Heavy metals are a growing environmental concern as they are unable to be metabolized in the environment, leading to bioaccumulation in the food chain and impacting human health. Treating heavy metals is difficult and expensive. Current methods include precipitation (which generates sludge that is costly to dispose of) or requires the use of a membrane, which fouls and requires regeneration. Microbial electrolysis cells (MECs) represent an alternative for treating heavy metal contaminated wastewater. Reactor components are cheap, and operation requires only a small amount of electricity. The electrically active biofilm oxidizes organics in the wastewater while transferring electrons first to the anode, then to the cathode, where aqueous metals are reduced to a solid deposit, a mechanism called electrodeposition. Few studies have been conducted to investigate the best operational conditions for heavy metal removal in MECs. In this study, the effects of hydrodynamics, applied voltage, and initial metal concentration on heavy metal removal mechanisms are investigated, and the best operational practices are determined on a high level. Mixing in the cathode chamber increased electrodeposition by 15%, decreased the cathode potential by -0.06 V, and increased current generation between 10-30%. Increasing the applied voltage from 0.6 V to 1.2 V increased electrodeposition by 22%. With both mixing and higher voltage applied, 93.35% of cadmium was removed from the catholyte in 24 hours. Although high voltage application maximized electrodeposition for short-term treatment, long-term treatment indicated lower applied voltage resulted in healthier MEC reactors, better overall metal recoveries, along with a more stable cathode potential. / Thesis / Master of Applied Science (MASc)

This thesis is missing page 89, no other copy of the thesis has this page. -Digitization Centre / The vanadium mediated electrolysis of hydrogen sulphide has been demonstrated in a bench top pilot plant. The first step in the process is the absorption of hydrogen sulphide from a sour gas stream into an carbonate buffered liquor, pH 9. In the presence of citrate ion, the vanadium (V) in the liquor is reduced to vanadium (IV) by (hydro) sulphide ion, which is oxidized to yellow elemental sulphur. The vanadium (IV) rich solution is then pumped to an electrolysis cell where the vanadium (IV) is reoxidized to vanadium (V) and protons are reduced to elemental hydrogen. The reoxidized liquor is then returned to the absorber. The oxidation of vanadium (IV) to vanadium (V) in the liquor was found to be electrochemically irreversible. The current efficiency for vanadium (IV) oxidation exceeded 90 percent. The voltametric half-wave potential at platinum, was 0.34 v (vs Ag/AgCl, sat. KC1). With the slippage of sulphide or polysulphide ion into the electrolysis cells, the electrodes became passivated with electrodeposited sulphur. This resulted in an increased anode potential demand which may promote the electrosynthesis of oxygen and sulphate ion. The oxidation of vanadium (IV) at the anode releases 4 protons and acidifies the solution adjacent the electrode surface. This may induce carbon dioxide evolution and inhibit the discharge of vanadium (IV). The inhibition appears as a suppressed current and an anodic shift in the voltametric half-wave potential. This inhibition can be minimized at high pH levels in the liquor, buffer capacity., and citrate concentration. The irreversibility of the vanadium (IV/V) couple allows electrolysis cells to be constructed without a cell membrane. This is a significant advantage which will offset the cost of large electrolysis cells. Large cells will enable high energy efficiencies to hydrogen production to be realized. Energy efficiencies greater than 0.28 m3 /kwhr may be indicated. This study features a critical review of sulphide electro-oxidation, a factorial designed voltametric experiment, and a newly identified catalytic response in the polarographic analysis of sulphide ion. / Thesis / Master of Science (MS)