The activity of polycrystalline thin film photoelectrodes is impacted by local variations of the material properties due to the exposure of different crystal facets and the presence of grain/domain ...boundaries. Here a multi‐modal approach is applied to correlate nanoscale heterogeneities in chemical composition and electronic structure with nanoscale morphology in polycrystalline Mo‐BiVO4. By using scanning transmission X‐ray microscopy, the characteristic structure of polycrystalline film is used to disentangle the different X‐ray absorption spectra corresponding to grain centers and grain boundaries. Comparing both spectra reveals phase segregation of V2O5 at grain boundaries of Mo‐BiVO4 thin films, which is further supported by X‐ray photoelectron spectroscopy and many‐body density functional theory calculations. Theoretical calculations also enable to predict the X‐ray absorption spectral fingerprint of polarons in Mo‐BiVO4. After photo‐electrochemical operation, the degraded Mo‐BiVO4 films show similar grain center and grain boundary spectra indicating V2O5 dissolution in the course of the reaction. Overall, these findings provide valuable insights into the degradation mechanism and the impact of material heterogeneities on the material performance and stability of polycrystalline photoelectrodes.
Understanding local chemical heterogeneity and its correlation with materials macroscopic performance can support the rational design of photoelectrodes. Probing Mo‐BiVO4 thin film photoelectrodes by scanning transmission microscopy (STXM) reveals chemical heterogeneity at the nanoscale. A general multimodal approach is used to combine STXM with atomic force microscopy and to determine relationships between local chemical composition, electronic structure, and nanoscale morphology.
Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover, contains a diverse and extensive record of aeolian deposition and erosion. This study focuses on a series of regularly ...spaced, curvilinear, and sometimes branching bedrock ridges that occur within the Glen Torridon region on the lower northwest flank of Aeolis Mons, the central mound within Gale crater. During Curiosity's exploration of Glen Torridon between sols ∼2300–3080, the rover drove through this field of ridges, providing the opportunity for in situ observation of these features. This study uses orbiter and rover data to characterize ridge morphology, spatial distribution, compositional and material properties, and association with other aeolian features in the area. Based on these observations, we find that the Glen Torridon ridges are consistent with an origin as wind‐eroded bedrock ridges, carved during the exhumation of Mount Sharp. Erosional features like the Glen Torridon ridges observed elsewhere on Mars, termed periodic bedrock ridges (PBRs), have been interpreted to form transverse to the dominant wind direction. The size and morphology of the Glen Torridon PBRs are consistent with transverse formative winds, but the orientation of nearby aeolian bedforms and bedrock erosional features raise the possibility of PBR formation by a net northeasterly wind regime. Although several formation models for the Glen Torridon PBRs are still under consideration, and questions persist about the nature of PBR‐forming paleowinds, the presence of PBRs at this site provides important constraints on the depositional and erosional history of Gale crater.
Plain Language Summary
Wind has played a major role in sculpting the surface of Mars. Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover since it landed there in 2012, contains a vast and varied record of deposition and erosion by the wind. This study focuses on a series of regularly spaced, generally straight bedrock ridges that occur within the clay‐bearing Glen Torridon region of Aeolis Mons (informally named Mount Sharp) in Gale crater. During Curiosity's exploration of the Glen Torridon region between sols ∼2300–3080 of the mission, the rover drove through this field of ridges, acquiring images and compositional observations along the way. This study characterizes the Glen Torridon ridges using orbiter and rover data to determine their shape, size, occurrence, and relationship to other wind‐formed features in the area. We find that the Glen Torridon ridges were carved by wind into the bedrock of Mount Sharp. Questions remain about the winds that formed these ridges, but this study provides important information about the history and environment of Gale crater and reports the first rover observations of this type of erosional feature on Mars.
Key Points
Decameter‐long, regularly spaced bedrock ridges oriented northeast‐southwest occur throughout the Glen Torridon region of Aeolis Mons
Glen Torridon ridges cross‐cut elevation contours and bedding, exhibit bifurcations, and are disrupted by small impact craters
Glen Torridon ridges are erosional periodic bedrock ridges whose formation places erosional and depositional constraints on Aeolis Mons
Photoelectrochemical (PEC) water splitting, which utilizes sunlight and water to produce hydrogen fuel, is potentially one of the most sustainable routes to clean energy. One challenge to success is ...that, to date, similar materials and devices measured in different labs or by different operators lead to quantitatively different results, due to the lack of accepted standard operating procedures and established protocols for PEC efficiency testing. With the aim of disseminating good practices within the PEC community, we provide a vetted protocol that describes how to prepare integrated components and accurately measure their solar-to-hydrogen (STH) efficiency (η
STH
). This protocol provides details on electrode fabrication, η
STH
test device assembly, light source calibration, hydrogen evolution measurement, and initial material qualification by photocurrent measurements under monochromatic and broadband illumination. Common pitfalls in translating experimental results from any lab to an accurate STH efficiency under an AM1.5G reference spectrum are discussed. A III–V tandem photocathode is used to exemplify the process, though with small modifications, the protocol can be applied to photoanodes as well. Dissemination of PEC best practices will help those approaching the field and provide guidance for comparing the results obtained at different lab sites by different groups.
In principle, the diameter and surface plasmon resonance (SPR) frequency of hollow metal nanostructures can be independently adjusted, allowing the formation of targeted photoactivated structures of ...specific size and optical functionality. Although tunable SPRs have been reported for various systems, the shift in SPR is usually concomitant with a change in particle size. As such, more advanced tunability, including constant diameter with varying SPR or constant SPR with varying diameter, has not been properly achieved experimentally. Herein, we demonstrate this advanced tunability with hollow gold nanospheres (HGNs). HGNs were synthesized through galvanic exchange using cobalt-based nanoparticles (NPs) as sacrificial scaffolds. Co2B NP scaffolds were prepared by sodium borohydride nucleation of aqueous cobalt chloride and characterized using UV–vis, dynamic light scattering, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Careful control over the size of the Co2B scaffold and its galvanic conversion is essential to realize fine control of the resultant HGN diameter and shell thickness. In pursuit of size control, we introduce B(OH)4 – (the final product of NaBH4 hydrolysis) as a growth agent to obtain hydrodynamic diameters ranging from ∼17–85 nm with relative standard deviation <3%. The highly monodisperse Co2B NPs were then used as scaffolds for the formation of HGNs. In controlling HGN shell thickness and uniformity, environmental oxygen was shown to affect both the structural and optical properties of the resultant gold shells. With careful control of these key factors, we demonstrate an HGN synthesis that enables independent variation of diameter and shell thickness, and thereby SPR, with unprecedented uniformity. The new synthesis method creates a truly tunable plasmonic nanostructure platform highly desirable for a wide range of applications, including sensing, catalysis, and photothermal therapy.
Charge transport mediators are commonly used in photoelectronic devices to promote selective charge transport and mitigate carrier losses. However, related investigations are mainly carried out by ...the trial‐and‐error method, and a deeper understanding of its local charge transport behavior is still lacking. Herein, a comprehensive study is performed on a BiVO4/Ti3C2 photoanode to reveal its local charge transport properties by combing microprobe technologies and numerical computations. For the first time, a nano‐Schottky junction is directly shown at the BiVO4/Ti3C2 interface and the band bending is quantified with promoted hole transport and prolonged photocarrier's lifetime. These mechanistic insights leverage a path to further optimize performance through interface engineering and achieve a photocurrent of 5.38 mA cm−2 at 1.23 V versus reversible hydrogen electrode. This work provides deeper insight into the function of charge transport mediators in view of interface contact rather than material nature and demonstrates a strategy to improve photoelectrochemical performance through Fermi‐level engineering.
Local photocurrent imaging analysis provides a deeper understanding of interfacial charge transport behavior at the nanoscale, which facilitates the development and optimization of charge select materials for the photoelectrochemical system to efficient solar fuel production.
Exciton dynamics of CdS films have been investigated using ultrafast laser spectroscopy with an emphasis on understanding defect-related recombination. Two types of CdS films were deposited on glass ...substrates via direct current pulse sputtering (DCPS) and chemical bath deposition (CBD) techniques. The films displayed distinct morphological, optical, and structural properties. Their exciton and charge carrier dynamics within the first 1 ns following photoexcitation were characterized by femotosecond pump probe spectroscopy. A singular value decomposition (SVD) global fitting technique was employed to extract the lifetime and wavelength dependence of transient species. The excited electrons of the DCPS sample decays through 1.8, 8, 65, and 450 ps time constants which were attributed to donor level electron trapping, valence band (VB) → conduction band (CB) recombination, shallow donor recombination, and deep donor recombination, respectively. The CBD sample shows time constants of 6, 65, and 450 ps which were attributed to CB → VB recombination, sulfur vacancy (V S) recombination, and V S → oxygen interstitial (Oi) donor–acceptor pair (DAP) recombination, respectively. It was found that the DCPS deposition technique produces films with lower defect density and improved carrier dynamics, which are important for high performance solar cell applications.
The challenge of fine compositional tuning and microstructure control in complex oxides is overcome by developing a general two‐step synthetic approach. Antimony‐alloyed bismuth vanadate, which is ...identified as a novel light absorber for solar fuel applications, is prepared in a wide compositional range. The bandgap of this quaternary oxide linearly decreases with the Sb content, in agreement with first‐principles calculations.
TRPM2 Ca(2+)-permeable cation channel is widely expressed and activated by markers of cellular stress. Since inflammation and stress play a major role in insulin resistance, we examined the role of ...TRPM2 Ca(2+) channel in glucose metabolism. A 2-h hyperinsulinemic euglycemic clamp was performed in TRPM2-deficient (KO) and wild-type mice to assess insulin sensitivity. To examine the effects of diet-induced obesity, mice were fed a high-fat diet for 4-10 mo, and metabolic cage and clamp studies were conducted in conscious mice. TRPM2-KO mice were more insulin sensitive partly because of increased glucose metabolism in peripheral organs. After 4 mo of high-fat feeding, TRPM2-KO mice were resistant to diet-induced obesity, and this was associated with increased energy expenditure and elevated expressions of PGC-1α, PGC-1β, PPARα, ERRα, TFAM, and MCAD in white adipose tissue. Hyperinsulinemic euglycemic clamps showed that TRPM2-KO mice were more insulin sensitive, with increased Akt and GSK-3β phosphorylation in heart. Obesity-mediated inflammation in adipose tissue and liver was attenuated in TRPM2-KO mice. Overall, TRPM2 deletion protected mice from developing diet-induced obesity and insulin resistance. Our findings identify a novel role of TRPM2 Ca(2+) channel in the regulation of energy expenditure, inflammation, and insulin resistance.
Abstract
Reactions of a dicopper(I)
tert
‐butoxide complex with alkynes possessing boryl or silyl capping groups resulted in formation of unprecedented tetracopper(I)
μ
‐acetylide/diyne complexes ...that were characterized by NMR and UV/Vis spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction. These compounds possess an unusual
μ
4
‐
η
1
:
η
1
:
η
1
:
η
1
coordination mode for the bridging organic fragment, enforced by the rigid and dinucleating nature of the ligand utilized. Thus, the central π system remains unperturbed and accessible for subsequent reactivity and modification. This has been corroborated by addition of a fifth copper atom, giving rise to a pentacopper acetylide complex. This work may provide a new approach by which metal‐metal cooperativity can be exploited in the transformation of acetylide and diyne groups to a variety of substrates, or as a starting point for the controlled synthesis of copper(I) alkyne‐containing clusters.
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