Search

Ni-based coordination compounds, during the oxygen evolution reaction (OER), self-reconstruct to produce NiOOH, which are the real active sites. Thus, encouraging the self-reconstruction of pre-catalysts to generate more NiOOH species has emerged as an effective strategy for enhancing the activity. In this research, we utilized three coordination compounds, Ni(N(CN)2)2, Ni(NCN), and Ni(HNCN)2, to examine the effect of three distinct ligands (–N(CN)2–, –HNCN–, and –NCN–) on the local electronic structure of coordinated Ni, aiming to promote the degree of self-reconstruction during the OER. XPS studies and in situ Raman spectroscopy revealed a significant relationship between the electron-donating properties of coordinated Ni and the self-reconstruction abilities of the pre-catalysts. Notably, Ni coordinated with –N(CN)2– exhibits a high tendency to donate electrons, leading to facile reconstruction of Ni(N(CN)2)2 into Ni(OOH)–(N(CN)2). As a result, Ni(OOH)–(N(CN)2) displays high OER activity (264 mV @ 10 mA cm−2 and Tafel slope of 40.80 mV dec−1) in comparison to Ni(OOH)–(NCN) (290 mV @ 10 mA cm−2 and Tafel slope of 55.63 mV dec−1) and Ni(OOH)–(HNCN) (307 mV @ 10 mA cm−2 and Tafel slope of 77.70 mV dec−1). These findings offer new perspectives on designing and developing innovative catalysts to enhance OER efficiency. [ABSTRACT FROM AUTHOR]

The replacement of the oxygen evolution reaction with a higher valuable oxidation process can overcome the sluggish kinetics to promote renewable hydrogen production, simultaneously achieving energy storage and environmental protection. However, the effective integration of two redox half-reactions in one photocatalytic reaction system is still a challenge. Here the p-diethynylbenzene and dibenzothiophene sulfone copolymer (PEB-DBT) is well-designed to couple with α-Fe2O3via a palladium-catalyzed Sonogashira cross-linking reaction, forming a heterojunction with strong interfacial interaction. In particular, there is a different preferred charge transfer path of PEB-DBT/α-Fe2O3via modulating the work function difference in various solutions. The results suggest that the Z-scheme electron transfer pathway is predominant in triethanolamine (TEOA) and ofloxacin (OFL) solutions, instead of the type-II heterojunction that forms in H2O or methylene blue (MB). The Z-scheme PEB-DBT/α-Fe2O3 heterojunction has excellent performance in the hydrogen evolution half-reaction and OFL degradation, which is about 2.7 times and 3.3 times higher than that of pure PEB-DBT, respectively. Finally, it successfully achieved simultaneous photocatalytic H2 evolution and OFL degradation under visible light. [ABSTRACT FROM AUTHOR]

Propane dehydrogenation (PDH) is an effective approach to produce propylene. Downsizing the Pt species to single atom catalysts (SACs) has become a hotspot, owing to the maximum utilization and excellent catalytic behavior. However, the agglomeration of SACs is the decisive limitation for high temperature PDH. Herein, single Pt atoms were anchored on graphene with different types of vacancies, and their catalytic performances on PDH were explored based on density functional theory (DFT). As the vacancy size increased, the catalytic activity decreased. It was because the combined site of the detached H atom in propane would transfer from the Pt atom to the C atom around vacancies, thus increasing the migration distance and lowering the activity. However, with the increase of vacancy size, the selectivity to propylene was improved, owing to the enhanced repulsion between C atoms in graphene and propylene. Therefore, instead of stabilizing the single atom, vacancies in carbon materials can also tailor the catalytic performance by geometric disturbance. This fundamental work opens up the possibility for purposeful SAC design in PDH. [ABSTRACT FROM AUTHOR]

Rationally constructing hetero-structures of iron species for efficient oxygen reduction reaction (ORR) remains challenging. Herein, an efficient and robust strategy has been developed for building and tailoring FeOx/Fe hetero-structures. By tuning the temperature of H2 treatment, highly dispersed FeOx/Fe hetero-structures with controllable composition and multiple exposed crystal planes have been obtained to increase the electro-conductivity and hydrophilicity for efficient ORR. The resulting as-prepared Fe2O3@NC-450 exhibited remarkable ORR activity with an Eonset value of 1.001 V, E1/2 of 0.838 V and limited current density of 6.71 mA cm−2, which are superior to those of commercial 20 wt% Pt/C (Eonset = 0.994 V, E1/2 = 0.828 V, 5.19 mA cm−2). Moreover, Fe2O3@NC-450 provided a high power density of 156.6 mW cm−2, which is 2.3 times that of 20 wt% Pt/C (68 mW cm−2) in a zinc–air battery test. In addition, Fe2O3@NC-450 had a discharge time of 29 h, which is longer than that of 20 wt% Pt/C (23.5 h). This work provides an alternative efficient way to rationally construct hetero-structures of metal oxides and metal for next-generation ORR catalysts and metal–air batteries. [ABSTRACT FROM AUTHOR]

Methylcyclopentadiene dimer and trimer based fuels are synthesized from 5-methyl furfural for the first time with yields as high as 74.4%. They exhibit both high density and high thermal stability that are better than those of widely used fossil based jet fuels such as JP-10 and JP-7, and represent types of high-performance fuels. This work also provides a potential and scale-up feasible route for synthesizing high-performance jet fuels from biomass. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT)-supported Ni-modified MoS2 catalysts with ultra-high loading were synthesized with the assistance of citric acid. The morphology of the nanoflake arrays could be controlled to give abundant stepped sites, which favored the hydrogenation desulfurization pathway of dibenzothiophene. The catalyst exhibited excellent performance and stability for hydrodesulfurization of model oil and coal-to-liquid fuel. [ABSTRACT FROM AUTHOR]

Clean energy and renewable fine chemicals including biofuels, hydrogen, and bicarbonates are critical for a sustainable and green future. In this study, the integrated production of naturally separated high density liquid biofuels (mainly C7 and C14 olefins), hydrogen gas, and fine chemicals is achieved in an electrochemical cell under ambient conditions. Biofuels are obtained by anodic decarboxylation of the carboxylates, hydrogen is obtained by cathodic reduction of water, and fine chemicals are obtained by the reaction between the alkaline aqueous solution and the anodic carbon dioxide products. An environmentally friendly and low-cost aqueous substitution method is employed to prepare self-supporting Pt nanospheres on 3D porous titanium sponge (Pt@TS) composite electrodes for such an integrated electrolysis. A Pt@TS anode with abundant Pt(100) facets exhibits enhanced activity and stability for electrocatalytic biofuel production as compared with commercial Pt anodes. [ABSTRACT FROM AUTHOR]

The photoinduced conversion of biomass-derived chemicals to high value chemicals and advanced fuels is of great significance but still challenging. Herein, a green and efficient self-sensitized [2 + 2] cycloaddition process is developed to convert biomass-derived β-pinene and isophorone to spirocyclic molecules, which cannot be achieved by thermal catalytic conversion. The photoreaction can take place with isophorone as the self-sensitizer, with high selectivity and a yield of up to 91.1%. A triplet sensitization mechanism is disclosed by a combination of triplet quenching, phosphorescence quenching, Stern–Volmer kinetic analysis, DFT calculations and photochemical kinetic studies. When combined with hydrodeoxygenation, spiro-fuel is obtained with an overall yield of 85.0% showing a high density of 0.911 g mL−1 which is 16.8% higher than that of conventional aviation kerosene (ca. 0.78 g mL−1), along with excellent cryogenic properties. Notably the self-sensitized cycloaddition strategy can be extended to a wide range of biomass derived α,β-unsaturated ketones and alkenes. Thus, this work provides a promising ring-increasing route to upgrade low-density bio-derived feedstocks to high-density hydrocarbons. [ABSTRACT FROM AUTHOR]

Defect engineering through grain boundaries, disordered regions, and atomic vacancies has the potential to achieve novel physical and chemical properties by modulating the atomic arrangements and electronic configurations. In particular, grain boundaries facilitates superior synergistic effects of different crystals. This work proposes an ingenious binder strategy to introduce grain boundaries in metal/semiconductor (M/MOx, M = Co, Ni) architectures via the thermal calcination of layered Co/Ni glycerolates bonded by melamine. XAFS and HRTEM results illustrate the abundant grain boundaries and disordered regions among the different crystals. DFT calculations demonstrate that the metal/semiconductor composite has metallic electrical conductivity with fast electron mobility, and the deformation of the electronic structure at the interface produces abundant reactive sites to improve the intrinsic activity. Therefore, this architecture (CoNim) shows excellent properties for electrocatalytic OER and ORR with a potential gap of 0.72 V at 10 mA cm−2, good stability (＞13 h for OER and ＞29 h for ORR) and perfect selectivity (electron transfer number, N = 4.0). As an air electrode for Zn–air batteries, it shows a long discharge time (23 h) and a peak power density of 81.7 mW cm−2. The facile binder strategy provides a new defect manufacturing method for the development of highly efficient bifunctional nanomaterials to be applied in energy devices. [ABSTRACT FROM AUTHOR]

Well-dispersed and highly efficient molybdenum nitrides on a nitrogen-doped carbon matrix (Mo2N@NC) are reported as a new and active electrocatalyst for hydrogen evolution in alkaline electrolyte. The key point in fabricating this catalyst is using HNO3-treated melamine, other than pristine melamine, as carbon and nitrogen pools to realize the complete nitridation of MoO3 to Mo2N nanoparticles of 4 nm size and at the same time to generate a nitrogen-doped carbon matrix to support these nanoparticles by thermolysis under an Ar atmosphere. The as-prepared Mo2N@NC exhibits excellent HER activity in 1 M KOH with a pretty low overpotential of 85 mV to achieve a current density of 10 mA cm−2 and a small Tafel slope of 54 mV dec−1, which is among the best for Mo-based compounds and better than those of most non-noble metal electrocatalysts to date in alkaline media. It is also much better than those of the incomplete nitride compounds (MoO2/Mo2N@NC) and the mixture of nitrides and carbides (Mo2N/Mo2C@NC) fabricated under similar conditions, from aspects of overpotential, Tafel slope, exchange current density, conductivity, active surface area and turnover frequencies. Therefore, Mo2N represents a new kind of very active HER catalyst in alkaline electrolyte. Also, this work provides an effective method to fabricate metal nitrides/carbon composites for other applications. [ABSTRACT FROM AUTHOR]

Metal-support interaction and corresponding interface regulation are of great importance for the preparation of well-defined, supported metal catalysts with outstanding performance. Herein a joint experimental-theoretical study has been conducted to investigate the role of polydopamine (PDA) as an interface facilitator for supported noble metal catalysts. The effects of PDA between various noble metals (Pt, Pd, Au, Ag) and a support (SBA-15) have been systematically investigated in the model reaction of 4-nitrophenol (4-NP) reduction by NaBH4. Based on the kinetic model of 4-NP reduction by NaBH4 and a set of density functional theory calculations on different 4-NP binding energies, a volcano-shaped relationship plot is obtained. The volcano-shaped dependence of the reaction rate constant on 4-NP adsorption energy is observed for supported noble metal catalysts with/without PDA. The general relationship indicates that PDA can effectively improve catalytic performance via adjusting 4-NP adsorption energy to a more suitable value. The results of charge density difference and Bader charge analysis illustrate the establishment of an ‘electron pool’ by PDA in the system to achieve controllable electronic charge redistribution for an optimized binding when the reactant molecule adsorbs on the metal nanoparticle. [ABSTRACT FROM AUTHOR]

Identification of active sites for oxygen evolution reaction (OER) plays a key role in the design and fabrication of high-performance cobalt-based electrocatalysts. Herein, we report the synthesis of two types of two-dimensional monometallic cobalt hydroxide nanoplates in aqueous solution for OER: α-Co(OH)2 with both Co2+Td and Co2+Oh sites and β-Co(OH)2 with Co2+Oh sites. Electrochemical characterization reveals that α-Co(OH)2 is more active than β-Co(OH)2 towards OER. The better activity can be attributed to the presence of Co2+Td sites in α-Co(OH)2, which are more active than Co2+Oh sites. Our finding clarifies the contribution of the two catalytic sites and helps future rational design of high-performance OER electrocatalysts. [ABSTRACT FROM AUTHOR]

A Ce–Mo–O catalyst prepared by a simple sol–gel method was proved to be highly active for aerobic oxidative desulfurization. Almost complete conversions of dibenzothiophene and 4,6-dimethyldibenzothiophene were achieved without any additional sacrificial agent at 100 °C and atmospheric pressure, and the conversion of benzothiophene could reach 97%. Reusability of the catalyst was also conducted, and ＞99% conversions could be achieved in three consecutive runs. As supported by carefully-designed control experiments, oxygen was activated by Ce species in the catalyst first, forming some reactive oxygen species, which oxidized DBT into DBTO2 with the assistance of Mo species. Furthermore, selective quenching experiments indicated the generation of superoxide species during the reaction. [ABSTRACT FROM AUTHOR]

The development of low cost and durable electrocatalysts for the oxygen evolution reaction (OER) for water splitting remains a great challenge. Here, we developed strongly coupled hybrid nanowires (NWs) of anion (Cl− and CO−) doped cobalt hydroxide coated with nanosheets of graphitic carbon nitride (Co(OH)2@g-C3N4) through an in situ hydrothermal method. With 5% g-C3N4 added in the synthesis, we obtained perfectly coated Co(OH)2 by g-C3N4 nanosheets with an overall diameter of ∼110 nm and a coating layer of ∼10 nm. The structural and compositional analyses confirm the strong interaction between g-C3N4 and Co(OH)2 that makes the hybrid highly effective for the OER. As a result Co(OH)2@g-C3N4 NWs exhibit an excellent over-potential of 0.32 V at 10 mA cm−2 as well as extraordinary stability, which are better than those of the state-of-the-art noble metals (IrO2 and RuO2) and most reported Co- and C3N4-based electrocatalysts although both Co(OH)2 and g-C3N4 separately display very fair performance. Furthermore, a combination of Co(OH)2@g-C3N4 and Pt/C delivers a current density of 80 mA cm−2 at 1.9 V for overall water splitting. [ABSTRACT FROM AUTHOR]

Transferring biomass-derived cyclic ketones such as cyclopentanone and cyclohexanone to a mono-condensed product through aldol self-condensation has great potential for the synthesis of a renewable high-density fuel. However, the selectivity is low for numerous catalysts due to the rapid formation of di-condensed by products. Herein, MIL-101-encapsulating phosphotungstic acid is synthesized to catalyze the self-condensation with selectivity of more than 95%. PTA clusters are uniformly dispersed in MOF cages and decrease the empty space (pore size), which provides both acidic sites and shape-selective capability. The optimal PTA amount decreases corresponding to the increase of reactant size. The shape-selectivity is also realized by changing the pore size of MOF such as from MIL-101 to MIL-100. Moreover, the catalyst is resistant to PTA leaching and performs stably after 5 runs. After hydrodeoxygenation of the mono-condensed product, high-density biofuels with densities of 0.867 g ml−1 and 0.887 g ml−1 were obtained from cyclopentanone and cyclohexanone, respectively. This study not only provides a promising route for the production of high-density biofuel but also suggests the advantage of MOF-based catalysts for shape-selective catalysis involving large molecular size. [ABSTRACT FROM AUTHOR]

3D dendritic WSe2 on conductive carbon nanofiber mats (d-WSe2/CFM) was designed and synthesized by a diffusion-controlled CVD method. The d-WSe2/CFM was directly used as a cathode for the HER. The substantially improved HER performance is ascribed to the novel 3D structure with effectively exposed edge sites. [ABSTRACT FROM AUTHOR]

Renewable high-density spiro-fuels are synthesized from lignocellulose-derived cyclic ketones for the first time, which show higher density, higher neat heat of combustion and lower freezing point compared with other biofuels synthesized from the same feedstock, and thus represent a new type of renewable high-density fuel attractive for practical applications. [ABSTRACT FROM AUTHOR]

V-doped TiO2 quantum dots (QDs) possessing many Ti3+ defects were fabricated by simple hydrolysis using MCM-41 as a support. The QDs show high charge-separation efficiency and high photocatalytic activity due to the quantum size effect and the newly formed defect- and dopant-mediated band levels. [ABSTRACT FROM AUTHOR]

Quantum dot (TiO2) self-decorated and defect-free anatase nanosheets were fabricated by a long-time hydrothermal strategy and subsequent defect healing. Such decoration provides a new and effective charge transfer pathway over the nanosheet surface, leading to remarkably high photoactivity. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT)-supported Ni-modified MoS 2 catalysts with ultra-high loading were synthesized with the assistance of citric acid. The morphology of the nanoflake arrays could be controlled to give abundant stepped sites, which favored the hydrogenation desulfurization pathway of dibenzothiophene. The catalyst exhibited excellent performance and stability for hydrodesulfurization of model oil and coal-to-liquid fuel.

Bismuth vanadate photoanode has shown great potential for photoelectrochemical (PEC) catalysis, but it needs to be further modified because of its relatively low charge-separation efficiency and poor stability. Herein, the bimetallic phosphide NiCoP decorated Mo-BiVO 4 is fabricated through the electrodeposition and drop-casting method, which significantly improves the charge separation and surface oxidation reaction. Therefore, the fabricated NiCoP/Mo-BiVO 4 photoanode exhibits a low onset potential of 0.21 V ( vs. RHE) and high photocurrent of 3.21 mA cm -2 at 1.23 V ( vs. RHE), which is 3.12 times higher than that of pure BiVO 4 . Importantly, the decoration of NiCoP significantly improve the stability of BiVO 4 photoanode., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

The utilization of solar energy in photoelectrochemical water splitting is a popular approach to store solar energy and minimize the dependence on fossil fuels. Herein, defected ZnWO 4 -decorated WO 3 nanorod arrays with type II heterojunction structures were synthesized via a two-step solvothermal method. By controlling the amount of Zn precursor, WO 3 nanorods were decorated in situ with tunable amounts of ZnWO 4 nanoparticles. Characterization confirmed the presence of abundant W 5+ species in the defected ZnWO 4 -decorated WO 3 samples, leading to enhanced light absorption and charge-separation efficiency. Therefore, the decorated WO 3 nanorod arrays show much higher photoelectrochemical (PEC) activity than pure WO 3 nanorod arrays. Specifically, the sample with optimal ZnWO 4 decoration and surface defects exhibits a current density of 1.87 mA cm -2 in water splitting at 1.23 V vs. RHE under 1 sun irradiation (almost 2.36 times higher than that of pure WO 3 ), a high incident photon-to-current efficiency of nearly 40% at 350 nm, and a relatively high photostability. However, the decoration of WO 3 with too much ZnWO 4 blocks the light absorption of WO 3 , inhibiting the PEC performance, even when many defects are present. This work provides a promising approach to rationally construct defected heterojunctions as highly active PEC anodes for practical applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Identification of active sites for oxygen evolution reaction (OER) plays a key role in the design and fabrication of high-performance cobalt-based electrocatalysts. Herein, we report the synthesis of two types of two-dimensional monometallic cobalt hydroxide nanoplates in aqueous solution for OER: α-Co(OH) 2 with both Co 2+ Td and Co 2+ Oh sites and β-Co(OH) 2 with Co 2+ Oh sites. Electrochemical characterization reveals that α-Co(OH) 2 is more active than β-Co(OH) 2 towards OER. The better activity can be attributed to the presence of Co 2+ Td sites in α-Co(OH) 2 , which are more active than Co 2+ Oh sites. Our finding clarifies the contribution of the two catalytic sites and helps future rational design of high-performance OER electrocatalysts.

Mesoporous hollow W18O49 spheres were fabricated by a facile solvent-induced assembly method using anhydrous WCl6 as a precursor and CH3COOH as a solvent. This unique structure exhibited remarkably enhanced photocatalytic and photoelectrocatalytic performance than other morphologies like urchin and nanowire due to the simultaneous enhancement in light harvesting, surface area and adsorption capability.

V-doped TiO2 quantum dots (QDs) possessing many Ti(3+) defects were fabricated by simple hydrolysis using MCM-41 as a support. The QDs show high charge-separation efficiency and high photocatalytic activity due to the quantum size effect and the newly formed defect- and dopant-mediated band levels.

Quantum dot (TiO2) self-decorated and defect-free anatase nanosheets were fabricated by a long-time hydrothermal strategy and subsequent defect healing. Such decoration provides a new and effective charge transfer pathway over the nanosheet surface, leading to remarkably high photoactivity.