Abstract
Probing the chemistry that occurs at catalyst interfaces under realistic process conditions is key to the rational design of better materials for industrial catalytic reactions. Ambient pressure X-ray photoelectron spectroscopy, has until recently been limited to pressures two orders of magnitude below atmosphere. However, the development of photoelectron transparent membranes based on two-dimensional materials that can maintain large pressure differences and yet have thicknesses approaching or even falling below the inelastic mean free path of photoelectrons, now allows the atmospheric pressure regime and above to be accessed. We introduce here the fundamental principles underlying this membrane-based approach to atmospheric pressure photoelectron spectroscopy, and in this context highlight some of the key design concepts and challenges in performing experiments with this technique. We discuss a number of recent proof-of-concept studies, and highlight the potential of the membrane-based approach for operando characterisation of catalyst interfaces under reaction conditions, as well as some current challenges and limitations in this area.
Highlights
Heterogeneous catalysis is essential for the synthesis and purification of industrial chemicals at the scale demanded by modern society, and in mitigating the impact of harmful pollutants on health and the environment by converting them to more inert products [1]
The advent of commercially available near ambient pressure X-ray photoelectron spectroscopy (NAPXPS) systems has further increased this limit into the tens of mbar regime [3], with multiple differentially pumped apertures used to achieve a large pressure drop between the sample and spectrometer, whilst electrostatic lenses focus the photoelectrons through the apertures to maintain the collection efficiency [4]
The cleanliness of this polymer-free transfer-process has been confirmed by scanning tunnelling microscopy (STM), which reveals the hexagonal graphene lattice with atomic resolution [38]
Summary
Heterogeneous catalysis is essential for the synthesis and purification of industrial chemicals at the scale demanded by modern society, and in mitigating the impact of harmful pollutants on health and the environment by converting them to more inert products [1]. Tender X-ray excitation allows probing of the solid–liquid interface, as the photoelectrons produced have sufficiently high kinetic energies that a significant proportion pass through the liquid film without being inelastically scattered and can be collected by a NAP-XPS analyser Maintaining such a meniscus of stable thickness over the course of hours needed for in situ measurements is far from straightforward, requiring control over the equilibrium vapour pressure to avoid changes in the solute concentration, and potentially cooling of the liquid to reduce its vapour pressure and avoid excessive photoelectron attenuation by gas-phase scattering. This approach is not without challenges, in the preparation of the membrane materials and the deposition of active catalyst or electrode materials, and these are critically discussed along with possible pathways to overcome some of the existing limitations of this technique
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
