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Li Kationen aktivieren NiFeOOH für die Sauerstoffentwicklung in Natrium und Kaliumhydroxid
Get PDFDie Effizienz der Elektrolyse wird durch die träge Sauerstoffentwicklung OER verringert. Neben den Katalysatoreigenschaften hängt die elektrokatalytische Aktivität auch von der Interaktion des Elektrokatalysators mit dem Elektrolyten ab. Hier zeigen wir, dass die Zugabe kleiner Mengen Li zu eisenfreien NaOH oder KOH Elektrolyten NiFeOOH für die OER aktiviert, verglichen mit monokationischen Elektrolyten. Au erdem blieb der aktivierte Zustand erhalten, wenn zu reiner NaOH zurück gewechselt wurde. Wichtig ist, dass wir zeigen, dass der Ursprung der Aktivierung durch Li Kationen in erster Linie nicht kinetischer Natur ist, da sich der Beginn der OER für den gemischten Elektrolyten nicht ändert und die Tafelsteigung bei niedriger Stromdichte in beiden Elektrolyten 30 amp; 8197;mV dec beträgt. Der Anstieg der Tafelsteigung bleibt jedoch bei steigenden Stromdichten in Gegenwart von Li geringer. Basierend auf elektrochemischen Quarzkristall Mikrowaagen und In situ Röntgenabsorptionsspektroskopie Messungen zeigen wir, dass diese Verringerung der nichtkinetischen Effekte auf eine verstärkte Interkalation von Natrium, Wasser und Hydroxid zurückzuführen ist. Diese verstärkte Elektrolytpenetration erleichtert die OER, insbesondere bei höheren Stromdichten und bei erhöhter Katalysatorbeladung. Unsere Arbeit zeigt, dass gemischte Elektrolyte, in denen verschiedene Kationen unterschiedliche Rollen einnehmen können, eine einfache und vielversprechende Strategie zur Verbesserung der OER Raten darstelle
How Can the Diterpene Synthase CotB2V80L Alter the Product Profile?
No full textStructural diversity of diterpenes is mediated by the enigmatic family of diterpene synthases. The overall enzymatic contribution hereby lies in a carefully concerted chemistry of highly reactive carbocation intermediates mainly guided by aromatic and polar amino acid side chains and the pyrophosphate cofactor. To date several studies aimed to shed light on the mechanism underlining terpene synthases chemistry. Specifically, the diterpene synthase CotB2 serves as model enzyme for detailed mutagenesis studies. Here we investigate the catalytic mechanism of CotB2 variant V80L in a holistic, biochemical, structural, and computational biology approach. We were able to identify an altered product profile compared to CotB2WT for the substrates geranylgeranyl diphosphate and farnesyl diphosphate. Moreover, we solved the crystal structure, and shed further light on terpene synthase chemistry by modelling of the substrate and intermediate bindin
Fullerene rotation dictated by benzene fullerene interactions
No full textThe movement of metal ions inside the fullerene cage signifies the unique structural character of metallofullerenes; however, concrete details on this movement are extremely difficult to observe. In this work, we elucidated the structure of Dy2ScN C80 using variable temperature single crystal X ray diffraction. Dynamic disorders with the Dy2ScN and C80 rotations driven by temperature were precisely presented in detail. The position of the solvent molecule benzene in the crystal lattice proved to have a powerful impact on hindering fullerene rotation. These results present a deep understanding of the unique structural character of metallofullerenes, facilitating their high accuracy structure property relationship investigatio
Minimizing Interfacial Recombination in 1.8 eV Triple Halide Perovskites for 27.5 Efficient All Perovskite Tandems
Get PDFAll perovskite tandem solar cells show great potential to enable the highest performance at reasonable costs for a viable market entry in the near future. In particular, wide bandgap WBG perovskites with higher open circuit voltage VOC are essential to further improve the tandem solar cells performance. Here, a new 1.8 eV bandgap triple halide perovskite composition in conjunction with a piperazinium iodide PI surface treatment is developed. With structural analysis, it is found that the PI modifies the surface through a reduction of excess lead iodide in the perovskite and additionally penetrates the bulk. Constant light induced magneto transport measurements are applied to separately resolve charge carrier properties of electrons and holes. These measurements reveal a reduced deep trap state density, and improved steady state carrier lifetime factor 2.6 and diffusion lengths factor 1.6 . As a result, WBG PSCs achieve 1.36 V VOC, reaching 90 of the radiative limit. Combined with a 1.26 eV narrow bandgap NBG perovskite with a rubidium iodide additive, this enables a tandem cell with a certified scan efficiency of 27.
Achieving a high performance sodium ion pouch cell by regulating intergrowth structures in a layered oxide cathode with anionic redox
No full textIn P2 type layered transition metal TM oxides, which are typical cathode materials for Na ion batteries, the presence of Li within the TM layer could lead to the formation of specific Na O Li configurations that trigger additional oxygen redox at high charging voltages. However, the prismatic type P type to octahedral type O type phase transition and irreversible TM migration could be simultaneously aggravated in high state of charge, resulting in structural distortion. Here we demonstrate that excessive desodiation of P2 Na0.67Li0.1Fe0.37Mn0.53O2 NLFMO induces the formation of neighbouring O type stacking faults with an intergrowth structure that is, interlacing of O and P type layers , which leads to out of lattice Li migration and irreversible oxygen loss. We show that, by controlling the depth of charge to tailor the intergrowth structure, a P type stacking state can be uniformly interspersed between the O type stacking state, thereby avoiding neighbouring O type stacking faults. Adjusting the O P intergrowth structure leads to both reversible migration of Li TM ions and reversible anionic redox in the NLFMO cathode. We thereby achieve a high performance pouch cell with an energy density of 165 amp; 8201;W amp; 8201;h amp; 8201;kg amp; 8722;1 based on the entire weight of the cell with both cationic and anionic redox activitie
Microscopic origins of radiative performance losses in thin film solar cells at the example of Ag,Cu In,Ga Se2 devices
Get PDFThe present work provides an overview of radiative performance losses in thin film solar cells, focusing on those related to the open circuit voltage, using Ag,Cu In,Ga Se2 devices as examples. The microscopic origins of these losses are outlined, highlighting the presence of compositional variations, strain, and inhomogeneously distributed point defects on various length scales as contributors to band gap and electrostatic potential fluctuations, which both make up for the broadening of the absorption edge in the absorptance or quantum efficiency QE spectra of the semiconductor absorber layer or the completed solar cell device. The relationship between this broadening and Urbach tails is discussed. It is shown that the photovoltaic band gap energy as well as the broadening can be determined reliably from the arithmetic mean and standard deviation extracted from Gaussian fits to the first derivative of the absorptance or quantum efficiency spectra around the absorption edge. The more enhanced the broadening, the more shifts the local maximum in the luminescence spectrum to smaller energies with respect to the band gap energy of the absorber layer, as verified for about 30 Ag,Cu In,Ga Se2 solar cell
A high spin alkylperoxo iron III complex with cis anionic ligands implications for the superoxide reductase mechanism
No full textThe N3O macrocycle of the 12 TMCO ligand stabilizes a high spin S 5 2 [FeIII 12 TMCO OOtBu Cl] 3 Cl species in the reaction of [FeII 12 TMCO OTf 2] 1 OTf 2 with tert butylhydroperoxide tBuOOH in the presence of tetraethylammonium chloride NEt4Cl in acetonitrile at amp; 8722;20 C. In the absence of NEt4Cl the oxo iron IV complex 2 [FeIV 12 TMCO O CH3CN ]2 is formed, which can be further converted to 3 Cl by adding NEt4Cl and tBuOOH. The role of the cis chloride ligand in the stabilization of the FeIII OOtBu moiety can be extended to other anions including the thiolate ligand relevant to the enzyme superoxide reductase SOR . The present study underlines the importance of subtle electronic changes and secondary interactions in the stability of the biologically relevant metal dioxygen intermediates. It also provides some rationale for the dramatically different outcomes of the chemistry of iron III peroxy intermediates formed in the catalytic cycles of SOR Fe O cleavage and cytochrome P450 O O bond lysis in similar N4S coordination environment
Field induced magnetic transitions in the highly anisotropic ferrimagnet ErFe5Al7 studied by high field x ray magnetic dichroism
No full textWe present a comprehensive study of the magnetic properties of the strongly anisotropic ferrimagnet ErFe5Al7 in pulsed magnetic fields up to 30 T applied along the hard magnetization axis within the basal plane of the tetragonal lattice around the compensation temperature Tcomp . Macroscopic measurements showed two anomalies at about 8 T and 25 T in a small temperature range around Tcomp. High field x ray magnetic circular dichroism XMCD data at the Er M5 and the Fe L3 edge resonances provide insight into the element selective magnetization processes, revealing a coherent rotation of Er 4f and Fe 3d moments, with stepwise jumps including an unexpected one from an easy to a hard magnetization axis. XMCD at the Er L3 edge resonance elucidates the role of Er 5d electrons in coupling the Er 4f and the Fe 3d moments. Finally, an in plane anisotropy constant was evaluated from a simulation of the magnetization process at temperatures well below Tcomp using a two sublattice mode
Electronic Fingerprint of the Protonated Imidazole Dimer Probed by X ray Absorption Spectroscopy
Get PDFProtons in low barrier superstrong hydrogen bonds are typically delocalized between two electronegative atoms. Conventional methods to characterize such superstrong hydrogen bonds are vibrational spectroscopy and diffraction techniques. We introduce soft X ray spectroscopy to uncover the electronic fingerprints for proton sharing in the protonated imidazole dimer, a prototypical building block enabling effective proton transport in biology and high temperature fuel cells. Using nitrogen core excitations as a sensitive probe for the protonation status, we identify the X ray signature of a shared proton in the solvated imidazole dimer in a combined experimental and theoretical approach. The degree of proton sharing is examined as a function of structural variations that modify the shape of the low barrier potential in the superstrong hydrogen bond. We conclude by showing how the sensitivity to the quantum distribution of proton motion in the double well potential is reflected in the spectral signature of the shared proto
Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe2 Integration
Get PDFMetal semiconductor nanocomposites have emerged as a viable strategy for concurrently tailoring both thermal and electronic transport properties of established thermoelectric materials, ultimately achieving synergistic performance. In this investigation, a series of nanocomposite thin films were synthesized, embedding metallic cobalt telluride CoTe2 nanophase within the nanocrystalline ternary skutterudite Co Ge1.22Sb0.22 Te1.58 or CGST matrix. Our approach harnessed composition fluctuation induced phase separation and in situ growth during thermal annealing to seamlessly integrate the metallic phase. The distinctive band structures of both materials have developed an ohmic type contact characteristic at the interface, which raised carrier density considerably yet negligibly affected the mobility counterpart, leading to a substantial improvement in electrical conductivity. The intricate balance in transport properties is further influenced by the metallic CoTe2 phase s role in diminishing lattice thermal conductivity. The presence of the metallic phase instigates enhanced phonon scattering at the interface boundaries. Consequently, a 2 fold enhancement in the thermoelectric figure of merit zT amp; 8764; 1.30 is attained with CGST 7 wt. CoTe2 nanocomposite film at 655 K compared to that of pristine CGS