Interface Sensitivity in Electron/Ion Yield X-ray Absorption Spectroscopy: The TiO₂–H₂O Interface

Abstract

To understand corrosion, energy storage, (electro)­catalysis, etc., obtaining chemical information on the solid–liquid interface is crucial but remains extremely challenging. Here, X-ray absorption spectroscopy (XAS) is used to study the solid–liquid interface between TiO2 and H2O. A thin film (6.7 nm) of TiO2 is deposited on an X-ray-transparent SiN x window, acting as the working electrode in a three-electrode flow cell. The spectra are collected based on the electron emission resulting from the decay of the X-ray-induced core-hole-excited atoms, which we show is sensitive to the solid–liquid interface within a few nm. The drain currents measured at the working and counter electrodes are identical but of opposite sign. With this method, we found that the water layer next to anatase is spectroscopically similar to ice. This result highlights the potential of electron-yield XAS to obtain chemical and structural information with a high sensitivity for the species at the electrode–electrolyte interface.

Revealing Solid Electrolyte Interphase Formation Through Interface-Sensitive Operando X-ray Absorption Spectroscopy

“…We note that this is essentially the same detection method as has been recently referred to as 'total ion yield' (TIY) XAS, [71,72] albeit with a voltage applied between the electrodes of the current amplifier to avoid short-circuiting the cell. However, we agree with the recent article by Spronsen et al [73] that this is not a bulk sensitive measure, and thus refer to it as TEY-XAS as in previous studies. [44,46,53] Although X-ray ionisation occurs within the bulk of the electrolyte, the short range over which the electrons scatter will mean they quickly recombine with ions such that local charge neutrality is maintained within the electrolyte.…”

Operando Resonant Soft X-ray Scattering Studies of Chemical Environment and Interparticle Dynamics of Cu Nanocatalysts for CO2 Electroreduction

“…The CO 2 reduction reaction (CO 2 RR) has emerged as a promising renewable technology to convert greenhouse gas into liquid fuels and chemicals. , Among many heterogeneous electrocatalysts investigated, Cu is the predominant candidate for selective CO 2 electroreduction to multicarbon products (C 2+ ). − However, understanding of the nature of active sites under reaction conditions has remained limited, particularly for high-performance Cu nanocatalysts, , which calls for further development of operando / in situ methods . Hard X-ray absorption spectroscopy (XAS) has been widely used to investigate the structural changes of bulk electrocatalysts, − due to the high penetration of high-energy X-rays and relatively low beam damage. , However, hard XAS (>5 keV) can only probe core electrons of the Cu atoms, which are not actively participating during electrocatalysis. , In comparison, soft XAS (<1 keV) can probe valence electrons (e.g., 3d electrons) by using transition metal L-edges, which are chemically more relevant in electrocatalysis. , Soft XAS is typically collected in either surface-sensitive total electron yield (TEY) mode or total fluorescence yield (TFY) mode that collects bulk signals. − Given the ultrahigh vacuum required for soft X-ray, it remains a great challenge to design a liquid cell that can enable reliable electrochemistry and simultaneous acquisition of sufficiently strong X-ray signals. − The few in situ soft XAS studies have investigated bulk Cu electrodes in TFY modes and delivered limited structural insights due to the weak X-ray signals or undesirable beam-induced damage caused by the large absorption cross section of soft X-rays …”

Near-infrared to visible and ultraviolet upconversion in TiO2 thin films modified with Er and Yb

“…The maxima of the O K lines at 531, 533, 539 and 544 eV can be assigned to 1s → t 2g , 1s → e g , and 1s → a 1g ,t 1u transitions (see also ref. 35 ). The O K line for the crystallized sample ( Fig.…”