Doctoral Defense in Physics - Atef Iqbal

Doctoral candidate:
Atef Iqbal

Title of thesis:
Electrochemical Ammonia Synthesis on Transition Metal Carbides and Carbonitrides

Opponents:
Dr. Max Garcia Melchor, Ikerbasque Research Professor, CIC Energigune, Vitoria, Spain Dr. Karoliina Honkala, Professor at the Department of Chemistry, University of Jyväskylä, Finland

Advisor:
Dr. Einar Örn Sveinbjörnsson, Professor at the Faculty of Physical Science, University of Iceland

Also in the doctoral committee:
Dr. Egill Skúlason, Professor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland. Dr. Younes Abghoui, Research Associate Professor at the Science Institute, University of Iceland. Dr. Einar Örn Sveinbjörnsson, Professor at the Faculty of Physical Science, University of Iceland. Dr. Helga Dögg Flosadóttir, CEO & co-founder at Atmonia, Iceland.

Chair of Ceremony:
Dr. Birgir Hrafnkelsson, prófessor og deildarforseti Raunvísindadeildar HÍ  / Dr. Birgir Hrafnkelsson, Professor and Head of the Faculty of Physical Sciences, University of Iceland

Abstract:

The world population is rising dramatically over the next 80 years, potentially reached to 11 billion people before stabilizing at the end of the century. This population growth will need higher food production, which can be accomplished more efficiently by using synthetic fertilizers instead of conventional manure. The large-scale catalytic Haber-Bosch process is currently used in the commercial production of synthetic fertilizers, notably ammonia. This method uses hydrogen gas (produced from natural gas or coal) and nitrogen as reagents to create ammonia over an iron-based catalyst, yielding carbon dioxide as a byproduct. Unfortunately, this strategy generates about 1% of world CO2 emissions, increasing climate change. Furthermore, due to the enormous energy requirements required to break the stable dinitrogen molecule, the process occurs at high pressures and temperatures, necessitating massive, centralized ammonia production plants. This thesis explores the electrochemical nitrogen reduction process, which has the potential to directly create ammonia from nitrogen and water using electricity as an energy source. This method could potentially result in a carbon-neutral process if the electricity is generated by renewable sources such as wind or solar power. Furthermore, the process may operate at (near) ambient conditions, allowing for localized production without the need for shipping or storage. We present the computational design of potential new, cost-efficient electrocatalysts composed of transition metal carbides and carbonitrides in this thesis. These materials are predicted to facilitate the electrochemical reduction of molecular nitrogen to ammonia in aqueous media under ambient conditions with only a small applied bias. Electronic structure calculations at the density functional theory level are utilized to evaluate the performance of this new class of materials for electrochemical ammonia formation. The predominant reaction mechanism enabling this process is identified as the Mars-van Krevelen mechanism, rather than the conventional associative or dissociative mechanisms. Among a range of transition metal carbides and carbonitrides explored in this thesis, WC, TaC, VCN, and NbCN emerge as the most promising electrocatalysts, based on a comprehensive density functional theory analysis. These four materials exhibit greater activity toward nitrogen reduction compared to the competing hydrogen evolution reaction, unlike pure metal catalysts, which predominantly evolve hydrogen. We also investigate its stability against possible decomposition under operating conditions and poisoning. It is shown that extremely effective ammonia creation depends on particular single-crystal surfaces since polycrystalline surfaces can cause catalyst decomposition. This work represents a significant step toward the development of a reasonably affordable process for synthesizing ammonia, therefore allowing the synthesis of high-value nitrogenous compounds directly from air, water, and renewable electricity under ambient conditions.

The thesis contains material from papers studying polynomial approximations of holomorphic functions in several variables. These approximations are weighted, in the sense that the norm used to assess the approximation is weighted, and polynomials used for the approximation are restricted to a certain subring of polynomials. The notion of the degree of a polynomial is also different from the classical setting. The main aim is to develop an analog of the Bernstein-Walsh-Siciak theorem, a quantitative counterpart of the Oka-Weil-Runge theorem. To aid this study the Siciak-Zakharyuta functions, sometimes called global extremal functions or pluricomplex Green functions, from pluripotential theory are generalized. They are then used to construct weights for Hörmander’s L2-estimates of solutions to d-bar-equations and the solutions to those equations are then used to construct the desired polynomials.

About the candidate:

Atef Iqbal was born in Karak, located in the Khyber Pakhtunkhwa province of Pakistan. He completed his bachelor's degree in Physics at Hazara University, Mansehra, in 2017, where he was recognized with the Prime Minister's Talent Award for his academic achievements. Pursuing further studies, Atef earned a Chinese Government Scholarship to attend Soochow University in Suzhou, China, where he completed his master's degree in Physics in 2020. His excellence was acknowledged once again when he received the "Outstanding International Student Award" from the Chinese government. Following his master's, he worked as a research assistant at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany from January to October 2021. In November 2021, Atef embarked on his PhD journey at the University of Iceland, set to be completed by November 2024.