Highest H2 Production Rate Research Articles

Carbon Quantum Dot Implanted Graphite Carbon Nitride Nanotubes: Excellent Charge Separation and Enhanced Photocatalytic Hydrogen Evolution.

Graphite carbon nitride (g-C3 N4 ) is a promising candidate for photocatalytic hydrogen production, but only shows moderate activity owing to sluggish photocarrier transfer and insufficient light absorption. Herein, carbon quantum dots (CQDs) implanted in the surface plane of g-C3 N4 nanotubes were synthesized by thermal polymerization of freeze-dried urea and CQDs precursor. The CQD-implanted g-C3 N4 nanotubes (CCTs) could simultaneously facilitate photoelectron transport and suppress charge recombination through their specially coupled heterogeneous interface. The electronic structure and morphology were optimized in the CCTs, contributing to greater visible light absorption and a weakened barrier of the photocarrier transfer. As a result, the CCTs exhibited efficient photocatalytic performance under light irradiation with a high H2 production rate of 3538.3 μmol g-1 h-1 and a notable quantum yield of 10.94 % at 420 nm.

Carbon Quantum Dot Implanted Graphite Carbon Nitride Nanotubes: Excellent Charge Separation and Enhanced Photocatalytic Hydrogen Evolution

AbstractGraphite carbon nitride (g‐C3N4) is a promising candidate for photocatalytic hydrogen production, but only shows moderate activity owing to sluggish photocarrier transfer and insufficient light absorption. Herein, carbon quantum dots (CQDs) implanted in the surface plane of g‐C3N4 nanotubes were synthesized by thermal polymerization of freeze‐dried urea and CQDs precursor. The CQD‐implanted g‐C3N4 nanotubes (CCTs) could simultaneously facilitate photoelectron transport and suppress charge recombination through their specially coupled heterogeneous interface. The electronic structure and morphology were optimized in the CCTs, contributing to greater visible light absorption and a weakened barrier of the photocarrier transfer. As a result, the CCTs exhibited efficient photocatalytic performance under light irradiation with a high H2 production rate of 3538.3 μmol g−1 h−1 and a notable quantum yield of 10.94 % at 420 nm.

Hydrothermally synthesized highly dispersed Na2Ti3O7 nanotubes and their photocatalytic degradation and H2 evolution activity under UV and simulated solar light irradiation

Photocatalytic water splitting technologies are currently being considered for alternative energy sources. However, the strong demand for a high H2 production rate will present conflicting requirements of excellent photoactivity and low-cost photocatalysts. The first alternative may be abundant nanostructured titanate-related materials as a photocatalyst. Here, we report highly dispersed Na2Ti3O7 nanotubes synthesized via a facile hydrothermal route for photocatalytic degradation of Rhodamine B (RhB) and the water splitting under UV-visible light irradiation. Compared with commercial TiO2, the nanostructured Na2Ti3O7 demonstrated excellent photodegradation and water splitting performance, thus addressing the need for low-cost photocatalysts. The as-synthesized Na2Ti3O7 nanotubes exhibited desirable photodegradation, and rate of H2 production was 1,755 μmol·g−1·h−1 and 1,130 μmol·g−1·h−1 under UV and simulated solar light irradiation, respectively; the resulting as-synthesized Na2Ti3O7 nanotubes are active in UV light than that of visible light response.

A low-cost, high-efficiency and durable homogeneous system for molecular hydrogen

High-efficiency hydrogen evolution is obtained from a novel fluorescein homogeneous system, comprising a noble metal free fluorescein as the photosensitizer, Pt nanoparticle as the cocatalyst and TEOA as the holes scavenger in an aqueous solution under visible light irradiation. The highest H2 production rate is 491.40 μmol/h (λ > 420 nm) and quantum efficiencies of our system are among the highest reported for the molecular hydrogen systems in the visible light range. Unlike many reported molecular hydrogen systems are either unstable under illumination and expensive, or have weak photocatalytic performances, our low-cost system exhibits excellent activity and endurance. We believe that this low-cost, high-efficiency and durable homogeneous system for molecular hydrogen may result in new breakthroughs for the hydrogen energy and solar energy utilization.

Simultaneous in situ reduction and embedment of Cu nanoparticles into TiO2 for the design of exceptionally active and stable photocatalysts

A facile approach for achieving homogenous Cu embedment in TiO2 for an exceptionally high and stable H2 production rate.

Microbial electrolysis treatment of post-hydrothermal liquefaction wastewater with hydrogen generation

Hydrothermal liquefaction (HTL) directly converts wet organic waste into biocrude oil, but it also generates post-HTL wastewater (PHWW) with concentrated nutrients that require further treatment before discharge or reuse. While traditional technologies showed limited success, this study demonstrates that microbial electrolysis cell (MEC) can be an effective approach to treat the swine manure PHWW and recover H2 for onsite HTL biocrude upgrading. The onsite H2 production and utilization makes MEC an ideal wastewater treatment process for HTL operations. Using actual swine manure PHWW, the MEC reactors showed excellent removals of organics (90–98%) and nitrogen (57–93%) under various organic loadings, applied voltages, and flow rates. Increasing organic loadings and applied voltages showed positive influences on system performance, while changes of flow rates showed limited impacts. The highest H2 production rate was 168.01 ± 7.01 mL/L/d with a H2 yield of 5.14 ± 0.22 mmol/kg COD (3000 mg COD/L, 1.0 V), and the highest cathodic H2 recovery and energy efficiency were 74.24 ± 0.11% and 120.56 ± 17.45%, respectively. System configuration and operation can be further optimized to improve system performance.

Integration of Plasmonic Effects and Schottky Junctions into Metal-Organic Framework Composites: Steering Charge Flow for Enhanced Visible-Light Photocatalysis.

A wide range of light absorption and rapid electron-hole separation are desired for efficient photocatalysis. Herein, on the basis of a semiconductor-like metal-organic framework (MOF), a Pt@MOF/Au catalyst with two types of metal-MOF interfaces integrates the surface plasmon resonance excitation of Au nanorods with a Pt-MOF Schottky junction, which not only extends the light absorption of the MOF from the UV to the visible region but also greatly accelerates charge transfer. The spatial separation of Pt and Au particles by the MOF further steers the formation of charge flow and expedites the charge migration. As a result, the Pt@MOF/Au presents an exceptionally high photocatalytic H2 production rate by water splitting under visible light irradiation, far superior to Pt/MOF/Au, MOF/Au and other counterparts with similar Pt or Au contents, highlighting the important role of each component and the Pt location in the catalyst.

Integration of Plasmonic Effects and Schottky Junctions into Metal–Organic Framework Composites: Steering Charge Flow for Enhanced Visible‐Light Photocatalysis

AbstractA wide range of light absorption and rapid electron–hole separation are desired for efficient photocatalysis. Herein, on the basis of a semiconductor‐like metal–organic framework (MOF), a Pt@MOF/Au catalyst with two types of metal–MOF interfaces integrates the surface plasmon resonance excitation of Au nanorods with a Pt‐MOF Schottky junction, which not only extends the light absorption of the MOF from the UV to the visible region but also greatly accelerates charge transfer. The spatial separation of Pt and Au particles by the MOF further steers the formation of charge flow and expedites the charge migration. As a result, the Pt@MOF/Au presents an exceptionally high photocatalytic H2 production rate by water splitting under visible light irradiation, far superior to Pt/MOF/Au, MOF/Au and other counterparts with similar Pt or Au contents, highlighting the important role of each component and the Pt location in the catalyst.

Noble metal-free NiCo nanoparticles supported on montmorillonite/MoS2 heterostructure as an efficient UV–visible light-driven photocatalyst for hydrogen evolution

In this study, a noble-metal-free photocatalyst, based on NiCo nanoparticles supported on montmorillonite/MoS2 heterostructure (MMT/MoS2/NiCo), was successfully synthesized and applied for photocatalytic water reduction to produce H2. Under UV–visible light irradiation, the composite showed improved photocatalytic performance for H2 evolution compared to MMT/MoS2, MMT/MoS2/Ni, MMT/NiCo, and MoS2/NiCo. The as-synthesized MMT/0.79MoS2/Ni8.14Co6.4 (0.79, 8.14 and 6.4 denote the weight ratios % of MoS2, Ni and Co in the catalyst) photocatalyst exhibited a high H2 production rate of 8.7 mmol g−1 h−1, 26.5 and 2.3 times higher than for MMT/0.79MoS2 and MMT/Ni8.14Co6.4, respectively. The enhanced photocatalytic performance was attributed to the loaded MoS2 and NiCo nanoparticles, introducing active sites, increasing the light-absorbing capacity and accelerating the charge transfer from the Eosin Y dye owing to their appropriate Fermi level energy alignment. This work presents a cost-effective method combining the 2D sheets of MMT and MoS2, and NiCo nanoparticles to form a quaternary photocatalytic system showing highly efficient hydrogen evolution from water without using noble metals.

Fragmented phosphorus-doped graphitic carbon nitride nanoflakes with broad sub-bandgap absorption for highly efficient visible-light photocatalytic hydrogen evolution

Graphitic carbon nitride (g-C3N4) has shown great promise in photocatalytic solar-energy conversion. However, photocatalytic activity of pristine g-C3N4 still remains restricted owing to its low surface area, insufficient visible-light harvesting, and ready charge recombination. Here, fragmented P-doped g-C3N4 nanoflakes (PCNNFs), which are prepared by a facile two-step processing combining P-doping via using phytic acid biomass as P source and urea as g-C3N4 precursor and nanostructure tailoring via a smart post-treatment, are reported. Particularly, PCNNFs exhibit narrowed sub-bandgap from valence band to the midgap states, extending light absorption up to 800 nm. The resultant PCNNFs sample shows a surface area of 223.2 m2 g−1, a highest value of P-doped g-C3N4 reported. The fragmented nanoflakes structure renders PCNNFs much shortened charge-to-surface migration distance in both vertical-plane and in-plane direction. Such PCNNFs are demonstrated to be highly efficient in charge transfer and separation. Attributed to the synergistic effect of P-doping and fragmented nanoflakes structure, PCNNFs exhibit a remarkable visible-light (>420 nm) photocatalytic H2 production rate of 15921 μmol h−1 g−1 and quantum efficiencies of 6.74% at 420 nm and 0.24% at 600 nm. Moreover, even under long wavelength light (>470 nm), PCNNFs still exhibit high H2 production rate of 9546 μmol h−1 g−1, over 62 times the rate of pure g-C3N4.

Catalytic properties of a pure Ni coil catalyst for methane steam reforming

A tightly rolled pure Ni coil catalyst was assembled to ensure a stable catalytic performance in a wide range of conditions for methane steam reforming. With a high geometric specific surface area of 88.1 cm2/cm3, the coil catalyst achieved the objective of this study in the range of the space velocity (455-2800 h−1), steam-to-carbon ratio (0.62–2.48), and temperature (973–1073 K), which was hard to achieve on our previously developed Ni honeycomb catalyst with a geometric specific surface area of 59.4 cm2/cm3. Methane steam reforming reaction was slightly accelerated by the reactant flow because of the mass transfer enhancement of H2, CO, and CO2. The conversion, selectivity, and yield of the products were evaluated as a function of the conditions mentioned above. The high H2 production rate per unit catalyst volume demonstrated the high potential of the Ni coil catalyst for applications to small-scale hydrogen production system.

Noble metal-free RGO/TiO2 composite nanofiber with enhanced photocatalytic H2-production performance

1D reduced graphene oxide (RGO)/TiO2 nanocomposite fibers were fabricated by a facile two-step method. These samples demonstrated high photocatalytic H2-production activity from methanol aqueous solution, even without the aid of noble metal. When the ratio of RGO is 0.25wt%, the highest H2-production rate was achieved. It increased by 10 fold than bare TiO2, reaching 149μmolh−1g−1 with quantum efficiency (QE) of 0.75%. The reasons were as follows. Firstly, the RGO nanosheets acted as electron acceptors. Secondly, some shallow trap states at the surface or interface of TiO2 were created by the reduction of GO during calcination. Thirdly, the redox potential position of graphene/graphene− was suitable. Fourthly, RGO could efficiently promote the separation of photogenerated electron-hole pairs and significantly enhance the photocatalytic H2-production activity. This interpretation was corroborated by transient photocurrent response. The aforementioned marvelous results provided a probable solution to replace noble metals (such as Pt) by graphene as an effective cocatalyst.

CuO[sbnd]Cr2O3 core-shell structured co-catalysts on TiO2 for efficient photocatalytic water splitting using direct solar light

Synthesis of core-shell structured CuOCr2O3 nanoparticles as co-catalyst to improve the photocatalytic hydrogen evolution performance of TiO2 was demonstrated. The effect of co-catalyst loading on TiO2 and the nature of the reactor was found to be more significant for H2 production under direct solar light. The formation of 9.3 nm Cr2O3 shell over CuO core in the CuOCr2O3 nanostructured co-catalyst was confirmed using transmission electron microscopy. A very high H2 production rate of 82.39 and 70.4 mmol h−1 g−1cat was observed with quartz and pyrex reactors under direct solar light of irradiation 96–100 mW/cm2, respectively. This is almost three times higher than that of bare TiO2 under similar experimental conditions. The core-shell co-catalyst loaded on TiO2 by simple mechanical mixing method which is useful for bulk scale synthesis in practical applications. The observed high H2 production was explained with plausible mechanism where the synergic effect of CuOCr2O3 co-catalyst loaded TiO2 surface that reduces the effective charge carriers recombination and impeded backward reaction by the Cr2O3 thin layer. The presence of Cu2+ and absence of Cu+ and metallic Cu was confirmed using XPS analysis. The effect of co-catalyst loading and sacrificial agent concentration on the photocatalytic hydrogen production was also reported. The stability of the CuOCr2O3 core-shell NPs loaded TiO2 photocatalyst under the direct solar light was examined by continuous cycling for three days and it was found to be 81 and 70% of photocatalyst activity is retained after 3 days in the quartz and pyrex reactor systems, respectively.

Effect of Metal Cofactors of Key Enzymes on Biohydrogen Production by Nitrogen Fixing Cyanobacterium Anabaena siamensis TISIR 8012

In N2-fixing cyanobacteria, three enzymes are involved in the H2 metabolism. Nitrogenase catalyzes the N2 fixation which produces H2 as a by-product. The produced H2 is taken up to protons and electrons by an activity of uptake hydrogenase. Reversible enzyme catalyzes both reactions of the H2 evolution and the H2 uptake. These enzymes are all metalloenzyme. The cyanobacterial nitrogenase normally requires molybdenum and iron as cofactors; however nitrogenase of few cyanobacterial species is dependent on vanadium. The cyanobacterial uptake and reversible hydrogenase requires nickel and iron as cofactors. This research aimed to investigate the effect of these metal cofactors on H2 production and hydrogenase activity by N2-fixing cyanobacterium Anabaena siamensis TISTR 8012 isolated from rice paddle field in Thailand. The result showed that A. siamensis cells incubated in N-deprived BG11 medium (BG110) gave clearly higher H2 production rate and hydrogenase activity than those in normal BG11 medium. Under nitrogen deprivation, an increase of iron, nickel, and molybdenum concentrations obviously enhanced H2 production rate. But only higher iron concentrations increased hydrogenase activity, indicating that the iron metal assisted in the function of reversible hydrogenase activity. In addition, vanadium seemed not to be a metal cofactor of key enzymes involving in H2 production in A. siamensis. The optimal concentrations of iron, nickel and molybdenum ions for H2 production rate by A. siamensis were 60 μM, 4 μM and 4 μM, respectively. The highest H2 production rate of 0.057 µmolH2 mg chl a-1 h-1 was observed in cells incubated in BG110 medium supplemented with 4 μM nickel ion.

Pyramid-like CdS nanoparticles grown on porous TiO2 monolith: An advanced photocatalyst for H2 production

Efficient production of H2 via solar-light-driven water splitting by a semiconductor-based photocatalyst without noble metals is crucial owing to increasingly severe global energy and environmental issues. However, many challenges, including the low efficiency of H2 evolution, low solar light absorption, excited electron–hole pair recombination, and slow transport of photoexcited carriers, must be resolved to enhance the H2 photoproduction efficiency and photocatalyst stability. Here, a two-step method is used to synthesize advanced H2-generating photocatalysts consisting of pyramid-like CdS nanoparticles grown on a porous TiO2 monolith, which show promising photocatalytic activity for the hydrogen evolution reaction. Furthermore, the stability of the photocatalysts is examined through long-term tests to verify their good durability. Without noble metals as cocatalysts, the photocatalyst can reach a high H2 production rate of 1048.7μmolh−1g−1 under UV–vis irradiation when the ratio of the CdS nanoparticles to TiO2 is 5mol%. This unusual photocatalytic activity arises from the wide-region light adsorption due to the narrow band gap of CdS, effective separation of electrons and holes due to conduction band alignment at the CdS–TiO2 interface, and favorable reaction sites resulting from the porous structure.

Optimization of Active Sites of MoS2 Nanosheets Using Nonmetal Doping and Exfoliation into Few Layers on CdS Nanorods for Enhanced Photocatalytic Hydrogen Production

Transition metal dichalcogenides (TMDs) have emerged as promising nonprecious noble-metal-free catalysts for photocatalytic applications. Among TMDs, MoS2 has been extensively studied as a cocatalyst due to its exceptional activity for photocatalytic hydrogen evolution. However, the catalytic activity of MoS2 is triggered only by the active S atoms on its exposed edges, whereas the majority of S atoms present on the basal plane are catalytically inactive. Doping of foreign nonmetals into the MoS2 system is an appealing approach for activation of the basal plane surface as an alternative for increasing the concentration of catalytically active sites. Herein, we report the development of earth-abundant, few-layered, boron-doped MoS2 nanosheets decorated on CdS nanorods (FBMC) employing simple methods and their use for photocatalytic hydrogen evolution under solar irradiation, with lactic acid as a hole scavenger, under optimal conditions. The FBMC material exhibited a high rate of H2 production (196 mmol·h–...

Well-designed Te/SnS2/Ag artificial nanoleaves for enabling and enhancing visible-light driven overall splitting of pure water

To produce hydrogen and oxygen from photocatalytic overall splitting of pure water provides a promising green route to directly convert solar energy to clean fuel. However, the design and fabrication of high-efficiency photocatalyst is challenging. Here we present that by connecting different nanostructures together in a rational fashion, components that cannot individually split water into H2 and O2 can work together as efficient photocatalyst with high solar-to-hydrogen (STH) energy conversion efficiency and avoid the use of any sacrificial reagent. Specifically, Te/SnS2/Ag artificial nanoleaves (ANLs) consist of ultrathin SnS2 nanoplates grown on Te nanowires and decorated with numerous Ag nanoparticles. The appropriate band structure of Te/SnS2 p-n junctions and the surface plasmon resonance of Ag nanoparticles synergistically enhance the quantum yield and separation efficiency of electron-hole pairs. As a result, Te/SnS2/Ag ANLs enable visible-light driven overall water-splitting without any sacrificial reagent and exhibit high H2 and O2 production rates of 332.4 and 166.2μmolh−1, respectively. Well-preserved structure after long-term measurement indicates its high stability. It represents a feasible approach for direct H2 production from only sunlight, pure water, and rationally-designed ANL photocatalysts.

Palladium Copper Chromium Ternary Nanoparticles Constructed In situ within a Basic Resin: Enhanced Activity in the Dehydrogenation of Formic Acid

AbstractPdCuCr ternary nanoparticles (NPs) responsible for the efficient production of H2 from formic acid are constructed in situ during the initial catalytic reaction within a macroreticular basic resin that possesses −N(CH3)2 functional groups. A high H2 production rate of 174 000 mL h−1 gpd−1 with a high turnover frequency of 830 h−1 based on Pd can be achieved, which is substantially higher than that obtained with bimetallic PdCu and PdCr and monometallic Pd NPs. Physicochemical characterization was performed by using X‐ray absorption fine structure analysis and high‐angle annular dark‐field scanning transmission electron microscopy. The kinetic isotope effect revealed not only the stabilization of highly dispersed NPs but also the boosting of the C−H bond dissociation step by a synergistic alloying effect induced by the introduction of Cr atoms, which plays an important role to achieve efficient catalytic activity. Moreover, this heterogeneous catalytic system exhibits high durability without agglomeration and leaching and has potential for applications in high‐pressure gas‐evolution systems.

NH2-MIL-125(Ti)/graphitic carbon nitride heterostructure decorated with NiPd co-catalysts for efficient photocatalytic hydrogen production

In this study, a highly efficient photocatalyst, NH2-MIL-125(Ti)/g-C3N4/NiPd (NH2-MIL-125(Ti)/CN/NiPd), was successfully synthesized for photocatalytic water reduction to produce H2. Under visible-light irradiation, the prepared NH2-MIL-125(Ti)/CN/NiPd composite clearly showed enhanced photocatalytic performance for H2 evolution compared to NH2-MIL-125(Ti), NH2-MIL-125(Ti)/CN, and NH2-MIL-125(Ti)/NiPd. The as-synthesized NH2-MIL-125(Ti)/0.75CN/Ni15.8Pd2.1 photocatalyst exhibited a high H2 production rate of 8.7mmolg−1h−1, 322 and 1.3 times higher than those of NH2-MIL-125(Ti)/0.75CN and NH2-MIL-125(Ti)/Ni15.8Pd4.1, respectively. The enhanced photocatalytic performance can be attributed to the intimate interfacial contact between NH2-MIL-125(Ti) and CN, accelerating the charge transfer, as well as loaded NiPd nanoparticles, increasing the light-absorbing capacity and accelerating the charge transfer of NH2-MIL-125(Ti)/CN. This work demonstrates that the addition of appropriate co-catalysts onto MOF/CN hybrid with intimate contact interface provides a new approach to design highly efficient and solar-energy-harvesting photocatalysts.

Macroporous ZnO/ZnS/CdS composite spheres as efficient and stable photocatalysts for solar-driven hydrogen generation

Solar-driven hydrogen (H2) generation utilizing photocatalysts has received extensive attention because of its potential to mitigate the global energy crisis and environmental problem. The implementation of efficient H2 production strongly relies on stable, active, and low-cost photocatalysts. In this work, we report the designed synthesis of macroporous ZnO/ZnS/CdS composite spheres as a highly active photocatalyst for H2 production via solar-driven water splitting. The composite spheres were synthesized by a facile solvothermal reaction paired with controllable ion-exchange processes. The resulting material exhibits superior photocatalytic activity, delivering a high H2 production rate of ~11.37 mmol h−1 g−1 under light illumination (250–780 nm, with an ultraviolet light intensity of 34 mW cm−2 and visible light intensity of 158 mW cm−2). Such performance enhancement can be mainly ascribed to the synergic effects of the composite structure: (1) formation of coherent ZnO/CdS and ZnS/CdS heterojunctions at nanoscale, facilitating charge separation of photoinduced electron/hole pairs, (2) highly accessible inner surface of the meso/macroporous ZnO/ZnS/CdS composites for rapid mass transfer of electrolyte, and (3) enhanced visible light scattering capability induced by their large particle size.