The new instrument for near‐ambient‐pressure X‐ray photoelectron spectroscopy which has been installed at the MAX II ring of the Swedish synchrotron radiation facility MAX IV Laboratory in Lund is ...presented. The new instrument, which is based on a SPECS PHOIBOS 150 NAP analyser, is the first to feature the use of retractable and exchangeable high‐pressure cells. This implies that clean vacuum conditions are retained in the instrument's analysis chamber and that it is possible to swiftly change between near‐ambient and ultrahigh‐vacuum conditions. In this way the instrument implements a direct link between ultrahigh‐vacuum and in situ studies, and the entire pressure range from ultrahigh‐vacuum to near‐ambient conditions is available to the user. Measurements at pressures up to 10−5 mbar are carried out in the ultrahigh‐vacuum analysis chamber, while measurements at higher pressures are performed in the high‐pressure cell. The installation of a mass spectrometer on the exhaust line of the reaction cell offers the users the additional dimension of simultaneous reaction data monitoring. Moreover, the chosen design approach allows the use of dedicated cells for different sample environments, rendering the Swedish ambient‐pressure X‐ray photoelectron spectroscopy instrument a highly versatile and flexible tool.
The aggravating extreme climate changes and natural disasters stimulate the exploration of low‐carbon/zero‐carbon alternatives to traditional carbon‐based fossil fuels. Solar‐to‐hydrogen (STH) ...transformation is considered as appealing route to convert renewable solar energy into carbon‐free hydrogen. Restricted by the low efficiency and high cost of noble metal cocatalysts, high‐performance and cost‐effective photocatalysts are required to realize the realistic STH transformation. Herein, the 2D FePS3 (FPS) nanosheets anchored with TiO2 nanoparticles (TiO2/FePS3) are synthesized and tested for the photocatalytic hydrogen evolution reaction. With the integration of FPS, the photocatalytic H2‐evolution rate on TiO2/FePS3 is radically increased by ≈1686%, much faster than that of TiO2 alone. The origin of the greatly raised activity is revealed by theoretical calculations and various advanced characterizations, such as transient‐state photoluminescence spectroscopy/surface photovoltage spectroscopy, in situ atomic force microscopy combined with Kelvin probe force microscopy (AFM‐KPFM), in situ X‐ray photoelectron spectroscopy (XPS), and synchrotron‐based X‐ray absorption near edge structure. Especially, the in situ AFM‐KPFM and in situ XPS together confirm the electron transport pathway in TiO2/FePS3 with light illumination, unveiling the efficient separation/transfer of charge carrier in TiO2/FePS3 step‐scheme heterojunction. This work sheds light on designing and fabricating novel 2D material‐based S‐scheme heterojunctions in photocatalysis.
Anchoring of TiO2 nanoparticles onto FePS3 nanosheets creates S‐scheme n‐p heterojunction of TiO2/FePS3 with a strong built‐in electric field, significantly raising the photocatalytic hydrogen evolution rate. Atomic force microscopy Kelvin probe force microscopy and X‐ray photoelectron spectroscopy confirm the photogenerated charge transfer pathway, corroborating the formation of a TiO2/FePS3 S‐scheme heterojunction with efficient charge separation and transfer.
Organolead halide perovskites currently are the new front‐runners as light absorbers in hybrid solar cells, as they combine efficiencies passing already 20% with deposition temperatures below 100 °C ...and cheap solution‐based fabrication routes. Long‐term stability remains a major obstacle for application on an industrial scale. Here, it is demonstrated that significant decomposition effects already occur during annealing of a methylammonium lead triiode perovskite at 85 °C even in inert atmosphere thus violating international standards. The observed behavior supports the view of currently used perovskite materials as soft matter systems with low formation energies, thus representing a major bottleneck for their application, especially in countries with high average temperatures. This result can trigger a broader search for new perovskite families with improved thermal stability.
It is shown that significant degradation effects of CH3NH3PbI3 already occur at 85 °C, independent of the atmosphere, where humidity is a catalyst but not the origin of the degradation. This represents an important message for the perovskite community and leads to recommendations for future perovskite developments.
An iridium oxide nanoparticle electrocatalyst under oxygen evolution reaction conditions was probed in situ by ambient‐pressure X‐ray photoelectron spectroscopy. Under OER conditions, iridium ...undergoes a change in oxidation state from IrIV to IrV that takes place predominantly at the surface of the catalyst. The chemical change in iridium is coupled to a decrease in surface hydroxide, providing experimental evidence which strongly suggests that the oxygen evolution reaction on iridium oxide occurs through an OOH‐mediated deprotonation mechanism.
The surface species of an iridium oxide electrocatalyst under oxygen evolution reaction (OER) conditions were probed by ambient‐pressure X‐ray photoelectron spectroscopy (APXPS). Under OER conditions, iridium undergoes a change in oxidation state from IrIV to IrV predominantly at the catalyst surface, indicating that the OER on iridium oxide occurs on a single iridium site, suggesting an OOH‐mediated mechanism.
Molybdenum‐based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum ...borides Mo2B, α‐MoB, β‐MoB, and MoB2 by arc‐melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X‐ray photoelectron spectroscopy (XPS) for the first time; MoB2 and β‐MoB show excellent activity in the same range as the recently reported α‐MoB and β‐Mo2C phases, while the molybdenum richest phase Mo2B show significantly lower HER activity, indicating a strong boron‐dependency of these borides for the HER. In addition, MoB2 and β‐MoB show long‐term cycle stability in acidic solution.
The more boron, the better: Two excellent and robust electrocatalysts for the hydrogen evolution reaction (HER), β‐MoB and MoB2, have been discovered in the Mo‐B system. Furthermore, as the boron content increases in the system, the catalytic performance of these borides also increases.
The electronic, optical, and magnetic properties of graphene nanoribbons (GNRs) can be engineered by controlling their edge structure and width with atomic precision through bottom‐up fabrication ...based on molecular precursors. This approach offers a unique platform for all‐carbon electronic devices but requires careful optimization of the growth conditions to match structural requirements for successful device integration, with GNR length being the most critical parameter. In this work, the growth, characterization, and device integration of 5‐atom wide armchair GNRs (5‐AGNRs) are studied, which are expected to have an optimal bandgap as active material in switching devices. 5‐AGNRs are obtained via on‐surface synthesis under ultrahigh vacuum conditions from Br‐ and I‐substituted precursors. It is shown that the use of I‐substituted precursors and the optimization of the initial precursor coverage quintupled the average 5‐AGNR length. This significant length increase allowed the integration of 5‐AGNRs into devices and the realization of the first field‐effect transistor based on narrow bandgap AGNRs that shows switching behavior at room temperature. The study highlights that the optimized growth protocols can successfully bridge between the sub‐nanometer scale, where atomic precision is needed to control the electronic properties, and the scale of tens of nanometers relevant for successful device integration of GNRs.
This work studies the growth, characterization, and device integration of 5‐atom wide armchair graphene nanoribbons (5‐AGNRs). 5‐AGNRs are synthesized under ultrahigh vacuum conditions from Br‐ and I‐substituted precursors. The authors show that I‐substituted precursors and optimized initial precursor coverage quintupled the average 5‐AGNR length. This significant length increase allows to integrate 5‐AGNRs into field‐effect transistors, showing switching behavior at room temperature.
Active and highly stable oxide‐supported IrNiOx core–shell catalysts for electrochemical water splitting are presented. IrNix@IrOx nanoparticles supported on high‐surface‐area mesoporous ...antimony‐doped tin oxide (IrNiOx /Meso‐ATO) were synthesized from bimetallic IrNix precursor alloys (PA‐IrNix /Meso‐ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA‐IrNix /Meso‐ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core–shell particles. The core–shell IrNiOx /Meso‐ATO catalyst displayed high water‐splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.
Water splitting: IrNiOx core–shell nanoparticles consisting of a thin IrOx shell and an Ir‐low/Ir‐free core supported on mesoporous antimony doped tin oxide are demonstrated to provide substantial advances toward more efficient, stable, and less expensive electrolytic water splitting catalysts.
Converting solar energy into chemical fuels is increasingly receiving a great deal of attention. In this work, CdS nanoparticles (NPs) are solvothermally anchored onto graphene nanoribbons (GNRs) ...that are longitudinally unzipped from multiwalled carbon nanotubes. The as‐synthesized CdS/GNR nanocomposites with recyclability present GNR content‐dependent activity in visible‐light‐driven hydrogen evolution from water splitting. In a range of 1–10 wt% GNRs, the CdS/GNR composites with 2 wt% GNRs achieves the greatest hydrogen evolution rate of 1.89 mmol h−1 g−1. The corresponding apparent quantum efficiency is 19.3%, which is ≈3.7 times higher than that of pristine CdS NPs. To elucidate the underlying photocatalytic mechanism, a systematic characterization, including in situ irradiated X‐ray photoelectron spectroscopy and Kelvin probe measurements, is performed. In particular, the interfacial charge transfer pathway and process from CdS NPs to GNRs is revealed. This work may open avenues to fabricate GNR‐based nanocomposites for solar‐to‐chemical energy conversion and beyond.
The charge transfer pathway and process of CdS/graphene nanoribbon composites with enhanced photocatalytic hydrogen evolution were revealed by in situ irradiated X‐ray photoelectron spectroscopy and Kelvin probe measurements.
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