Dendritic copper oxide catalyst engineering weak-polarity Cu-O bond for high-efficiency nitrate electroreduction.

Nitrate reduction reaction (NO3RR) is deemed a promising pathway for both ammonia synthesis and water purification. Developing a high-efficiency catalyst with excellent NH3 selectivity and catalytic stability is desirable but remains challenging. In this work, a dendritic copper oxide catalyst (Cu-B2) has been developed to efficiently catalyze NO3RR for ammonia production, the Cu-B2 exhibits excellent catalytic performance, achieving an NH3 Faradaic efficiency as high as 94 % and an NH3 yield of 16.9 mg h-1 cm-2 with a current density of 192.3 mA cm-2 at - 0.6 V (vs. RHE, reversible hydrogen electrode). During NO3RR testing, the Cu-B2 catalysts are reduced in situ to form highly active Cu0/Cu+ sites, while retaining its dendritic morphology. Compared with other catalysts, the Cu-O bond in Cu-B2 catalyst has weaker polarity, resulting in Cu0/Cu+ sites in lower oxidation states. In situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies reveal the Cu-B2 catalyst exhibits a potential-independent capability for *NO3- adsorption and high conversion efficiency of NO2- intermediate into ammonia, DFT calculations reveal that Cu-B2 exhibts higher NO3- adsorption energy and lower NO3- adsorption energy barrier than Cu-B1, thus endowing it with a remarkably improved catalytic activity and durability.

Engineering iron carbide catalyst with aerophilic and electron-rich surface for improved electrochemical CO2 reduction.

Highly efficient electrocatalyst for carbon dioxide reduction (CO2RR) is desirable for converting CO2 into carbon-based chemicals and reducing anthropogenic carbon emission. Regulating catalyst surface to improve the affinity for CO2 and the capability of CO2 activation is the key to high-efficiency CO2RR. In this work, we develop an iron carbide catalyst encapsulated in nitrogenated carbon (SeN-Fe3C) with an aerophilic and electron-rich surface by inducing preferential formation of pyridinic-N species and engineering more negatively charged Fe sites. The SeN-Fe3C exhibits an excellent CO selectivity with a CO Faradaic efficiency (FE) of 92 % at -0.5 V (vs. RHE) and remarkably enhanced CO partial current density as compared to the N-Fe3C catalyst. Our results demonstrate that Se doping reduces the Fe3C particle size and improves the dispersion of Fe3C on nitrogenated carbon. More importantly, the preferential formation of pyridinic-N species induced by Se doping endows the SeN-Fe3C with an aerophilic surface and improves the affinity of the SeN-Fe3C for CO2. Density functional theory (DFT) calculations reveal that the electron-rich surface, which is caused by pyridinic N species and much more negatively charged Fe sites, leads to a high degree of polarization and activation of CO2 molecule, thus conferring a remarkably improved CO2RR activity on the SeN-Fe3C catalyst.

Corrosion Inhibition Studies of 8-Hydroxyquinoline Derivatives for N80 Steel in a 1.0 M HCl Solution: Experimental, Computational Chemistry, and Quantitative Structure-Activity Relationship Studies.

Twelve kinds of 8-hydroxyquinoline derivatives were synthesized and characterized. The weight loss method was used to evaluate their inhibition efficiencies (IEs) in a 1.0 M HCl solution at 333 K. The results showed that the alkyl chain length, heteroatoms (S, N, and O), and number of benzene rings significantly affect the IE. Herein, the IE of 5-[(dodecylthio)methyl]-8-quinolinol reached 98.71%. Meanwhile, the potentiodynamic polarization results indicated that all 8-hydroxyquinoline derivatives were mixed-type inhibitors. Electrochemical impedance spectroscopy results revealed that 8-hydroxyquinoline derivatives can increase polarization resistance, supporting their adsorption on the N80 steel surface. Moreover, according to density functional theory (DFT), the frontier orbital distribution and quantum chemical parameters (EHOMO, ELUMO, dipole moment µ, etc.) were calculated, and the results confirmed that the substituents of protonated 8-hydroxyquinoline derivatives significantly influenced the frontier orbital distribution. Molecular dynamics simulation illustrated that all protonated 8-hydroxyquinoline derivatives were adsorbed parallel to the Fe(110) surface, and the interaction energy (Eint) evidenced that the molecular size would affect their strength of adsorption on the Fe(110) surface. The linear and nonlinear quantitative structure-activity relationship models were established by linear regression (LR) methods and BP neural networks (NN), respectively. The LR model was established by using Eint and µ, and the coefficient of determination (R2) was 0.934. In addition, the nonlinear NN model was obtained according to IE and all parameters (DFT parameters and Eint). Then, the two calculation inhibition efficiencies (IEcal) were obtained from the LR and NN models, and the R2 values of the linear correlation between the IEcal and the experimental IE were 0.940 and 0.951, respectively. In addition, the IE of the tested inhibitor was 51.86% and the IEcal values predicted by the LR and NN models were 52.68% and 53.06%, respectively. Our results demonstrate that both the LR and NN models have good fits and predictive ability.

In-Situ Hydrogen-Bond Tailoring To Construct Ultrathin Bi2 O2 O/Bi2 O2 (OH)(NO3 ) Nanosheets: Interactive CO2 RR Promotion and Bismuth-Oxygen Moiety Preservation.

Bismuth-oxygen moieties are beneficial for high-efficiency electrochemical CO2 reduction (CO2 RR) to produce formate; however, preserving bismuth-oxygen moieties while applying a cathodic potential is challenging. This work reports the preparation of ultrathin Bi2 O2 O/Bi2 O2 (OH)(NO3 ) nanosheets (BiON-uts) by in-situ tailoring of hydrogen bonds in a Bi2 O2 (OH)(NO3 ) precursor. The BiON-uts exhibits a formate faradaic efficiency of 98 % with higher partial current density than that of most reported bismuth-based catalysts. Mechanistic studies demonstrate that the ultrathin nanosheet morphology facilitates ion-exchange between BiON-uts and the electrolyte to produce Bi2 O2 CO3 as intermediate, and adsorption of CO2 with surface Bi2 O2 O. DFT calculations reveal that the rate-limiting first electron transfer is effectively improved by the high electron affinity of Bi2 O2 CO3 . More importantly, high-efficiency CO2 RR in turn protects the bismuth-oxygen moieties from being reduced and thus helps to maintain the excellent CO2 RR activity. This work offers an interactive mechanism of CO2 RR promotion and bismuth-oxygen moiety preservation, opening up new opportunities for developing high-performance catalysts.

Selectively Upgrading Lignin Derivatives to Carboxylates through Electrochemical Oxidative C(OH)-C Bond Cleavage by a Mn-Doped Cobalt Oxyhydroxide Catalyst.

Oxidative cleavage of C(OH)-C bonds to afford carboxylates is of significant importance for the petrochemical industry and biomass valorization. Here we report an efficient electrochemical strategy for the selective upgrading of lignin derivatives to carboxylates by a manganese-doped cobalt oxyhydroxide (MnCoOOH) catalyst. A wide range of lignin-derived substrates with C(OH)-C or C(O)-C units undergo efficient cleavage to corresponding carboxylates in excellent yields (80-99 %) and operational stability (200 h). Detailed investigations reveal a tandem oxidation mechanism that base from the electrolyte converts secondary alcohols and their derived ketones to reactive nucleophiles, which are oxidized by electrophilic oxygen species on MnCoOOH from water. As proof of concept, this approach was applied to upgrade lignin derivatives with C(OH)-C or C(O)-C motifs, achieving convergent transformation of lignin-derived mixtures to benzoate and KA oil to adipate with 91.5 % and 64.2 % yields, respectively.

Author Correction: Improved ethanol electrooxidation performance by shortening Pd-Ni active site distance in Pd-Ni-P nanocatalysts.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Selective Chromogenic Recognition of Copper(II) Ion by Thiacalix[4]arene Tetrasulfonate and Mechanism.

Detection of biologically important transition metal ions such as copper by using a simple method is desirable and of great importance. In this work, we firstly reported that water-soluble thiacalix[4]arene tetrasulfonate (TCAS) exhibited selective chromogenic recognition towards copper(II) ion over other transition metal ions. Color change from colorless to salmon pink was observed in TCAS solution, weak bathochromic shift was induced in UV absorption spectrum of TCAS upon addition of copper(II) ion, and the absorbance of characteristic absorption band at 312 nm increased linearly with copper(II) ion concentration. The recognition mechanism of TCAS to copper(II) ion was investigated by a comparative study with calix[4]arene tetrasulfonate (CAS) and time-dependent density functional theory(TD-DFT) study, and the absorption bands were assigned based on transition orbital analysis.

Structural insight into [Fe-S2-Mo] motif in electrochemical reduction of N2 over Fe1-supported molecular MoS2.

The catalytic synthesis of NH3 from the thermodynamically challenging N2 reduction reaction under mild conditions is currently a significant problem for scientists. Accordingly, herein, we report the development of a nitrogenase-inspired inorganic-based chalcogenide system for the efficient electrochemical conversion of N2 to NH3, which is comprised of the basic structure of [Fe-S2-Mo]. This material showed high activity of 8.7 mgNH3 mgFe -1 h-1 (24 µgNH3 cm-2 h-1) with an excellent faradaic efficiency of 27% for the conversion of N2 to NH3 in aqueous medium. It was demonstrated that the Fe1 single atom on [Fe-S2-Mo] under the optimal negative potential favors the reduction of N2 to NH3 over the competitive proton reduction to H2. Operando X-ray absorption and simulations combined with theoretical DFT calculations provided the first and important insights on the particular electron-mediating and catalytic roles of the [Fe-S2-Mo] motifs and Fe1, respectively, on this two-dimensional (2D) molecular layer slab.

Hydrogen Embrittlement and Improved Resistance of Al Addition in Twinning-Induced Plasticity Steel: First-Principles Study.

Understanding the mechanism of hydrogen embrittlement (HE) of austenitic steels and developing an effective strategy to improve resistance to HE are of great concern but challenging. In this work, first-principles studies were performed to investigate the HE mechanism and the improved resistance of Al-containing austenite to HE. Our results demonstrate that interstitial hydrogen atoms have different site preferences in Al-free and Al-containing austenites. The calculated binding energies and diffusion barriers of interstitial hydrogen atoms in Al-containing austenite are remarkably higher than those in Al-free austenite, indicating that the presence of Al is more favorable for reducing hydrogen mobility. In Al-free austenite, interstitial hydrogen atoms caused a remarkable increase in lattice compressive stress and a distinct decrease in bulk, shear, and Young's moduli. Whereas in Al-containing austenite, the lattice compressive stress and the mechanical deterioration induced by interstitial hydrogen atoms were effectively suppressed.

Dendrimer-grafted bioreducible polycation/DNA multilayered films with low cytotoxicity and high transfection ability.

Controlled release of incorporated foreign DNA from multilayered films plays an important role in surface-mediated gene delivery. Herein, multilayered polyelectrolyte complex thin films, composed of dendrimer-grafted bio-reducible cationic poly(disulfide amine) and plasmid DNA, were fabricated via layer-by-layer (LBL) assembly for in vitro localized gene delivery. The UV absorbance and thickness of the LBL films were found to have linear correlation with the numbers of poly(disulfide amine)/DNA bilayers. Although LBL films were stable in PBS buffer, their degradation could be triggered by reducing agents (i.e. glutathione, GSH). The degradation rate of the films is directly proportional to the GSH concentration, which in turn affected the corresponding gene expression. All poly(disulfide amine)/DNA films exhibited lower cytotoxicity and higher transfection activity in comparison with PEI/DNA multilayered films. Moreover, LBL films showed the highest transfection efficiency in the presence of 2.5 mM GSH when cultured with 293T cells, with ~36% GFP-positive 293T cells after 5-days of co-culture. These DNA-containing reducible films could potentially be useful in gene therapy and tissue engineering by controlling the release of incorporated DNA.

Antiradical and Antioxidative Activity of Azocalix[4]arene Derivatives: Combined Experimental and Theoretical Study.

Developing antioxidants with high efficiency is fundamentally important for the protection of living cells and engineering materials against oxidative damage. In this present study, two azocalix[4]arene derivatives were synthesized via a diazo coupling reaction between calix[4]arene and diazonium salts. Their antiradical and antioxidative performances were evaluated by hydroxyl radical scavenging and pyrogallol autoxidation inhibition experiments. Combined with theoretical studies, the antiradical and antioxidative mechanisms have been explored. The results demonstrated that these two azocalix[4]arene derivatives both exhibited remarkable antiradical and antioxidative activity. The macrocyclic framework of the calix[4]arene and para-azo substituent group at the upper rim of calix[4]arene contributed synergistically and importantly to its excellent antiradical and antioxidant activity.

Transition metal atom doping of the basal plane of MoS2 monolayer nanosheets for electrochemical hydrogen evolution.

Surface sites of extensively exposed basal planes of MoS2 monolayer nanosheets, prepared via BuLi exfoliation of MoS2, have been doped with transition metal atoms for the first time to produce 2D monolayer catalysts used for the electrochemical hydrogen evolution reaction (HER). Their HER activity is significantly higher than the corresponding thin and bulk MoS2 layers. HAADF-STEM images show direct proof that single transition metal atoms reside at the surface basal sites, which subtly modify the electro-catalytic activity of the monolayer MoS2, dependent on their electronic and stereospecific properties. It is found that these dopants play an important role in tuning the hydrogen adsorption enthalpies of the exposed surface S atoms and Mo atoms in HER. We report electrochemical testing, characterization and computational modelling and demonstrate that Co can significantly enhance the HER activity by the dominant Co-S interaction, whereas Ni substantially lowers the HER rate due to the Ni-Mo interaction at the same basal site. The two transition metal dopants show opposite doping behavior despite the fact that they are neighbors in the periodic table.

Carbon- and Binder-Free Core-Shell Nanowire Arrays for Efficient Ethanol Electro-Oxidation in Alkaline Medium.

To achieve high electrochemical surface area (ECSA) and avoid carbon support and binder in the anode catalyst of direct ethanol fuel cell, herein, we design freestanding core-shell nickel@palladium-nickel nanowire arrays (Ni@Pd-Ni NAs) without carbon support and binder for high-efficiency ethanol electro-oxidation. Bare Ni nanowire arrays (Ni NAs) are first prepared using the facile template-assistant electrodeposition method. Subsequently, the Ni@Pd-Ni NAs are formed using one-step solution-based alloying reaction. The optimized Ni@Pd-Ni NA electrode with a high ECSA of 64.4 m2 g-1Pd exhibits excellent electrochemical performance (peak current density: 622 A g-1Pd) and cycling stability for ethanol electro-oxidation. The facilely obtained yet high-efficiency core-shell Ni@Pd-Ni NA electrode is a promising electrocatalyst, which can be utilized for oxygen reduction reaction, urea, hydrazine hydrate, and hydrogen peroxide electro-oxidation, not limited to the ethanol electro-oxidation.

Improved ethanol electrooxidation performance by shortening Pd-Ni active site distance in Pd-Ni-P nanocatalysts.

Incorporating oxophilic metals into noble metal-based catalysts represents an emerging strategy to improve the catalytic performance of electrocatalysts in fuel cells. However, effects of the distance between the noble metal and oxophilic metal active sites on the catalytic performance have rarely been investigated. Herein, we report on ultrasmall (∼5 nm) Pd-Ni-P ternary nanoparticles for ethanol electrooxidation. The activity is improved up to 4.95 A per mgPd, which is 6.88 times higher than commercial Pd/C (0.72 A per mgPd), by shortening the distance between Pd and Ni active sites, achieved through shape transformation from Pd/Ni-P heterodimers into Pd-Ni-P nanoparticles and tuning the Ni/Pd atomic ratio to 1:1. Density functional theory calculations reveal that the improved activity and stability stems from the promoted production of free OH radicals (on Ni active sites) which facilitate the oxidative removal of carbonaceous poison and combination with CH3CO radicals on adjacent Pd active sites.

Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters.

Understanding of the "structure-activity" relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au(3+) ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size.

Catalytic Effects of Cr on Nitridation of Silicon and Formation of One-dimensional Silicon Nitride Nanostructure.

The catalytic effects of chromium (Cr) on the direct nitridation of silicon (Si) and morphology of nitridation product were investigated. Cr dramatically improved the conversation of Si to silicon nitride (Si3N4). The complete conversion was achieved at 1350 °C upon addition of 1.25 wt% Cr. This temperature was much lower than that required in the case without using a catalyst. Meanwhile, Cr played an important role in the in-situ growth of one-dimensional (1-D) α-Si3N4 nanostructures. α-Si3N4 nanowires and nanobelts became the primary product phases when 5 wt% Cr was used as the catalyst. The growth processes of the 1-D α-Si3N4 nanostructures were governed by the vapor-solid mechanism. First-principle calculations suggest that electrons can be transferred from Cr atoms to N atoms, facilitating the Si nitridation.

Preparation and Catalytic Activities of Au/Co Bimetallic Nanoparticles for Hydrogen Generation from NaBH4 Solution.

A series of poly(N-vinyl-2-pyrrolidone)-protected Au/Co bimetallic nanoparticles (BNPs) were prepared by a simple route based on dropwise addition of NaBH4. Their structures, particle sizes, and chemical compositions were characterized by Ultraviolet-visible spectrophotometry, X-ray photo- electron spectroscopy, Transmission electron microscopy and High-resolution transmission electron microscopy, and their catalytic activity for the hydrogen generation from hydrolysis of an alkaline NaBH4 solution was examined. As-prepared alloy-structured Au/Co BNPs had an average size between 2.8 and 3.6 nm and showed a higher catalytic activity for the hydrogen generation than the corresponding Au and Co monometallic nanoparticles (MNPs). Of all the MNPs and BNPs, Au20Co80 BNPs exhibited the highest catalytic activity, and a hydrogen generation rate of 480 mol-H2 · h(-1) · mol-M(-1) was achieved. The high catalytic activity of the BNPs can be ascribed to the formation of negatively charged Au atoms and positively charged Co atoms as a result of the electronic charge transfer effects in the BNPs.

Catalytic Activities for Glucose Oxidation of Au/Pd Bimetallic Nanoparticles Prepared via Simultaneous NaBH4 Reduction.

Au/Pd bimetallic nanoparticles (BNPs) were prepared by simultaneous reduction method using NaBH4 as a reducing reagent. The effects of particle size, electronic structure and composition upon the catalytic activities of the BNPs for aerobic glucose oxidation were investigated. The PVP-protected Au/Pd BNPs of about 2.0 nm in diameter synthesized via rapid injection of NaBH4 possessed a high catalytic activity for aerobic glucose oxidation. The catalytic activity of BNPs with the Au/Pd atomic ratio of 60/40 was more than two times higher than that of Au nanoparticles (NPs) though the latter were smaller. This can be ascribed to the presence of negatively charged Au atoms arisen from electron donation from neighboring Pd atoms via electronic charge transfer. In contrast, Au/Pd BNPs synthesized via dropwise addition of NaBH4 into the starting solution and having the large mean particle sizes, showed a low catalytic activity.

A Family of High-Efficiency Hydrogen-Generation Catalysts Based on Ammonium Species.

Development of highly active, low cost, ecologically friendly, and durable homogenous catalysts for hydrogen generation from hydrolysis of borohydride is one of the most desirable pathways for future hydrogen utilization. The unexpected catalytic activities of inorganic ammonium species and the corresponding mechanisms underpinning them are studied. The catalytic activities of the ammonium species are higher than or comparable to those of mostly investigated noble-metal/transition-metal catalysts (such as Pd, Pt, Ni, and Co) but are considerably cheaper, more environmentally friendly, and more readily available. Quantum chemical calculations indicate that the unique ammonium-induced reaction pathway involved with a barrierless elementary reaction at the reaction entrance and the formation of the highly active intermediate BH3 are responsible for the unexpected catalytic activities and the significantly accelerated hydrogen generation.

Synthesis and catalytic activity of crown jewel-structured (IrPd)/Au trimetallic nanoclusters.

Crown-jewel-structured (IrPd)/Au trimetallic nanoclusters are prepared by a galvanic replacement reaction using Ir/Pd nanoclusters with a structure of Ir rich in the core and Pd rich in the shell as mother clusters. The catalytic activity of the top Au atoms for aerobic glucose oxidation of the trimetallic nanoclusters is the highest ever reported among all supported and colloidal catalysts.