(4gp) How Electrolyte Composition Influences Electrocatalytic Water Splitting Activity

My dissertation work has focused on studying how the composition of aqueous electrolytes affects electrocatalytic water splitting mechanisms over transition metal catalysts. Next, I am interested in expanding my electrochemistry skills to studying electrochemical materials performance in non-aqueous and solid-state systems. I am excited to apply the existing knowledge from research in electrolyte composition for aqueous systems to understanding non-aqueous and solid-state electrochemical materials. Then, insights from non-aqueous and solid-state systems can be used to further hone our understanding of aqueous systems. I believe the broader chemical toolbox that organic chemistry offers compared to aqueous media can give great fundamental insights on how the electrochemical environment can be leveraged to understand and improve sustainable electrochemical technologies.

Another research interest that I have is developing in-situ spectroscopic techniques for studying electrochemical interfaces to connect macroscopic material performance measurements with atomic scale theoretical models. Traditionally, research in catalysis combines macroscopic activity and selectivity measurements with atomic scale theoretical models to form conclusions on reaction mechanisms and activity descriptors. However, these models fail to capture how catalyst structure evolves with time under intermittent and even steady-state reaction conditions. What is needed is a suite of experimental methods to quickly probe transient catalyst structure at mesoscopic length scales still representative of macroscopic reaction conditions. I believe spectroscopy offers a nice solution because it leverages the transient interaction between light and matter to quickly study electrified materials in real time.

Throughout graduate school, I had several opportunities to collaborate with other graduate students to study electrochemical interfaces using spectroscopic techniques. I experimentally probed the electric field felt by surface adsorbates using Infrared Vibrational Stark Spectroscopy to understand the role of organic tetra-n-alkylammonium cations on electrochemical CO₂ reduction in aprotic solvents. In addition, I used Raman Spectroscopy to understand the role of transition metal ion incorporation from potassium hydroxide electrolytes into nickel oxides for electrocatalytic and charge storage applications. I enjoyed these collaborations and want to further develop these spectroscopic techniques and electrochemical cell designs to probe catalyst and reaction intermediate structure.

Teaching Interests

As a principal investigator and as a teacher, the greatest accomplishment that I could achieve over the course of my career is equipping my students with the skills they need to attain their professional goals and grow as humans. I would not have experienced the academic success that I have so far had it not been for the positive impact of my past instructors and mentors. Therefore, I view my role as an instructor and mentor as an opportunity to return a favor. The foundation of my classroom and research group will be the beginner’s mindset – the belief that what we must learn far exceeds what we know. I will guide my students towards adopting this mentality through accomplishing the following two goals: First, I will create an equitable space by tailoring each student’s experience to their learning needs. Second, I want to push each other out of our comfort zones to be collaborative critical thinkers. We will recognize the outer limits of our knowledge and know how to strike the perfect balance between when to solve problems on our own and when to engage with others for assistance. Ultimately, I will train my students to be self-directed learners who are aware of their strengths and weaknesses. They will leverage their strengths to help less experienced colleagues but more importantly will be eager for opportunities to develop new skills.

My experience mentoring my undergraduate research assistants has helped me articulate these five skills I want each student to achieve by the time they complete their graduate studies: (1) Students can identify open and compelling research questions that the field needs; (2) Can design experiments to test those questions; (3) Can collect high fidelity and reliable data; (4) Can interpret that data in a meaningful way; (5) Can eloquently communicate it to draw attention to draw attention to new open and compelling research questions. As their research advisor, I am committed to placing my students’ professional aspirations at the forefront of their learning experience and ensuring that they are the ones in the driver’s seat. For the advisor to student relationship, I view my role as empowering my students to ask me for advice and feedback on their scientific careers. To effectively manage my entire research group, I want to use a participative leadership style giving advice and feedback to my students who will be the ones who ultimately determine my lab’s daily operations. However, I believe it is still important for me to be viewed as the lab’s leader which I will accomplish by following up with my students on their research plans that they crafted. Finally, I understand that coming into my laboratory each student will be better at certain skills than others, so I plan to cultivate a collaborative culture of forming my students into teams based on complementary skills but using the beginner’s mindset and influence them into being excited to teach those with less experience in one area and more importantly excited to learn from those with more experience in other areas.

Doctoral research on the role of electrolyte composition on water splitting reactions

My doctoral research uses changes in supporting electrolyte composition as a handle to fundamentally understand electrocatalytic water splitting reaction mechanisms. Using alkali metal cations or changes in pH, we are interested in understanding how they mediate the electric field in the electrochemical double layer felt by surface adsorbates. This body of work seeks to: (1) understand the role of alkali metal cations on the hydrogen evolution reaction (HER) in acidic and alkaline solutions; (2) develop criteria for when the oxygen reduction reaction (ORR) rates will be influenced by alkali metal cation size; (3) understand the origin for superior ORR rates in alkaline over acidic electrolytes; and (4) generalize the criteria for predicting alkali metal cation effects for the oxidation of small alcohol molecules.

Key contributions from my doctoral dissertation in both peer-reviewed publications and in practice include the following. (1) Alkali metal cations stabilize the products and transition state of water dissociation, an elementary step that is particular to the hydrogen evolution reaction mechanism in alkaline electrolytes. This is beneficial for noble metal catalysts (Cu, Ag, Au) whose rates are limited by this step but detrimental for reactive metal catalysts (Ir, Pd, Pt) whose rates are limited by the removal of the products of water dissociation. The role of cation size is its energetics to approach the electrode surface with large cations having the greatest effect with slowing rates over reactive metals and accelerating rates over noble metals. In practice, this research can help make green hydrogen production more economically viable by providing electrolyte design guidelines for enhancing HER rates over a particular metal catalyst depending on its rate-determining step.

(2) Compared to the HER, the ORR occurs at significantly more positive electrical potentials and cation effects are less general. We learned that the potential window where the ORR occurs relative to the metal catalyst’s potential of zero total charge (PZTC) can predict if rates will be influenced by electrolyte composition. For metals whose PZTC is positive of their ORR operating potential (Pt, Ir, Ru, Au) the surface is negatively charged during catalysis allowing cations to accumulate in the double layer and influence the stability of ORR reaction intermediates. For these metals, ORR rates increase with cation size. For metals whose PZTC is negative of their ORR potential window (Ag and Pd), cations are electrostatically repelled from the surface resulting in measured ORR rates being insensitive to electrolyte composition. (3) Increasing electrolyte pH by switching from acidic to alkaline electrolytes electrostatically stabilizes gaseous oxygen adsorption to the metal surface. This speeds up the ORR reaction over metal catalysts whose rates are limited by this elementary step (Ag and Au). In practice, this research can shed light to opportunities to when electrolyte composition will be able to enhance ORR rates for hydrogen fuel cell metal catalysts depending on the potential where the reaction occurs relative to its PZTC using alkali metal cations or if ORR rates are limited by the necessary elementary steps to enhance rates using electrolyte pH.

(4) Finally, we generalized the understanding gained from the criteria to predict cation effects for the ORR to the electrochemical oxidation of methanol, glycerol, and ethylene glycol. We learned that these reactions will also be influenced by alkali metal cation size if they occur negative of the metal catalyst’s PZTC. In practice, these findings can enhance hydrogen evolution reaction rates by providing an oxidant (a small alcohol) that can oxidize more easily than water to circumvent the high overpotential needed for the oxygen evolution reaction. Ultimately, the findings from my dissertation are fundamental explanations on the role electrolyte composition plays for important green heterogeneous electrocatalytic reactions and shed light on opportunities to upgrade metal electrocatalysts to enable green hydrogen technology to be more economically viable.