Ambient Pressure Photoelectron Spectroscopy in Surface and Interface Studies

Ambient Pressure Photoelectron Spectroscopy (APXPS) has emerged as a transformative technique for probing the chemical composition and electronic structure of surfaces under realistic environmental conditions. By allowing measurements at pressures up to tens of millibars, this approach bridges the gap between ultra-high vacuum investigations and practical working environments, enabling direct interrogation of gas–solid and liquid–solid interfaces. The method exploits the photoelectric effect, using X-ray or ultraviolet photons to excite electrons from the sample surface; analysing their kinetic energy yields detailed information on elemental identity, chemical state and local electronic environment. Recent advances in instrumentation, particularly the integration of tender and hard X-ray sources, have enhanced probing depth and sensitivity, opening new frontiers in catalysis, electrochemistry and environmental science. Techniques such as the ‘dip and pull’ method facilitate the stabilisation of nanometre-thin liquid layers on solid electrodes, allowing in situ observation of interfacial processes, including redox reactions and adsorption phenomena. Interdisciplinary applications range from monitoring active sites in operando catalytic systems to elucidating charge transfer at electrochemical interfaces, underscoring the global significance of APXPS for energy conversion, materials design and atmospheric chemistry.

Research from Nature Portfolio

In a foundational study, researchers introduced a novel tender-X-ray ambient pressure XPS endstation capable of detecting high-energy photoelectrons at pressures of up to 110 Torr. By combining this setup with a dip-and-pull approach, a stable nanometre-thick aqueous layer was maintained on a platinum electrode, enabling direct in situ tracking of Pt oxidation states during the oxygen evolution reaction. This work demonstrated the formation of mixed Pt2+ and Pt4+ species at reaction potentials, offering unprecedented molecular-level insight into electrochemical interfaces. The integration of soft and tender X-ray regimes has since set a benchmark for interrogating solid–liquid interfaces, facilitating studies on electrode surfaces under realistic operating conditions.

Ambient Pressure Photoelectron Spectroscopy in Surface and Interface Studies publication trend

The graph below shows the total number of articles in ambient pressure photoelectron spectroscopy in surface and interface studies across all publications each year (not limited to Nature Index journals).

Technical terms

Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS): A technique for analysing surface composition and chemical states at pressures up to tens of millibars, enabling in situ studies under realistic conditions.

Dip and pull method: A sample handling approach in which a solid electrode is dipped into and withdrawn from a liquid electrolyte, creating a stable nanometre-thin aqueous film for interfacial analysis.

Synchrotron radiation: High-brightness X-ray or ultraviolet light produced by accelerated electron beams in a synchrotron facility, used to excite photoelectrons in APXPS.

Oxidation state: The formal charge on an atom in a compound, indicative of its electron density and valence, and determinable by analysing shifts in photoelectron binding energy.

Operando measurements: In situ experiments conducted under working conditions, allowing real-time observation of active sites and reaction intermediates.

References

1. Shining light on electrochemistry: a synchrotron-based X-ray spectroscopic interrogation. Chemical Synthesis (2024).
2. Lab‐based electrochemical X‐ray photoelectron spectroscopy for in‐situ probing of redox processes at the electrified solid/liquid interface. Electrochemical Science Advances (2023).
3. In Situ Electrical Detection of Methane Oxidation on Atomically Thin IrO2 Nanosheet Films Down to Room Temperature. Advanced Materials Interfaces (2023).
4. Using “Tender” X-ray Ambient Pressure X-Ray Photoelectron Spectroscopy as A Direct Probe of Solid-Liquid Interface. Scientific Reports (2015).
5. Present and new frontiers in materials research by ambient pressure x-ray photoelectron spectroscopy. Journal of Physics Condensed Matter (2020).