Atomically dispersed transition metal active sites have emerged as one of the most important fields of study because they display promising performance in catalysis and have the potential to serve as ...ideal models for fundamental understanding. However, both the preparation and determination of such active sites remain a challenge. The structural engineering of carbon- and nitrogen-coordinated metal sites (M–N–C, M = Fe, Co, Ni, Mn, Cu, etc.) via employing new heteroatoms, e.g., P and S, remains challenging. In this study, carbon nanosheets embedded with nitrogen and phosphorus dual-coordinated iron active sites (denoted as Fe-N/P-C) were developed and determined using cutting edge techniques. Both experimental and theoretical results suggested that the N and P dual-coordinated iron sites were favorable for oxygen intermediate adsorption/desorption, resulting in accelerated reaction kinetics and promising catalytic oxygen reduction activity. This work not only provides efficient way to prepare well-defined single-atom active sites to boost catalytic performance but also paves the way to identify the dual-coordinated single metal atom sites.
Iron phthalocyanine‐based polymers (PFePc) are attractive noble‐metal‐free candidates for catalyzing oxygen reduction reaction (ORR). However, the low site‐exposure degree and poor electrical ...conductivity of bulk PFePc restricted their practical applications. Herein, laminar PFePc nanosheets covalently and longitudinally linked to graphene (3D‐G‐PFePc) was prepared. Such structural engineering qualifies 3D‐G‐PFePc with high site utilization and rapid mass transfer. Thence, 3D‐G‐PFePc demonstrates efficient ORR performance with a high specific activity of 69.31 μA cm−2, a high mass activity of 81.88 A g−1, and a high turnover frequency of 0.93 e s−1 site−1 at 0.90 V vs. reversible hydrogen electrode in O2‐saturated 0.1 M KOH, outperforming the lamellar PFePc wrapped graphene counterpart. Systematic electrochemical analyses integrating variable‐frequency square wave voltammetry and in situ scanning electrochemical microscopy further underline the rapid kinetics of 3D‐G‐PFePc towards ORR.
Exfoliated laminar iron phthalocyanine‐based polymer (PFePc) nanosheets covalently and longitudinally linked to graphene (3D‐G‐PFePc) are designed as noble‐metal‐free candidates for catalyzing the oxygen reduction reaction (ORR). Comprehensive variable‐frequency square wave voltammetry and in situ scanning electrochemical microscopy measurements further reveal the rapid ORR kinetics of the prepared 3D‐G‐PFePc.
The quick‐EXAFS (QEXAFS) method adds time resolution to X‐ray absorption spectroscopy (XAS) and allows dynamic structural changes to be followed. A completely new QEXAFS setup consisting of ...monochromator, detectors and data acquisition system is presented, as installed at the SuperXAS bending‐magnet beamline at the Swiss Light Source (Paul Scherrer Institute, Switzerland). The monochromator uses Si(111) and Si(311) channel‐cut crystals mounted on one crystal stage, and remote exchange allows an energy range from 4.0 keV to 32 keV to be covered. The spectral scan range can be electronically adjusted up to several keV to cover multiple absorption edges in one scan. The determination of the Bragg angle close to the position of the crystals allows high‐accuracy measurements. Absorption spectra can be acquired with fast gridded ionization chambers at oscillation frequencies of up to 50 Hz resulting in a time resolution of 10 ms, using both scan directions of each oscillation period. The carefully developed low‐noise detector system yields high‐quality absorption data. The unique setup allows both state‐of‐the‐art QEXAFS and stable step‐scan operation without the need to exchange whole monochromators. The long‐term stability of the Bragg angle was investigated and absorption spectra of reference materials as well as of a fast chemical reaction demonstrate the overall capabilities of the new setup.
Maneb is a manganese(II)‐containing fungicide with a multi‐site effect and no resistance, therefore it is widely applied in many parts of the world. There is, however, mounting evidence for ...neurotoxic effects with Parkinson‐like symptoms (manganism) related to usage of Maneb. Due to its insolubility in most solvents and its paramagnetism, structural elucidation is not trivial, and thus its exact molecular structure remains unknown. We report herein a synthesis procedure to prepare Maneb reproducibly in pure form and the use of various analytical techniques including X‐ray diffraction, X‐ray absorption spectroscopy and electron diffraction to determine the molecular structure of Maneb in the solid state and also in solution.
Molecular structure of Maneb determined: Over 70 years after patent publication, the mystery of the structure of the surprisingly stable manganese(II)‐containing ethylene bis(dithiocarbamate) fungicide, which is extensively used in agriculture, has finally been solved.
The development of porous carbon materials as highly efficient, durable, and economic electrocatalysts for oxygen reduction reaction (ORR) is of great importance for realizing practical applications ...of many significant energy conversion and storage devices. Herein, we demonstrate a general approach to porous carbons decorated with boron centers and atomically dispersed Fe–N x species (denoted as FeBNC). The as-prepared FeBNC can serve as efficient electrocatalysts for ORR in an alkaline medium with a half-wave potential of 0.838 V vs RHE, comparable to that of the state-of-the-art porous carbon catalysts and the benchmark system Pt/C. Theoretical calculation reveals that incorporation of boron dopant into traditional Fe–N x species-enriched porous carbons significantly lowers the energy barrier for oxygen reduction and therefore boosts the overall performance. This work not only provides an easy method to synthesize B-doped Fe–N x centers-enriched porous carbons as highly efficient electrocatalysts for ORR and Zn-air batteries but also proves the origin of the catalytic performance from both B dopants and Fe–N x sites.
For large‐scale and high‐throughput production of organic solar cells (OSCs), liquid processing of the functional layers is desired. We demonstrate inverted bulk‐heterojunction organic solar cells ...(OSCs) with a sol–gel derived V2O5 hole‐extraction‐layer on top of the active organic layer. The V2O5 layers are prepared in ambient air using Vanadium(V)‐oxitriisopropoxide as precursor. Without any post‐annealing or plasma treatment, a high work function of the V2O5 layers is confirmed by both Kelvin probe analysis and ultraviolet photoelectron spectroscopy (UPS). Using UPS and inverse photoelectron spectroscopy (IPES), we show that the electronic structure of the solution processed V2O5 layers is similar to that of thermally evaporated V2O5 layers which have been exposed to ambient air. Optimization of the sol gel process leads to inverted OSCs with solution based V2O5 layers that show power conversion efficiencies similar to that of control devices with V2O5 layers prepared in high‐vacuum.
Inverted organic solar cells employing a solution processed V2O5 (sV2O5) hole‐extraction‐layer on top of the active organic layer are demonstrated. Even without any post‐deposition treatment, the electronic structure of the sV2O5 layers is similar to that of thermally evaporated V2O5 (eV2O5) layers which have been exposed to ambient air. Optimized devices with sV2O5 layers show power conversion efficiencies similar to that of devices with eV2O5 layers.
The quick-EXAFS (QEXAFS) method adds time resolution to X-ray absorption spectroscopy (XAS) and allows dynamic structural changes to be followed. A completely new QEXAFS setup consisting of ...monochromator, detectors and data acquisition system is presented, as installed at the SuperXAS bending-magnet beamline at the Swiss Light Source (Paul Scherrer Institute, Switzerland). The monochromator uses Si(111) and Si(311) channel-cut crystals mounted on one crystal stage, and remote exchange allows an energy range from 4.0keV to 32keV to be covered. The spectral scan range can be electronically adjusted up to several keV to cover multiple absorption edges in one scan. The determination of the Bragg angle close to the position of the crystals allows high-accuracy measurements. Absorption spectra can be acquired with fast gridded ionization chambers at oscillation frequencies of up to 50Hz resulting in a time resolution of 10ms, using both scan directions of each oscillation period. The carefully developed low-noise detector system yields high-quality absorption data. The unique setup allows both state-of-the-art QEXAFS and stable step-scan operation without the need to exchange whole monochromators. The long-term stability of the Bragg angle was investigated and absorption spectra of reference materials as well as of a fast chemical reaction demonstrate the overall capabilities of the new setup.
Secondary phases zinc sulfide/selenide and copper sulfide in Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) thin film samples are investigated by X-ray absorption near edge structure (XANES) analysis at the ...chalcogen K-edges. Because of the formation of secondary phases the composition of the kesterite phase can deviate significantly from the total sample composition. For a large set of non-stoichiometric samples we find that the cation ratios of the kesterite phase never exceed Zn/Sn = 1 even for Zn-rich CZTS and CZTSe, with all excess Zn being contained in secondary phases. For CZTS the cation ratios are found to be additionally constrained by Cu/Sn ≤ 2, which means that Cu-excess always leads to the formation of CuxS secondary phases. These results give clear bounds on the Cu-rich and Zn-rich sides of the single phase region in polycrystalline CZTS/Se thin films.
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