Article
Impact of PHI XPS instruments on scientific discovery
In 2024, PHI X-ray Photoelectron Spectroscopy (XPS) instruments PHI Genesis, PHI VersaProbe, PHI Quantes, and PHI Quantera continued to play a pivotal role across multiple fields in advancing scientific research for industrial applications as shown in over 4,200 scientific publications and 184 papers in high-impact journals (Nature and Science portfolios).
The role of PHI XPS instruments in scientific discoveries stems from their ability to probe the chemical properties of materials only within nanometers below their surfaces. This spotlight highlights two key studies from 2024 that utilized these instruments to gain new ground in highly anticipated fields including battery materials and catalysts.
Using a PHI VersaProbe 4 XPS instrument in a Nature publication, researchers at Stanford University uncovered a mechanism of action in a previously unknown pathway for restoring battery capacity in lithium metal batteries (LMBs). While they are a promising alternative to lithium-ion batteries (LIBs) for their higher energy densities, LMBs are prone to shorter battery lifespans. Metallic lithium becomes electronically isolated from the battery circuit over time, degrading its capacity.1
Figure 1: Fluorine F 1s XPS spectra of the solid electrolyte interphase (SEI) of a lithium metal battery (LMB) with and without rest after discharge.
The study demonstrated that resting the LMBs in a discharged state improves capacity by recapturing the isolated metallic lithium. XPS was instrumental in identifying the dissolution of organofluorine material from the solid electrolyte interphase (SEI) into the liquid electrolyte as a benefit of discharged-state resting. This dissolution of organic fluorine (Figure 1) thins the insulating matrix surrounding aggregates of isolated lithium, allowing them to reactivate in the subsequent charging cycle. This paper has already gained 53 citations, indicating the lasting impact of the researchers’ discoveries, enabled by XPS, on the battery field.
The second study details an initiative led by researchers at Northwest University in China to develop a high-performing catalyst system consisting of high-density single atoms.2 Such single-atom catalysts can be tuned to have specific coordination environments that favor certain reaction pathways over others. This precision allows for greater control over the selectivity of the catalytic process, reducing the formation of unwanted by-products and enabling many potential catalysis applications. Thus, maximizing the number of single atoms on the surface without collapsing them into agglomerations due to high density has become a key research area in catalysis.
 |
|
Figure 2: The formation of single atoms of platinum on the polymeric carbon nitride substrate instead of metallic clusters by annealing the material in vacuum in presence of platinum precursor.
The authors show that by annealing polymeric carbon nitride (PCN) in the presence of a chlorinated platinum precursor in vacuum, single atoms of platinum are formed on the PCN substrate instead of clusters of metallic platinum that might be obtained via annealing at ambient pressure (Figure 2). The mechanism is explained as the accelerated removal of chlorine in the platinum precursor at reduced pressure.
The XPS data obtained by PHI VersaProbe III was instrumental in showing that the high number of single platinum atoms are not coordinated to other platinum atoms on the PCN substrate after vacuum annealing (Figure 3). The single platinum atoms are instead coordinated to nitrogen atoms, in agreement with complementary analytical techniques including transmission electron microscopy (TEM). In a nitrogen-coordinated environment, the platinum photoelectron binding energy is shifted: Pt 4f7/2 at 72.7 eV and Pt 4f5/2 at 76.0 eV, where metallic platinum is absent at 71.1 eV and 74.4 eV respectively.
Figure 3: XPS survey spectrum of polymeric carbon nitride containing single atoms of platinum on the surface and the accompanying high-resolution Pt 4f XPS spectrum showing the absence of metallic platinum which is a key indicator of catalytic performance.
The ability to probe the polymeric carbon nitride (PCN) surface only within nanometers below the surface makes XPS remarkably sensitive to the single atoms of platinum at the surface, resulting in a deepened understanding of novel catalytic materials. The researchers’ work has resulted in many citations to the Nature paper in 2024 alone, highlighting the important role of PHI XPS instruments in guiding the design of next-generation catalytic materials.
These two Nature papers are prime examples among many that showcase the substantial impact of PHI XPS instruments across various fields in 2024. Their role in these studies underscores PHI's dedication to advancing science and industry.