(4pa) Circularizing Chemical Commodity Production through Fundamental Electrochemical Investigations

Developing carbon negative forms of commodity chemical production is crucial to addressing the anthropogenic threat of global warming. However, mitigating the effects of “sticky” forms of carbon emissions—such as the industrial-scale production of commodity chemicals—remains unresolved. Conventional commodity chemical production relies upon linear economies; converting high-value chemical commodities into low-value wastes that are distributed throughout the environment (e.g. ammonia into nitrate, fuel into carbon dioxide, etc.). In contrast, my group aims to identify circular forms of commodity chemical production, upgrading distributed waste products back into value-added chemical commodity feedstocks (e.g. nitrate to ammonia and amination products, nitrogen to nitrate, etc.). Through fundamental scientific investigations, we will provide mechanistic insights by developing periodic trends in reaction kinetics and selectivity while probing the spatially finite electrode-electrolyte interface to address questions surrounding active site formation and electrochemical double layer energetics.

1.1 Periodic Trends in Double Layer Capacitance: Expanding Conventional Gouy-Chapman-Stern

Heterogeneous (photo)electrocatalysis provides a carbon-free (when coupled with renewable electrons) alternative to conventional fossil-based commodity chemical production, where large electric fields (~10⁸-10⁹ V/m) are generated within a narrow electrochemical double layer (EDL). Understanding fundamental physicochemical structure-property relations underpinning the formation of the EDL are then crucial to accurate assessment of (photo)electrocatalyst surface area and development of increasingly efficient catalyst architectures. Challenging understanding, however, are the finite spatial dimensions of the EDL—typically defined as three Debye lengths (<30 nm)—where electric fields, and therefore catalysis, are determined by the composition and structure of both the solid electrode and aqueous electrolyte. My research group would utilize a suite of electrochemical and spectroscopic techniques and analyses to: (I) further existing models of the EDL by identifying periodic trends in solid electrode capacitances; and (II) provide the electrochemistry community with a robust method for reporting electrochemically active surface area (ECSA) by developing semi-empirical models for the double layer capacitance accounting for electrode and electrolyte composition and applied potential.

1.2 Unlocking the Potential of Electrocatalytic Nitrate Reduction: Deriving Value from Mechanistic Understanding of Complex Reaction Environments

The electrochemical conversion of waste nitrate to value-added chemical commodities (e.g. ammonia) has recently attracted attention as a cyclic and renewable means to displace conventional carbon-intensive processes (e.g. Haber-Bosch). While ammonia Faradaic efficiencies from nitrate reduction approaching 100% have been demonstrated, these have only been achieved in pristine electrolytes containing intentionally-dosed ions and nitrate salts. Limiting industrial application, however, is an understanding of the role that complex electrolytes (containing e.g. hardness and dissolved organic matter) typical of nitrate rich waste sources plays on nitrate reduction activity and ammonium selectivity. Here, I propose to systematically investigate the role of these complex electrolytes to derive fundamental understanding of the limitations and possibilities of this process by: (I) targeting each constituent component of typical wastewater to understand implications on nitrate reduction activity and ammonium Faradaic efficiency, anticipating the reactivity of organic functionality is expected to influence nitrate reduction selectivity; and (II) investigating the role of 3d transition metal electronic structure on the synchronous reduction of nitrate and a model organic contaminant, positing catalyst electronic structure dictates selective amination of either the aldehyde or 2-ene site of crotonaldehyde.

1.3 Developing a Roadmap Towards Nitrogen Oxidation to Nitrate: Fundamental Insight Through Periodic Investigations

Nitric acid (HNO₃) is conventionally produced by oxidation of ammonia (NH₃), the latter synthesized by Haber-Bosch reduction of gaseous dinitrogen—societies most carbon-intensive commodity chemical production process. Contrasting this circuitous and inefficient route, direct (photo)electrochemical oxidation of dinitrogen into nitric oxide represents a promising carbon-free alternative. Initial theoretical screening studies of rate-limiting nitrogen oxidation intermediate adsorption and activation energies suggest promising catalysts, though robust and consistent empirical approaches to assessing performance are missing. Though conceptually attractive, challenges in mass transfer for poorly-soluble dinitrogen and ambient nitrogen oxide and ammonia contamination have hounded the analogous field of nitrogen reduction to ammonia since its inception. I seek to actively address these challenging questions in a systematic and robust manner, proposing to: (I) develop robust electrochemical nitrogen oxidation techniques and nitrate detection reporting procedures, based on empirically identifiable sources and levels of ambient nitrate and minimum; and (II) testing group V, VI, and VII transition metal oxides, positing they demonstrate appreciable N₂OR selectivity, increasing with row number (i.e. from 3d to 5d).

Teaching Statement

Each student brings to bear a diverse set of perspectives that shape their physical understanding of the world. Effective educators must then seek to meet students where they are at an individual level, even, contrarily, in the increasingly common >100 student lecture halls. Evidence-based teaching practices provide tools for providing both conventional didactic lectures as a high-throughput form of passive knowledge transfer and addressing the need for students to actively engage with course material through lecture based conceptual question-answer activities, small-group cooperative learning, and projects aimed at addressing open-ended questions facilitated by guided questioning. While conventional Chemical Engineering curriculum provides students with necessary technical skills, missing are opportunities for honing communication skills. I would therefore like to incorporate more opportunities for students to receive, and act upon, communication feedback received at an individual level through their coursework; analogous to the tutelage received during a functional research group meeting.

As a first-generation undergraduate—and later graduate—student, I am intimately familiar with the importance of opportunities in determining career trajectories; how a chance few interactions have afforded me with an otherwise unimaginable life. As a mentor, I seek to provide students with similarly transformative experiences. Throughout my academic career, I have employed pedagogical strategies to mentoring undergraduate and graduate students in the research lab, demonstrating successful mentorship of undergraduate students to understand and communicate their science with award winning results (see Students Mentored in CV). I have treated the research lab as the ultimate extension of inquiry-based learning outside of the classroom. Here, through guided inquiry approaches, I encourage students to interpret their data at a fundamental physical level, helping to develop the same sense of “chemical intuition” that has served me through my own academic journey.

I am comfortable teaching any course from a conventional Chemical Engineering curriculum, though my research experience has given me considerable insight into reaction engineering, thermodynamics, mass and momentum transport, and mass and energy balance courses. I am also interested in developing graduate and undergraduate courses specific to renewable and cyclic energy technologies, (photo)electrochemical methods, reactions, and surface science techniques used to study heterogeneous interfaces.

Select Publications

. O.Q. Carvalho, Z.G. Schichtl, L. Wilder, J. Tan. S. Saund, M. Gish, M. Burke, A. Nielander, and A.L. Greenaway Chemistry of Materials Underpinning Photoelectrochemical Solar Fuel Production. Under Review, 2024.

6. O.Q. Carvalho, H.K.K. Nguyen, S.K.M. Padavala, L. árnadóttir, and K.A. Stoerzinger. Interaction of Nitric Oxide with Late 3d Transition Metals: Dissociation and Metal Oxidation. Under Review, 2024.
7. O.Q. Carvalho, S.R.S. Jones, A.E. Berninghaus, R.F. Hilliard, T.S. Radniecki, and K.A. Stoerzinger. Role of oxide support in electrocatalytic nitrate reduction on Cu. Electrochemical Science Advances 2022, e2100201.
8. O.Q. Carvalho, R. Marks, H.K.K. Nguyen, M.E. Vitale-Sullivan, S.C. Martinez, L. árnadóttir, and K.A. Stoerzinger. Role of electronic structure on nitrate reduction to ammonium: a periodic journey. Journal of the American Chemical Society 2022, 144(32), 14809-14818.
9. O.Q. Carvalho, Ethan J. Crumlin, and K.A. Stoerzinger. X-ray and electron spectroscopy of (photo)electrocatalysts: Understanding activity through electronic structure and adsorbate coverage. Journal of Vacuum Science & Technology A 2021, 39, 040802.
10. O.Q. Carvalho, P. Adiga, L. Wang, J. Liu, E. Jia, Y. Du, S. Nemšák, and K.A. Stoerzinger. Probing adsorbates on La_1‑xSr_xNiO_3-δ surfaces under humid conditions: implications for the oxygen evolution reaction. Journal of Physics D: Applied Physics 2021, 54, 274003.
11. O.Q. Carvalho, P. Adiga, S.K. Murthy, J.L. Fulton, O.Y. Gutiérrez, and K.A. Stoerzinger. Understanding the Role of Surface Heterogeneities in Electrosynthesis Reactions. iScience 2020, 23, 101814.