Directional Electrosynthesis of Adipic Acid and Cyclohexanone by Controlling the Active Sites on NiOOH.

Dicarboxylic acids and cyclic ketones, such as adipic acid (AA) and cyclohexanone (CHN), are essential compounds for the chemical industry. Although their production by electrosynthesis using electricity is considered one of the most promising strategies, the application of such processes has been hampered by a lack of efficient catalysts as well as a lack of understanding of the mechanism. Herein, a series of monolithic msig/ea-NiOOH-Ni(OH)2/NF were prepared by means of self-dissolution of metal matrix components, interface growth, and electrochemical activation (denoted as msig/ea). The as-synthesized catalysts have three-dimensional cuboid-like structures formed by interconnecting nanosheets composed of NiOOH. By theoretically guided regulation of the amounts of Ni3+ and oxygen vacancies (OV), a 96.5% yield of CHN from cyclohexanol (CHA) dehydrogenation and a 93.6% yield of AA from CHN oxidation were achieved. A combined experimental and theoretical study demonstrates that CHA dehydrogenation and CHN oxidation were promoted by the formation of Ni3+ and the peroxide species (*OOH) on OV. This work provides a promising approach for directional electrosynthesis of high-purity chemicals with in-depth mechanistic insights.

Electronic Structure Engineering of Pt Species over Pt/WO3 toward Highly Efficient Electrocatalytic Hydrogen Evolution.

Pt-based supported materials, a widely used electrocatalyst for hydrogen evolution reaction (HER), often experience unavoidable electron loss, resulting in a mismatching of electronic structure and HER behavior. Here, a Pt/WO3 catalyst consisting of Pt species strongly coupled with defective WO3 polycrystalline nanorods is rationally designed. The electronic structure engineering of Pt sites on WO3 can be systematically regulated, and so that the optimal electron-rich Pt sites on Pt/WO3 -600 present an excellent HER activity with only 8 mV overpotential at 10 mA cm-2 . Particularly, the mass activity reaches 7015 mA mg-1 at the overpotential of 50 mV, up to 26-fold higher than that of the commercial Pt/C. The combination of experimental and theoretical results demonstrates that the O vacancies of WO3 effectively mitigate the tendency of electron transfer from Pt sites to WO3 , so that the d-band center could reach an appropriate level relative to Fermi level, endowing it with a suitable Δ G H ∗ $\Delta {G_{{{\rm{H}}^ * }}}$ . This work identifies the influence of the electronic structure on catalytic activity.

Promoting Amination of Furfural to Furfurylamine by Metal-Support Interactions on Pd/MoO3-x Catalysts.

The reductive amination of carbonyl compounds is one of the most straightforward protocols to construct C-N bonds, but highly desires active and selective catalysts. Herein, Pd/MoO3-x catalysts are proposed for furfural amination, in which the interactions between Pd nanoparticles and MoO3-x supports can be easily ameliorated by varying the preparation temperature toward efficient catalytic turnover. Thanks to the synergistic cooperation of MoV -rich MoO3-x and highly dispersed Pd, the optimal catalysts afford the high yield of furfurylamine (84 %) at 80 °C. Thereinto, MoV species not only acts as the acidic promoter to facilitate the activation of carbonyl groups, but also interacts with Pd nanoparticles to promote the subsequent hydrogenolysis of Schiff base N-furfurylidenefurfurylamine and its germinal diamine. The good efficiency of Pd/MoO3-x within a broad substrate scope further highlights the key contribution of metal-support interactions to the refinery of biomass feedstocks.

Molybdenum Carbide-Oxide Heterostructures: In Situ Surface Reconfiguration toward Efficient Electrocatalytic Hydrogen Evolution.

Heterostructured Mo2 C-MoOx on carbon cloth (Mo2 C-MoOx /CC), as a model of easily oxidized electrocatalysts under ambient conditions, is investigated to uncover surface reconfiguration during the hydrogen evolution reaction (HER). Raman spectroscopy combined with electrochemical tests demonstrates that the MoVI oxides on the surface are in situ reduced to MoIV , accomplishing promoted HER in acidic condition. As indicated by density functional theoretical calculations, the in situ reduced surface with terminal Mo=O moieties can effectively bring the negative ΔGH* on bare Mo2 C close to a thermodynamic neutral value, addressing difficult H* desorption toward fast HER kinetics. The optimized Mo2 C-MoOx /CC only requires a low overpotential (η10 ) of 60 mV at -10 mA cm-2 in 1.0 m HClO4 , outperforming Mo2 C/CC and most non-precious electrocatalysts. In situ surface reconfiguration are shown on W2 C-WOx , highlighting the significance to boost various metal-carbides and to identify active sites.

Converting surface-oxidized cobalt phosphides into Co2(P2O7)-CoP heterostructures for efficient electrocatalytic hydrogen evolution.

Exploring noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is a key issue in a hydrogen economy blueprint. As one of the promising candidates, transition metal phosphides unfortunately suffer from inevitable surface oxidation which obstructs active-site exposure. Herein, a facile reduction followed by a surface phosphorization is introduced to convert surface-oxidized cobalt phosphides to a Co2(P2O7)-CoP heterostructure embedded in N-doped carbon (Co2(P2O7)-CoP/NC), accomplishing an efficient HER in both acidic and alkaline electrolytes. It affords low overpotentials (η 10) of 88 and 97 mV to reach a current density of -10 mA cm-2, and small Tafel slopes of 51 and 61 mV dec-1 in 0.5 M H2SO4 and 1.0 M KOH, respectively, outperforming the parent surface-oxidized Co2P and most previously-reported Pt-free electrocatalysts. The remarkably improved electrocatalysis should be ascribed to the strong surface acidity of the Co2(P2O7) component and thereby the promoted HER kinetics on Co2(P2O7)-CoP interfaces. This work will encourage the development of cost-efficient electrocatalysts via surface engineering.

MoS2 nanosheets with peroxidase mimicking activity as viable dual-mode optical probes for determination and imaging of intracellular hydrogen peroxide.

The authors describe a dual-mode (colorimetric-fluorometric) nanoprobe for H2O2 that was fabricated by covering molybdenum disulfide nanosheets (MoS2 NS) with ortho-phenylenediamine (OPD). The probe (OPD-MoS2 NS) was applied to the optical determination of H2O2, to the quantitation of cell numbers, and to the detection of intracellular concentrations of H2O2. Oxidation by H2O2 leads to a colored and fluorescent product (oxidized OPD) with absorption/excitation/fluorescence peaks at 450/450/557 nm. The nanoprobe can detect H2O2 in down to 500 nM concentrations, and HeLa cells at levels of 100 cells mL-1. The detection limit for intracellular H2O2 is in the 5.5 to 12.6 µM concentration range when the method is applied to cells at levels of 102-106 cells mL-1. Due to its good biocompatibility and easy cell uptake, the nanoprobe also permits sensitive fluorometric imaging of intracellular H2O2. It can also comparatively discriminate the change of intracellular oxidation state in living cancerous and normal cells. Graphical abstract Editor, we provided image with high resolution. Please find it in a folder name "MIAC-D-18-00081" in the FTP site. A dual-mode (colorimetric-fluorometric) detection nanoplatform based on OPD-modified MoS2 nanosheets is used to quantitatively detect H2O2, cell numbers and intracellular H2O2. The MoS2 nanoprobes also permit sensitive fluorescence imaging of intracellular H2O2, and can discriminate intracellular oxide states in living cancerous and normal cells.

Enhancing Metal-Support Interactions by Molybdenum Carbide: An Efficient Strategy toward the Chemoselective Hydrogenation of α,ß-Unsaturated Aldehydes.

Metal-support interactions are desired to optimize the catalytic turnover on metals. Herein, the enhanced interactions by using a Mo2C nanowires support were utilized to modify the charge density of an Ir surface, accomplishing the selective hydrogenation of α,ß-unsaturated aldehydes on negatively charged Ir(δ-) species. The combined experimental and theoretical investigations showed that the Ir(δ-) species derive from the higher work function of Ir (vs. Mo2C) and the consequently electron transfer. In crotonaldehyde hydrogenation, Ir/Mo2C delivered a crotyl alcohol selectivity as high as 80%, outperforming those of counterparts (<30%) on silica. Moreover, such electronic metal-support interactions were also confirmed for Pt and Au, as compared with which, Ir/Mo2C was highlighted by its higher selectivity as well as the better activity. Additionally, the efficacy for various substrates further verified our Ir/Mo2C system to be competitive for chemoselective hydrogenation.

Single-dose vaccine against tick-borne encephalitis.

Tick-borne encephalitis (TBE) virus is the most important human pathogen transmitted by ticks in Eurasia. Inactivated vaccines are available but require multiple doses and frequent boosters to induce and maintain immunity. Thus far, the goal of developing a safe, live attenuated vaccine effective after a single dose has remained elusive. Here we used a replication-defective (single-cycle) flavivirus platform, RepliVax, to generate a safe, single-dose TBE vaccine. Several RepliVax-TBE candidates attenuated by a deletion in the capsid gene were constructed using different flavivirus backbones containing the envelope genes of TBE virus. RepliVax-TBE based on a West Nile virus backbone (RV-WN/TBE) grew more efficiently in helper cells than candidates based on Langat E5, TBE, and yellow fever 17D backbones, and was found to be highly immunogenic and efficacious in mice. Live chimeric yellow fever 17D/TBE, Dengue 2/TBE, and Langat E5/TBE candidates were also constructed but were found to be underattenuated. RV-WN/TBE was demonstrated to be highly immunogenic in Rhesus macaques after a single dose, inducing a significantly more durable humoral immune response compared with three doses of a licensed, adjuvanted human inactivated vaccine. Its immunogenicity was not significantly affected by preexisting immunity against WN. Immunized monkeys were protected from a stringent surrogate challenge. These results support the identification of a single-cycle TBE vaccine with a superior product profile to existing inactivated vaccines, which could lead to improved vaccine coverage and control of the disease.

Synergistic enhancement of electrocatalytic nitroarene hydrogenation over Mo2C@MoS2 heteronanorods with dual active-sites.

Electrocatalytic hydrogenation (ECH) enables the sustainable production of chemicals under ambient conditions, in which catalysts catering for the different chemisorption of reactants/intermediates are desired but still challenging. Here, Mo2C@MoS2 heteronanorods with dual active-sites are developed to accomplish efficient nitroarene ECH according to our theoretical prediction that the binding of atomic H and nitro substrates would be synergistically strengthened on Mo2C-MoS2 interfaces. They afford high faradaic efficiency (>85%), yield (>78%) and selectivity (>99%) for the reduction of 4-nitrostyrene (4-NS) to 4-vinylaniline (4-VA) in neutral electrolytes, outperforming not only the single-component counterparts of Mo2C nanorods and MoS2 nanosheets, but also recently reported noble-metals. Accordingly, in situ Raman spectroscopy combined with electrochemical tests clarifies the rapid ECH of 4-NS on Mo2C-MoS2 interfaces due to the facilitated elementary steps, quickly refreshing active sites for continuous electrocatalysis. Mo2C@MoS2 further confirms efficient and selective ECH toward functional anilines with other well-retained reducible groups in wide substrate scope, underscoring the promise of dual-site engineering for exploring catalysts.

Enhancing Benzylamine Electro-oxidation and Hydrogen Evolution through in-situ Electrochemical Activation of CoC2O4 Nanoarray.

The sluggish anodic oxygen evolution reaction (OER) seriously restricts the overall efficiency of water splitting. Here, we present an environmentally friendly and efficient aniline oxidation (BOR) to replace the sluggish OER, accomplishing the co-production of H2 and high value-added benzonitrile (BN) at low voltages. Cobalt oxalates grown on cobalt foam (CoC2O4·2H2O/CF) are adopted as the pre-catalysts, which further evolve into working electrocatalysts active for BOR and HER after appropriate electrochemical activation. Thereinto, cyclic voltammetry activation at positive potentials is performed to reconstruct cobalt oxalate via extensive oxidation, resulting in enriched Co(III) species and nanoporous structures beneficial for BOR, while chronoamperometry at negative potentials is introduced for the cathodic activation toward efficient HER with obvious improvement. The two activated electrodes can be combined into a two-electrode system, which achieves a high current density of 75 mA cm-2 at the voltage of 1.95 V, with the high Faraday efficiencies of both BOR (90.0%) and HER (90.0%) and the satisfactory yield of BN (76.8%).

Cr-doping promoted surface reconstruction of Ni3N electrocatalysts toward efficient overall water splitting.

Understanding and utilizing the dynamic changes of electrocatalysts under working conditions are important for advancing the sustainable hydrogen production. Here, we for the first time report that Cr-doping can promote the in situ reconstruction of a self-supported Ni3N electrocatalyst (Cr-Ni3N/NF) during oxygen and hydrogen evolution reactions (OER and HER), and therefore improve the electrocatalytic water splitting performance. As identified by in situ measurements and theoretical calculations, Cr-doping enhances OH- adsorption during OER at anode and thereby boosts the transformation of Ni3N pre-catalysts to defect-rich nickel oxyhydroxide (NiOOH) active species. Meanwhile, it facilitates the generation of Ni3N/Ni(OH)2 at cathodes due to effective H2O activation, leading to the fast HER kinetics on the Ni3N/Ni(OH)2 interfaces. Notably, the optimal Cr-Ni3N/NF displays good OER and HER performance in 1.0 M KOH electrolytes, with low overpotentials of 316 and 188 mV to achieve the current density of ± 100 mA cm-2, respectively. Benefiting from its bi-functionality and self-supporting property, an alkaline electrolyzer equipped with Cr-Ni3N/NF as both anode and cathode affords a small voltage of 1.72 V at 100 mA cm-2, along with 100 h operation stability. Elucidating that Cr-doping can boost in situ reconfiguration and consequently the electrocatalytic activity, this work would shed new light on the rational design and synthesis of electrocatalysts via directional reconstructions.

Restructuring multi-phase interfaces from Cu-based metal-organic frameworks for selective electroreduction of CO2 to C2H4.

Multi-phase interfaces are promising for surmounting the energy barriers of electrochemical CO2 reduction involving multiple electron transfer steps, but challenges still remain in constructing interfacial micro-structures and unraveling their dynamic changes and working mechanism. Herein, highly active Ag/Cu/Cu2O heterostructures are in situ electrochemically restructured from Ag-incorporating HKUST-1, a Cu-based metal-organic framework (MOF), and accomplish efficient CO2-to-C2H4 conversion with a high faradaic efficiency (57.2% at -1.3 V vs. RHE) and satisfactory stability in flow cells, performing among the best of recently reported MOFs and their derivatives. The combination of in/ex situ characterizations and theoretical calculations reveals that Ag plays a crucial role in stabilizing Cu(i) and increasing the CO surface coverage, while the active Cu/Cu2O interfaces significantly reduce the energy barrier of C-C coupling toward the boosted ethylene production. This work not only proves MOFs as feasible precursors to derive efficient electrocatalysts on site, but also provides in-depth understanding on the working interfaces at an atomic level.

Enhancing Low-Potential Electrosynthesis of 2,5-Furandicarboxylic Acid on Monolithic CuO by Constructing Oxygen Vacancies.

Electrosynthesis of 2,5-furandicarboxylic acid (FDCA) from the biomass-derived 5-hydroxymethylfurfural (HMF) is one of the most potential means to produce a bioplastic monomer. Copper oxide (CuO) catalyst shows promising prospects due to its high surface activity, conductivity, and stability, but relatively poor capability of oxygen evolution; however, the weak adsorption of substrates and the lack of facile synthetic strategies largely restrict its practical application. Here, a novel facile in situ method, alternate cycle voltammetry (denoted as c) and potentiostatic electrolysis (denoted as p), was proposed to prepare a monolithic cpc-CuO/Cu-foam electrocatalyst. Along with the increment of CuO and its surficial oxygen vacancies (OV), the FDCA yield, productivity, and Faradaic efficiency can reach up to ∼98.5%, ∼0.2 mmol/cm2, and ∼94.5% under low potential of 1.404 VRHE. Such an efficient electrosynthesis system can be easily scaled up to afford pure FDCA powders. In a combinatory analysis via electron paramagnetic resonance spectroscopy, H2 temperature-programmed reduction, open circuit potential, infrared spectroscopy, zeta potential, electrochemical measurement, and theoretical calculation, we found that the CuO was the active phase and OV generated on CuO surface can dramatically enhance the adsorption of *HMF and *OH (* denotes an active site), accounting for its superior FDCA production. This work offers an excellent paradigm for enhancing biomass valorization on CuO catalysts by constructing surficial defects.

Redox regulation of Ni hydroxides with controllable phase composition towards biomass-derived polyol electro-refinery.

Electrocatalytic refinery from biomass-derived glycerol (GLY) to formic acid (FA), one of the most promising candidates for green H2 carriers, has driven widespread attention for its sustainability. Herein, we fabricated a series of monolithic Ni hydroxide-based electrocatalysts by a facile and in situ electrochemical method through the manipulation of local pH near the electrode. The as-synthesized Ni(OH)2@NF-1.0 affords a low working potential of 1.36 VRHE to achieve 100% GLY conversion, 98.5% FA yield, 96.1% faradaic efficiency and ∼0.13 A cm-2 of current density. Its high efficiency on a wide range of polyol substrates further underscores the promise of sustainable electro-refinery. Through a combinatory analysis via H2 temperature-programmed reduction, cyclic voltammetry and in situ Raman spectroscopy, the precise regulation of synthetic potential was discovered to be highly essential to controlling the content, phase composition and redox properties of Ni hydroxides, which significantly determine the catalytic performance. Additionally, the 'adsorption-activation' mode of ortho-di-hydroxyl groups during the C-C bond cleavage of polyols was proposed based on a series of probe reactions. This work illuminates an advanced path for designing non-noble-metal-based catalysts to facilitate electrochemical biomass valorization.

Highly efficient hydrodesulfurization driven by an in-situ reconstruction of ammonium/amine intercalated MoS2 catalysts.

Hydrodesulfurization (HDS) is a commonly used route for producing clean fuels in modern refinery. Herein, ammonium/amine-intercalated MoS2 catalysts with various content of 1T phase and S vacancies have been successfully synthesized. Along with the increment of 1T phase and S vacancies of MoS2, the initial reaction rate of the HDS of dibenzothiophene (DBT) can be improved from 0.09 to 0.55 µmol·gcat-1·s-1, accounting for a remarkable activity compared to the-state-of-the-art catalysts. In a combinatory study via the activity evaluation and catalysts characterization, we found that the intercalation species of MoS2 played a key role in generating more 1T phase and S vacancies through the 'intercalation-deintercalation' processes, and the hydrogenation and desulfurization of HDS can be significantly promoted by 1T phase and S vacancies on MoS2, respectively. This study provides a practically meaningful guidance for developing more advanced HDS catalysts by the intercalated MoS2-derived materials with an in-depth understanding of structure-function relationships.

Chlorine-mediated electrodeposition of hierarchical and hydrophobic copper electrocatalysts for efficient CO2 electroreduction to ethylene.

Hierarchical Cu dendrites fabricated via Cl-mediated electrodeposition afford high C2H4 efficiency (58% faradaic efficiency at -0.9 V vs. RHE) for CO2 electroreduction thanks to not only the optimal hydrophobicity/aerophilicity, but also the dominant distribution of active (100) and (110) facets.

Roughness-Dependent Electro-Reductive Coupling of Nitrobenzenes and Aldehydes on Copper Electrodes.

The electro-reductive coupling of nitro and carbonyl compounds enables a facile, environmentally friendly and energy benign transformation toward value-added nitrones or imines, but the selectivity is still challenging. Here, the surface roughness of Cu electrodes is introduced for the first time as the determinant to switch products from nitrones to imines owing to the controllable reduction of nitroarenes to hydroxylamines or amines on tailored CuI /Cu0 interfaces. The roughness-dependent selectivity, that is the decrease of nitrones and the increase of imines with enhanced roughness, is visible in the electro-reductive coupling of nitrobenzene and furfural. Thus, the high selectivity of nitrone (98 %) and imine (80 %) can be achieved on a surface smooth Cu foil and the one electrochemically roughened in the presence of I- , respectively. Such roughness-dependence of nitrone/imine selectivity on Cu electrodes is further verified in a wide substrate scope, highlighting the promise of surface/interfacial engineering for electrochemical synthesis.

Promoted electrocatalytic hydrogenation of furfural in a bi-phasic system.

The promoted electrocatalytic hydrogenation of biomass-derived furfural to 2-methylfuran is for the first time identified in a water/oil bi-phasic system, in which the oil phase can quickly separate hydrophobic products from the electrode/electrolyte interfaces, resulting in a beneficial equilibrium toward hydrodeoxygenation.

Activating Commercial Nickel Foam to a Highly Efficient Electrocatalyst for Oxygen Evolution Reaction through a Three-Step Surface Reconstruction.

It is highly desired to directly use commercial nickel foam (CNF) as an electrocatalyst for the oxygen evolution reaction (OER) via simple surface reconstruction. In our research, a simple three-step preactivation process was proposed to reconstruct CNF as an efficient OER catalyst, including calcination, high-voltage treatment, and immersing in electrolyte. The optimal CNF after three-step activation reaches an excellent OER performance of 228 and 267 mV at η10 and η100 in alkaline media and can tolerate long-term tests under a large current density of 500 mA·cm-2. The promotion of each step was explored. The calcination step leads to a reconstructive surficial morphology with an enlarged active surface, providing a prerequisite for the following construction steps. The high-voltage treatment changes the valence of surface Ni species, generating phases with higher catalytic activity, and the immersing process introduces Fe heteroatoms into the surface of CNF, boosting the catalytic performance of CNF through Ni-Fe interactions. This research provides a simple method of making high-performance catalysts with accessible nickel foam, a potential for large-scale application in practical industry, and new thinking for the manipulation of Ni-based catalysts.

Nickel sulfide-oxide heterostructured electrocatalysts: Bi-functionality for overall water splitting and in-situ reconstruction.

Bi-functional electrocatalysts are desired for both hydrogen and oxygen evolution reactions (HER and OER). Herein, facile O2-plasma activation is introduced to improve the bi-functionality via constructing nickel sulfide-oxide heterostructures. Ni3S2-NiOx supported by nickel foam delivers obviously elevated HER and OER activity in comparison with pristine Ni3S2 and recently reported NiSx-based electrocatalysts, featured by the low overpotentials for HER (104 mV) and OER (241 mV) at ±10 mA cm-2 in 1.0 M KOH, as well as a voltage of 1.52 V for overall water splitting. As revealed by in-situ Raman spectroscopy, on the one hand, Ni(OH)2 generated from Ni3S2 during alkaline HER accelerates water dissociation toward the gradually improved performance; on the other hand, this heterostructure undergoes extensive oxidation during OER, leading to excessive NiOOH covering on Ni3S2 and thereby declining activity. These changes are interpreted by the distinct thermodynamic relationship under specific electrochemical conditions via density functional theory calculations.