Highest H2 Production Research Articles

(Invited) Photoinduced Hydrogen Evolution with Ni-Fe Hydrogenase-Viologen-Porphyrin Immobilized ITO Electrode

Hydrogenase-viologen-porphyrin triad was immobilized on ITO electrode and carried out photoinduced hydrogen evolution. This system can reductively generate hydrogen by electron donation from the photoexcited porphyrin to hydrogenase via viologen.Hydrogen production by water splitting (electrochemical, photochemical, or thermal) offers an obvious way to capture solar energy. Catalysts are a crucial issue for Hydrogen production, and there is intense interest in finding alternatives to noble metals that are capable of converting water into hydrogen close to the thermodynamic potential.As a biological alternative, enzymes known as hydrogenases catalyze the reduction of protons into hydrogen at active sites composed of iron- or nickel/iron complexes: importantly, the electrochemical reaction is reversible with a small overpotential. Determination of the structures of hydrogenases from several organisms paired with detailed spectroscopic and electrochemical investigations have considerably improved our understanding of these enzymes in recent years.Hydrogenases also show high H2 production yields in photocatalytic schemes within sacrificial electron donors in pH neutral aqueous solution. In these systems with hydrogenase, a photoexcited photosensitizer provides electrons to the active site where proton reduction occurs via an internal electron transfer iron sulfur clusters. Examples are the immobilization of a hydrogenase on Ru-sensitised TiO2, on Cd-based, quantum dotsas well as homogeneous systems using the hydrogenases with a covalently linked photosystem I or in combination with an organic dye,and multi-component systems with a dye and a soluble redox mediator.In this study, we report on ITO electrode system with hydrogenase, where Ni-Fe hydrogenase immobilized on ITO surface using a linker contains both a viologen and a porphyrin. [NiFe]-Hydrogenase from Desulfovibrio vulgaris (Miyazaki) is approximately 90 kDa in size, with large and small subunits of 60 kDa and 30 kDa, respectively. The Ni-Fe active site is located to the surface of the enzyme. Three Fe-S clusters from the putative electron transfer pathway between the active site. The proximal [4Fe4S] cluster lies closest to the active site while the distal [4Fe4S] cluster is found near the surface of the enzyme. A [3Fe4S] cluster is located in between the two [4Fe4S] clusters and is known as the medial cluster. The distal [4Fe4S] cluster works as the first electron acceptor of the [NiFe]-hydrogenase in the case of hydrogen evolution.Figure 1 shows the ITO electrode system prepared in this study. Hydrogenase was immobilized via the 4,4’-(3-aminopropyl)-bipyridinium (DAPV) by a glutamate-rich patch of hydrogenase where the distal Fe-S cluster is located.The photoexcited state of Tetrakis(4-carboxyphenyl)porphyrin (TCPP) donates electrons to [NiFe]-hydrogenase via the 4,4’-(3-aminopropyl)-bipyridinium (DAPV) bridging between the two. DAPV was linked to acidic amino acid near the distal [4Fe4S] cluster, electron entrance, of [NiFe]-Hydrogenase in order to efficiently donate electrons to the [NiFe]-Hydrogenase.Photoinduced hydrogen evolution were carried out under applied -0.3V vs.SHE. During light irradiation, cathodic continuous current was observed due to the hydrogen evolution. The photoexcited state of TCPP donate electrons to hydrogenase via the viologen, and ITO electrode play an electron donor to HOMO of the TCPP. Therefore, photoinduced hydrogen evolution occur in TCPP-DAPV-hydrogenase triads on ITO electrode. Figure 1

Enhancement of Ni Catalyst Using CeO2–Al2O3 Support Prepared with Magnetic Inducement for ESR

The effect of magnetic inducement in support preparation was studied to reduce coke and improve the activity of Ni catalysts for ethanol steam reforming (ESR) at 550–650 °C. Magnetic inducement was introduced to prepare 5 mol % CeO2 in Al2O3 support in order to control the composition and the distribution of Ce in Al2O3. The results show that using CeO2–Al2O3 support with magnetic inducement affects both hydrogen production and coke reduction, where Ni/CeO2–Al2O3 support prepared under magnetic inducement with N–N pole arrangement (Ni/CeO2–Al2O3 (N–N)) exhibited the highest hydrogen production and the lowest coke formation among the catalysts used in this work. Compared with Ni/CeO2–Al2O3 (no magnet), Ni/CeO2–Al2O3 (N–N) catalysts yield 14.0% higher H2 production and 31.7% less coke production. The modified catalyst preparation process used in this study could create catalysts for hydrogen production from ESR which are high in performance and stability but low in preparation cost.

A homogeneous Cu-based polyoxometalate coupled with mesoporous TiO2 for efficient photocatalytic H2 production

Developing a photocatalytic system for water splitting to H2 is a promising strategy to address fossil fuel consumption. Exploring photocatalysts with high-performance, steady and low-cost has been the essential goals toward photo-reduction of water. Herein, noble-metal-free polyoxometalate Na12[(α-SbW9O33)2Cu3(H2O)3]·46H2O (Cu3POM) was coupled with mesoporous, multiphase TiO2 (Meso-TiO2) for the first time to catalyze hydrogen production. The composite system exhibited excellent photocatalytic hydrogen production activity. After 2.5 h of illumination, the activity was enhanced 77 times (1284.8 μmol/g) in the presence of Cu3POM compared to the blank Meso-TiO2 (16.6 μmol/g). Nitrogen adsorption–desorption isotherms results reveal the mesoporous characteristics of Meso-TiO2 which could increase the active sites of the reaction. The cycling experiment demonstrated the composite system remained stable after five cycles without activity loss. Multiple characterizations reveal that Ti3+ is generated after the reaction, which further narrows the band gap and promotes the photocatalytic performance of the composite system. The suitable LUMO energy level of Cu3POM was confirmed by electrochemical tests. It accelerates the transfer of photo-generated electrons from the CB of Meso-TiO2 to the protons in the solution, resulting in a high photocatalytic H2 production performance. The combination of Meso-TiO2 with reductive polyoxometalate innovatively provides novel insights into the design of efficient photocatalytic materials for H2 production.

Hydrogen production from absorption-enhanced steam gasification of Enteromorpha prolifera and its char using Ce-doped CaO material

In this work, H2 production performances from Enteromorpha prolifera and its char by absorption-enhanced steam gasification using Ce-doped CaO material were investigated. The Ce-doped CaO material improves the H2 production from Enteromorpha prolifera by steam gasification, which achieves 79.0 vol% H2 in the syngas. The Ce-doped CaO material with the mass ratio of CeO2/CaO = 10:90 seems more appropriate for high H2 production, tar and char conversion. The presence of CeO2 leads to good cyclic stability in H2 production from Enteromorpha prolifera char during the gasification/calcination cycles. After 20 cycles, H2 concentration and yield from Enteromorpha prolifera char achieve 77.8 vol% and 141.8 mL/g using Ce-doped CaO material, respectively. The CeO2 facilitates the conductivity of electrons in CaO surface due to the existence of Ce3+ species, thus CO2 capture, water gas shift, and steam methane reforming reactions are promoted by CeO2. The Ce-doped CaO material maintains the porous microstructure and fine particles during the cycles due to the support of CeO2. Therefore, H2 productions from Enteromorpha prolifera and its char by absorption-enhanced steam gasification using Ce-doped CaO material appear promising.

Short-chain fatty acids and hydrogen production in one single anaerobic fermentation stage using carbohydrate-rich food waste

This study assessed the feasibility of melon and watermelon residues for the co-production of short-chain fatty acids (SCFAs) and hydrogen (H2) via single-stage anaerobic fermentation. The high content of carbohydrates and readily biodegradable organic matter in the wastes, along with the acid pH (5.6–5.8) imposed in the reactors, were key factors to reach high SCFAs and H2 co-production efficiencies. Mentioned conditions promoted a specialized microbial community dominated by Ruminococcus involved in the prevalence of the reverse β-oxidation pathway. This microbial metabolism caused the accumulation of isobutyric and caproic acids (76% of total SCFAs), resulting in a SCFAs production efficiency higher than 40% with concomitant high H2 production yields (395.5 and 62.7 mL H2/g volatile solids influent for melon and watermelon fermentation). A high hydraulic retention time (HRT) of 27 days, an organic loading rate of 3 g of volatile solids per day and liter of working volume and a fermentation temperature of 25 °C were also crucial for maximizing H2 production at acid pH. Overall, melon and watermelon wastes bioconversion efficiencies into H2 and SCFAs reached 64.0 and 58.7%, demonstrating the successful co-production of different bioproducts in a single-stage fermentation by establishing proper operational conditions.

Production of Biohydrogen and/or Poly-β-hydroxybutyrate by Rhodopseudomonas sp. Using Various Carbon Sources as Substrate.

The polyhydroxyalkanoates (PHA) are family of biopolyesters synthesized by numerous bacteria which are attracting a great attention due to their thermoplastic properties. Polyhydroxybutyrate (PHB) is the most common type of PHA which presents thermoplastic and biodegradable properties. It is synthesized under stressful conditions by heterotrophic bacteria and many photosynthetic microorganisms such as purple non-sulfur bacteria and cyanobacteria. Biological hydrogen (H2) production is being evaluated for use as a fuel since it is a promising substitute for carbonaceous fuels owing to its high conversion efficiency and high specific content. In the present work, the purple non-sulfur photosynthetic bacterium Rhodopseudomonas sp. for the simultaneous H2 photo-evolution and poly-β-hydroxybutyrate (PHB) production has been investigated. Three different types of carbon sources were tested in the presence of glutamate as a nitrogen source in a batch cultivation system, under continuous irradiance. The results indicated the fact that the type of carbon source in the culture broth affects in various ways the metabolic activity of the bacterial biomass, as evidenced by the production of PHB and/or H2 and biomass. The best carbon source for PHB accumulation and H2 production by Rhodopseudomonas sp. turned out to be the acetate, having the highest H2 production (2286 mL/L) and PHB accumulation (68.99 mg/L, 18.28% of cell dry weight).

Au nanodots@thiol-UiO66@ZnIn2S4 nanosheets with significantly enhanced visible-light photocatalytic H2 evolution: The effect of different Au positions on the transfer of electron-hole pairs

Herein, a new type of photocatalysts, Au nanodots@thiol-UiO-66@ZnIn2S4 nanosheets (Au@UiOS@ZIS), is elaborately designed for the photocatalytic H2 evolution from water splitting, where Au nanodots (NDs) are anchored in the pore space of thiol-functionalized UiO66 metal-organic framework (MOF) and ZnIn2S4 nanosheets are wrapped around the UiO66 MOF containing Au NDs. It is found that the different Au positions have a grateful effect on the transfer of photogenerated charge carriers. In Au@UiOS@ZIS, the photoexcited electrons transfers from ZnIn2S4 to UiOS and then to Au NDs, establishing a smooth transmission channel of electrons. As expected, the optimal sample (Au4@UiOS@ZIS40) presents a high photocatalytic H2 production rate of 391.6 μmol/h (10 mg of catalyst) under visible light irradiation, which is 435.1, 61.2 and 10.2 times higher than that of the pure UiOS, ZnIn2S4 and UiOS@ZIS, respectively.

Carbon Dot Loaded Integrative CoFe2O4/g‐C3N4 P‐N Heterojunction: Direct Solar Light‐Driven Photocatalytic H2 Evolution and Organic Pollutant Degradation

AbstractIn this report, the novel carbon dot (CD) loaded CoFe2O4/g‐C3N4 p‐n heterojunction for photocatalytic H2 evolution and tetracycline (TCN) degradation under sunlight irradiation has been proposed. The wet chemical method was used to prepare the photocatalysts. The heterojunction formation between the CoFe2O4 and g‐C3N4 facilitates to improve the solar light absorption ability which was confirmed by UV‐vis‐diffused reflectance spectroscopy. Moreover, the CD loading improves the charge carrier's separation. Comparison with the pure and binary nanocomposite photocatalysts, the CD loaded ternary heterojunction photocatalyst exhibits the greater photocatalytic performance with high H2 production (2715 μmol/g) and TCN degradation (95 %) under sun‐light irradiation. Moreover, the recycling process shows the excellent stability nature of ternary composite photocatalyst. The probable photocatalytic mechanism and the main active radicals for the degradation process were well defined with the help of elemental trapping experiment.

Synergistic effects of carbon doping and coating of TiO2 with exceptional photocurrent enhancement for high performance H2 production from water splitting

The “one pot” simultaneous carbon coating and doping of TiO2 materials by the hydrolysis of TiCl4 in fructose is reported. The synergistic effect of carbon doping and coating of TiO2 to significantly boost textural, optical and electronic properties and photocurrent of TiO2 for high performance visible light H2 production from water splitting has been comprehensively investigated. Carbon doping can significantly increase the thermal stability, thus inhibiting the phase transformation of the Titania material from anatase to rutile while carbon coating can suppress the grain aggregation of TiO2. The synergy of carbon doping and coating can not only ensure an enhanced narrowing effect of the electronic band gap of TiO2 thus extending the absorption of photocatalysts to the visible regions, but also promote dramatically the separation of electron-hole pairs. Owing to these synergistic effects, the carbon coated and doped TiO2 shows much superior photocatalytic activity for both degradation of organics and photocatalytic/photoelectrochemical (PEC) water splitting under simulated sunlight illumination. The photocatalytic activity of obtained materials can reach 5, 4 and 2 times higher than that of pristine TiO2, carbon doped TiO2 and carbon coated TiO2, respectively in the degradation of organic pollutants. The carbon coated and doped TiO2 materials exhibited more than 37 times and hundreds of times photocurrent enhancement under simulated sunlight and visible light, respectively compared to that of pristine TiO2. The present work providing new comprehensive understanding on carbon coating and doping effect could be very helpful for the development of advanced TiO2 materials for a large series of applications.

Atomic insights for Ag Interstitial/Substitutional doping into ZnIn2S4 nanoplates and intimate coupling with reduced graphene oxide for enhanced photocatalytic hydrogen production by water splitting

For the purpose of realizing effective visible-light-driven photocatalysis, Ag-doped ZnIn2S4 nanoplates were synthesized in situ onto reduced graphene oxide (RGO) sheets (denoted as Ag:ZnIn2S4/RGO). The high photocatalytic activity is predominantly attributed to the doping effect of Ag+ ions into ZnIn2S4 crystal structure. Interstitial and substitutional doping modes help introduce both acceptor and donor states, as supported by our calculations. Such a doping greatly increases the carrier density and charge transport efficiency. Meanwhile, there is a well-contacted interface between Ag:ZnIn2S4 nanoplates and RGO that renders RGO an electron collector and transporter to effectively lengthen the lifetime of the photogenerated charge carriers. As expected, the optimum nanocomposite exhibits a high H2-production rate of 6343.86 μmol g-1 h-1, about 10.3 and 4.0 times higher than that of pure ZnIn2S4 and 0.15 wt% Ag:ZnIn2S4 samples, respectively. Similarly importantly, the photocatalysts exhibit long-term stability (≥100 h) under visible light irradiation.

CuCo2S4 Deposited on TiO2: Controlling the pH Value Boosts Photocatalytic Hydrogen Evolution

Metallic spinel‐type CuCo2S4 nanoparticles were deposited on nanocrystalline TiO2 (P25®), forming heterostructure nanocomposites. The nanocomposites were characterized in detail by X‐ray powder diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM), nitrogen sorption (BET) and UV/Vis spectroscopy. Variation of the CuCo2S4:TiO2 ratio to an optimum value generated a catalyst which shows a very high photocatalytic H2 production rate at neutral pH of 32.3 µmol/h (0.72 mL h–1), which is much larger than for pure TiO2 (traces of H2). The catalyst exhibits an extraordinary long‐term stability and after 70 h irradiation time about 2 mmol H2 were generated. An increased light absorption and an efficient charge separation for the sample with the optimal CuCo2S4:TiO2 ratio is most probably responsible for the high catalytic activity.

UTILIZATION OF LACTIC ACID RICH MEDIUM AND CASSAVA STARCH WASTEWATER FOR BIOLOGICAL HYDROGEN PRODUCTION

H2 production from lactic acid rich medium and H2 production from cassava starch wastewater by isolated bacteria were investigated. The isolation of H2 producing bacteria from heat treated sludge was carried out. The H2 production from lactic acid rich medium which used 1.5 g/L sodium acetate, 1.5 g/L sodium lactate and 1 g/L sucrose as carbon sources. The effects of inoculums size of 10, 20, 30 and 40 % (v/v) and incubation temperature of 35, 45 and 55oC using cassava starch wastewater as the substrate on H2 production by isolation strains were investigated. Results showed 6 isolated strains i.e. isolation code of MK01to MK06 indicated the H2 production capability when cultured in lactic acid rich medium. However, 3 isolated strains i.e. MK01, MK04, and MK06 were preferred to use as seed inoculums for further experiments depend on a high H2 production capacity obtained. Results indicated that the optimal condition of H2 production from cassava starch wastewater was 30% (v/v) inoculum size of MK06 under 35oC of incubation temperature. The maximum H2 production potential, H2 yield and H2 production rate of 4.20 L H2/L medium, 1.47 L H2/g substrate consumed, and 14.00 mL H2/L/h was obtained. Identification and characterization of MK06 were investigated using 16S rRNA gene sequence analysis followed by phylogenetic analysis. The 100% similarity of 16S rDNA compare with closely related species was indicated Klebsiella pneumoniae subsp. pneumoniae DSM 30104(T).

A catalytic composite membrane reactor system for hydrogen production from ammonia using steam as a sweep gas

For catalytic reactions involving H2 extraction, the membrane reactor is an attractive option for enhancing the equilibrium and kinetics while eliminating excessive purification steps. In this study, a steam carrier adopted composite membrane reactor system is developed to produce pure H2 (>99.99%) from ammonia with high H2 productivity (>0.35 mol-H2 gcat−1 h−1) and ammonia conversion (>99%) at a significantly reduced operating temperature (<723 K). Coupling of a custom developed palladium/tantalum composite metallic membrane and ruthenium on lanthanum-doped alumina catalysts allowed stable operation of the membrane system with significant mass transfer enhancement. Various reactor assemblies involving as-fabricated membranes and catalysts are experimentally compared to suggest the optimal configuration and operating conditions for future applications. Steam is adopted as a sweep gas, presenting efficient H2 recovery (>91%) while replacing conventionally utilized noble carrier gases that require additional gas separation processes. The steam carrier presents similar membrane reactor performance to that of noble gases, and the water reservoir used for steam generation acts as an ammonia buffer via scrubbing effects. Finally, electricity generation is demonstrated using a commercial fuel cell along with process simulation, substantiating potential of the proposed membrane system in practical applications for H2 production from ammonia and on-site power generation.

Optimization of H2 Production through Minimization of CO2 Emissions by Mixed Cultures of Purple Phototrophic Bacteria in Aqueous Samples

One of the current challenges in the treatment of wastewater is the recovery and/or transformation of their resources into high value-added products, such as biohydrogen. The aim of the present study was to optimize the production of hydrogen by mixed cultures of purple phototrophic bacteria (PPB), targeting in low CO2 emission. Batch assays were conducted using different carbon (malic, butyric, acetic acid) and nitrogen (NH4Cl, Na-glutamate, N2 gas) sources by varying the chemical oxygen demand to nitrogen ratio (COD:N 100:3 to 100:44), under infrared radiation as sole energy source. Malate-glutamate (COD:N 100:5.5) and malate-NH4-N (COD:N 100:3) fed cultures, exhibited high H2 production rates of 2.3 and 2.5 mLH2/Lh, respectively. It was observed that the use of glutamate decreased the CO2 emission by 74% (13.4 mLCO2/L) as compared to NH4-N. The H2 production efficiency achieved by organic carbon substrates in combination with glutamate, was in the order of malic (370 mLH2/L) &gt; butyric (145 mLH2/L) &gt; acetic acid (95 mLH2/L). These substrates entailed partitioning of reducing power into biomass at 64%, 50% and 48%, respectively, whereas reductants were derived to biohydrogen at 5.8%, 6.1% and 2.1%, respectively. These results suggest that nitrogen source and carbon dioxide emissions play an important role in the optimization of hydrogen production by PPB.

Rational design of hollow core-double shells hybrid nanoboxes and nanopipes composed of hierarchical Cu-Ni-Co selenides anchored on nitrogen‐doped carbon skeletons as efficient and stable bifunctional electrocatalysts for overall water splitting

It is of prime importance to develop efficient nonprecious noble-metal-free water splitting bifunctional electrocatalysts for both H2 and O2 evolution reactions (HER and OER), which remains a grand challenge. However, the design of hollow nanostructured based on di- and tri-metal selenides, particularly non-spherical hollow nanostructures, is scarcely reported. Herein, for the first time, novel tri-metal selenides based on hollow Cu0.4Ni0.3Co0.3Se2 mesoporous nanosheet double shell were successfully designed on hollow N-doped carbon nanoboxes (Cu0.4Ni0.3Co0.3Se2@N-C n-box) and nanopipes (Cu0.4Ni0.3Co0.3Se2@N-C n-pipe). The hollow N-C n-box and N-C n- pipe skeletons were obtained from the related Fe2O3 nanocubes and nanorods templates that have prepared with completely different morphologies via only a minor change in synthesis step. Remarkably, benefiting from the special electronic structure engineering and unique hollow hierarchical design with high surface areas, open channels for effective gas releasing, fast electron/mass transport, the resulting advanced electrocatalysts provide outstanding OER activity as well as desirable HER performance in the alkaline medium. Moreover, an overall water splitting device is assembled using two symmetrical Cu0.4Ni0.3Co0.3Se2@N-C n-box electrodes as anode and cathode, which can deliver a current density of 10 mA cm−2 at a cell voltage as low as 1.53 V. More significantly, in addition to extraordinary operational stability of the electrolyzer, it can achieve high current density of 100 mA cm−2 with only cell voltage of 1.79 V, respectively, which are very useful for practical application. This work offers a rational strategy for the structure engineering of advanced hollow hybrid nanostructures as a nonprecious noble-metal-free water splitting bifunctional electrocatalyst, which can push forward the development of high efficient and low cost H2 production.

Synthesis and optimization of NixMn1-xFe2O4 catalyst in chemical looping steam methane reforming process

The NixMn1-xFe2O4 oxygen carrier is synthesized through the chemical precipitation method to be applied in the chemical looping steam methane reforming process (CL-SMR). The response surface method (RSM) is adopted based on the central composite design (CCD) model to evaluate the effect of the independent variables on the responses’ functionality and to predict the best response volume. The variables: reaction temperature (550-750°C), oxygen carrier (OC) loading rate (0.1-0.9), steam per methane ratio (S/C) (1.5-3.5), oxidation-reduction cycles’ count (1-9) and the responses consisting of CH4 conversion percentage, CO/CO2 molar ratio and H2 production yield are assessed. The analysis of variance (ANOVA) results indicates that reaction temperature and the OC type are the most effective, while the oxidation-reduction cycles’ count is the least effective on CH4 conversion percentage and H2 production yield. By implementing the optimized results in laboratory conditions, it is revealed that the Ni0.6Mn0.4Fe2O4 OC at operating conditions at 650°C, S/C=2.5 and 9 redox cycles, the best response to the CH4 conversion percentage, CO/CO2 molar ratio, and H2 production yield with 99.6, 15.7 and 77.6, respectively. The improved stability and functionality of the OC reveal that during the 24 redox cycle the self-supported Ni0.6Mn0.4Fe2O4 OC is of high stability, high CH4 conversion percentage means, and high H2 production yield. The OCs samples are characterized by applying FT-IR, XRD, FESEM with X-ray spectroscopy EDX, BET, and TGA.

Sorption enhanced–chemical looping steam methane reforming: Optimizing the thermal coupling of regeneration in a fixed bed reactor

Sorption enhanced–chemical looping steam methane reforming is a promising process for hydrogen production. In this process, the reformer contains, in addition to a solid CO2 sorbent, an oxygen transfer material (OTM). Ιn–situ CO2 capture by the sorbent shifts the overall reaction to the products' side, leading to high purity H2 production in a single step. The saturated sorbent is then regenerated in a second reactor at higher temperatures. The OTM is simultaneously reoxidized, generating significant amount of heat which is in–situ used for sorbent's regeneration. In this work, the optimization of heat coupling during the regeneration step of the intensified process was studied experimentally using a NiO/ZrO2 OTM–reforming catalyst, mechanically mixed with a CaZrO3–promoted CaO sorbent. The effect of two key operating parameters during regeneration was considered: the residence time of the feed stream and the type of oxidant (air, pure O2). Higher space velocities increased the percentage of CaCO3 decomposition without external heat supply. The use of pure O2 can provide in situ 47% of the heat requirements of the sorbent's regeneration, a value which is very close to the theoretical degree of autothermicity under the investigated conditions (57%), while producing a pure, ready for sequestration CO2 stream.

Long-term Operation of Continuous Culture of the Hyperthermophilic archaeon, Thermococcus onnurineus for Carbon Monoxide-dependent Hydrogen Production

In this study, we performed a kinetic analysis of CO-dependent H2 production by metabolically engineered Thermococcus onnurineus NA1, MC01 in terms of the cell activity as well as mass transfer rate. We conducted continuous cultures with varying dilution rate, CO flow rate, or agitation speed. Despite oscillations in cell density, the cultures reached steady states at all operating conditions. As the dilution rate increased from 0.1 to 0.3 h−1, specific activity of H2 production (SAHP) and volumetric cell production rate were linearly increased. Also, the SAHP remained almost constant at the fixed dilution rate of 0.3 h−1 even though the CO transfer rate was changed by adjusting the CO flow rate or the agitation speed. This relationship could be expressed as a typical Luedeking-Piret model, implying that high cell density culture with a sufficient growth rate is essential to obtain higher H2 productivity. On the other hand, more elevated CO transfer at the same dilution rate improved H2 production rate (HPR) by the increase of the cell density, not in the rise of SAHP. Through the continuous culture, 108 mmol/g-cell/h and 121 mmol/L/h of SAHP and HPR, respectively, could be achieved at a dilution rate of 0.3 h−1 with CO supply rate of 0.07 vvm and agitation speed of 700 rpm. Considering high H2 production activity and long-term stability of the strain over 1,000 h, MC01 is confirmed to have an outstanding potential for CO-dependent H2 production.

Synthesis of core-shell nanostructured Cr2O3/C@TiO2 for photocatalytic hydrogen production

In this study, the Cr2O3/C@TiO2 composite was synthesized via the calcination of yolk–shell MIL-101@TiO2. The composite presented core–shell structure, where Cr-doped TiO2 and Cr2O3/C were the shell and core, respectively. The introduction of Cr3+ and Cr2O3/C, which were derived from the calcination of MIL-101, in the composite enhanced its visible light absorbing ability and lowered the recombination rate of the photogenerated electrons and holes. The large surface area of the Cr2O3/C@TiO2 composite provided numerous active sites for the photoreduction reaction. Consequently, the photocatalytic performance of the composite for the production of H2 was better than that of pure TiO2. Under the irradiation of a 300 W Xe arc lamp, the H2 production rate of the Cr2O3/C@TiO2 composite that was calcined at 500 °C was 446 μmol h−1 g−1, which was approximately four times higher than that of pristine TiO2 nanoparticles. Moreover, the composite exhibited the high H2 production rate of 25.5 μmol h−1 g−1 under visible light irradiation (λ > 420 nm). The high photocatalytic performance of Cr2O3/C@TiO2 could be attributed to its wide visible light photoresponse range and efficient separation of photogenerated electrons and holes. This paper offers some insights into the design of a novel efficient photocatalyst for water-splitting applications.

Anaerobic granular sludge and zero valent scrap iron (ZVSI) pre-treated with green tea as a sustainable system for conversion of CO2 to CH4

Global climate change is a worldwide concern that requires the dramatic reduction of greenhouse gases. Innovation in sustainable technologies for CO2 utilization to other high value products is therefore an emerging and rising field. It was found that CO2 as a sole carbon source can be converted to CH4 (higher than 97%) in a system consisted of anaerobic granular sludge, water and zero valent scrap iron. In this system (zero valent scrap iron, anaerobic granular sludge and CO2), pre-exposure of zero valent scrap iron to green tea resulted in a higher conversion rate and total CH4 production compared to bare zero valent scrap iron response. At the abiotic system (no anaerobic sludge) the zero valent scrap iron pre-treated with green tea also showed around 10% higher H2 production as well as higher final pH compared to zero valent scrap iron. The dominant crystalline product of the process both at the abiotic and at the biological system was siderite (FeCO3). It is likely that the formation of siderite on the zero valent scrap iron outer surface have reduced the amount of H2 release from zero valent scrap iron, shielding the substrate for methanogens. The presence of green tea compounds can form an iron-tannate complex with iron ions and this can possibly decrease or slow down the siderite layer, as a result more H2 was released when zero valent scrap iron was pre-exposed to green tea. Anaerobic spent filtered media was independently added to zero valent scrap iron to examine the effect of extracellular enzymes, however slight increase of the H2 production rate was found. The examined system combines potential solutions for two environmental problems; production of siderite derived from zero valent scrap iron for environmental applications and utilization of CH4 generated from CO2 for energy purposes.