A restricted dynamic surface self-reconstruction toward high-performance of direct seawater oxidation.

The development of highly efficient electrocatalysts for direct seawater splitting with bifunctionality for inhibiting anodic oxidation reconstruction and selective oxygen evolution reactions is a major challenge. Herein, we report a direct seawater oxidation electrocatalyst that achieves long-term stability for more than 1000 h at 600 mA/cm2@η600 and high selectivity (Faraday efficiency of 100%). This catalyst revolves an amorphous molybdenum oxide layer constructed on the beaded-like cobalt oxide interface by atomic layer deposition technology. As demonstrated, a new restricted dynamic surface self-reconstruction mechanism is induced by the formation a stable reconstructed Co-Mo double hydroxide phase interface layer. The device assembled into a two-electrode flow cell for direct overall seawater electrolysis maintained at 1 A/cm2@1.93 V for 500 h with Faraday efficiency higher than 95%. Hydrogen generation rate reaches 419.4 mL/cm2/h, and the power consumption (4.62 KWh/m3 H2) is lower than that of pure water (5.0 KWh/m3 H2) at industrial current density.

Nitrogen Plasma Activates CoMn-Layered Double Hydroxides for Superior Electrochemical Oxygen Evolution.

Bimetallic layered double hydroxide is considered an ideal electrocatalytic material. However, due to the poor electrical conductivity of the bimetallic layered structure, obtaining highly active and stable catalysts through facile regulation strategies remains a great challenge. Herein, we use a simple corrosion strategy and nitrogen plasma technology to convert cobalt-based metal-organic frameworks into nitrogen-doped CoMn bimetallic layered double hydroxides (CoMn-LDH). Under the condition of regulating the local coordination environment of the catalytic active site and the presence of rich oxygen vacancy defects, N@CoMn-LDH/CC generates a low overpotential of 219 mV at 10 mA cm-2, which exceeds that of the commercial RuO2 catalyst. Density functional theory calculation shows that nitrogen doping improves the adsorption energy of the Mn site for oxygen evolution intermediates and reduces the reaction energy barrier of the Co site. Meanwhile, experiments and theoretical calculations verify that the mechanism of nitrogen doping regulating the oxygen evolution reaction (OER) follows the lattice oxygen oxidation mechanism, avoiding the collapse of the structure caused by catalyst reconstruction, thus improving the stability of oxygen evolution. This work provides a new simple strategy for the preparation of catalysts for a superior electrocatalytic oxygen evolution reaction.

Reaction mechanism of nickel sulfide atomic layer deposition using bis(N,N'-di-tert-butylacetamidinato)nickel(II) and hydrogen sulfide.

As a unique nanofabrication technology, atomic layer deposition (ALD) has been used in the microelectronics, catalysis, environmental and energy fields. As an energy and catalytic material, nickel sulfide has excellent electrochemical and catalytic activities and has attracted extensive attention. In this work, the reaction mechanism for nickel sulfide ALD from an amidine metal precursor was investigated using density functional theory (DFT) calculations. The results show that the first amidine ligand of bis(N,N'-di-tert-butylacetamidinato)nickel(II) [Ni(tBu-MeAMD)2] can be easily eliminated on the sulfhydrylated surface. The second amidine ligand can also react with the adjacent sulfhydryl group to generate the N,N'-di-tert-butylacetamidine (tBu-MeAMD-H) molecule, which can strongly interact with the Ni atom on the surface and be difficult to be desorbed. In the subsequent H2S reaction, the tBu-MeAMD-H molecule can be exchanged with the H2S precursor. Ultimately, the tBu-MeAMD-H molecule can be desorbed and H2S can be dissociated to form two sulfhydrylated groups on the surface. Meanwhile, the -SH of a H2S molecule can be exchanged with the second tBu-MeAMD ligand. These insights into the reaction mechanism of nickel sulfide ALD can provide theoretical guidance to design the metal amidinate precursors and improve the ALD process for metal sulfides.

Bivalent Cobalt as Efficient Catalyst Intercalation Layer Improves Polysulfide Conversion in Lithium-Sulfur Batteries.

Herein, we investigated in detail the effect of metal valences in different cobalt-based organic framework compounds on the kinetics of sulfur reaction in lithium-sulfur batteries (LSBs). On this basis, two organic framework compounds of zeolite-imidazole-based cobalt organic framework compound (Co-ZIF) and tetrakis(4-benzoic acid) porphyrinato-CoIII chloride [Co-TBP(III)] with different valences were constructed as the functional intercalation separators of LSBs, and explored the effects of different valences on improving the reaction kinetics of polysulfides and inhibiting the shuttle effect. Experiments and theoretical calculations prove that CoII exhibits the best catalytic activity. This is mainly due to the fact that +2 valence shows a strong adsorption energy for polysulfides and a higher Fermi level compared with +3 valence, thus improving the efficiency of the rapid catalytic conversion of sulfur species. As expected, the discharge specific capacity of Co-ZIF as the catalytic layer of the LSBs reached 772.7 mAh g-1 at a high current density of 5 C. More importantly, the initial specific capacity is 839.6 mAh g-1 at high current 3 C, and after 720 cycles, the attenuation rate of per cycle is only 0.092 %, and the coulombic efficiency remains above 92 %.

Flower-Like NiS2 /WS2 Heterojunction as Polysulfide/sulfide Bidirectional Catalytic Layer for High-Performance Lithium-Sulfur Batteries.

The slow sulfur oxidation-reduction kinetics are one of the key factors hindering the widespread use of lithium-sulfur batteries (LSBs). Herein, flower-shaped NiS2 -WS2 heterojunction as the functional intercalation of LSBs is successfully prepared, and effectively improved the reaction kinetics of sulfur. Flower-like nanospheres composed of ultra-thin nanosheets (≤10 nm) enhance quickly transfer of mass and charge. Meanwhile, the heterostructures simultaneously serve as an electron receptor and a donor, thereby simultaneously accelerating the bidirectional catalytic activity of reduction and oxidation reactions in the LSBs. In addition, the adsorption experiment, chemical state analysis of elements before and after the reaction and theoretical calculation have effectively verified that NiS2 -WS2 heterojunction nanospheres optimize the adsorption capacity and bidirectional catalytic effect of polysulfides. The results show that the initial discharge capacity of NiS2 -WS2 functional intercalation is as high as 1518.7 mAh g-1 at 0.2 C. Even at a high current density of 5 C, it still shows a discharge specific capacity of 615.7 mAh g-1 , showing excellent rate performance. More importantly, the capacity is 258.9 mAh g-1 after 1500 cycles at 5 C, and the attenuation per cycle is only 0.039%, and the Coulomb efficiency remains above 95%.

First-Principles Molecular Dynamics Simulations on Water-Solid Interface Behavior of H2O-Based Atomic Layer Deposition of Zirconium Dioxide.

As an important inorganic material, zirconium dioxide (ZrO2) has a wide range of applications in the fields of microelectronics, coating, catalysis and energy. Due to its high dielectric constant and thermodynamic stability, ZrO2 can be used as dielectric material to replace traditional silicon dioxide. Currently, ZrO2 dielectric films can be prepared by atomic layer deposition (ALD) using water and zirconium precursors, namely H2O-based ALD. Through density functional theory (DFT) calculations and first-principles molecular dynamics (FPMD) simulations, the adsorption and dissociation of water molecule on the ZrO2 surface and the water-solid interface reaction were investigated. The results showed that the ZrO2 (111) surface has four Lewis acid active sites with different coordination environments for the adsorption and dissociation of water. The Zr atom on the surface can interacted with the O atom of the water molecule via the p orbital of the O atom and the d orbital of the Zr atom. The water molecules could be dissociated via the water-solid interface reaction of the first or second layer of water molecules with the ZrO2 (111) surface. These insights into the adsorption and dissociation of water and the water-solid interface reaction on the ZrO2 surface could also provide a reference for the water-solid interface behavior of metal oxides, such as H2O-based ALD.

Reaction mechanism of atomic layer deposition of zirconium oxide using zirconium precursors bearing amino ligands and water.

As a unique nanofabrication technology, atomic layer deposition (ALD) has been widely used for the preparation of various materials in the fields of microelectronics, energy and catalysis. As a high-κ gate dielectric to replace SiO2, zirconium oxide (ZrO2) has been prepared through the ALD method for microelectronic devices. In this work, through density functional theory calculations, the possible reaction pathways of ZrO2 ALD using tetrakis(dimethylamino)zirconium (TDMAZ) and water as the precursors were explored. The whole ZrO2 ALD reaction could be divided into two sequential reactions, TDMAZ and H2O reactions. In the TDMAZ reaction on the hydroxylated surface, the dimethylamino group of TDMAZ could be directly eliminated by substitution and ligand exchange reactions with the hydroxyl group on the surface to form dimethylamine (HN(CH3)2). In the H2O reaction with the aminated surface, the reaction process is much more complex than the TDMAZ reaction. These reactions mainly include ligand exchange reactions between the dimethylamino group of TDMAZ and H2O and coupling reactions for the formation of the bridged products and the by-product of H2O or HN(CH3)2. These insights into surface reaction mechanism of ZrO2 ALD can provide theoretical guidance for the precursor design and improving ALD preparation of other oxides and zirconium compounds, which are based ALD reaction mechanism.

Nickel(II) Cluster-Based Pillar-Layered Metal-Organic Frameworks for High-Performance Supercapacitors.

Most metal-organic frameworks (MOFs) cannot be used as electrode materials for supercapacitors because of their high costs, poor stabilities in aqueous solutions, inferior intrinsic electrocatalytic activities, and poor conductivities. Herein, the application of two nickel(II) cluster-based pillar-layered MOFs, Ni-mba-Na ([Ni8(mba)6(Cl)2Na(OH-)3]n, H2mba is 2-mercaptobenzoic acid) and Ni-mba-K ([Ni8(mba)6(Cl)2K(OH-)3]n), as electrode materials are reported. They differ from conductive MOFs because they are insulators with small specific surface areas (<10 m2 g-1), and H2mba is an inexpensive raw material. The conductivities of Ni-mba-Na and Ni-mba-K at 30 °C were 4.002 × 10-10 and >10-11 S cm-1, respectively. They showed excellent supercapacitor performance and stabilities and high inherent densities and specific capacitances. The specific powers of their asymmetric supercapacitors could reach up to 16,000 W kg-1; the specific energies of Ni-mba-Na and Ni-mba-K were 16.9 and 21.8 Wh kg-1, respectively. Design recommendations for these MOFs are provided based on their structure and performance differences. This paper shows a novel application of nonconductive MOFs in the energy storage field and design of high-performance electrode materials for supercapacitors.

Tuning the Interface of Co1-xS/Co(OH)F by Atomic Replacement Strategy toward High-Performance Electrocatalytic Oxygen Evolution.

The construction of heterostructures is one of the most promising strategies for engineering interfaces of catalysts to perform high-efficiency oxygen evolution reaction (OER). However, accurately tuning heterostructures' interface during operation remains a challenge. Herein, we fabricated the needled-like heterostructure Co1-xS/Co(OH)F supported on flexible carbon fiber cloth via an atomic substitution strategy, in which sulfur atoms are simultaneously grafted into F vacancies after the partial removal of F atoms from Co(OH)F during the electrodeposition, thus achieving the growth of cobalt sulfide on the interface of Co(OH)F. This electrocatalyst with such design exhibits the following advantages: (1) The lattice distortion caused by atomic substitution leads to the increase of active sites; (2) Co1-xS constructed on the surface of Co(OH)F by the atomic replacement strategy optimizes the adsorption (OH-) and desorption (O2) energy in the OER process; (3) the needle-like structure possesses the tip-enhanced local electric field effect. As a result, the Co1-xS/Co(OH)F/CC catalyst exhibits very high OER catalytic performance with an overpotential of 269 mV at a current density of 10 mA cm-2 and a Tafel slope of 71 mV dec-1. The asymmetric electrode shows superior catalytic activity and stability in overall water splitting. The catalytic mechanism of these highly efficient Co1-xS/Co(OH)F/CC catalysts was investigated via DFT theoretical calculations and ex situ characterizations. This atomic substitution strategy displays universality for other transition metal sulfides (metal = Ni, Mn, Cu).

Bright tunable luminescence of Sb3+ doping in zero-dimensional lead-free halide Cs3ZnCl5 perovskite crystals.

Lead-free zero-dimensional (0D) perovskite nanocrystals (NCs) with isolated octahedral structures have attracted considerable attention due to their unique photoelectric properties, such as highly efficient emissions with broadband features. A series of phosphors composed of Sb3+-doped 0D perovskite crystals Cs3ZnCl5 with wavelength-tunable emission spectra have been obtained using a facile recrystallization method at room temperature in air. By controlling the doping concentration of Sb3+ in Cs3ZnCl5 lattice, bright emissions from red to orange have been achieved under excitation at 320 nm due to the expansion of the crystal lattice, and the emission excited at 275 nm is bluish-white, spanning the full visible region. Inductively coupled plasma emission spectrometry (ICP) demonstrates the Sb3+ substitutes for Zn2+ rather than Cs+ due to the similar charges and ionic radii. The luminescence performance of phosphor Cs3ZnCl5:Sb3+ can be improved obviously by replacing 3 mol% of Cs+ with Rb+ or K+ due to the further distortion of the crystal lattice. The present approach allows the synthesis of large-scale emissive lead-free 0D perovskites activated by Sb3+ with tunable luminescence color.

Mechanochemical Divergent Syntheses of Oxindoles and α-Arylacylamides via Controllable Construction of C-C and C-N Bonds by Copper and Piezoelectric Materials.

Herein, we present the divergent syntheses of α-arylacylamides and oxindoles via mechanoredox chemistry by using easily accessible α-bromo N-sulfonyl amides as starting materials. Our system consists of a catalytic amount of CuII precatalyst and piezoelectric materials. The highly polarized BaTiO3 or PbTiO3 under mechanical agitation can act as an electron donor to realize the recycling of CuII and CuI . Control experiments and density functional theory calculations have been performed to support the proposed mechanistic rationale for the cascade reactions.

A Tandem Interfaced (Ni3 S2 -MoS2 )@TiO2 Composite Fabricated by Atomic Layer Deposition as Efficient HER Electrocatalyst.

Reported herein is a highly active and durable hydrogen evolution reaction (HER) electrocatalyst, which is constructed following a tandem interface strategy and functional in alkaline and even neutral medium (pH ≈ 7). The ternary composite material, consisting of conductive nickel foam (NF) substrate, Ni3 S2 -MoS2 heterostructure, and TiO2 coating, is synthesized by the hydrothermal method and atomic layer deposition (ALD) technique. Representative results include: (1) versatile characterizations confirm the proposed composite structure and strong electronic interactions among comprised sulfide and oxide species; (2) the material outperforms commercial Pt/C by recording an overpotential of 115 mV and a Tafel slope of 67 mV dec-1 under neutral conditions. A long-term stability in alkaline electrolytes up to 200 h and impressive overall water splitting behavior (1.56 V @ 10 mA cm-2 ) are documented; (3) implementation of ALD oxide tandem layer is crucial to realize the design concept with superior HER performance by modulating a variety of heterointerface and intermediates electronic structure.

Hydroxylated Multi-Walled Carbon Nanotubes Covalently Modified with Tris(hydroxypropyl) Phosphine as a Functional Interlayer for Advanced Lithium-Sulfur Batteries.

We have successfully constructed a new type of intercalation membrane material by covalently grafting organic tris(hydroxypropyl)phosphine (THPP) molecules onto hydroxylated multi-walled carbon nanotubes (CNT-OH) as a functional interlayer for the advanced LSBs. The as-assembled interlayer has been demonstrated to be responsible for the fast conversion kinetics of polysulfides, the inhibition of polysulfide shuttle effect, as well as the formation of a stable solid electrolyte interphase(SEI) layer. By means of spectroscopic and electrochemical analysis, we further found THPP plays a key role in accelerating the conversion of polysulfides into low-ordered lithium sulfides and suppressing the loss of polysulfides, thus rendering the as-designed lithium-sulfur battery in this work a high capacity, excellent rate performance and long-term stability. Even at low temperatures, the capacity decay rate was only 0.036 % per cycle for 1700 cycles.

Corrigendum: Reaction mechanism of atomic layer deposition of zirconium oxide using zirconium precursors bearing amino ligands and water.

[This corrects the article DOI: 10.3389/fchem.2022.1035902.].

The mobility and solvation structure of a hydroxyl radical in a water nanodroplet: a Born-Oppenheimer molecular dynamics study.

Hydroxyl radicals (OH*) play a crucial role in atmospheric chemistry and biological processes. In this study, Born-Oppenheimer molecular dynamics simulations are performed under ambient conditions for a hydroxyl radical in a water nanodroplet containing 191 water molecules. Density functional theory calculations are performed at the BLYP-D3 level with some test calculations at the B3LYP-D3 level. In two 150 ps trajectories, either with OH* initially located in the interior region or at the surface of the water nanodroplet, the OH* radical ends up in the subsurface layer of the nanodroplet, which is different from the "surface preference" predicted from previous empirical force field simulations. The solvation structure of OH* contains fluctuating hydrogen bonds, as well as a two-center three-electron hemibond in some cases. The mobility of OH* is enhanced by hydrogen transfer, which has a free energy barrier of ∼4.6 kcal mol-1. The results presented in this study deepen our understanding of the structure and dynamics of OH* in aqueous solutions, especially around the air-water interface.

Reaction mechanism of atomic layer deposition of aluminum sulfide using trimethylaluminum and hydrogen sulfide.

Atomic layer deposition (ALD) is a nanopreparation technique for materials and is widely used in the fields of microelectronics, energy and catalysis. ALD methods for metal sulfides, such as Al2S3 and Li2S, have been developed for lithium-ion batteries and solid-state electrolytes. In this work, using density functional theory calculations, the possible reaction pathways of the ALD of Al2S3 using trimethylaluminum (TMA) and H2S were investigated at the M06-2X/6-311G(d, p) level. Al2S3 ALD can be divided into two consecutive and complementary half-reactions involving TMA and H2S, respectively. In the TMA half-reaction, the methyl group can be eliminated through the reaction with the sulfhydryl group on the surface. This process is a ligand exchange reaction between the methyl and sulfhydryl groups via a four-membered ring transition state. TMA half-reaction with the sulfhydrylated surface is more difficult than that with the hydroxylated surface. When the temperature increases, the reaction requires more energy, owing to the contribution of the entropy. In the H2S half-reaction, the methyl group on the surface can further react with the H2S precursor via a four-membered ring transition state. The orientation of H2S and more molecules have minimal effect on the H2S half-reaction. The reaction involving H2S through a six-membered ring transition state is unfavorable. In addition, the methyl and sulfhydryl groups on the surface can both react with the adjacent sulfhydryl group on the subsurface to form and release CH4 or H2S in the two half-reactions. Furthermore, sulfhydryl elimination occurs more easily than methyl elimination on the surface. These findings for the TMA and H2S half-reactions of Al2S3 ALD may be used for studying precursor chemistry and improvements in the preparation of other metal sulfides for emerging applications.

Oxygen doping in antimony sulfide nanosheets to facilitate catalytic conversion of polysulfides for lithium-sulfur batteries.

A high-performance catalyst, O-doped Sb2S3 nanosheets (SS-O NSs), is synthesized and introduced into lithium-sulfur batteries. Owing to their good conductivity, strong adsorbability/catalytic effect to polysulfides and fast Li+ diffusion, the SS-O NSs-modified cathodes can effectively mitigate the shuttle effect, thus achieving outstanding electrochemical performance.

Interfacial Molecule Mediators in Cathodes for Advanced Li-S Batteries.

The complicated reactions at the cathode-electrolyte interface in Li-S batteries are a large barrier for their successful commercialization. Herein, we developed a molecular design strategy and employed three small molecules acting as interfacial mediators to the cathodes of Li-S batteries. The theoretical calculation results show that the incorporation of tris(4-fluorophenyl)phosphine (TFPP) has a strong binding performance. The experimental results demonstrate that the strong chemical interactions between polysulfides and the F, P atoms in TFPP not only modify the kinetics of the electrochemical processes in the electrolyte but also promote the formation of short-chain clusters (Li2Sx, x = 1, 2, 3, and 4) at the interface during the charge-discharge process. As a result, an optimized electrode exhibits a low capacity decay rate of 0.042% per cycle when the current rate is increased to 5 C over 1000 cycles.

Growth Mechanism, Ambient Stability, and Charge Trapping Ability of Ti-Based Maleic Acid Hybrid Films by Molecular Layer Deposition.

Ti-based maleic acid (MA) hybrid films were successfully fabricated by molecular layer deposition (MLD) using organic precursor MA and inorganic precursor TiCl4. The effect of deposition temperature on the growth rate, composition, and bonding mode of hybrid thin films has been investigated systematically. With increasing temperature from 140 to 280 °C, the growth rate decreases from 1.42 to 0.16 Å per MLD cycle with basically unchanged composition ratio of C:O:Ti in the films. Fourier transform infrared spectra indicate that all hybrid films show preference for bidentate bonding mode. Further analyses of X-ray photoelectron spectroscopy and in situ quartz crystal microbalance elucidate that as-deposited MLD Ti-MA hybrid films consist of inorganic Ti-O-Ti units and organic-inorganic Ti-MA units. In addition, the density functional theory calculation was performed to investigate the possible reaction mechanism of the TiCl4-MA MLD process, which is well consistent with experimental results. More importantly, upon comparison with the TiCl4-fumaric acid MLD system, it is demonstrated that the cis- and trans-configurations of butenedioic acid influence the MLD growth, bonding mode, stability, and charging ability of MLD hybrid films. Ti-MA hybrid films exhibit better stability and charging ability than Ti-FA hybrid films, benefiting from the inorganic Ti-O-Ti units in the hybrid films.

Stoichiometric evolutions of PH3 under high pressure: implication for high-T c superconducting hydrides.

The superconductivity of hydrides under high pressure has attracted a great deal of attention since the recent observation of the superconducting transition at 203 K in strongly compressed H2S. It has been realized that the stoichiometry of hydrides might change under high pressure, which is crucial in understanding the superconducting mechanism. In this study, PH3 was studied to understand its superconducting transition and stoichiometry under high pressure using Raman, IR and X-ray diffraction measurements, as well as theoretical calculations. PH3 is stable below 11.7 GPa and then it starts to dehydrogenate through two dimerization processes at room temperature and pressures up to 25 GPa. Two resulting phosphorus hydrides, P2H4 and P4H6, were verified experimentally and can be recovered to ambient pressure. Under further compression above 35 GPa, the P4H6 directly decomposed into elemental phosphorus. Low temperature can greatly hinder polymerization/decomposition under high pressure and retains P4H6 up to at least 205 GPa. The superconductivity transition temperature of P4H6 is predicted to be 67 K at 200 GPa, which agrees with the reported result, suggesting that it might be responsible for superconductivity at higher pressures. Our results clearly show that P2H4 and P4H6 are the only stable P-H compounds between PH3 and elemental phosphorus, which is helpful for shedding light on the superconducting mechanism.