(2gp) Driving Electron and Photon Induced Chemistries to Enable a Sustainable Economy

Research Interests and Vision

All pathways toward decarbonizing the chemical industry will involve a transition from the use of fossil-based resources such as natural gas for process energy, to renewable electricity. In the context of this transition, direct electron and photon driven chemistries offer a versatile toolkit for enabling a sustainable economy. Such a transition must require the development of: (i) highly distributed on-site energy storage and generation, and chemical manufacturing, coupled with (ii) site specific centralized production of specialty chemicals and platform molecules via electrification of manufacturing centers. Further, integration of sustainable feedstocks, with renewable electrons and photons to drive chemical transformations will minimize impacts on the governing carbon and nitrogen cycles.

To facilitate technological breakthroughs for electron and photon driven chemical transformations, numerous fundamental challenges need to be addressed. At the core of these, must be the rational design and development of active, selective and highly stable heterogeneous catalysts that allow for precise manipulation of chemical bonds. These catalysts should also exhibit high electrical conductivity, ability to absorb photons etc. which present new complications that are different from the design of thermal catalysts. Additional challenges that need to be overcome include, the structural response of as-synthesized catalytic materials under operating conditions, the role of interfaces as tuning knobs in electrochemical systems, decoupling transient charge transfer and secondary effects in photochemical systems, and long-term catalyst stability.

To overcome these grand challenges, I will leverage my experiences during my PhD and Postdoc to develop fundamental insights by working at the crossroads of: (i) embracing the dynamism of active site environments under reactive conditions, (ii) modulating the electrode-electrolyte interface to drive highly efficient chemical transformations, (iii) probing the photon properties including wavelength, and flux to decouple secondary effects from photocatalytic rate and selectivity enhancements, and (iv) developing in situ and operando characterization of catalytic interfaces, coupled with accelerated stability testing to allow for incorporating catalyst deactivation as a metric for catalyst design. Such an approach will be applied to reactions that are central to both short-term and long-term energy and chemical landscape. In particular, my group will: (i) study the use of energy dense carbon neutral liquid fuels such as ammonia for energy generation (e.g., using ammonia fuel cells), as well for hydrogen generation at scale, (ii) couple the synthesis of platform organic molecules from sustainable feedstocks on one electrode, while targeting hydrogen generation at the other, and (iii) selectively tailoring efficient reaction pathways in high energy density alkali metal-air batteries. Finally, my group will use technoeconomic analysis in conjunction with sensitivity analysis to identify the factors that have the largest impact on the final processes. These insights will guide the development of catalytic centers to enable technological breakthroughs that drive the transition from a linear economy to a circular closed loop economy.

Doctoral Research

The overarching goal of my doctoral research with Professor Eranda Nikolla, centered around the identification of robust design strategies to develop active, selective, and stable mixed metal oxide electrocatalysts belonging to the perovskite family.¹ This was studied for applications in electrochemical water splitting and aprotic lithium-oxygen batteries.^1,2 Such strategies are crucial given the innumerable opportunities to tune the electronic and geometric properties of active centers in these perovskite oxides. In the case of aqueous phase oxygen electrocatalysis, we identified that the oxide surface reducibility can be used to describe their electrocatalytic performance.^3–6 Oxide surface reducibility also captures effects from dynamism in oxide surface structure, in addition to its composition and crystal symmetry, on the measured electrocatalytic activity, selectivity, and stability. Another advantage of oxide surface reducibility is that one can leverage tools commonly used in thermal catalysis like temperature programmed reduction, to empirically estimate it. Coupling such complementary techniques with detailed characterization of the electrode, and the electrolyte, allowed us to engineer active and stable solid-liquid interfaces in electrochemical systems.

In the case of aprotic lithium-oxygen batteries, a fundamental framework to identify the factors that allow for selectively catalyzing the formation of conductive solid discharge products on atomically precise electrocatalysts was developed.⁷ This enabled us to understand solid-solid interfacial catalysis to target selective transformations, crucial for enhancing the efficiency of high energy density alkali metal-air batteries. This research resulted in new collaborations with theoreticians, and X-ray absorption spectroscopists.^2,5,7

In summary, the insights developed in my dissertation lays the foundation for: (i) using measurable properties of as-synthesized catalysts to describe their electrocatalytic performance, and (ii) embracing the dynamism of heterogeneous catalysts to engineer active and stable surfaces at solid-liquid electrochemical interfaces.

Postdoctoral Research

To expand my repertoire as a postdoc, my research with Professor Phillip Christopher has centered around photocatalytic non-oxidative conversion of methane using group III-nitrides. Specifically, we identified the factors that dictate the performance of supported GaN photocatalysts for small-scale methane dehydroaromatization, allowing for simultaneous upgrading of methane to aromatics, and hydrogen. This research has broadened my expertise by including synthesis and characterization of semiconductor photocatalysts and the associated reactivity measurements. I synthesized rod-shaped GaN nanostructures and studied its properties using electron microscopy, in combination with probe molecule IR and UV-vis spectroscopy to develop an understanding of the nanostructure, nature of surface sites, and the band structure, respectively. These insights are coupled with controlled kinetic experiments to provide important insights into the design of nitride catalysts for non-oxidative methane activation.⁸

Teaching Interests

My fervor to share science by teaching, either in a classroom, or in a research laboratory, are the driving forces for me pursuing an academic career. Being a trained chemical engineer, I am well prepared to teach any core course in the chemical engineering curriculum. However, given my research expertise, I prefer to teach chemical reaction engineering and thermodynamics. I am also interested in developing specialized courses on: (i) principles of reaction kinetics and heterogeneous catalysis, and (ii) Electrochemistry for Engineers.

At the core of my pedagogical philosophy, is the fact that a teacher hasn’t taught until a student has learned. As such, active learning techniques will be central to my approach of teaching to ensure that the students have learned and retained long-term problem-solving skills. To achieve this, I will instill critical thinking and curiosity among the students via opportunities for problem development. This should inspire the students to find innovative solutions to the problems that they develop. These techniques will be intertwined with engaging the students in laboratory experiences, relevance to current technology, and discussion of scientific literature. Such an iterative approach should allow for long-term knowledge retention and their ability to be independent thinkers. As a teaching assistant for undergraduate reaction engineering, I have adopted these approaches to supplement student learning and interaction.

From a mentorship perspective, I believe that a research group serves as an additional opportunity for holistic development of students. Some of the techniques that I have used to mentor two graduate students and five undergraduate researchers are discussed here. I will adopt an open-door policy, as well as have open communication channels to foster collaborative environment between all group members. I will also instill a highly inclusive environment inside and outside the lab such that everyone feels welcome and comfortable with sharing opinions. In addition to scientific discussions, I will encourage discussions on the projects pursued by the group from a policy and societal perspective. The specific aim here is to allow for scientists to be well informed with the current policies and be able to guide the policy decisions of tomorrow. These techniques should inspire the next generation researchers to develop holistically, thus enabling them to shape our future.

Selected References

(1) Gu, X.^†.; Samira, S^†.; Nikolla, E. Oxygen Sponges for Electrocatalysis: Oxygen Reduction/Evolution on Nonstoichiometric, Mixed Metal Oxides. Chemistry of Materials 2018, 30, 2860–2872.

(2) Samira, S.; Deshpande, S.; Greeley, J.; Nikolla, E. Aprotic Alkali Metal-O₂ Batteries: Role of Cathode Surface-Mediated Processes and Heterogeneous Electrocatalysis. ACS Energy Letters 2021, 6, 665–672.

(3) Samira, S.; Gu, X.; Nikolla, E. Design Strategies for Efficient Nonstoichiometric Mixed Metal Oxide Electrocatalysts: Correlating Measurable Oxide Properties to Electrocatalytic Performance. ACS Catalysis 2019, 9, 10575–10586.

(4) Samira, S.; Camayang, J.; Patel, K.; Gu, X.; Nikolla, E. Modulating Catalytic Properties of Targeted Metal Cationic Centers in Nonstoichiometric Mixed Metal Oxides for Electrochemical Oxygen Reduction. ACS Energy Letters 2021, 6, 1065–1072.

(5) Samira, S.; Hong, J.; Camayang, J; Sun, K.; Hoffman, A.; Bare, S.; Nikolla, E. Dynamic Surface Reconstruction Unifies the Electrocatalytic Oxygen Evolution Performance of Nonstoichiometric Mixed Metal Oxides. JACS Au 2021, 1, 2224–2241.

(6) Gu, X.; Carneiro, J..; Samira, S.; Das, A.; Ariyasingha, N. M.; Nikolla, E. Efficient Oxygen Electrocatalysis by Nanostructured Mixed-Metal Oxides. Journal of the American Chemical Society 2018, 140, 8128–8137.

(7) Samira, S.; Deshpande, S.; Roberts, C.; Nacy, A.; Kubal, J.; Matesić, K.; Oesterling, O.; Greeley, J.; Nikolla, E. Nonprecious Metal Catalysts for Tuning Discharge Product Distribution at Solid–Solid Interfaces of Aprotic Li–O₂Batteries. Chemistry of Materials 2019, 31, 7300–7310.

(8) Samira, S., Anderson, R., Christopher, P., Design of GaN/Co-catalytic Interfaces for Thermal and Photoinduced Activation of Methane. In preparation, 2023.