Periodic Reporting for period 1 - Adv-SAEC (Advanced Single-Atom Electrocatalyst design: Exploration, Evaluation and Evolution from fundamental insights)
Reporting period: 2022-11-03 to 2024-11-02
Hydrogen are widely recognized as one of the next generation main energy source such as fuel-cell mobility. Currently, the industrial production method are mainly based on so-call water-gas shift reaction which requires also high energy consumption. Green hydrogen which are produced from electrolysis are growing in the potion of global hydrogen source. Search for cheap and abundant alternatives to Pt for the hydrogen evolution reaction (HER) has led to many efforts to develop new catalysts. To our knowledge, no earth-abundant catalyst material comes close to Pt in terms of intrinsic activity for hydrogen evolution reaction. Therefore, one practical strategy is to expose acitve sites as many as possible to increase the turnover frequency (TOF), which is defined as the number of molecules (e.g. H2) produced per second per site. In this project, we investigate the strategy to utilize so-call Single atom alloys (SAAs) as a model system for hydrogen evolution reaction (HER) in acid electrolyte. SAAs are a type of single- site catalyst generally comprised of reactive dopants atomically isolated in a less reactive metal host. The strong host–dopant interactions that lead to mixing are responsible for the thermal stability of SAAs in terms of keeping the dopant sites isolated. The simple and very well-defined nature of the active sites in SAAs makes understanding reaction mechanisms relatively easy and enables a new approach to the rational design of SAA catalysts via complementary surface science model studies and theory. Our fundamental research will contribute to understand the process of hydrogen adsorption, activation, and generation on single Pt atoms, in the long term, in order to rational design of next generation of electrocatalyst.
Specifically, we prepared and optimized two types of Pt1 SAAs, where the host materials are Cu(111) and Au(111) separately. With rational controlling of both sample temperature and Pt deposition condition, we could modify the existence of Pt evolving from isolated embedded SAAs, embedded clusters to sub-surface species. Later, We show that with just one simple drop of clean water from our home-built ’cold-finger’ device, crystal prepared from ultrahigh vacuum (UHV) can be transferred to complicated electrochemical environment against contamination. We further characterize the HER performance with different Pt coverage and geometry on Au(111). Results indicated that the sample where Pt embedded as single atom alloy shows the highest turnover frequency than others as small clusters or bulk.
Main achievements are listed as follows:
We develop and optimize a method to prepare Pt single atom alloy on Au(111) and Cu(111) surface with well characterization by atomic resolved UHV-STM and XPS.
• Water-drop protection operated in a home-design unit significantly improves the cleanliness during sample transfer from UHV condition to electrochemical environment.
• Based on the results of TOF and kinetics, single Pt atoms embedded on the surface can be recognized as active sites which introduce a different reaction path than Pt particles or clusters. Sub-layer Pt also contributes to HER performance compared to host Au(111), potentially due to a shift of local electric density of state rather than directly participating in hydrogen activation.
Main achievements are listed as follows:
We develop and optimize a method to prepare Pt single atom alloy on Au(111) and Cu(111) surface with well characterization by atomic resolved UHV-STM and XPS.
• Water-drop protection operated in a home-design unit significantly improves the cleanliness during sample transfer from UHV condition to electrochemical environment.
• Based on the results of TOF and kinetics, single Pt atoms embedded on the surface can be recognized as active sites which introduce a different reaction path than Pt particles or clusters. Sub-layer Pt also contributes to HER performance compared to host Au(111), potentially due to a shift of local electric density of state rather than directly participating in hydrogen activation.
During this project, we combined the surface physics knowledge from host groups and electrochemical knowledge from the researcher to explore the next generation of hydrogen electrolysis catalyst. From fundamental research aspect, we successfully illustrate that even down to single atom level, Pt can still process impressive hydrogen generation activity. To our surprise, rather than dimer or trimer, single embedded Pt atom hold the potential to adsorb and active protons. Those model systems with clear surface structure definitely bring a better view to the single atom electro-catalyst community. Additionally, we also demonstrate that water-drop protection strategy is a practical and effective method for bridging the research gap between UHV surface science and electrochemistry.