Surface structural transitions and active sites are identified using X-ray scattering and density functional theory.

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The high precious metal loading and high overpotential of the oxygen evolution reaction (OER) prevents the widespread utilization of polymer electrolyte membrane (PEM) water electrolyzers. Herein we explore the OER activity and stability in acidic electrolyte of a combined IrO/RuO system consisting of RuO thin films with submonolayer (1, 2, and 4 Å) amounts of IrO deposited on top. Operando extended X-ray absorption fine structure (EXAFS) on the Ir L-3 edge revealed a rutile type IrO structure with some Ir sites occupied by Ru, IrO being at the surface of the RuO thin film. We monitor corrosion on IrO/RuO thin films by combining electrochemical quartz crystal microbalance (EQCM) with inductively coupled mass spectrometry (ICP-MS). We elucidate the importance of submonolayer surface IrO in minimizing Ru dissolution. Our work shows that we can tune the surface properties of active OER catalysts, such as RuO, aiming to achieve higher electrocatalytic stability in PEM electrolyzers.

Probing the nanoscale structure of the catalytically active overlayer on Pt alloys with rare earths, Nano Energy, http://dx.

Herein we present surface sensitive operando XAS L-edge measurements on IrO/RuO thin films as well as mass-selected RuO and Ru nanoparticles. We observed shifts of the white line XAS peak toward higher energies with applied electrochemical potential. Apart from the case of the metallic Ru nanoparticles, the observed potential dependencies were purely core-level shifts caused by a change in oxidation state, which indicates no structural changes. These findings can be explained by different binding energies of oxygenated species on the surface of IrO and RuO. Simulated XAS spectra show that the average Ir oxidation state change is strongly affected by the coverage of atomic O. The observed shifts in oxidation state suggest that the surface has a high coverage of O at potentials just below the potential where oxygen evolution is exergonic in free energy. This observation is consistent with the notion that the metal-oxygen bond is stronger than ideal.

We present in vivo images of the human brain acquired with an ultralow field MRI (ULFMRI) system operating at a magnetic field B 0 ∼ 130 μT. The system features prepolarization of the proton spins at B p ∼ 80 mT and detection of the NMR signals with a superconducting, second-derivative gradiometer inductively coupled to a superconducting quantum interference device (SQUID). We report measurements of the longitudinal relaxation time T 1 of brain tissue, blood, and scalp fat at B 0 and B p , and cerebrospinal fluid at B 0 . We use these T 1 values to construct inversion recovery sequences that we combine with Carr-Purcell-Meiboom-Gill echo trains to obtain images in which one species can be nulled and another species emphasized. In particular, we show an image in which only blood is visible. Such techniques greatly enhance the already high intrinsic T 1 contrast obtainable at ULF. We further present 2D images of T 1 and the transverse relaxation time T 2 of the brain and show that, as expected at ULF, they exhibit similar contrast. Applications of brain ULFMRI include integration with systems for magnetoencephalography. More generally, these techniques may be applicable, for example, to the imaging of tumors without the need for a contrast agent and to modalities recently demonstrated with T 1ρ contrast imaging (T 1 in the rotating frame) at fields of 1.5 T and above. . 3D magnetic field gradients specify a unique magnetic field and thus an NMR frequency or phase in each voxel of the subject, so that with appropriate signal decoding one can acquire a 3D image (4).Clinical MRI systems with B 0 = 1:5 T achieve a spatial resolution of typically 1 mm; 3-T systems are becoming increasingly widespread in clinical practice (5), offering a higher signal-tonoise ratio (SNR) and thus higher spatial resolution. Nonetheless, there is ongoing interest in less expensive MRI systems operating at lower fields. Commercially available 0.2-to 0.5-T systems based on permanent magnets offer both lower cost and wider patient aperture than their higher field counterparts, at the expense of spatial resolution. At the still lower field of 0.03 T maintained by a room temperature solenoid, Connolly and coworkers (6, 7) obtained clinically useful SNR and spatial resolution by prepolarizing the protons in a field B p of 0.3 T. Prepolarization (8) enhances the magnetization of the proton ensemble over that produced by the lower precession field; after the polarizing field is removed, the higher magnetization produces a correspondingly larger signal during its precession in B 0 . Using the same method, Stepisnik et al. (9) obtained MR images in the Earth's magnetic field (∼ 50 μT).In recent years there has been increasing interest (10-36) in NMR and MRI at fields ranging from a few nanotesla to the order of 100 μT. The enormous reduction in the detected signal amplitude compared with the high field value is overcome partly by using prepolarization and partly by detecting the signal with an untuned superconducting input circuit inductively coupl...

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