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Near Ambient Pressure X-Ray Photoelectron Spectroscopy


Characterization Tools


Complete understanding of hydrogenation and dehydrogenation requires knowledge of the dynamic composition and chemical state of the surface while the reactions are taking place. Surface/gas reactions are believed to be a rate-limiting factor for many H storage materials and are controlled by the chemical and physical state of the surface and near-surface regions. Traditional XPS can only be used in ultra-high vacuum conditions, allowing only ex-situ hydrogenation experiments and subsequent XPS measurements in vacuum. But the chemical reactivity and surface species can vary greatly with and without gas pressure. Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) provides this information. In situ studies with NAP-XPS can reveal the complex coupling between transport, surface reaction rates, and oxidation state changes when hydrogen storage materials (hydrides, sorbents) operate.1–9

System Specifications

Pressure range: UHV to 25 mbar

Sample temperature: Liquid N2 to >1,000°C

Energy resolution: <2.5 meV

Kinetic energy range: 5–3,500 eV

Detector: fast delay-line detector with 190 ps time resolution


Online and available for use in collaboration with HyMARC.

Near-ambient pressure XPS electron energy analyzer SPECS PHOIBOS150.

Fig. 1. Near-ambient pressure XPS electron energy analyzer SPECS PHOIBOS150.


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  2. J. A. Whaley, et al., “Note: Fixture for characterizing electrochemical devices in-operando in traditional vacuum systems,” Rev Sci Instrum 81 (2010).
  3. C. J. Zhang, et al., “Measuring fundamental properties in operating solid oxide electrochemical cells by using in situ X-ray photoelectron spectroscopy,” Nat Mater 9 (2010): 944–949.
  4. W. C. Chueh, et al., “Highly Enhanced Concentration and Stability of Reactive Ce3+ on Doped CeO2 Surface Revealed In Operando,” Chem Mater 24 (2012): 1876–1882.
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  6. Q. L. Chen, et al., “Observation of Oxygen Vacancy Filling under Water Vapor in Ceramic Proton Conductors in Situ with Ambient Pressure XPS,” Chem Mater 25 (2013): 4690–4696.
  7. W. C. Chueh, et al., “Intercalation Pathway in Many-Particle LiFePO4 Electrode Revealed by Nanoscale State-of-Charge Mapping,” Nano Lett 13 (2013): 866–872.
  8. Z. L. A. Feng, F. El Gabaly, X. F. Ye, Z. X. Shen, and W. C. Chueh, “Fast vacancy-mediated oxygen ion incorporation across the ceria-gas electrochemical interface,” Nat Commun 5 (2014).
  9. C. B. Gopal, F. El Gabaly, A. H. McDaniel, and W. C. Chueh, “Origin and Tunability of Unusually Large Surface Capacitance in Doped Cerium Oxide Studied by Ambient-Pressure X-Ray Photoelectron Spectroscopy,” Adv Mater 28 (2016): 4692–4697.