
Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Mechanical and Materials Engineering
Supervisor
Xueliang Sun
Abstract
The energy crisis and environmental concerns stemming from fossil fuel use have emphasized the urgency for sustainable energy solutions, spurring the development of advanced catalytic materials for electrochemical processes. Catalysts with atomic-level reactive sites (CALRs) have gained significant attention due to their 100% atomic utilization, greatly reducing precious metal costs. Additionally, CALRs with multiple active sites offer unique advantages for catalyzing complex reactions. However, CALRs still face several challenges: (1) rational design and synthesis of CALRs, and (2) understanding the interaction mechanisms. This thesis focuses on the controlled synthesis of CALRs with multiple active sites using atomic layer deposition (ALD) and mechanism investigation via advanced characterization and theoretical calculations.
Firstly, we employed a well-designed phosphorus modified atomic layer deposition (P-ALD) strategy to anchor atomic phosphorus sites coordinated one-to-one A-B bimetallic dimer structures (Pt1W1-P dimer) on various substrates. The Pt1W1-P dimer catalysts demonstrated a unique interatomic hydrogen adsorption mechanism, revealing W sites as the primary site for hydrogen adsorption, subsequently extending to the Pt single atom, leading to a 60-fold improvement in mass activity compared to commercial Pt/C for hydrogen evolution reactions (HER).
Secondly, by incorporating an additional oxygen cycle modulation into the P-ALD technology, we successfully synthesized a one-to-one-to-one A-B-C trimetallic trimer catalyst (Ru₁Pt₁W₁ trimer). The ternary active sites facilitated optimal adsorption and desorption of intermediates in complex reactions, outperforming dimer catalysts and commercial Pt/C in hydrogen oxidation reactions (HOR) and HER.
Thirdly, we examined the effects of coordination environment and interatomic spatial arrangement on metal site interactions. The three-dimensional asymmetrically coordinated one-to-one A-B bimetallic dimer catalyst (Pt1Fe1-TAC) dimer showed superior HER performance due to strong interatomic interactions and a unique electron transfer pathway from Fe to Pt site.
Lastly, we investigated how changes in the coordination structure of atomic sites during reactions impact catalyst performance and stability. A surface stress engineering strategy was proposed, coating RuO₂ with a ~1 nm atomic W layer, forming WAL-RuO₂ catalyst. The W layer undergoes site reconstruction, transitioning from tensile stress that enhances catalytic activity to compressive stress that stabilizes the RuO₂ lattice, thereby achieving outstanding efficiency and durability for acidic oxygen evolution reaction (OER).
These findings provide valuable insights for developing low-cost, high-performance electrocatalysts for energy conversions.
Summary for Lay Audience
The rising use of fossil fuels and associated environmental issues have increased the demand for sustainable energy solutions. Hydrogen (H₂), with zero emissions and high energy density, is a promising alternative. However, hydrogen-based energy systems require efficient catalysts to drive the necessary reactions. Catalysts with atomic-level reactive sites (CALRs) have gained attention due to their 100% atomic utilization, significantly lowering the cost of precious metals. CALRs with multiple active sites, such as dimer and trimer catalysts, show potential for efficient catalysis of complex reactions. Despite this, challenges remain, including the rational design and controlled synthesis of CALRs, and understanding the interaction mechanisms of active sites. This thesis investigates the controllable synthesis and mechanism investigation of CALRs.
1. For the controllable synthesis of CALRs: First, we anchor high-density one-to-one A-B bimetallic Pt₁-W₁ dimers on carbon materials using ALD, where the P-W₁-P sites selectively adsorb Pt precursors, ensuring precise dimer synthesis. The Pt₁-W₁ sites exhibit synergistic interactions, leading to high activity and stability in hydrogen evolution reactions (HER). Next, using a phosphorus/oxygen ALD method, we synthesize a one-to-one-to-one A-B-C trimetallic trimer catalyst (Ru₁Pt₁W₁ trimer), demonstrating superior hydrogen oxidation (HOR) and HER performance over commercial Pt/C catalysts.
2. For the mechanism investigation of CALRs: We explore Pt1Fe1 dual-atom catalysts (Pt1Fe1DACs) to understand how spatial configurations influence catalytic activity. The catalytic performance of Pt₁Fe₁-TAC is significantly enhanced due to its unique three-dimensional asymmetric spatial configuration, which facilitates a distinct electron transfer pathway from Fe to Pt. Furthermore, we also propose a surface stress engineering approach, coating RuO₂ with a ~1 nm atomic W layer (WAL-RuO₂) to induce active site reconstruction. During the reaction, changes in the coordination structure of the W atomic layer led to a transition from tensile stress, which enhances catalytic activity, to compressive stress, which stabilizes the RuO₂ lattice. This transformation results in exceptional efficiency and durability for acidic oxygen evolution reactions (OER).
These findings provide valuable insights for developing low-cost, high-performance electrocatalysts for energy conversions.
Recommended Citation
Guan, Yi, "Controllable Synthesis and Mechanism Investigation of Catalysts with Atomic-Level Reactive Sites for Energy Conversions" (2025). Electronic Thesis and Dissertation Repository. 10600.
https://ir.lib.uwo.ca/etd/10600