Developing exceptionally durable and efficient oxygen reduction reaction (ORR) catalysts is of paramount importance but still challenging for widespread commercialization of proton exchange membran... Description

The design and capabilities of a novel Quick scanning Extended X-ray Absorption Fine Structure (QEXAFS) monochromator are presented. The oscillatory movement of the crystal stage is realized by means of a unique open-loop driving scheme operating a direct drive torque motor. The entire drive mechanics are installed inside of a goniometer located on the atmospheric side of the vacuum chamber. This design allows remote adjustment of the oscillation frequency and spectral range, giving complete control of QEXAFS measurements. It also features a real step-scanning mode, which operates without a control loop to prevent induced vibrations. Equipped with Si(111) and Si(311) crystals on a single stage, it facilitates an energy range from 4.0 keV to 43 keV. Extended X-ray absorption fine structure spectra up to k = 14.4 Å⁻¹ have been acquired within 17 ms and X-ray absorption near edge structure spectra covering more than 200 eV within 10 ms. The achieved data quality is excellent as shown by the presented measurements.

The layout and the characteristics of the Quick scanning EXAFS (QEXAFS, ref. [1]) setup at beamline P64 at the storage ring PETRA III, DESY, Germany are described. The quickly oscillating cryo-cooled monochromator allows measurements from 4.5 keV to 44 keV with frequencies up to 100 Hz. The effect of tapering of the undulator on spectra as well as the different detection schemes with transmission, reflectivity and fluorescence are discussed. The data acquisition is explained in detail. Reference spectra at different frequencies and examples of time resolved user experiments are shown. The influence of noise and filtering on the spectra is analysed.