(4nk) Computational Design of Catalysts for CO2 Conversion and Water Splitting

As a researcher in the field of electrochemistry, computational catalysis, and computational materials, my work revolves around understanding fundamental processes at the molecular level with potential applications in sustainable energy conversion. Computational catalysts design for storing energy in chemical bonds ­—the conversion of CO₂ into value-added chemicals (CO₂ER) and oxygen evolution reaction (OER) — is my current focus of the research that has a great potential for significant contribution in the field of sustainability.

Computational studies are key to providing insight into “What is happening on the catalysts in the reaction chamber or on an electrode/catalysts surface in the electrochemical cell”. In the field of catalysis, computational studies either predict trends of selectivity and efficiency or explain the origin of exceptional reactivity demonstrated by experimental studies. In particular, studying the effect of tuning the active site on the trends in efficiency and selectivity helps design new catalysts. The regulation of reactivity and selectivity by systematic tuning of active sites in homogeneous catalysts (both metal centers and ligands) and heterogenous catalysts, investigated by using computational tools enables us to track what modification in active site causes what changes in selectivity by modifying energy profiles. Generally, fundamental insights learned from homogenous (molecular) catalysts lay the foundations for building heterogeneous catalysts. Easily tunable active sites (like in molecular catalysts) anchored in a heterogenous fashion (like solid surface) are two features together for efficient and selective catalyst design for industrial-scale deployment.

For a fundamental understanding of catalysis, I started my research on homogeneous catalysts and extended it to heterogeneous catalysts. My first research during my Ph.D. is the electrochemical reduction of CO₂ (CO₂ER) on homogeneous catalysts including d-metal complexes of cyclam and porphyrin. In the cyclam-based study, we identified some efficient and selective cyclam-based molecular catalysts for the electrochemical reduction of CO₂ to HCOO^- and CO. The effect of changing the metal centers in cyclam on product selectivity (either HCOO^- or CO), limiting potential and competitive hydrogen evolution reaction (HER) was studied (Dalton Trans. 2021, 50(33), 11446-11457). On porphyrin complexes, we explained the origin of selectivity for CO on cobalt porphyrin and the selectivity of HCOO^- on Ir- and Rh-porphyrin. Additionally, we identified the descriptors for product selectivity among CO, HCOO^- and HER and the optimal pH range for selective CO₂ reduction (Molecules 2023, 28(1), 375-386).

Next, I switched my focus to the heterogenous catalysis on metal/metal-oxide interfaces ((MO)₄/Cu(100), M = Fe, Co and Ni) for electrochemical reduction of CO₂ to C₁ products using computational hydrogen electrode model (CHE). This study demonstrates that tuning of (MO)₄/Cu(100) and using appropriate solvent provides an opportunity to regulate product selectivity and limiting potential for CO₂ER (Catalysis Today 2023, 409, 53-62). The objective of computational studies, sometimes, also requires the validation of computed limiting potentials and selectivity’s with improved models. Therefore, we conducted CO₂ER and OER on the same model catalysts as the previous one using the Constant Electrode Potential (CEP model). The CEP model is an improved computational model that intrinsically accommodates the field effect generated by applied potential. This study demonstrated that the CEP model is better for multi-step proton-electron transfer steps, but still, CHE works well for simple reactions like OER (J. Phys. Chem. C 2023, 127(48), 23170-23179).

Computational tools are very important to explain reaction mechanism—which is otherwise difficult to observe—in catalysis or validate materials models in material chemistry. In my first collaborative projects with Dr. Shaowei Chen from the University of California Santa Cruze, I explained the origin of high reactivity and low overpotential for OER on Cl-rich NiFe₂O₄ spinel (Ni(OH)Fe₂O₄(Cl)). This project provided me with an opportunity to construct catalyst models from experimental data. Using control experiment techniques, this project also helped me identify active ensembles among possible candidates. For example, catalysts contained NiFe₂O₄ (Fe-Ni spinels), Fe₃O₄ and NiO with the presence of OH and Cl on the surface. Therefore, I constructed Ni(OH)Fe₂O₄(Cl), Ni(OH)Fe₂O₄, Fe(OH)Fe₂O₄(Cl), Fe(OH)Fe₂O₄, Ni(OH)NiO(Cl), Ni(OH)NiO as possible candidates as an active ensemble for OER. Among all ensembles tested, Ni(OH)Fe₂O4(Cl) was identified as an active ensemble for OER due to close agreement between calculated (90 mV) and experimental overpotential values (200 mV) (Research, 2022, 2022, 13 pages).

In my second collaborative project with the same group, I validated the structural and photoluminescent properties of organically capped CuOH nanostructures. Capping ligands, 4-ethylphenyacetylene (EPA) and 1-hexadecyne (HC16) were used as the acetylene derivatives and 4-ethylphenylthiol (EPT) as a mercapto derivative to stabilize CuOH. Acetylene derivatives form Cu-C* linkages, whereas mercapto ligands form the Cu-S- interfacial bonds. In order to understand the origin of emission spectra and interfacial electronic coupling, time-dependent density-functional theory (TDDFT) based UV-vis spectrum, natural transition orbitals (NTO) analysis, the bandgap of CuOH nanostructures, and charge density difference analysis were carried out. This analysis based on electronic structures helped to validate the model of CuOH nanostructures and the origin of photochemical activity. (Adv. Mater. 2023, 35, 2208665. doi.10.1002/adma.202208665).

After my Ph.D. I joined the research group of Dr. Bin Wang at The School of Sustainable Chemical, Biological and Material Engineering, University of Oklahoma (as a postdoc). Here, I worked on computational catalyst designs for the carboxylation of alkenes with CO₂ to produce unsaturated carboxylic acids on heterogeneous catalysts. In my first project, we aim to provide insights on CO₂-ethylene coupling on metal-exchanged MFI-zeolites and identify Scandium (Sc) and yttrium (Y) dispersed in MFI zeolites as promising catalysts with low activation barriers. Additionally, we demonstrated that the electronegativity of metal atoms is the descriptor for the activation barriers for beta-hydrogen transfer, a rate-limiting step. ACS Sustainable Chem. Eng. 2024, 12(18), 6960–6968 (Featured on Journal Cover page). In our next work, we demonstrated that co-adsorbed water could work as a proton shuttle and lower the energy barrier for beta-hydrogen transfer in the direct coupling of CO₂ and C₂H₄ over atomically dispersed metal at graphene Edges (Chem. Eng. Journal. 2024, 488, 150922). As for now, I have completed two more studies on dispersed active sites in the MFI cage and the manuscripts are being revised. Currently, I am investigating CO₂-Alkene coupling to produce unsaturated carboxylic acids on metallic dimer sites on defective graphene sheets.

Before the start of my Ph.D. (during my Masters), I explored electron transfer kinetics for chemically coupled reactions using electrochemical methods. (J. Electroanal. Chem. 2016, 775, 157-162 and Electrochem 2024, 5 (1), 57-69). This research sparked me to start applied research in electrocatalysis. Furthermore, these two papers have integral educational parts providing methodologies to explore any electron-coupled chemical reaction on the electrode surface.

In summary, I have extensive research experience in catalysis applied to CO₂ conversion and oxygen evolution reaction, both topics are very demanding for sustainability and potentially can be funded by the Department of Energy, National Science Foundation, and ACS Petroleum Research Fund. This funding will have a strong component of graduate and undergraduate research. Additionally, my collaborative experience can be used to conduct joint research projects with high-ranked universities which will be beneficial for boosting the department's ranking.

For my future potential research, my experience of homogenous and heterogeneous catalysis in the field of CO₂ER and water splitting will leverage upon building research at the interface of homogenous and heterogeneous catalysts. Based on my learning from both systems, I will extend my research on single metal atom catalysis for CO₂conversion into hydrocarbons and oxygeneates and water splitting. In water splitting, I will study OER and thermal hydrogen production.

Teaching Statement:

Based on my extensive training in chemistry and chemical engineering, I am confident that I can teach courses in chemistry and a few from chemical engineering. Chemistry courses include General, Inorganic, Analytical and Physical Chemistry. In chemical engineering, I can lead Catalysis, Surface Chemistry, Electrochemistry, Kinetics and Thermodynamics. Being a computational chemist, I can introduce new interdisciplinary courses like computational material science for graduate and undergraduate students.