Doctoral defence in Chemical Engineering - Narges Atrak

Doctoral candidate: Narges Atrak

Dissertation title: Modeling electrochemical CO2 reduction reaction on transition metal oxides

Opponents:
Dr. Anders Hellman, Professor at Chalmers University of Technology, Gothenburg, Sweden
Dr. Federico Calle-Vallejo, Ikerbasque Research Associate and Visiting Professor at the University of the Basque Country, San Sebastian, Spain

Advisor: Dr. Egill Skúlason, Professor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland

Also in the doctoral committee: Dr. Hannes Jónsson, Professor at the Faculty of Physical Sciences, University of Iceland
Dr. Elvar Örn Jónsson, Researcher at the University of Iceland

Chair of Ceremony: Dr. Rúnar Unnþórsson, Professor and Head of the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland

Abstract

The main target of this thesis is to use density functional theory (DFT)-based simulations to study electrochemical CO2 reduction reactions (CO2RR) on transition metal oxides (TMOs) employing thermochemical model and computational hydrogen electrode. We utilize models of rutile oxide (110) surfaces to investigate trends and limitations of CO2RR on those TMOs. We construct scaling law based thermodynamic volcano relation for CO2RR. Accordingly, we propose guidelines for hydrogen and OH binding free energy range where low overpotentials and high selectivity are predicted for CO2RR using certain oxides. Therefore, this provides guidance to future development of oxide catalysts for CO2RR. First, we investigate the effect of solvent on the stability of intermediates in CO2RR toward methanol and formic acid formation and the competing hydrogen evolution reaction (HER). To study the solvent effect, one monolayer of water is included in the free energy calculations of adsorbates in CO2RR and HER and compared with the results when water is absent. The emphasis is on the catalytic trends where limiting potential volcano plots for the products are obtained through the scaling relations of adsorbates. We find that the presence of cooperative adsorbed (co-adsorbed) water alters the interaction between each CO2RR intermediate and TMO surfaces, resulting in a change in overpotentials for the formation of formic acid and methanol, ranging from 0.2 to 0.5 V while the potential determining steps remain unaltered. In addition, our research reveals that when water is co-adsorbed, it destabilizes HCOOH on surfaces which is significant because HCOOH is a crucial component for CO2RR to advance toward methanol production. Consequently, this destabilization alters the selectivity of methanol formation. Furthermore, we conducted a comprehensive study to investigate oxygen, carbon, and hydrogen affinities for TMOs and their roles in catalyst’s activity and selectivity. Our detail investigation shows that the CO coverage has a considerable influence on the selectivity. For all TMOs in this investigation, moderate CO coverage is desirable for both formic acid and methanol synthesis. Additionally, MoO2 and HfO2 are predicted to convert CO2 to methanol at lower overpotentials with moderate or high CO coverage than low coverage. Moreover, our data indicate that increased CO coverage on TMOs can lower HER somewhat.

The research also highlights the significance of understanding the multiple adsorption sites and their correlation with active and selective catalysts for the synthesis of methanol from CO2RR using the proper screening criteria for the adsorption energy of the key intermediates. The outcome of these investigations has led us to our final work where we analyze and identify the active sites for CO2RR towards CO and formic acid on TiO2/RuO2 and SnO2/RuO2 alloys using DFT. To determine experimental trends and to gain insights into the catalytic active sites, Ru atoms are substituted in varying ratios and compositions for Ti and Sn atoms in TiO2 and SnO2, respectively. We found that alternate Ru-Ti binding sites for COOH/OCHO intermediates have higher overpotentials than the reference RuO2 surface, while active sites with Ru-Ru or Ti-Ti exhibit lower overpotentials for CO formation. For formic acid formation, Ru-Ru sites have the lowest overpotentials, whereas Ti-Ti binding sites result in large overpotentials. We also discovered that replacing one Ru atom with Cu in a RuO2 overlayer on TiO2 reduces the overpotential for both formic acid and CO formation. Additionally, substituting Sn with Ru in coordinatively unsaturated sites of SnO2/RuO2 alloys decreases the overpotential due to electronic effects. These findings are useful for designing active sites for CO2RR, improving selectivity while decreasing the required overpotential.

About the doctoral candidate: 

Narges Atrak was born and raised in Zanjan, Iran, and earned a bachelor's degree in Applied Chemistry from Zanjan University in 2014. During her undergraduate studies, she conducted research on the removal of heavy metals from polluted water using bio sorbents under the guidance of Prof. Mohammad Reza Yaftian.

Right after graduation, Narges went on to earn a master's degree in Physical Chemistry at the Institute for Advanced Studies in Basic Sciences, Zanjan, Iran, where she studied the structural and electronic properties of Phosphorene sheets using a DFT approach with Dr. Fariba Nazari as her supervisor.

In 2018, Narges pursued doctoral studies abroad in Chemical Engineering at the University of Iceland, where she worked with Prof. Egill Skúlason on electrocatalysis research for the past five years. Her research involved performing quantum mechanical simulations to investigate reaction mechanisms for CO2 reduction reactions.

Narges's dedication to academic research and her desire to expand her knowledge will lead her to start her post-doctoral research at the University of Calgary upon her graduation.