A nanowire photoanode SrTaO 2 N, a semiconductor suitable for overall water-splitting with a band gap of 2.3 eV, was coated with functional overlayers to yield a core−shell structure while maintaining its one-dimensional morphology. The nanowires were grown hydrothermally on tantalum, and the perovskite-related oxynitride structure was obtained by nitridation. Three functional overlayers have been deposited on the nanowires to enhance the efficiency of photoelectrochemical (PEC) water oxidation. The deposition of TiO x protects the oxynitride from photocorrosion and suppresses charge-carrier recombination at the surface. Ni(OH) x acts a hole-storage layer and decreases the dark-current contribution. This leads to a significantly improved extraction of photogenerated holes to the electrode−electrolyte surface. The photocurrents can be increased by the deposition of a cobalt phosphate (CoP i ) layer as a cocatalyst. The heterojunction nanowire photoanode generates a current density of 0.27 mA cm −2 at 1.23 V vs the reversible hydrogen electrode (RHE) under simulated sunlight (AM 1.5G). Simultaneously, the dark-current contribution, a common problem for oxynitride photoanodes grown on metallic substrates, is almost completely minimized. This is the first report of a quaternary oxynitride nanowire photoanode in core− shell geometry containing functional overlayers for synergetic hole extraction and an electrocatalyst.
Sn2O(CN2) was obtained from a solid-state metathesis. Its crystal structure incorporates a Sn2+ ion with a 5s2 lone pair and was analyzed in relation to that of SnO by electronicstructure calculations and a COHP bonding analysis.
We propose a semi-quantitative quantum-chemical model correctly ranking the ubiquitous carbon allotropes diamond and graphite in terms of energy despite their drastic structural differences.
Aquatris(3‐cyanopentane‐2, 4‐dionato)scandium(III) undergoes two transformations which can be monitored by X‐ray diffraction as well as solid‐state NMR spectroscopy: At 145 K, the mononuclear complex shows a reversible phase transition; in agreement with the symmetry principle, this transition of the t2 type proceeds from the monoclinic room temperature phase to triclinic twins at low temperature, the twin law corresponding to a twofold rotation. Under vacuum at room temperature, the aqua ligand of the complex is irreversibly eliminated and the structure rearranges, forming a 1D chain polymer. In both phases of the mononuclear complex as well as in the polymer, the coordination polyhedra around the ScIII atom represent distorted capped trigonal prisms. Solid‐state 45Sc NMR spectroscopic investigations on powder samples reveal a reversible phase transition of the monoclinic complex at low temperatures. Changes of the NMR signal line shapes for the room and low temperature complex as well as the 1D chain polymer are a fingerprint for different scandium bonding situations.
We report the oxidation-controlled synthesis of the ytterbium amides Yb(NH2)2 and Yb(NH2)3 and the first rare-earth-metal guanidinates YbC(NH)3 and Yb(CN3H4)3 from liquid ammonia. For Yb(NH2)2, we present experimental atomic displacement parameters from powder X-ray diffraction (PXRD) and density functional theory (DFT)-derived hydrogen positions for the first time. For Yb(NH2)3, the indexing proposal based on PXRD arrives at R3̅, a = 6.2477(2) Å, c = 17.132(1) Å, V = 579.15(4) Å(3), and Z = 6. The oxidation-controlled synthesis was also applied to make the first rare-earth guanidinates, namely, the doubly deprotonated YbC(NH)3 and the singly deprotonated Yb(CN3H4)3. YbC(NH)3 is isostructural with SrC(NH)3, as derived from PXRD (P63/m, a = 5.2596(2) Å, c = 6.6704(2) Å, V = 159.81(1) Å(3), and Z = 2). Yb(CN3H4)3 crystallizes in a structure derived from the [ReO3] type, as studied by powder neutron diffraction (Pn3̅, a = 13.5307(3) Å, V = 2477.22(8) Å(3), and Z = 8 at 10 K). Electrostatic and hydrogen-bonding interactions cooperate to stabilize the structure with wide and empty channels. The IR spectra of the guanidinates are compared with DFT-calculated phonon spectra to identify the vibrational modes. SQUID magnetometry shows that Yb(CN3H4)3 is a paramagnet with isolated Yb(3+) (4f(13)) ions. A CONDON 2.0 fit was used to extract all relevant parameters.
We present structural and electrochemical analyses of a new double-wolframite compound: AgNa(VO2F2)2 or SSVOF. SSVOF is fully ordered and displays electrochemical characteristics that give insight into electrode design for energy storage beyond lithium-ion chemistries. The compound contains trioxovanadium fluoride octahedra that combine to form one-dimensional chain-like basic building units, characteristic of wolframite (NaWO4). The 1D chains are stacked to create 2D layers; the cations Ag(+) and Na(+) lie between these layers. The vanadium oxide-fluoride octahedra are ordered by the use of cations (Ag(+), Na(+)) that differ in polarizability. In the case of sodium-ion batteries, thermodynamically, the use of a sodium anode introduces a 300 mV loss in overall cell voltage as compared to a lithium anode; however, this can be counter-balanced by introduction of fluoride into the framework to raise the reduction potentials via an inductive effect. This allows sodium-ion batteries to have comparable voltages to lithium systems. With SSVOF as a baseline compound, we have identified new materials design rules for emerging sodium-ion systems that do not apply to lithium-ion systems. These strategies can be applied broadly to provide materials of interest for fundamental structural chemistry and appreciable voltages for sodium-ion electrochemistry.
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