A new QEXAFS system on the general XAFS beamline at the Shanghai Synchrotron Radiation Facility.

A new quick-scanning extended X-ray absorption fine-structure (QEXAFS) system for in situ studies has been developed and tested on the general XAFS beamline at the Shanghai Synchrotron Radiation Facility. In the new system, an analog-to-digital converter (ADC) with 1 MHz sampling rate is used to acquire the detector data while one scaler is used to precisely calculate the scanning energy. Two external hardware trigger signals were adopted to synchronize the data collection of the ADC and the scaler. The software development platforms of the double-crystal monochromator control system and the new QEXAFS system have been unified with the Experimental Physics and Industrial Control System. By comparing the spectra acquired by the conventional step-by-step XAFS system with an energy range of 1200 eV at the 7.5um Cu foil K-edge, the new system demonstrates satisfactory signal-to-noise ratio and energy resolution. The previous shortcomings, including distortion of the spectrum and energy shift, have been overcome. The tests with different integration times indicated that appropriate parameters not only ensure good experimental results but also enhance the smoothness of the XAFS spectrum at high energy zones. The reliability of the new system has also been verified.

Atomic-Level Fe-N-C Coupled with Fe3 C-Fe Nanocomposites in Carbon Matrixes as High-Efficiency Bifunctional Oxygen Catalysts.

Highly active and durable bifunctional oxygen electrocatalysts are of pivotal importance for clean and renewable energy conversion devices, but the lack of earth-abundant electrocatalysts to improve the intrinsic sluggish kinetic process of oxygen reduction/evolution reactions (ORR/OER) is still a challenge. Fe-N-C catalysts with abundant natural merits are considered as promising alternatives to noble-based catalysts, yet further improvements are urgently needed because of their poor stability and unclear catalytic mechanism. Here, an atomic-level Fe-N-C electrocatalyst coupled with low crystalline Fe3 C-Fe nanocomposite in 3D carbon matrix (Fe-SAs/Fe3 C-Fe@NC) is fabricated by a facile and scalable method. Versus atomically FeNx species and crystallized Fe3 C-Fe nanoparticles, Fe-SAs/Fe3 C-Fe@NC catalyst, abundant in vertical branched carbon nanotubes decorated on intertwined carbon nanofibers, exhibits high electrocatalytic activities and excellent stabilities both in ORR (E1/2 , 0.927 V) and OER (EJ=10 , 1.57 V). This performance benefits from the strong synergistic effects of multicomponents and the unique structural advantages. In-depth X-ray absorption fine structure analysis and density functional theory calculation further demonstrate that more extra charges derived from modified Fe clusters decisively promote the ORR/OER performance for atomically FeN4 configurations by enhanced oxygen adsorption energy. These insightful findings inspire new perspectives for the rational design and synthesis of economical-practical bifunctional oxygen electrocatalysts.

Operando Spectroscopic Identification of Active Sites in NiFe Prussian Blue Analogues as Electrocatalysts: Activation of Oxygen Atoms for Oxygen Evolution Reaction.

Developing highly efficient oxygen evolution reaction (OER) catalysts and understanding their activity are pivotal for electrochemical conversion technologies. Here, we report NiFe Prussian blue analogue (PBA) as a promising electrocatalyst for OER in alkaline conditions. This material has an impressively low overpotential of 258 mV that reaches a current density of 10 mA cm-2. Post-mortem characterization showed that the as-prepared catalyst is entirely transformed into amorphous nickel hydroxide after the electrochemical treatment, and Ni(OH)2 acts as the active species. Operando X-ray spectroscopic studies further found that this in situ generated Ni(OH)2 displays an unique feature that allows deprotonation under applied potential creating NiOOH2- x that contains Ni4+ ions. The deprotonation reaction is reversible and potential-dependent, i.e., the amount of Ni4+ increases with increasing applied potential. Theoretical calculations were used to show that the role of Ni4+ is to trigger oxidized oxygen ions as electrophilic centers with the subsequent activation of anion redox reactions for OER.

Manipulating local coordination of copper single atom catalyst enables efficient CO2-to-CH4 conversion.

Electrochemical CO2 conversion to methane, powered by intermittent renewable electricity, provides an entrancing opportunity to both store renewable electric energy and utilize emitted CO2. Copper-based single atom catalysts are promising candidates to restrain C-C coupling, suggesting feasibility in further protonation of CO* to CHO* for methane production. In theoretical studies herein, we find that introducing boron atoms into the first coordination layer of Cu-N4 motif facilitates the binding of CO* and CHO* intermediates, which favors the generation of methane. Accordingly, we employ a co-doping strategy to fabricate B-doped Cu-Nx atomic configuration (Cu-NxBy), where Cu-N2B2 is resolved to be the dominant site. Compared with Cu-N4 motifs, as-synthesized B-doped Cu-Nx structure exhibits a superior performance towards methane production, showing a peak methane Faradaic efficiency of 73% at -1.46 V vs. RHE and a maximum methane partial current density of -462 mA cm-2 at -1.94 V vs. RHE. Extensional calculations utilizing two-dimensional reaction phase diagram analysis together with barrier calculation help to gain more insights into the reaction mechanism of Cu-N2B2 coordination structure.

QXAFS system of the BL14W1 XAFS beamline at the Shanghai Synchrotron Radiation Facility.

The quick-scanning XAFS (QXAFS) method is achieved at the BL14W1 XAFS beamline at the Shanghai Synchrotron Radiation Facility based on the EPICS and LabVIEW systems. This is realised by the unprecedented use of LabVIEW's data logging and supervisory control module for communication with EPICS in synchrotron radiation facilities. A fine QXAFS spectrum with an energy range of 1.2 keV at the Cu K-edge has been collected in 2 s with stable beam position and the data quality is comparable with that of the step-mode XAFS spectrum. Analog-to-digital converter and double-crystal monochromator set-ups have been optimized in order to acquire optimal parameters for the QXAFS experiments. Signal-to-noise ratios of these spectra have been calculated in order to estimate the importance of these parameters.