Electrochemical Performance of SrFeO_{3−<i>δ</i>} for Application as a Symmetric Electrode in Solid Oxide Fuel Cells

SrFeO3−δ has been earlier reported to exhibit a large area-specific resistance even though it possesses high mixed ionic–electronic conductivity both in oxidizing and reducing conditions. The present study clarifies this aspect and investigates the defect chemistry and electrochemical performance correlations in SrFeO3−δ for the possible use as a symmetric electrode in solid oxide fuel cells. A conventional solid-state reaction method is adopted for powder synthesis. Structural characterization indicates an orthorhombic perovskite phase formation with a δ of 0.21. High dc electrical conductivities of ∼114.9 and 0.26 S·cm–1 are observed at 800 °C in air and reducing conditions, respectively. The area-specific resistance (ASR) for the SrFeO3−δ electrode is measured in a symmetrical half-cell configuration under various gas environments. At 800 °C, SrFeO3−δ offered low ASRs of 0.082, 0.055, and 0.122 Ω·cm2 in air, oxygen, and 3% H2O/H2, respectively. Although the ASR possesses excellent temporal stability in an oxidizing atmosphere, it increases to 0.42 Ω·cm2 after 100 h in reducing conditions owing to the brownmillerite phase formation. The redox cycling performance is also affected with the ASR rising from 0.13 to 0.24 Ω·cm2 at 800 °C in 3% H2O/H2 after 20 cycles. A maximum power density of 202 mW·cm−2 is achieved from the electrolyte-supported symmetric single cell based on the SrFeO3−δ electrodes at 800 °C. The results demonstrate the viability of using a SrFeO3−δ-based electrode for symmetrical solid oxide fuel cells

Photoelectrochemical Generation of Hydrogen from Water Using a CdSe Quantum Dot-Sensitized Photocathode

The present study reports photelectrochemical H₂ evolution using a water-solubilized S₃-cap-CdSe quantum dot-sensitized NiO as the photocathode and either [Co­(bdt)₂]⁻ (bdt =1,2-benzenedithiolate) or Ni­(DHLA)_<i>x</i> (DHLA= the anion of dihydrolipoic acid) complex as the H₂-forming catalyst. The NiO-S₃-cap-CdSe/[Co­(bdt)₂]⁻ system produces H₂ with a turnover frequency of 3000 per CdSe mol·h. Faradaic efficiency for this system is essentially quantitative. Both systems are stable for more than 16 h

Comparison of interactions of catalytic aspartates in the structures at pH 2.0 and pH7.0.

<p>Comparison of interactions of catalytic aspartates in the structures at pH 2.0 and pH7.0.</p

Fit of carboxy terminal product peptide and active site water molecules into 2Fo-Fc electron density.

<p>The electron density map is contoured at 1.0σ level. The carboxyl product peptide ( violetpurple) and the active site water molecules are shown in the two orientations.</p

Structural comparison of present complex with tetrahedral intermediate complex [21] and product peptide complex [22]:

<p>Stereo diagram showing the ligand atoms at the catalytic centre along with catalytic aspartates. Protein Cα atoms are used in the structural superposition. WAT1 is within 1 Å from an oxygen atom in the newly generated gem-diol <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007860#pone.0007860-Kumar1" target="_blank">[21]</a> or carboxyl group <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007860#pone.0007860-Das1" target="_blank">[22]</a>.</p

Comparison of conformation of catalytic aspartates in the structures at pH 2.0 and pH7.0.

<p>Comparison of conformation of catalytic aspartates in the structures at pH 2.0 and pH7.0.</p

Relative positions of WAT1 and the modelled substrate in the active site:

<p>Diagram showing superposition of three structures: 1) present structure (yellow carbon), 2) unliganded HIV-1 protease (magenta carbon, PDB Id 1LV1) and 3) inactive HIV-1 protease/substrate complex (green carbon, PDB Id 1KJH). Water molecule observed in unliganded HIV-1 protease is also shown (magenta). The distances to the scissile carbon atom are indicated. SA OMIT density contoured at 3σ level is also shown for WAT1.</p

Data collection and refinement statistics.

<p>*Data for highest resolution shell are given in the parenthesis.</p

9-Oxidophenalenone: A Noninnocent β-Diketonate Ligand?

The redox systems [Ru­(L)­(bpy)₂]^<i>k</i>, [Ru­(L)₂(bpy)]^<i>m</i>, and [Ru­(L)₃]^<i>n</i> containing the potentially redox-active ligand 9-oxidophenalenone = L^– were investigated by spectroelectrochemistry (UV–vis–near-IR and electron paramagnetic resonance) in conjunction with density functional theory (DFT) calculations. Compounds [Ru­(L^–)­(bpy)₂]­ClO₄ ([<b>1</b>]­ClO₄) and [Ru­(L^–)₂(bpy)]­ClO₄ ([<b>2</b>]­ClO₄) were structurally characterized. In addition to establishing electron-transfer processes involving the Ru^II/Ru^III/Ru^IV and bpy⁰/bpy^•– couples, evidence for the noninnocent behavior of L^– was obtained from [Ru^IV(L^•)­(L^–)­(bpy)]³⁺, which exhibits strong near-IR absorption due to ligand-to-ligand charge transfer. In contrast, the lability of the electrogenerated anion [Ru­(L)₂(bpy)]⁻ is attributed to a resonance situation [Ru^II(L^•2–)­(L^–)­(bpy)]⁻/[Ru^II(L^–)₂ (bpy^•–)]⁻, as suggested by DFT calculations

Nickel Complexes for Robust Light-Driven and Electrocatalytic Hydrogen Production from Water

A series of nickel bis­(chelate) complexes having square planar coordination are studied for light-driven and electrocatalytic hydrogen production from water. The complexes Ni­(abt)₂ (abt = 2-aminobenzenethiolate), Ni­(mp)₂ (mp = 2-mercaptophenolate) and Ni­(mpo)₂ (mpo = 2-mercaptopyridyl-<i>N</i>-oxide) are found to be active catalysts under light-driven conditions, using fluorescein (Fl) as the photosensitizer (PS) and triethanolamine (TEOA) as the sacrificial electron donor in water under basic pH (pH = 9.8). These molecular systems achieve a turnover number (TON) of ∼6000 (relative to catalyst) and are stable for more than 100 h under H₂-generating conditions. When water-soluble CdSe quantum dots with tripodal S-donor capping agents are employed as PS and ascorbic acid (AA) is used as the sacrificial electron donor at pH 4.5, an active and robust system is obtained for the light-driven generation of H₂ from aqueous protons. A TON of over 280 000 is achieved for the three active catalysts. These complexes are also examined electrochemically in organic solvents with weak organic acids as the proton source and in aqueous and aqueous/organic media for proton reduction. The most active photochemical catalysts also show excellent electrocatalytic activity in neutral pH water, achieving Faradaic yields close to 100% under anaerobic conditions and ∼80% under aerobic conditions