Thesis Format
Monograph
Degree
Doctor of Philosophy
Program
Mechanical and Materials Engineering
Supervisor
Sun, Xueliang
Abstract
Proton exchange membrane fuel cells are considered as the next-generation energy conversion system due to their high efficiency, simple structure and cleanness. However, the main impediment to the commercialization of proton exchange membrane fuel cells is the high cost of their noble metal Pt electrocatalysts in the electrodes. Thus, three challenges including (1) low atom utilization efficiency, (2) poor stability under long-term operation, and (3) low catalytic activity, especially during practical fuel cell applications need to be resolved before the large-scale commercialization of the Pt based electrocatalysts.
To address these challenges, several strategies were explored in this thesis:
Firstly, Ni-O-W dimer atoms decorated with Pt nanoparticles were prepared via atomic layer deposition. The surface stable compressive strain induced by the compact Ni-W dimer structure greatly enhanced the catalysts’ performance for oxygen reduction reaction both in rotating disk electrode and practical fuel cell applications.
Secondly, three additional elements, including Co, Ru, and W, were integrated and selectively deposited on the concave surface of PtNi octahedral nanoparticles to further improve their performance. The high entropy of the single atom alloy created a stable compressive strain that resulted in a tenfold increase in catalytic activity compared to commercial Pt/C catalysts. Notably, investigations of spatial effects revealed that randomly distributed high-entropy atoms did not improve catalytic activity.
Furthermore, to increase Pt atom utilization efficiency, Pt single atoms were successfully synthesized on an amorphous tantalum oxide support, featuring short Pt-O bonding paths. The compact Pt-O bonding from the amorphous structure led to a threefold increase in hydrogen evolution reaction activity compared to traditional Pt-N coordination.
Lastly, the site-specific strain of Pt nanoclusters of various sizes was analyzed using high-precision scanning transmission electron microscopy. A volcano-shaped relationship was discovered between active site characteristic strain, the d-band center, and catalytic activity. Computational studies further confirmed this relationship and proposed an optimized site-specific strain for improved hydrogen electrocatalysis.
In summary, these findings in this thesis contribute to overcoming the key challenges associated with Pt-based electrocatalysts and bring fuel cells closer to large-scale commercialization.
Summary for Lay Audience
Proton exchange membrane fuel cells are an innovative and promising technology for clean energy applications. They are highly efficient and produce electricity with only water and heat as byproducts, making them ideal for powering vehicles. However, the widespread use of proton exchange membrane fuel cells is still limited by one major hurdle: the high cost of platinum (Pt), which is heavily used in the electrodes as a catalyst. To make this system more affordable and practical, we need to overcome three main challenges: 1) Improving the efficiency of platinum use: we need to reduce platinum consumption while maintaining or improving performance. 2) Enhancing long-term durability: fuel cells must perform reliably over time without degrading. 3) Boosting catalytic activity: the catalyst must work efficiently under real-world conditions. In our research, we've developed new strategies to address these challenges and improve the performance of platinum-based catalysts in fuel cells.
We improved fuel cell efficiency by enhancing oxygen reduction reaction and hydrogen evolution reaction through various innovative strategies. Using atomic layer deposition, we placed nickel and tungsten atoms on platinum nanoparticles, creating compressive strain that boosted oxygen reduction reaction efficiency and reduced platinum usage. Additionally, we introduced multiple elements—cobalt, ruthenium, and tungsten—into platinum-nickel octahedral nanoparticles, forming a high-entropy alloy with tenfold oxygen reduction reaction activity compared to the initial platinum activity. To increase platinum utilization, we synthesized individual platinum atoms on an amorphous tantalum oxide support, tripling hydrogen evolution reaction activity compared with reference catalysts. Lastly, using advanced scanning transmission electron microscopy, we identified the ideal strain value in platinum nanoclusters to maximize catalytic performance, facilitating the development of more efficient fuel cell catalysts.
In summary, these new advancements in catalyst design offer several promising solutions to the challenges facing platinum-based fuel cells. By improving the efficiency of platinum usage, enhancing the stability of the catalysts, and boosting catalytic activity, we are making significant progress toward reducing the cost of fuel cells and improving their long-term performance. These breakthroughs move us closer to the goal of making proton exchange membrane fuel cells a more affordable and widely adopted technology for clean, sustainable energy production.
Recommended Citation
Yao, Xiaozhang, "Strain engineering of advanced Pt based electrocatalysts via atomic layer deposition" (2025). Electronic Thesis and Dissertation Repository. 10663.
https://ir.lib.uwo.ca/etd/10663
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