Cryomilled Ni-Co-Se Enables Water Oxidation Electrocatalysts Durable at High Current Densities

The oxygen evolution reaction (OER) limits electrocatalysis due to the high overpotential incurred by the poor reaction kinetics; this problem worsens over time if the performance of the OER electrocatalyst diminishes during operation. Here, we report the synthesis of immiscible Ni-Co-Se nanoparticles (<10 nm) for alkaline OER using milling at a cryogenic temperature. Milling at such low temperatures promotes thermodynamically stable nanocrystalline intermetallics with a high density of coordinatively unsaturated active sites. Using operando synchrotron spectroscopy, electron microscopy, and density functional theory we found that during the OER, Se ions leaches out of the nanocrystalline structure activating the electrocatalyst by hydrating and transforming defective Ni and Co sites into active and stable oxyhydroxides. Activated (NiCo)3Se4 electrocatalyst required only an overpotential of 279 mV at 0.5 A.cm-2 and 329 mV at 1 A.cm-2 for 500 hours in 1M KOH. Using anion exchange membrane, we report the lowest cell voltage for an alkaline water electrolyser delivering 2 A.cm-2 at 2 V.

Identifying Thermal Decomposition Products of Nitrate Ester Explosives Using Gas Chromatography–Vacuum Ultraviolet Spectroscopy: An Experimental and Computational Study

Analysis of nitrate ester explosives (e.g., nitroglycerine) using gas chromatography–vacuum ultraviolet spectroscopy (GC–VUV) results in their thermal decomposition into nitric oxide, water, carbon monoxide, oxygen, and formaldehyde. These decomposition products exhibit highly structured spectra in the VUV that is not seen in larger molecules. Computational analysis using time-dependent density functional theory (TDDFT) was utilized to investigate the excited states and vibronic transitions of these decomposition products. The experimental and computational results are compared with those in previous literature using synchrotron spectroscopy, electron energy loss spectroscopy (EELS), photoabsorption spectroscopy, and other computational excited state methods. It was determined that a benchtop GC–VUV detector gives comparable results to those previously reported, and TDDFT could predict vibronic spacing and model molecular orbital diagrams.

Synchrotron spectroscopy of the CSH-bending and CH3-rocking bands of methyl mercaptan

The CSH-bending and CH3-rocking infrared bands of CH3SH have been investigated in Fourier transform spectra recorded at 0.001 cm−1 resolution employing synchrotron radiation at the Canadian Light Source in Saskatoon. The relative band strengths and structures are quite different from those of the CH3OH methanol analogue, with the CSH bend being very weak and both the in-plane and out-of-plane CH3 rocks being strong with intensities greater than the C–S stretch. The CSH bend has parallel a-type character with no detectable b-type component. The out-of-plane CH3 rock is a purely c-type perpendicular band, whereas the in-plane rock is of mixed a/b character. Sub-bands have been assigned for A and E torsional species up to about K = 10 for each vibrational mode, providing upper-state term values from which K-reduced substate origins were determined. For the CSH bend, the origins follow the customary oscillatory torsional pattern as a function of K with a sharply reduced amplitude of 0.362 cm−1 compared to the 0.653 cm−1 for the ground state. The torsional energy curves for the out-of-plane rock are also well-behaved but have inverted ordering of the A–E torsional splitting components and a larger amplitude of 1.33 cm−1. In contrast, the substate origins for the in-plane rock are scattered over a range of about 2 cm−1 without clear oscillatory structure. Several instances of coupling among the lower modes and the ground state via resonances between accidentally near-degenerate levels have been observed and characterized. Ab initio calculations are found to give a good representation of the frequency and relative intensity patterns for the lower vibrational modes.

In situ XAFS of acid-resilient iridate pyrochlore oxygen evolution electrocatalysts under operating conditions

Electrocatalytic water splitting using iridate pyrochlores studied using synchrotron spectroscopy reveals a response from all iridium in the conducting oxide.