Published two‐body bond‐valence parameters for cation–oxygen bonds have been evaluated via the root mean‐square deviation (RMSD) from the valence‐sum rule for 128 cations, using 180 194 filtered bond ...lengths from 31 489 coordination polyhedra. Values of the RMSD range from 0.033–2.451 v.u. (1.1–40.9% per unit of charge) with a weighted mean of 0.174 v.u. (7.34% per unit of charge). The set of best published parameters has been determined for 128 ions and used as a benchmark for the determination of new bond‐valence parameters in this paper. Two common methods for the derivation of bond‐valence parameters have been evaluated: (1) fixing B and solving for Ro; (2) the graphical method. On a subset of 90 ions observed in more than one coordination, fixing B at 0.37 Å leads to a mean weighted‐RMSD of 0.139 v.u. (6.7% per unit of charge), while graphical derivation gives 0.161 v.u. (8.0% per unit of charge). The advantages and disadvantages of these (and other) methods of derivation have been considered, leading to the conclusion that current methods of derivation of bond‐valence parameters are not satisfactory. A new method of derivation is introduced, the GRG (generalized reduced gradient) method, which leads to a mean weighted‐RMSD of 0.128 v.u. (6.1% per unit of charge) over the same sample of 90 multiple‐coordination ions. The evaluation of 19 two‐parameter equations and 7 three‐parameter equations to model the bond‐valence–bond‐length relation indicates that: (1) many equations can adequately describe the relation; (2) a plateau has been reached in the fit for two‐parameter equations; (3) the equation of Brown & Altermatt (1985) is sufficiently good that use of any of the other equations tested is not warranted. Improved bond‐valence parameters have been derived for 135 ions for the equation of Brown & Altermatt (1985) in terms of both the cation and anion bond‐valence sums using the GRG method and our complete data set.
We show that the Fu–Kane–Mele invariant of the 2d time-reversal invariant crystalline insulators is equal to the properly normalized Wess–Zumino action of the so-called sewing-matrix field defined on ...the Brillouin torus. Applied to 3d, the result permits a direct proof of the known relation between the strong Fu–Kane–Mele invariant and the Chern–Simons action of the non-Abelian Berry connection on the bundle of valence states.
A computer program, 3DBVSMAPPER, was developed to generate bond‐valence sum maps and bond‐valence energy landscapes with minimal user intervention. The program is designed to calculate the spatial ...distributions of bond‐valence values on three‐dimensional grids, and to identify infinitely connected isosurfaces in these spatial distributions for a given bond‐valence mismatch or energy threshold and extract their volume and surface area characteristics. It is implemented in the Perl scripting language embedded in Accelrys Materials Studio and has the capacity to process automatically an unlimited number of materials using crystallographic information files as input.
Abstract Electrochemical water splitting is a common way to produce hydrogen gas, but the sluggish kinetics of the oxygen evolution reaction (OER) significantly limits the overall energy conversion ...efficiency of water splitting. In this work, a highly active and stable, meso–macro hierarchical porous Ni 3 S 4 architecture, enriched in Ni 3+ is designed as an advanced electrocatalyst for OER. The obtained Ni 3 S 4 architectures exhibit a relatively low overpotential of 257 mV at 10 mA cm −2 and 300 mV at 50 mA cm −2 . Additionally, this Ni 3 S 4 catalyst has excellent long‐term stability (no degradation after 300 h at 50 mA cm −2 ). The outstanding OER performance is due to the high concentration of Ni 3+ and the meso–macro hierarchical porous structure. The presence of Ni 3+ enhances the chemisorption of OH − , which facilitates electron transfer to the surface during OER. The hierarchical porosity increases the number of exposed active sites, and facilitates mass transport. A water‐splitting electrolyzer using the prepared Ni 3 S 4 as the anode catalyst and Pt/C as the cathode catalyst achieves a low cell voltage of 1.51 V at 10 mA cm −2 . Therefore, this work provides a new strategy for the rational design of highly active OER electrocatalysts with high valence Ni 3+ and hierarchical porous architectures.
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•Nitrogenase-inspired MIL-53(FeII/FeIII) is first synthesized for N2 photo fixation.•Mixed-valence FeII/FeIII clusters mimic the active center in nitrogenase.•FeII are in-situ formed ...by ethylene glycol reductant in solvothermal process.•FeII/FeIII ratio is vital to coordinate catalytic activity and framework stability.•MIL-53(FeII/FeIII) stably yields 306 μmol h−1 g−1 NH3 under visible light.
Biological nitrogenases exhibit superior nitrogen fixation efficiency owing to their unique multi-iron metallocluster (Fe2+3Fe3+4M3+, M = Mo, V, Fe) coordinated by organic polypeptide. Herein, we design a kind of metal organic framework (MOF) photocatalyst, MIL-53(FeII/FeIII) (MIL = Material from Institute Lavoisier), in which the FeII and FeIII constitute the mixed-valence metalloclusters to mimic the Fe2+ active sites and high-valence metal ions in nitrogenases, respectively. Both the FeII and FeIII are coordinated by organic ligands (terephthalic acid), which afford the electron transfer chains as well as the support of monodispersed FeII active sites. The FeIII in MIL-53(FeII/FeIII) is partly in-situ reduced into FeII by ethylene glycol (EG) via one-step solvothermal method, and the FeII/FeIII ratio is regulated from 0.18:1 to 1.21:1 by varying the EG content. Our results show that the FeII/FeIII ratio can significantly affect the photocatalytic activity and structure stability, and MIL-53(FeII/FeIII)-1 with optimal FeII/FeIII ratio (1.06:1) achieves the highest ammonia evolution rate up to 306 μmol h−1 g−1, nearly 10-fold higher than that of other framework-based materials, while remaining stable after 24 h irradiation. Such nitrogenase-like design in MIL-53(FeII/FeIII) endows the efficient electron transfer, exposed active sites, and in particular rational synergy between the catalytic function and non-catalytic function. This work may open a new avenue to the rational design of nitrogen fixation photocatalysts based on framework materials.
Abnormalities in valence processing – the processing of aversive or appetitive stimuli – may be an underrecognized component of obsessive-compulsive disorder (OCD). Preclinical rodent models have ...been critical in furthering pathophysiological understanding of OCD, yet there is a dearth of investigations examining whether rodent models of compulsive behavior show alterations in valence systems congruent with those seen in individuals with OCD. In this study, we sought to assess valence processing in a preclinical rodent model of compulsive behavior, the SAPAP3 knockout (KO) mouse model, and compare our preclinical findings to similar behavioral phenomena in OCD patients. In SAPAP3 KO mice, we used auditory fear conditioning and extinction to examine alterations in negative valence processing and reward-based operant conditioning to examine alterations in positive valence processing. We find that SAPAP3 KO mice show evidence of heightened negative valence processing through enhanced fear learning and impaired fear extinction. SAPAP3 KO mice also show deficits in reward acquisition and goal-directed behavior, suggesting impaired positive valence processing. In OCD patients, we used validated behavioral tests to assess explicit and implicit processing of fear-related facial expressions (negative valence) and socially-rewarding happy expressions (positive valence). We find similar trends towards enhanced negative and impaired positive valence processing in OCD patients. Overall, our results reveal valence processing abnormalities in a preclinical rodent model of compulsive behavior similar to those seen in OCD patients, with implications for valence processing alterations as novel therapeutic targets across a translational research spectrum.
High‐valence metal‐doped multimetal (oxy)hydroxides outperform noble metal electrocatalysts for the oxygen evolution reaction (OER) owing to the modified energetics between 3d metals and high‐valence ...dopants. However, the rational design of sufficient and subtle modulators is still challenging. With a multimetal layered double hydroxide (LDH) as the OER catalyst, this study introduces a series of operando high‐valence dopants (Cr, Ru, Ce, and V), which can restrict the 3+ valence states in the LDH template to prevent phase separation and operando transfer to the >3+ valence states for sufficient electronic interaction during the OER process. Through density functional theory simulations, ultrathin Cr‐doped NiFe (NiFeCr) LDH is synthesized with strong electronic interaction between Cr dopants and NiFe bimetallic sites, evidenced by X‐ray absorption spectroscopy. The resulting NiFeCr‐LDH catalyzes the OER with ultralow overpotentials of 189 and 284 mV, obtaining current densities of 10 and 1000 mA cm–2, respectively. Further, a NiFeCr‐LDH anode is coupled in the anion exchange membrane electrolyzers to promote alkaline water splitting and CO2‐to‐CO electrolysis, which achieves low full cell voltages at high current densities.
Guided by theoretical simulations, ultrathin Cr‐doped NiFe layered double hydroxide (LDH) is synthesized. The resulting NiFeCr‐LDH motivates the oxygen evolution reaction with ultralow overpotentials of 189 and 284 mV to obtain current densities of 10 and 1000 mA cm−2, respectively, and achieves low full‐cell voltages at high current densities for hydrogen production and CO2 electroreduction in anion exchange membrane electrolyzers.
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