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Multicomponent nanoparticle exsolution has emerged as a promising process for obtaining highly active catalysts supported on perovskite oxides. For instance, FeCoNi alloys can be exsolved from Sr2FeCo0.2Ni0.2Mn0.1Mo0.5O6−δ, boosting the electrocatalytic properties of these electrodes. However, due to differences in cation diffusion properties, the composition of the nanoparticles is uneven and strongly affected by process conditions such as temperature. An additional key feature of exsolution is its reversibility, which could help in catalyst regeneration if poisoned. Nevertheless, there is little knowledge on the reversibility mechanisms of multicomponent exsolved alloys. For that purpose, a combination of synchrotron-based in situ X-ray Diffraction (XRD) and Near-Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) was employed in this work to uncover these missing aspects of multicomponent alloyed exsolution. These techniques allowed determination of the crystallographic and surface-related phenomena occurring during reversible exsolution both to the nanoparticles and the perovskite oxide support. This enabled the identification of the exsolution onset temperature and the range at which the double perovskite to Ruddlesden–Popper transition occurred, a process that has notable implications for the electrocatalytic performance. Finally, in combination with microscopy analyses, it was possible to reveal the morphological and compositional changes that the exsolved nanoparticles experienced upon reduction–oxidation cycles. This resulted in a re-arrangement of the surface species and a variation in the composition (Fe enrichment) of the regenerated ternary alloyed exsolved nanoparticles. These results indicate that reversible exsolution might alter the catalytic properties of the exsolved nanoparticles, with profound implications in the performance of (electro)catalytic processes. [ABSTRACT FROM AUTHOR]

Nanostructured tungsten disulfide (WS2) is one of the most promising candidates for being used as active nanomaterial in chemiresistive gas sensors, as it responds to hydrogen gas at room temperature. This study analyzes the hydrogen sensing mechanism of a nanostructured WS2 layer using near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT). The W 4f and S 2p NAP-XPS spectra suggest that hydrogen makes physisorption on the WS2 active surface at room temperature and chemisorption on tungsten atoms at temperatures above 150 °C. DFT calculations show that a hydrogen molecule physically adsorbs on the defect-free WS2 monolayer, while it splits and makes chemical bonds with the nearest tungsten atoms on the sulfur point defect. The hydrogen adsorption on the sulfur defect causes a large charge transfer from the WS2 monolayer to the adsorbed hydrogen. In addition, it decreases the intensity of the in-gap state, which is generated by the sulfur point defect. Furthermore, the calculations explain the increase in the resistance of the gas sensor when hydrogen interacts with the WS2 active layer. [ABSTRACT FROM AUTHOR]

Ultrathin atomic layer deposited ceria films (<20 nm) are capable of H 2 heterolytic activation at room temperature, undergoing a significant reduction regardless of the absolute pressure, as measured under in-situ conditions by near ambient pressure X-ray photoelectron spectroscopy. ALD-ceria can gradually reduce as a function of H 2 concentration under H 2 /O 2 environments, especially for diluted mixtures below 10 %. At room temperature, this reduction is limited to the surface region, where the hydroxylation of the ceria surface induces a charge transfer towards the ceria matrix, reducing Ce 4+ cations to Ce 3+ . Thus, ALD-ceria replicates the expected sensing mechanism of metal oxides at low temperatures without using any noble metal decorating the oxide surface to enhance H 2 dissociation. The intrinsic defects of the ALD deposit seem to play a crucial role since the post-annealing process capable of healing these defects leads to decreased film reactivity. The sensing behavior was successfully demonstrated in sensor test structures by resistance changes towards low concentrations of H 2 at low operating temperatures without using noble metals. These promising results call for combining ALD-ceria with more conductive metal oxides, taking advantage of the charge transfer at the interface and thus modifying the depletion layer formed at the heterojunction., (© 2025 The Author(s). ChemSusChem published by Wiley-VCH GmbH.)

Ni-Fe nanocatalysts supported on CeO 2 have been prepared for the catalysis of methane steam reforming (MSR) aiming for coke-resistant noble metal-free catalysts. The catalysts have been synthesized by traditional incipient wetness impregnation as well as dry ball milling, a green and more sustainable preparation method. The impact of the synthesis method on the catalytic performance and the catalysts' nanostructure has been investigated. The influence of Fe addition has been addressed as well. The reducibility and the electronic and crystalline structure of Ni and Ni-Fe mono- and bimetallic catalysts have been characterized by temperature programmed reduction (H 2 -TPR), in situ synchrotron X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Their catalytic activity was tested between 700 and 950 °C at 108 L g cat -1 h -1 and with the reactant flow varying between 54 and 415 L g cat -1 h -1 at 700 °C. Hydrogen production rates of 67 mol g met -1 h -1 have been achieved. The performance of the ball-milled Fe 0.1 Ni 0.9 /CeO 2 catalyst was similar to that of Ni/CeO 2 at high temperatures, but Raman spectroscopy revealed a higher amount of highly defective carbon on the surface of Ni-Fe nanocatalysts. The reorganization of the surface under MSR of the ball-milled NiFe/CeO 2 has been monitored by in situ near-ambient pressure XPS experiments, where a strong reorganization of the Ni-Fe nanoparticles with segregation of Fe toward the surface has been observed. Despite the catalytic activity being lower in the low-temperature regime, Fe addition for the milled nanocatalyst increased the coke resistance and could be an efficient alternative to industrial Ni/Al 2 O 3 catalysts., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The present study proposes a laser irradiation method to superficially reduce BiVO 4 photoelectrodes and boost their water oxidation reaction performance. The origin of this enhanced performance toward oxygen evolution reaction (OER) was studied using a combination of a suite of structural, chemical, and mechanistic advanced characterization techniques including X-ray photoelectron (XPS), X-ray absorption spectroscopy (XAS), electrochemical impedance spectroscopy (EIS), and transient absorption spectroscopy (TAS), among others. We found that the reduction of the material is localized at the surface of the sample and that this effect creates effective n-type doping and a shift to more favorable energy band positions toward water oxidation. This thermodynamic effect, together with the change in sample morphology to larger and denser domains, results in an extended lifetime of the photogenerated carriers and improved charge extraction. In addition, the stability of the reduced sample in water was also confirmed. All of these effects result in a two-fold increase in the photocurrent density of the laser-treated samples.