(4ht) Catalyst Synthesis and Fundamental Investigation of Electrochemical Reactions

Overview. The commercial viability of electrochemical processes depends on the development of catalysts with improved activity, selectivity, and stability. My goal is to guide the design of more selective and active electrocatalysts by developing mechanistic frameworks of various electrochemical reactions. The group will be able to predict how changes at the interface (electrode-electrolyte) can modify the reaction kinetics and product distribution.

Motivation. Catalytic reactions usually conducted at elevated temperatures and pressures can be carried out under milder conditions through electron-proton driven pathways. The control of an electrochemical process can be achieved by varying the chemical potential of electrons. Electrochemical methods could play a central role in the mitigation of global energy and environmental challenges. This thrust will investigate processes with applications in sustainable energy conversion and storage, fuel and chemical production, and wastewater treatment. In addition, homogeneous radical promoters and electrochemical cycles will be assessed as a strategy to facilitate redox processes. The development of effective catalysts for many of these reactions will accelerate the application of electron-driven chemical transformations.

Proposed Research. Electrochemical reactions are highly attractive, in which cheap, clean, renewable electricity can be leveraged to synthesize valuable products. The state-of-the-art catalysts of alcohol oxidation and nitrate reduction are mostly platinum group materials such as Pt, Ir, Ru, Pd, etc. However, their high cost, low stability, low selectivity, poisoning tendency have discouraged their commercial utilization. Different methods, such as doping, alloys, carbides, metal oxides, etc., have been investigated as potential alternatives. Even though the significant development in various catalysts, their degradation and catalytic mechanism under electrochemical reactions is still under debate. To design more active, selective, and stable catalysts requires identifying active catalyst sites and understanding the degradation mechanism and electrocatalytic processes.

Catalyst evaluation and fundamental understanding of electrochemical reactions.

3. Formation of C-N bonds. In recent years, significant advances in the formation of carbon-nitrogen bonds by different groups. Particularly interesting is the demonstration of C-N bond formation during carbon monoxide electrolysis on the Cu electrode. Mechanistic studies have shown that acetate is formed through nucleophilic attack of OH^- on a ketene-like intermediate under alkaline conditions (Fig. 3a). A study from Jouny et al. shows that ketene intermediates readily react with nucleophilic agents such as ammonia to form C-N bonds. However, despite these promising results, the ongoing research on this exciting area remains relatively limited. Electrochemical synthesis of C-N bonds will be studied on various pure metals or alloys. We will explore the contribution of various nucleophilic agents such as hydrazine (N₂H₄), hydroxylamine (NH₂OH), methylamine (CH₃NH₂), etc., in co-electrolysis with CO₂ or CO. Using this approach, we will be able to produce chemicals beyond multicarbon species like amides, aldimine, etc (Fig. 3). Operando measurements and isotopic labeling studies will provide impactful information about the reaction mechanism of C-N bond formation. In addition, we will optimize the microenvironment near the catalyst surface by using ion-conducting ionomers. Ionomer coatings control the local pH (through Donnan exclusion) and the reactant to H₂O ratio. The tailored microenvironment could influence the concentration and adsorption of charged species, impacting C-N bonds formation.

3. NO_x reduction. Anthropogenic perturbations in the nitrogen cycle from fertilizer (use and production), animal waste, and underground septic systems have led to unsafe levels of nitrates (NO₃^– ) in-ground and wastewater, which cause blue-baby syndrome and is a carcinogen. The existing primary method for denitrification is biological, which relies on various enzymes within bacterial communities. However, biological denitrification cannot be used in wastewater where bacterial growth is not viable, nor in drinking water treatment, due to the risk of pathogenic bacteria. Therefore, electrochemical denitrification is a compelling alternative for mitigating nitrate contamination, whereby NO₃^– is electrochemically reduced to N₂ or NH₃. Current challenges in this process are catalyst activity, cost, and selectivity towards a target product.

The group will perform a systematic mechanistic study of NO₃R on transition metals to various products (Fig. 4). We will first determine trends in the reaction pathways across transition metals and then evaluate each catalyst's selectivity. Experimental studies suggest that good catalysts for the initial NO₃^– to NO₂^– reduction steps do not necessarily have optimal activity towards N₂ or NH₃. This challenge may be circumvented by tandem catalysts optimized for activity towards both of these processes, and screening efforts will first examine overlayer and alloy catalysts based on this principle. Many researchers have focused on elucidating nitrate's reaction mechanism (NO₃^-), nitrite (NO₂^-), and NO_x reduction on various electrocatalysts.However, the electrochemical reduction of NO₃^- to nitrogen, ammonia (NH₃), or even hydrazine (N₂H₄) has not been fully understood due to the lack of reliable analytical methods and the highly complex and numerous reactions involved in the process (Fig. 4). Understanding the mechanism by which the products are formed during NO_x reduction is essential for developing selective and active electrocatalysts. This knowledge is crucial to predict how changes in an electrochemical environment can modify the reaction kinetics and product formation. To identify the reaction mechanism, we will study the reduction of different postulated intermediates (e.g., NO, NO₂, N₂O, hydroxylamine (NH₂OH), ammonia (NH₃), and nitramide (NO₂NH₂)). A similar technique has been successfully performed to identify reaction intermediates during various electrochemical reactions such as CO₂ and CO reduction.

A tandem pathway towards ammonia production. Generally, nitrate and nitrite are more active species than nitrogen and can be reduced easily to hydroxylamine (NH₂OH), ammonia (NH₃), and hydrazine (N₂H₄). Currently, nitrate and nitrate are industrially produced from ammonia through the Ostwald process (energy-consuming process). A promising alternative is a production of these species from a non-thermal plasma process, which can activate atmospheric nitrogen and produce a solution containing NO₃^- and NO₂^-. Herein, my group will collaborate with plasma groups in order to develop a hybrid plasma-electrochemical process. The plasma group will optimize the production rate of nitrate/nitrite and process energy efficiency. We will determine the role of the catalyst on the product selectivity and rate. To date, a complete study that highlights the role of the catalyst in the electrochemical reduction of nitrate/nitrate-containing electrolytes has yet to be demonstrated. Also, we will investigate the effect of the concentration of nitrate and nitrite on the overall performance. These results will help us to understand how the ratio of nitrate/nitrite affects product selectivity. These results will have important implications for other electrosynthesis methods and highlight the advantages of electrolysis for reactions that feature reactive intermediates

Alcohol oxidation reaction. Alcohol oxidation reactions can be used to produce electricity using a galvanic cell (fuel cell with alcohol feeding instead of H₂) or useful high-value chemicals (electrolytic cell) (Fig. 4 shows the glycerol oxidation towards various high-value products). Both cases face their challenges. For example, the main requirement for a galvanic cell's anode catalyst is the complete alcohol oxidation to CO₂ (ideally E<0.5 V vs. SHE) and C-C bond cleavage. On the other hand, the electrolytic cell demands an anode that leads to the desired product minimizing the overall energy input and control electrochemical reactor residence time to avoid further oxidation of target products. As most of the alcohols oxidize at lower potentials than H₂O, the combination of selective alcohol oxidation and H₂ evolution at the cathode leads to the production of value-added chemicals on both sides of the cell. Alcohol oxidation will be studied in a customized electrochemical cell using synthesized or commercial catalysts. Their performance will also be evaluated for co-production in a paired electrolysis cell (flow reactor or MEA configuration).

The results from these proposed researches are expected to have implications beyond the development of novel materials and serve as a basis for understanding some critical electrochemical reactions with substantial environmental impact. Fundamental studies will also be conducted for the partial oxidation of low molecular weight alkanes or alkenes. Their oxidation to corresponding alcohols at low temperature and pressure is considered one of the grand challenges in catalysis and energy. Methane is a key target because it is the primary component of natural gas and potent greenhouse gas, but selective partial oxidation is a challenging part due to its low reactivity. Consequently, we will also be broadened to the electro-oxidation of ethane, propane, ethylene, etc.

Teaching Statement

I would consider teaching at a University level one of the most critical factors that lead to both students' academic success, both students and the professor themselves' academic success. I believe that it is our duty as educators to teach undergraduate/graduate students to enjoy learning of a specific subject and think out of the box. This approach often allows them to develop analytical thinking and reach their full potentials. Through teaching and mentoring, it is possible to expand our knowledge as professors from students’ questions and interests. In some ways, students help our thinking and make us reframe our understanding and teaching approach in a better and exciting way. Here, I outline the teaching experience and approach, as well as the mentoring process.

Teaching experience. I have had the opportunity to teach five undergraduate and two graduate courses in chemical engineering and physics departments throughout the years. The feedback/evaluation from students has always been very positive, and I have had an excellent collaboration with the primary instructor. Teaching undergraduate courses have offered me the unique opportunity to observe how young students see and understand science from a fundamental perspective. On the other hand, graduate courses have given me the chance to pass on the knowledge that I have gained in the field of Electrochemistry and teach them how to solve more real-life problems. Having served as the head teaching assistant for all the courses, I believe that I have the experience to teach chemical engineering courses at an undergraduate and graduate level.

Teaching approach. One of the primary responsibilities of an educator is to generate relatable lecture content and problem sets. My goal as an educator and advisor is to engage all students and foster their growth as a whole. To do so, my teaching approach would be: by encouraging students to explore their ideas; by asking for their feedback, which will be used to adapt course content; by designing group-oriented projects; by implementing a flipped classroom model, which emphasizes active engagement in the classroom. I have seen that all approaches significantly impact student understanding and lead to critical evaluation of academic strength and assessment. To ensure that students remain at a high level throughout the semester and evaluate their overall performance, I will also provide frequent quizzes and assignments relevant to what was taught in the prior 1 or 2 weeks.

Mentoring approach. As a research advisor, I will encourage students to explore their ideas and embrace uncertainty and risk as a part of the research and learning process. In the beginning, they will have well-defined projects, and as they progress, I will provide more open-ended and challenging problems that contain higher risk but offer higher rewards. Students will present their work and ideas in group meetings. This process will help them understand their work deeper, gain confidence in presentations, and plan future work. I will encourage them to attend webinars/seminars from different groups and scientific areas to improve their skills. I will use the process of group feedback as a means to hone the students’ writing skills. I believe that their labmates and I's initial feedback will improve their writing skills and make them better understand how to prepare a manuscript, highlight key points, and use concise language. I will actively encourage senior students or postdocs to participate in proposal writings. In my experience, this strategy is one of the most effective ways of improving proposed research, encouraging collaboration, and inspiring an “academic career”.

I would greatly appreciate the opportunity to teach at the department and interact with your students. I would particularly enjoy teaching core courses in Chemical Kinetics and Reaction Engineering, Chemical Engineering Thermodynamics, Physics, and Physical Chemistry. Additionally, I am interested in developing or adapting courses on special topics in the fields of Heterogeneous Catalysis and Electrochemistry. I look forward to contributing to lab courses that aim to incorporate the use of easily-programmable and adaptable microcontrollers for the acquisition and processing of data pertaining to key chemical engineering phenomena. Finally, I recognize the capacity of motivated undergraduates to provide non-biased perspectives, and the importance of fostering entry-level opportunities for the next generations of scientists and engineers. Thus, I would welcome undergraduate researchers to learn in and contribute to my research program.