One- or Two-Electron Water Oxidation, Hydroxyl Radical, or H₂O₂ Evolution

Electrochemical or photoelectrochemcial oxidation of water to form hydrogen peroxide (H₂O₂) or hydroxyl radicals (^•OH) offers a very attractive route to water disinfection, and the first process could be the basis for a clean way to produce hydrogen peroxide. A major obstacle in the development of effective catalysts for these reactions is that the electrocatalyst must suppress the thermodynamically favored four-electron pathway leading to O₂ evolution. We develop a thermochemical picture of the catalyst properties that determine selectivity toward the one, two, and four electron processes leading to ^•OH, H₂O₂, and O₂

In Situ Hard X‑ray Photoelectron Study of O₂ and H₂O Adsorption on Pt Nanoparticles

To improve the efficiency of Pt-based cathode catalysts in polymer electrolyte fuel cells, understanding of the oxygen reduction process at surfaces and interfaces in the molecular level is essential. In this study, H₂O and O₂ adsorption and dissociation as the first step of the reduction process were investigated by in situ hard X-ray photoelectron spectroscopy (HAXPES). Pt 5d valence band and Pt 3d, Pt 4f core HAXPES spectra of Pt nanoparticles upon H₂O and O₂ adsorption revealed that H₂O adsorption has a negligible effect on the electronic structure of Pt, while O₂ adsorption has a significant effect, reflecting the weak and strong chemisorption of H₂O and O₂ on the Pt nanoparticle, respectively. Combined with ab initio theoretical calculations, it is concluded that Pt 5d states responsible for Pt–O₂ bonding reside within 2 eV from the Fermi level

Field-Induced Slow Magnetic Relaxation in an Octacoordinated Fe(II) Complex with Pseudo‑<i>D</i>_2<i>d</i> Symmetry: Magnetic, HF-EPR, and Theoretical Investigations

An octacoordinated Fe­(II) complex, [Fe^II(dpphen)₂]­(BF₄)₂·1.3H₂O (<b>1</b>; dpphen = 2,9-bis­(pyrazol-1-yl)-1,10-phenanthroline), with a pseudo-<i>D</i>_2<i>d</i>-symmetric metal center has been synthesized. Magnetic, high-frequency/-field electron paramagnetic resonance (HF-EPR), and theoretical investigations reveal that <b>1</b> is characterized by uniaxial magnetic anisotropy with a negative axial zero-field splitting (ZFS) (<i>D</i> ≈ −6.0 cm^–1) and a very small rhombic ZFS (<i>E</i> ≈ 0.04 cm^–1). Under applied dc magnetic fields, complex <b>1</b> exhibits slow magnetic relaxation at low temperature. Fitting the relaxation time with the Arrhenius mode combining Orbach and tunneling terms affords a good fit to all the data and yields an effective energy barrier (17.0 cm^–1) close to the energy gap between the ground state and the first excited state. The origin of the strong uniaxial magnetic anisotropy for <b>1</b> has been clearly understood from theoretical calculations. Our study suggests that high-coordinated compounds featuring a <i>D</i>_2<i>d</i>-symmetric metal center are promising candidates for mononuclear single-molecule magnets