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The global shift towards sustainability has made decarbonization a critical goal in addressing climate change and reducing greenhouse gas emissions. At the same time, the growing demand for energy, driven by population growth and rising living standards, highlights the need for clean and renewable energy solutions. Hydrogen plays a key role as a promising energy carrier and has the potential to contribute to sustainable energy and transportation systems.

Entirely carbon-free green hydrogen

Hydrogen can be produced through electrolysis, where water is split into hydrogen and oxygen using electricity. When powered by renewable energy sources like wind or solar, the resulting ‘green hydrogen’ is entirely carbon-free throughout its production and consumption. Despite its potential, hydrogen currently plays a limited role in the global energy supply due to high production costs. Improving the efficiency of electrolyzers is crucial to making hydrogen a more viable contributor to energy systems.

Bubbles significantly impact electrolysis

Bubble formation plays a key role in the efficiency of the electrolysis process. Using an in-house Fortran code and the immersed boundary method for numerical analysis, explored how flow rate, ambient pressure, bubble surface mobility, and solutal Marangoni flow affect bubble growth and detachment in a 30% potassium hydroxide solution. Her research provides detailed insights into the hydrodynamic forces acting on hydrogen and oxygen bubbles.

The study shows that higher ambient pressure significantly reduces hydrogen bubble growth by increasing the hydrogen density inside the bubble. This slows bubble expansion and improves current density at the electrode, enhancing electrolysis efficiency. Higher flow velocities have a smaller effect, slightly reducing bubble size and aiding mass transfer.

Effects of solutal Marangoni flow

Differences between hydrogen and oxygen bubble dynamics were also observed. Hydrogen bubbles experience greater drag forces, while lift forces acting on the bubbles increase with current density. Solutal Marangoni flow influences bubble detachment behavior in opposite ways. At the cathode, Marangoni flow accelerates hydrogen bubble detachment, improving efficiency. At the anode, however, it delays oxygen bubble detachment, which impacts bubble growth rates.

To ensure accuracy, the research involved a grid refinement study and rigorous validation against analytical solutions and results from ANSYS-Fluent simulations. The validated model successfully captures the effects of bulk velocity, ambient pressure, and Marangoni forces on bubble dynamics and electrochemical quantities.

A reliable simulation tool

The findings demonstrate that higher operating pressures and optimized flow rates can improve electrolysis efficiency by reducing bubble growth and enhancing mass transfer. Understanding the role of solutal Marangoni flow and hydrodynamic forces provides essential guidance for improving the design and performance of electrolyzers.

By developing a reliable simulation tool and uncovering the mechanisms governing bubble behavior, this research forms a solid foundation for future studies on electrolysis and bubble dynamics. It contributes to building a more realistic and comprehensive model for enhancing water electrolysis efficiency, advancing hydrogen production technologies, and supporting the global transition to sustainable energy.

Watch the 'Growth of Hydrogen Bubble'.

Title of PhD thesis: . Supervisors: Prof. Bert Vreman, Prof. Niels Deen, and Dr. Yali Tang.

An interview with Faeze Khalighi

What was the most significant finding from your research, and what aspects turned out to be most important to you?

The most important finding from our research was understanding how the hydrodynamic forces behave differently in hydrogen and oxygen bubbles. We also explored how bubble surface mobility and factors such as velocity and ambient pressure influence bubble dynamics and electrochemical quantities. What mattered most to me was developing a reliable simulation tool. This tool not only helped explain some behaviours but also has the potential to incorporate additional factors and phenomena. Developing the model could lead to improved strategies for optimizing alkaline water electrolysis.

What was your motivation to work on this research project?

Climate change has always been a concern to me, especially when I hear about wildfires, droughts, melting polar ice, and other alarming effects. When I came across this project, I became familiar with green hydrogen and recognized it as a potential and promising solution to climate change that could help mitigate its impact. I realized that, even in a small role, I could contribute to addressing this global problem. This project also gave me the opportunity to combine my concerns with my research interests and skills. It was an amazing experience.

What was the greatest obstacle that you met on the PhD journey?

My biggest obstacle came during the third year of my PhD when my code didn’t work for nine months, and I couldn’t figure out why. It was very frustrating, but I learned that slow progress is a normal part of research. Sometimes, there are long periods where nothing seems to work, followed by sudden breakthroughs. When finally the issue is solved, everything fell into place, and I could write two papers using the corrected code.

What did you learn about yourself during your PhD research journey? Did you develop additional new skills over the course of the PhD research?

One of the most important lessons I learned was how to handle stress, especially during tough times when progress was slow or problems seemed hard to solve. During this journey, I improved my time management and organizational skills. My communication skills also grew as I participated in many meetings and conferences, worked with others, supervised several master’s students, and was as a teaching assistant. Overall, my PhD journey was a very positive experience that helped me become more focused, and better equipped to face future challenges.

What are your plans for after your PhD research?

I started a postdoc position, which has helped me further develop my research skills and gain deeper insights into my field. Looking ahead, I’m exploring different possibilities for the next steps in my career. While I initially aimed for a professorial role in academia, I now see the value in considering both academic and industry opportunities. My postdoc experience is helping me understand where my skills and interests can have the most impact, whether in academia, industry, or a mix of both. I’m open to opportunities that allow me to keep learning, contribute to meaningful projects, and apply my expertise in new ways. My goal is to stay flexible and make the most of the opportunities that come my way in the future.