Crystalline Disorder, Surface Chemistry, and Their Effects on the Oxygen Evolution Reaction (OER) Activity of Mass-Produced Nanostructured Iridium Oxides

In the present study, three mass-produced commercial IrOx 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 Ir$^{3+}$ along with Ir$^{4+}$. 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

Beam damage in operando X-ray diffraction studies of Li-ion batteries

Operando powder X-ray diffraction (PXRD) is a widely employed method for 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. In this study, we investigate the extent of X-ray beam damage during operando powder X-ray diffraction synchrotron experiments of 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 tests 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. Our investigation reveals that beam damage depends strongly both on X-ray energy, amount of exposure and that it depends strongly on the cell chemistry, i.e. the chemical composition of the electrode

Beam damage in operando X-ray diffraction studies of Li-ion batteries

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