In the present study, three mass-produced commercial IrO x samples from different suppliers were studied to establish correlations between various properties and their OER activities. The structures of the electrocatalysts at different scales were explored through laboratory instrumentation, powder X-ray diffraction, and synchrotron-based X-ray total scattering experiments combined with pair distribution function analysis. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy using a transmission electron microscope were used to determine respectively the surface and the bulk elemental compositions of the samples. The coherent domain size (CDS) values of IrO x phases within the catalyst particles were estimated to be ∼10, ∼ 19, and ∼ 54 Å for the three IrO x samples. Surprisingly, the sample with a CDS of ∼19 Å turned out as the best OER electrocatalyst among the three in terms of mass-specific activity, I OER(m), followed by the 10 and 54 Å species. The amount of surface native compound oxygen was found to be a key parameter for the interface electrochemical accessibility. The intrinsic OER activity, evaluated using area-specific activity, I OER(a), suggests that the oxide with lattice disorder presenting a mixture of tetragonal and orthorhombic phases (70:20 w/w) is of superior intrinsic OER activity; however, the oxide with the presence of a monoclinic-like phase is of inferior intrinsic OER activity, which may also be due to the surface presence of Ir3+ along with Ir4+. The classic belief that the pure tetragonal phase is the best crystalline structure as the OER catalyst is challenged. Iridium oxides with disordered crystallinities may offer a class of highly active oxygen evolution electrocatalysts. The knowledge thus obtained should have a significant impact on the understanding, selection, and processing of IrO x -based OER electrocatalysts.

Operando powder X-ray diffraction (PXRD) is a widely employed method for the investigation of structural evolution and phase transitions in electrodes for rechargeable batteries. Due to the advantages of high brilliance and high X-ray energies, the experiments are often carried out at synchrotron facilities. It is known that the X-ray exposure can cause beam damage in the battery cell, resulting in hindrance of the electrochemical reaction. This study investigates the extent of X-ray beam damage during operando PXRD synchrotron experiments on battery materials with varying X-ray energies, amount of X-ray exposure and battery cell chemistries. Battery cells were exposed to 15, 25 or 35 keV X-rays (with varying dose) during charge or discharge in a battery test cell specially designed for operando experiments. The observed beam damage was probed by µPXRD mapping of the electrodes recovered from the operando battery cell after charge/discharge. The investigation reveals that the beam damage depends strongly on both the X-ray energy and the amount of exposure, and that it also depends strongly on the cell chemistry, i.e. the chemical composition of the electrode.

A cloud-hosted web-based software application, nmfMapping, for carrying out a non-negative matrix factorization of a set of powder diffraction or atomic pair distribution function datasets is described. This application allows structure scientists to find trends rapidly in sets of related data such as from in situ and operando diffraction experiments. The application is easy to use and does not require any programming expertise. It is available at https://pdfitc.org/.

Iron(iii) hydroxide phosphate hydrate Fe1.13(PO4)(OH)0.39(H2O)0.61 is investigated for the first time as a Na-ion battery cathode. The material exhibits similar storage capacities for Na- and Li-ions at relatively low current rates (i.e. C/10).

Lithium vanadium fluorophosphate, LiVPO 4 F, is a promising cathode material for Li-ion batteries due to its high intercalation potential (4.24 V vs Li/Li + ) and high stability. However, recent studies show that as-synthesized LiVPO 4 F very often contains oxygen-defects on the fluoride site giving rise to a general composition of LiVPO 4 F 1-y O y with vanadium in a mixed +III/+IV valence state. The inclusion of oxygen naturally influences the electrochemical properties greatly, and a thorough material characterization is necessary to understand the performance. In this study, we synthesize lithium vanadium fluorophosphate by two common strategies: solid-state and hydrothermal synthesis.We show that solid-state synthesis provides LiVPO 4 F, while the hydrothermal method, in contrast to previous reports, leads to inclusion of ca. 35 % oxygen on the fluoride site and significant disorder in the material. The different electrochemical properties were probed by operando synchrotron X-ray powder diffraction to investigate the effects of oxygen inclusion on the structural evolution during electrochemical lithiation and delithiation. This reveals that while LiVPO 4 F exhibits a typical biphasic phase evolution, the sample with oxygen inclusion on the fluoride site displays extended solid-solution behavior. This explains previous observations of improved capacity retention due to defects.