Controllable Synthesis and Mechanism Investigation of Catalysts with Atomic-Level Reactive Sites for Energy Conversions

Yi Guan

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 W_AL-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.