We are almost past the first quarter of the 21st century, yet the reliance on fossil fuels like coal, oil, and natural gas remains high, as do greenhouse gas emissions. The consequences for our climate and the future of our planet are severe. In response, scientists and engineers turn to a surprisingly simple fuel as a substitute: hydrogen. However, shifting from fossil fuels to hydrogen presents significant challenges. Issues like the efficiency of hydrogen production and consumption, infrastructure for transportation and storage, and overall economic viability are all active areas of research. This growing effort falls under the umbrella of the Hydrogen economy.
My journey begins: the role of simulations for energetics
Imagine my excitement when I was given the chance to contribute to such an important and complex field. Although leaving home and moving to a different country seemed daunting, the opportunity was too valuable to miss. This marked the start of my doctoral project, aimed at understanding how a water molecule splits into hydrogen and oxygen under an applied electric potential. More specifically, I set out to uncover how the oxygen molecule forms on the surface of a particular catalyst. The catalyst in question is Pentlandite, a material identified by experimentalists as promising due to its affordability and efficiency. However, the reason behind its efficiency remains unclear, and this is where computer simulations play a crucial role.
It might seem that performing theoretical calculations is as simple as plugging numbers into a formula to get an answer. However, this is far from the case with atomistic simulations, where numerous parameters need to be carefully chosen, often based on chemical intuition rather than well-defined rules. Imagine a pilot’s cockpit, but instead of knobs and dials, you have only a screen and a keyboard. With a single calculation potentially taking several days on a powerful computer, and each project requiring hundreds of calculations, setting the parameters at the project's early stages is vital. Interestingly, despite the scale of these computations, the main outcome is often just one number—the total energy of the system—but getting that number right is crucial. By surveying the literature, I could determine reasonable values for each parameter, effectively setting the "position" of each knob on my control panel.
Building up the model
With the parameters dialed in, I was ready to build the model for the catalyst surface. Imagine it as a Lego set, where colorful spheres represent atoms. However, instead of following a step-by-step manual, one applies general chemistry knowledge and data from the literature. Key questions had to be addressed: What is the structure of an isolated surface? How does it change under reaction conditions? While these questions are common in similar projects, getting the answers right for pentlandites is particularly challenging due to the material's complexity. To tackle this, there was no shortcut—I had to pay close attention to detail and develop a dedicated procedure to create a realistic model for the surface under reaction conditions. It took nearly six months to get this right, but the main challenge was still ahead.
Oxygen formation on the pentlandite surface
At last, I was ready to simulate the formation of the oxygen molecule itself. Since four proton-electron transfers are required to oxidize water into oxygen, there must be at least three distinct reaction intermediates before the oxygen is released. But what exactly are these reaction intermediates? Could there be more than three? The answer is yes, leading to many possible mechanisms. To be thorough, all of them need to be considered!
Even with the available computational resources, this was a challenging task, taking months of calculations. However, by carefully constructing the systems and evaluating the results, I was able to simulate all the reasonable mechanisms discussed in the literature. The likelihood of each mechanism was determined based on the calculated energies. Interestingly, the simplest mechanism emerged as the most probable! I have to admit, it was a bit disappointing to see that after so much work, the easy answer turned out to be the correct one. But this effort was necessary to be certain that it was indeed the right conclusion.
What comes next?
As I reach the end of this stage of my academic journey, I can look back with a sense of fulfillment, even if things hadn’t always gone as planned. The challenges I faced along the way turned out to be valuable learning opportunities. The work I've shared here is just the tip of the iceberg, and there is much more to explore in the field of hydrogen research. If you’re interested in diving deeper, my compiled articles provide a more detailed view of my findings and insights.
Looking ahead, I am excited to see how the hydrogen economy will continue to develop and how my work may contribute, even in a small way, to a more sustainable future. The path has been demanding, but it’s also rewarding to know that my efforts are part of a larger movement towards cleaner energy solutions.
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