In Situ Probing of Small‐Molecule Electrolysis Using Ambient‐Pressure X‐Ray Photoelectron Spectroscopy

Electrocatalytic small-molecule conversion addresses the need to couple renewable electricity with sustainable fuel and chemical production, yet challenges remain in resolving the dynamic gas/solid/liquid interfaces that govern catalytic activity, selectivity and stability. A key challenge is to correlate catalyst structures, reaction intermediates and local interfacial environments under comparable operating conditions. Ambient-pressure x-ray photoelectron spectroscopy (APXPS) provides surface-sensitive and chemically specific information on catalyst chemical states, interfacial species and local electrostatic environments at the same working interface, enabling direct correlations between catalyst evolution and reaction intermediates. We offer a forward-looking review of APXPS for probing gas/solid/liquid interfaces in small-molecule electrolysis. We discuss three categories of electrochemical XPS/APXPS configurations: quasi-in situ XPS, in which electrochemically treated catalysts are transferred under protected conditions for post-reaction analysis; thin-electrolyte-film (dip-and-pull) APXPS, which probes a potential-controlled interface through a nanometer-scale liquid film; and membrane-based APXPS, which accesses catalyst-ionomer-electrolyte interfaces. We introduce present-day challenges in electrochemical APXPS and describe a vision towards more realistic operating conditions, higher time resolution and multimodal measurements integrated with theoretical and data-driven spectral analysis. These developments provide potential avenues to establish reliable structure-intermediate-environment relationships in the further development of small-molecule electrocatalysis.