Hydrogen Formation Rate Research Articles

Turning Cellulose Waste Into Electricity: Hydrogen Conversion by a Hydrogenase Electrode

Hydrogen-producing thermophilic cellulolytic microorganisms were isolated from cow faeces. Rates of cellulose hydrolysis and hydrogen formation were 0.2 mM L-1 h-1 and 1 mM L-1 h-1, respectively. An enzymatic fuel cell (EFC) with a hydrogenase anode was used to oxidise hydrogen produced in a microbial bioreactor. The hydrogenase electrode was exposed for 38 days (912 h) to a thermophilic fermentation medium. The hydrogenase activity remaining after continuous operation under load was 73% of the initial value.

Silver Exchange of Layered Metal Oxides and Their Photocatalytic Activities

Layered Dion–Jacobson phases RbLaNb2O7 and RbA2Nb3O10 (A = Ca, Sr) and the Ruddlesden–Popper phase Rb2La2Ti3O10 were prepared by solid-state methods at a reaction time of 50 h and a temperature of 1100 °C. The products were silver-exchanged within a AgNO3 flux at a reaction time of 24 h and a temperature of 250 °C. Substitution of silver cations into the interlayer spacing of the layered structures is found to decrease the optical bandgap sizes on average by ∼0.5 to ∼1.0 eV. The products were found by scanning electron microscopy (SEM) to exhibit irregularly shaped platelet morphologies with an average size of ∼1–5 μm across their lateral dimensions and stepped edges ranging from ∼20 to ∼300 nm in height. Significant increases in photocatalytic hydrogen production rates for all silver-exchanged products were observed. The silver-exchanged RbA2Nb3O10 layered structures exhibited the highest photocatalytic hydrogen formation rates under ultraviolet and visible irradiation (∼13,616 μmol H2·g–1·h–1). These ra...

Hydrogen evolution at the negative electrode of the all-vanadium redox flow batteries

This work demonstrates a quantitative method to determine the hydrogen evolution rate occurring at the negative carbon electrode of the all vanadium redox flow battery (VRFB). Two carbon papers examined by buoyancy measurements yield distinct hydrogen formation rates (0.170 and 0.005 μmol min−1 g−1). The carbon papers have been characterized using electron microscopy, nitrogen gas adsorption, capacitance measurement by electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). We find that the specific electrochemical surface area (ECSA) of the carbon material has a strong influence on the hydrogen generation rate. This is discussed in light of the use of high surface area material to obtain high reaction rates in the VRFB.

Quantum yield with platinum modified TiO2 photocatalyst for hydrogen production

The present study reports quantum yields for hydrogen production using a Pt modified titanium dioxide (DP25) photocatalyst in a slurry medium, under near-UV irradiation. The photocatalyst was prepared using the incipient wetness impregnation method. The modified photocatalyst exhibited a reduced energy band of 2.73eV upon Pt addition. Experiments were performed in a Photo CREC Water II Reactor. This unit allows the establishment of macroscopic radiation balances. These irradiation balances showed a maximum LVREA (local volumetric rate of energy absorption) of 0.15g/L. Regarding hydrogen formation via H radicals, the addition of a 2vol.% ethanol scavenger allowed achieving significant amounts of hydrogen free of oxygen. It was noticed that the rate of hydrogen formation in the presence of ethanol is a function of the pH of the water solution. It was also observed that the calculated 7.8% quantum efficiency showed good degree of photon utilization and confirmed the value of the Pt modified TiO2 photocatalyst and Photo CREC Water II Unit set up for hydrogen production, via water splitting.

Non-equilibrium cooling rate for a collisionally cooled metal-enriched gas

We present self-consistent calculations of non-equilibrium (time-dependent) cooling rates for a dust-free collisionally controlled gas in wide ranges of temperature (10 ≤ T ≤ 108 K) and metallicity (10−4 ≤ Z ≤ 2 Z⊙). We confirm that molecular hydrogen dominates cooling at 102 ≲ T ≲ 104 K and Z ≲ 10− 3 Z⊙. We find that the contribution from H2 into the cooling rate around T ∼ (4–5) × 103 K stimulates thermal instability in the metallicity range Z ≲ 10− 2 Z⊙. Isobaric cooling rates are generally lower than isochoric cooling rates, because the associated increase of gas density leads to both more efficient hydrogen recombination and equilibration of the fine-structure level populations. Isochoric cooling means that the ionization fraction remains quite high at T ≲ 104 K – up to ∼0.01 at T ≃ 103 K and Z ≲ 0.1 Z⊙, and even higher at higher metallicity – unlike isobaric cooling, where it is at least an order of magnitude lower. Despite this increase in ionization fraction, the gas-phase formation rate of molecular hydrogen (via H−) decreases with metallicity, because higher metallicity shortens the evolution time. We implement our self-consistent cooling rates into the multidimensional parallel code zeus-mp in order to simulate the evolution of a supernova remnant. We compare it to an analogous model with tabulated cooling rates published in previous studies. We find significant differences between the two descriptions, which might appear, for example, in the mixing of the ejected metals in the circumstellar medium.

Exogenous trehalose differentially modulate antioxidant defense system in wheat callus during water deficit and subsequent recovery

To elucidate the resistance mechanism of exogenous trehalose on water deficit further, we investigated the effect of exogenous trehalose (50 mM) in wheat callus during water deficit and subsequent recovery. Enhanced levels of endogenous trehalose were detected in calli exposed to water deficit (W) and trehalose (T) medium, moreover, W plus T treatment showed an additive effect. Water deficit elevated the accumulation of ROS (hydrogen peroxide and formation rate of O 2 .− ) and the endogenous MDA (Malonaldehyde), and resulted in the decrease of cell viability and biomass. Exogenous trehalose (TW) could alleviate the damage induced by water deficit, which was involved in the decrease of MDA and the generation of ROS, and resulted in elevating cell viability and biomass. Additionally, water deficit induced activity of antioxidative enzymes (Peroxidase, POD; Catalase, CAT; Glutathione reductase, GR). Content of AsA (Reduced ascorbate) was also increased by water deficit, while the content of GSH (Glutathione) showed the opposite effect. The combined effect of T and W treatment led to a higher activity of enzymatic antioxidants including SOD (Superoxide dismutase) and GR, and elevated the content of nonenzymatic antioxidants including AsA and GSH, but had a negative effect on enzymatic antioxidants including POD and CAT in comparison to the water deficit treatment alone. During recovery, calli treated by TW showed a greater reduction in ROS resulted in enhancing a higher cell viability and biomass. The scavenging mechanism of ROS by exogenous trehalose is mainly dependent on nonenzymatic antioxidants, especially AsA-GSH cycle, rather than enzymatic mechanisms and trehalose itself.

Hydrogen gas production from vinegar fermentation wastewater by electro-hydrolysis: Effects of initial COD content

Vinegar fermentation wastewater with different initial COD contents (9.66–48.6 g L−1) were used for hydrogen gas production with simultaneous COD removal by electro-hydrolysis. The applied DC voltage was constant at 4 V. The highest cumulative hydrogen production (3197 ml), hydrogen yield (2766 ml H2 g−1 COD), hydrogen formation rate (799 ml d−1), and percent hydrogen (99.5%) in the gas phase were obtained with the highest initial COD of 48.6 g COD L−1. The highest energy efficiency (48%) was obtained with the lowest COD content of 9.66 g L−1. Hydrogen gas production by water electrolysis was less than 250 ml and wastewater control resulted in less than 25 ml H2 in 96 h. The highest (12%) percent COD removal was obtained with the lowest COD content. Hydrogen gas was produced by reaction of (H+) ions present in raw WW ( pH = 3.0) and protons released from acetic acid with electrons provided by electrical current. Electro-hydrolysis of vinegar wastewater was proven to be an effective method of H2 gas production with some COD removal.

Electrohydrolysis of Vinegar Fermentation Wastewater for Hydrogen Gas Production Using Different Types of Electrodes

AbstractVinegar fermentation wastewater with an initial chemical oxygen demand (COD) content of 33.16 g·L−1 was subjected to electrohydrolysis using aluminium, copper, and stainless-steel electrodes for hydrogen gas production. The applied DC voltage was constant at 4 V. The highest cumulative hydrogen production (2,098 ml), hydrogen yield (1,210 ml H2 g−1 COD), hydrogen formation rate (525 ml·d−1), percent hydrogen (99.5%) in the gas phase, percent COD removal (12%), and energy efficiency (21.3%) was obtained with the aluminium electrode. Hydrogen gas production by water electrolysis was 260 ml with the Al electrode, and wastewater control resulted in nearly 23 ml H2 in 96 h. Hydrogen gas was produced by reaction of (H+) ions released from acetic acid and electrons provided by DC current. Aluminium electrode was the most suitable one among the others tested.

Interspecies distances between propionic acid degraders and methanogens in syntrophic consortia for optimal hydrogen transfer

A mixed culture from an anaerobic biowaste digester was enriched on propionate and used to investigate interspecies hydrogen transfer in dependence of spatial distances between propionate degraders and methanogens. From 20.3 mM propionate, 20.8 mM acetate and 15.5 mM methane were formed. Maximum specific propionate oxidation and methane formation rates were 49 and 23 mmol mg(-1) day(-1), respectively. Propionate oxidation was inhibited by only 20 mM acetate by about 50 %. Intermediate formate formation during inhibited methanogensis was observed. The spatial distribution and the biovolume fraction of propionate degraders and of methanogens in relation to the total population during aggregate formation were determined. Measurements of interbacterial distances were conducted with fluorescence in situ hybridization by application of group-specific 16S rRNA-targeted probes and 3D image analyses. With increasing incubation time, floc formation and growth up to 54 μm were observed. Propionate degraders and methanogens were distributed randomly in the flocs. The methanogenic biovolume fraction was high at the beginning and remained constant over 42 days, whereas the fraction of propionate degraders increased with time during propionate feeding. Interbacterial distances between propionate degraders and methanogens decreased with time from 5.30 to 0.29 μm, causing an increase of the maximum possible hydrogen flux from 1.1 to 10.3 nmol ml(-1) min(-1). The maximum possible hydrogen flux was always higher than the hydrogen formation and consumption rate, indicating that reducing the interspecies distance by aggregation is advantageous in complex ecosystems.

Kinetics of the steam gasification of a phenolic circuit board in the presence of carbonates

Steam gasification of a phenolic board in the presence of molten carbonate was studied as a means to recover useful metals effectively from electronic waste while also converting its plastic fraction into clean fuel gas. In the steam gasification of the phenolic board, the presence of carbonate considerably accelerated the conversion of tar and char into gaseous products. When pulverized phenolic board particles <0.15mm were gasified, carbonate and steam permeated the sample particles, and the resulting gasification proceeded was well modeled by a homogeneous kinetic model. On the other hand relatively large phenolic board particles appeared to undergo two different hydrogen-producing gasification processes: the observed hydrogen formation rates suggest that an initial gasification occurred in the surface layer, which carbonate and steam were able to infiltrate into, and after this layer was consumed, the gasification proceeded only on the surface of the resulting char. The reactivity of char in the steam gasification depends sensitively on the conditions whereby the char is produced: rapid pyrolysis of the phenolic board produced highly reactive char, evidenced by markedly increased hydrogen formation rates in the steam gasification of chars formed under more rapid heating. However, once the char was pulverized finely, no obvious difference in reactivity was observed in the steam gasification based on the size of the phenolic board particles used to produce the char.

Oxidation and accumulation of molecular hydrogen in a beryllium-water system upon radiation thermal treatment

The kinetics of radiation thermal oxidation of beryllium with water vapor and the accumulation of molecular hydrogen in a Be-H2O system at temperatures of 473–673 K under the effect of gamma radiation is studied. The oxidation is shown to proceed according to a parabolic law and be limited by diffusion. A sharp change (by a factor of 16) in the formation rate of molecular hydrogen and an increase in its concentration by an exponent depending on the oxidation degree and defectiveness of beryllium plates is observed and confirmed by AFM images. The activation energies of the formation of hydrogen are estimated as E a = 12 and 34 kJ/mol.

Oxygen free conversion of natural gas to useful hydrocarbons and hydrogen over monometallic Mo and bimetallic Mo–Fe, Mo–Co or Mo–Ni/HZSM-5 catalysts prepared by mechanical mixing

This work aims to approach a compromise of the activities of Mo/HZSM-5 catalyst as well known high performance aromatization catalyst after substituting half its Mo with Fe, Co or Ni (well known active hydrogen releasing metals) for hydrocarbons and hydrogen production. The catalysts were prepared by the mechanical mixing procedure in order to keep the zeolitic pores almost free of metal incorporation and hence reducing the metal/zeolite acid interaction. The catalytic performance of the catalysts was investigated during the non-oxidative conversion of natural gas to hydrocarbons and hydrogen in a fixed bed flow reactor at 700°C and gas hourly space velocity (GHSV) of 1500ml/g/h. The catalysts were characterized by XRD and TGA, where the results showed that the bimetallic 3%Mo-3%Fe, 3%Mo-3%Co or 3%Mo-3%Ni containing catalysts significantly decreased hydrocarbon (ethylene and aromatics) yield and selectivity as compared to the monometallic 6%Mo/HZSM-5 catalyst. The substitution of group VIII metals enhances the rate of coke and hydrogen formation in the direction of going from Fe→Co→Ni. This behavior can be attributed to the electronic properties of these metals, where maximum reaction rates are exhibited by the metals with six to eight d-electrons.

Bio-hydrogen production from cheese whey powder (CWP) solution: Comparison of thermophilic and mesophilic dark fermentations

Cheese whey powder (CWP) solution was used as the raw material for hydrogen gas production by mesophilic (35 °C) and thermophilic (55 °C) dark fermentations at constant initial total sugar and bacteria concentrations. Thermophilic fermentation yielded higher cumulative hydrogen formation (CHF = 171 mL), higher hydrogen yield (111 mL H2 g−1 total sugar), and higher hydrogen formation rate (3.46 mL H2 L−1 h−1) as compared to mesophilic fermentation. CHF in both cases were correlated with the Gompertz equation and the constants were determined. Despite the longer lag phase, thermophilic fermentation yielded higher specific H2 formation rate (2.10 mL H2 g−1cells h−1). Favorable results obtained in thermophilic fermentation were probably due to elimination of H2 consuming bacteria at high temperatures and selection of fast hydrogen gas producers.

Efficient visible-light-driven photocatalytic hydrogen production using CdS@TaON core–shell composites coupled with graphene oxide nanosheets

Large-scale hydrogen production through water splitting using photocatalysts with solar energy can potentially produce clean fuel from renewable resources. In this work, photocatalytic evolution of H2 with a high efficiency was achieved using graphene oxide (GO) nanosheets decorated with CdS sensitized TaON core–shell composites (GO–CdS@TaON). The CdS@TaON core–shell nanocomposites were prepared by an ion-exchange route with assistance from a hydrothermal process on GO as the support. The TaON core–shell composites containing 1 wt% CdS nanocrystals showed a high rate of H2-production at 306 μmol h−1 with an apparent quantum efficiency (QE) of 15% under 420 nm monochromatic light. The rate of hydrogen formation was 68 times faster in comparison with the rate observed on pure TaON. The rate was further increased to 633 μmol h−1 with a high quantum efficiency of 31% when the GO–CdS@TaON hybrid composite was coupled with 1 wt% of graphene oxide and 0.4 wt% of Pt (about 141 times higher than that of the pristine TaON). This high photocatalytic H2-production activity is ascribed firstly to the presence of CdS nanocrystals that alter the energy levels of the conduction and valence bands in the coupled semiconductor system; secondly to the involvement of graphene oxide that serves as an electron collector and transporter to efficiently lengthen the lifetime of the photogenerated charge carriers from CdS@TaON composites. This investigation can open up new possibilities for the development of highly efficient TaON-based photocatalysts that utilize visible light as an energy source.

Hydrogen production from acid hydrolyzed molasses by the hydrogen overproducing Escherichia coli strain HD701 and subsequent use of the waste bacterial biomass for biosorption of Cd(II) and Zn(II)

This study was devoted to investigate production of hydrogen gas from acid hydrolyzed molasses by Escherichia coli HD701 and to explore the possible use of the waste bacterial biomass in biosorption technology. In variable substrate concentration experiments (1, 2.5, 5, 10 and 15 g L−1), the highest cumulative hydrogen gas (570 ml H2 L−1) and formation rate (19 ml H2 h−1 L−1) were obtained from 10 g L−1 reducing sugars. However, the highest yield (132 ml H2 g−1 reducing sugars) was obtained at a moderate hydrogen formation rate (11 ml H2 h−1 L−1) from 2.5 g L−1 reducing sugars. Subsequent to H2 production, the waste E. coli biomass was collected and its biosorption efficiency for Cd2+ and Zn2+ was investigated. The biosorption kinetics of both heavy metals fitted well with the pseudo second-order kinetic model. Based on the Langmuir biosorption isotherm, the maximum biosorption capacities (qmax) of E. coli waste biomass for Cd2+ and Zn2+ were 162.1 and 137.9 (mg/g), respectively. These qmax values are higher than those of many other previously studied biosorbents and were around three times more than that of aerobically grown E. coli. The FTIR spectra showed an appearance of strong peaks for the amine groups and an increase in the intensity of many other functional groups in the waste biomass of E. coli after hydrogen production in comparison to that of aerobically grown E. coli which explain the higher biosorption capacity for Cd2+ or Zn2+ by the waste biomass of E. coli after hydrogen production. These results indicate that E. coli waste biomass after hydrogen production can be efficiently used in biosorption technology. Interlinking such biotechnologies is potentially possible in future applications to reduce the cost of the biosorption technology and duplicate the benefits of biological H2 production technology.

Hydrogen gas production from acid hydrolyzed wheat starch by combined dark and photo-fermentation with periodic feeding

Hydrogen gas production from acid hydrolyzed waste wheat starch by combined dark and photo-fermentation was investigated in continuous mode with periodic feeding and effluent removal. A mixture of heat treated anaerobic sludge and Rhodobacter sphaeroides (NRRL-B 1727) were used as the seed culture for dark and light fermentations, respectively with biomass ratio of Rhodobacter/sludge = 3. Hydraulic residence time (HRT) was changed between 1 and 8 days by adjusting the feeding periods. Ground waste wheat was acid hydrolyzed at pH = 3 and 121 °C for 30 min using an autoclave and the resulting sugar solution was used as the substrate for combined fermentation after pH adjustment and nutrient addition. The highest daily hydrogen gas production (41 ml d −1), hydrogen yield (470 ml g −1 total sugar = 3.4 mol H 2 mol −1glucose), volumetric and specific hydrogen production rates were obtained at the HRT of 8 days. The highest biomass and the lowest total volatile fatty acids (TVFA) concentrations were also realized at HRT = 8 days indicating VFA fermentation by Rhodobacter sp. at high HRTs. The lowest total sugar loading rate of 0.625 g L −1 d −1 resulted in the highest hydrogen yield and formation rate. Hydrogen gas production by combined fermentation with periodic feeding was proven to be an effective method resulting in high hydrogen yields at long HRTs.

Dark fermentative bio-hydrogen production from waste wheat starch using co-culture with periodic feeding: Effects of substrate loading rate

Dark fermentation experiments were performed for bio-hydrogen production from ground wheat starch solution (10 ± 1 g l −1) using periodic feeding and effluent removal. A mixed culture of Clostridium butyricum-NRRL 1024 and Clostridium pasteurianum-NRRL B-598 were used with an initial biomass ratio of 1/1.Effects of wheat starch loading rate on the rate and yield of bio-hydrogen formation were investigated. Substrate loading rate was varied between 0.54 and 5.52 g d −1 (HRT = 6–60 h). The highest hydrogen formation rate (280 ml d −1), volumetric hydrogen formation rate (1857 ml H 2 l −1 d −1) and volatile fatty acids (VFAs) concentration were obtained with a substrate loading rate of 5.52 g d −1 (HRT = 6 h). The highest hydrogen yield (109 ml H 2 g TS −1) was obtained with a substrate loading rate of 1.38 g d −1.

Photo-fermentative hydrogen gas production from dark fermentation effluent of acid hydrolyzed wheat starch with periodic feeding

Hydrogen gas production by photo-fermentation of dark fermentation effluent of acid hydrolyzed wheat starch was investigated at different hydraulic residence times (HRT = 1–10 days). Pure Rhodobacter sphaeroides (NRRL B-1727) culture was used in continuous photo-fermentation by periodic feeding and effluent removal. The highest daily hydrogen gas production (85 ml d −1) was obtained at HRT = 4 days (96 h) while the highest hydrogen yield (1200 ml H 2 g −1 TVFA) was realized at HRT = 196 h. Specific and volumetric hydrogen formation rates were also the highest at HRT = 96 h. Steady-state biomass concentrations and biomass yields increased with increasing HRT. TVFA loading rates of 0.32 g L −1 d −1 and 0.51 g L −1 d −1 resulted in the highest hydrogen yield and formation rate, respectively. Hydrogen gas yield obtained in this study compares favorably with the relevant literature reports probably due to operation by periodic feeding and effluent removal.

메탄올 수증기 개질반응에서의 상용촉매 비교연구

메탄올 수증기 개질반응에 대한 적용가능성을 파악하기 위하여 메탄올 합성용 촉매인 ICI-M45와 수성가스 전환반응용 촉매인 MDC-3와 MDC-7을 비교 연구하였다. 또한 수성가스전환 반응에 대한 세 촉매의 비교실험도 수행하였다. 그 결과 MDC-7이 메탄올 수증기 개질반응에서 가장 높은 전화율을 보였으며, <TEX>$H_2$</TEX>와 <TEX>$CO_2$</TEX> 생성속도 또한 높게 나타났다. 수성가스 전환반응용 촉매인 MDC-7과 메탄올 합성촉매인 ICI-M45를 이용하여 촉매 충진 방법에 따른 메탄올의 전화율에서의 변화를 살펴본 결과, MDC-7 단독보다 낮은 메탄올의 전화율을 보였다. 수성가스 전환반응에서도 DC- 7, MDC-3, 그리고 ICI-M45의 순으로 반응성이 감소하였다. 상기 두 반응에서 MDC-7이 가장 우수한 이유로는 높은 비표면적과 Cu의 분산도, 그리고 적절한 Cu와 Zn의 비율에 기인함을 확인할 수 있었다. The comparison work was conducted for the methanol steam reforming among commercial Cu-based catalysts, viz. ICI-M45, which is for the methanol synthesis, MDC-3 and MDC-7, which are for the water-gas shift reaction. The catalytic activity for the water-gas shift reaction was also compared over three catalysts. Among them, MDC-7 showed the highest methanol conversion and formation rate of hydrogen and carbon dioxide at 473 K for the methanol steam reforming. To find out any promotional effect between ICI-M45 and MDC-7, three different packing methods with these two catalysts were examined. However, no synergistic effect was observed. The catalytic activity for watergas shift reaction decreased in the following order: MDC-7 > MDC-3 > ICI-M45. The highest activity of MDC-7 for the methanol steam reforming as well as the water-gas shift reaction can be due to its high surface area, copper dispersion, and an adequate Cu/Zn ratio.

Thermophilic dark fermentation of acid hydrolyzed waste ground wheat for hydrogen gas production

Batch dark fermentation experiments were performed to investigate the effects of biomass and substrate concentration on bio-hydrogen production from acid hydrolyzed ground wheat at 55 °C. In the first set of experiments, the substrate concentration was constant at 20 g total sugar L−1 and biomass concentration was varied between 0.52 and 2.58 g L−1. Total sugar concentration was varied between 4.2 and 23.7 g L−1 in the second set of experiments with a 1.5 g L−1 constant biomass concentration. The highest cumulative hydrogen formation (582 mL, 30 °C, 1 atm), formation rate (5.43 mL h−1) and final total volatile fatty acid (TVFA) concentration (6.54 g L−1) were obtained with 1.32 g L−1 biomass concentration. In variable substrate concentration experiments, the highest cumulative hydrogen (365 mL) and TVFA concentration (4.8 g L−1) were obtained with 19.25 g L−1 initial total sugar concentration while hydrogen gas formation rate (12.95 mL h−1) and the yield (200 mL H2 g−1 total sugar) were the highest with 4.2 g L−1 total sugar concentration.