Hydrogen Photoproduction Research Articles

Sustainable synthesis of AgNPs/strontium-titanate-perovskite-like catalysts for the photocatalytic production of hydrogen

Abstract SrTiO3-cubic-like photocatalysts with average size of 35–40 nm were synthesized in 2 h without further calcination treatment. Structural defects or contamination were negligible according to the DRX and FTIR analyzes. The H2 generation rates were 386 and 463 μmol h−1 g−1 using an ethanol-water scavenger suspension with the SrTiO3 and Ag/SrTiO3 oxides, respectively. In comparison with other works reported in the literature, the hydrothermal synthesis of SrTiO3 and the UV-pen lamp radiation used for the H2 production may open a new strategy for the sustainable synthesis of 3-dimensional photoactive nanomaterials. The functionalization of nanocubes with highly monodispersed silver or rhodium nanoparticles provided an additional increase in the hydrogen photoproduction rate. In this sense, the silver nanoparticles (AgNPs) act as a sink for the photogenerated electrons through a Schottky barrier in the metal-perovskite contact region, boosting up the separation of the charge carriers. The identification of the surface species by XPS as well as the Rhodamine B photo-oxidation were performed to better understand the surface backward reaction in the photocatalytic production of hydrogen. The AgNPs worked as co-catalysts, preserving the stability of the most photoactive catalysts for 32 h.

Exogenic glucose as an electron donor for algal hydrogenases to promote hydrogen photoproduction by Chlorella pyrenoidosa

In this work, glucose addition (0.7 g l−1) almost doubled hydrogen yield of Chlorella pyrenoidosa (121.1 ml l−1 vs 65.5 ml l−1), with a positive correlation between hydrogen production and glucose consumption (−0.977, P < 0.01). When the electrons transport from water photolysis to algal hydrogenase was inhibited, the hydrogen productivity declined by 21.1%; whereas it dramatically decreased by 70.9% when the algal nicotinamide adeninedinucleotide dehydrogenase (NADH) was inhibited. Therefore, in the presence of glucose, the electrons for algae based hydrogen production would be mainly from glucose glycolysis rather than water photolysis. Further deuterated-glucose trial indicated that the glucose might serve as an electron donor for algal hydrogenases. Finally, a tentative electron transport route from glucose to algal hydrogenase was proposed, hoping to provide more scientific direction for further algae-based hydrogen production improvement.

3D printed microstructured Au/TiO2 catalyst for hydrogen photoproduction

We successfully 3D printed Au/TiO2 monoliths for photogenerating hydrogen from water/ethanol gaseous mixtures under dynamic conditions. Monolith designs were printed by additive superposition of microfilaments of titania-based pastes. Factors influencing the efficiency of the photocatalytic reactions, including impregnation of gold nanoparticles (Au NPs), calcination temperature, diameter of microfilaments and monolith design, are investigated. The use of preformed Au NPs assured a constant Au particle size (ca. 4nm) for all samples, which allowed to a precise assessment of the effect of the design of 3D-printed titania monoliths on photocatalytic activity. The impregnation of preformed Au NPs before or after the 3D printing process has a strong influence on the photocatalytic efficiency. The pre-impregnated monoliths have a homogeneous Au NPs distribution throughout the microfilaments, whereas the post-impregnated ones present an asymmetric distribution of Au NPs, observing a high gold concentration at the surface and lower gold concentrations in the inner regions of the printed microfilaments. The gold concentration of the Au-loading suspension was reduced ca. 10 times in post-impregnated samples to ensure a similar amount of Au NPs anchored at the surface of the microfilaments, according to an XPS analysis of the pre- and post-impregnated samples. Although the photocatalytic performance of the pre-impregnated monoliths was improved when samples were calcined at 400°C, due to a stronger contact between the Au NPs and the microfilament supports, the post-impregnated samples with 100 times lower Au concentration (0.005wt.%) exhibited enhanced catalytic performances. Under similar geometric open section and photon absorption conditions, the photoproduction of hydrogen on a weight (or volume) basis increased strongly as the diameter of the filaments decreased, which is explained by a progressive increase of the surface-to-weight and surface-to-volume ratios. The best photoactivity was obtained with a post-impregnated titania monolith 3D printed with microfilaments with 200μm in diameter, which yielded 0.24molH2min−1gAu−1.

Acetic acid is key for synergetic hydrogen production in Chlamydomonas-bacteria co-cultures

This study is a proof of concept for the synergetic biohydrogen production in alga-bacteria co-cultures. Algal hydrogen photoproduction was obtained in sugar-containing media only when the green alga Chlamydomonas reinhardtii was co-cultured with Pseudomonas putida (40.8 ml H2·L−1), Escherichia coli (35.1 ml H2·L−1) and Rhizobium etli (16.1 ml H2·L−1). Hydrogen photo-production in these co-cultures was not only linked to the induction of hypoxia, but to the ability of the bacteria to produce acetic acid from sugars. Synergetic hydrogen production was achieved by integrating the photobiological and fermentative production in Chlamydomonas and Escherichia coli co-cultures supplemented with glucose, which resulted in 60% more H2 production than the sum of the respective monocultures. This cooperation relied on the ability of the alga to consume the excreted bacterial acetic acid, which benefited both bacterial and algal hydrogen production. This knowledge may open new possibilities for the biohydrogen production from industrial wastes.

Effect of TiO2 nanoshape on the photoproduction of hydrogen from water-ethanol mixtures over Au3Cu/TiO2 prepared with preformed Au-Cu alloy nanoparticles

A series of TiO2 nanoshapes (microurchins, nanobelts, nanowires, microrods and nanotubes) were prepared and decorated with preformed nanoparticles of Au-Cu alloy (Au:Cu = 3:1 molar, 1 wt.% metal content). The resulting photocatalysts were tested for the photogeneration of hydrogen using water-ethanol gaseous mixtures (H2O:EtOH = 1:9 molar basis) under dynamic conditions (26,000 h−1) and compared with a conventional sample prepared using P25. The use of preformed nanoparticles of Au-Cu alloy with the same geometric and electronic characteristics ensured a proper assessment of the influence of the different TiO2 supports on the photoproduction of hydrogen by providing a similar number and quality of metal-support contact points. The yield of hydrogen produced on a weight basis over the Au3Cu/TiO2 samples followed the trend microrods ∼P25 > >nanotubes > nanowires > nanobelts > microurchins. A stable hydrogen photogeneration rate of ca. 270 μmol H2 g−1 min−1 was obtained over titania microrods decorated with Au3Cu whereas the photogeneration of hydrogen over P25 decorated with Au3Cu decreased progressively over time on stream.

Optimization for enhanced hydrogen production from Rhodobacter sphaeroides using response surface methodology

In the present study, Rhodobacter sphaeroides isolated from sewage water was investigated for photoproduction of hydrogen under different cultural conditions. The variation was done in carbon and nitrogen sources along with growth factors. It was found that lactose promoted more amounts of hydrogen production under anaerobic light conditions followed by mannitol, galactose, and sucrose respectively. Uracil was observed as a better nitrogen source as compared to histidine and thiourea. After screening most appropriate carbon source, nitrogen source and growth factor by the classical approach, statistical optimization technique opted for the enhancement of hydrogen production. The response surface methodology adopted in the present work is an efficient tool for strategic experimental design for optimizing process parameters of a multivariable process. Firstly, experiments were performed according to Box-Behnken design. The model predicted is quadratic with a high value of R2 i.e. 0.9681 and maximum production recorded was 6.8 ml/30 ml. Thereafter, Central composite design based experiments were performed and 7.6 ml/30 ml production was achieved with an R2 value of 0.8848 fitted inthe quadratic model. The work presented here suggests a green approach of enhanced hydrogen production to meet the future demand of clean fuel.

Photohydrogen production from lactose and lactate by recombinant strains of Rhodobacter capsulatus: Modeling and optimization

Photofermentative hydrogen production from synthetic mixtures of lactose and lactate mimicking cheese whey was modeled and optimized using Design of Experiments and Response Surface Methodology. Five continuous parameters (light intensity, pH, lactose, lactate and glutamate concentrations) were studied as a function of buffer type (KPi or Borax) using two recombinant bacterial strains. For Rhodobacter capsulatus B10(lacZ), buffer type influenced the optimal parameter values but the optimal responses were similar in both buffers. In contrast, for R. capsulatus IR3(lacZ), responses were higher in Borax buffer than in KPi and were significantly higher than in strain B10(lacZ). Thus, the experimental optimized responses for specific volumetric H2 production, volumetric H2 production rate and substrate (lactose plus lactate) to H2 conversion rate in Borax buffer, were 12,150 ml L−1, 48.5 ml L−1 h−1 and 41.2%, respectively, for IR3(lacZ) compared to 6150 ml L−1, 33.5 ml L−1 h−1 and 32.5%, respectively, for B10(lacZ).

Inoculum density and buffer capacity are crucial for H2 photoproduction from acetate by purple bacteria

The increase of inoculum density of Rhodobacter sphaeroides B-3059 above 2.0 mg bacteriochlorophyll/l in 15 mM K-phosphate buffer inhibited hydrogen photoproduction but favored PHB synthesis. This inhibition was substrate-specific and was observed on media containing acetate. The inhibition resulted from sharp increase in pH above 10 due evidently to fast acetate consumption. The lower the buffer concentration, the lower the inhibitory inoculum density was. The dependence of H2 photoproduction from acetate on buffer concentration at low and high inoculum density was different for different strains of purple bacteria. However, conditions were found to provide H2 production by each of 9 tested strains. Acetate-dependent hydrogen photoproduction in 10 mM K-phosphate buffer was unreliable even with low inoculum density. Ammonium traces and high acetate concentration also facilitated medium alkalization and, consequently, inhibited H2 production. The increase of buffer concentration above 20 mM helped to prevent pH rise independent of the triggering factor.

Bimetallic Pt-Pd co-catalyst Nb-doped TiO2 materials for H2 photo-production under UV and Visible light illumination

In this work we synthesized a series of binary PtPd co-catalysts supported on a Nb-doped TiO2 support. The catalytic solids and corresponding monometallic reference systems are characterized using X-ray diffraction, X-ray photoelectron, and UV–vis spectroscopies, together with microscopy and porosimetry tools. Such characterization was able to show the formation of PtPd alloy particles in the bimetallic catalysts. The mono and bimetallic TiO2-based powders were tested in the photo-production of hydrogen from methanol:water mixtures under UV and visible illumination conditions. Analysis of catalytic properties was carried out through the measurement of the optical properties of the materials and the calculation of the true quantum efficiency parameter. Results indicate that the PtPd co-catalysts have superior performance that the Pt and Pd monometallic counterparts both under UV and visible illumination conditions. Optimum performance was achieved with a material having a Pt:Pd 1:1 atomic ratio. A remarkable increase in the use of the visible range and thus in sunlight utilization is achieved with the 1:1 Pt:Pd bimetallic system with respect to the monometallic counterparts. The evolution of the bimetallic co-catalysts under reaction conditions as well as their key properties to interpret photo-activity were analyzed with the help of the above mentioned techniques as well as photoluminescence spectroscopy and an in-situ infrared analysis of the materials under reaction conditions. Results point out the critical role that both PtPd alloying and the metal-support interface play in the reaction.

Enhancing photocatalytic performance of TiO2 in H2 evolution via Ru co-catalyst deposition

A series of ruthenium catalysts supported into pure anatase titania were tested in the photo-production of hydrogen from methanol:water mixtures under UV and visible illumination conditions. Catalysts containing 1, 2, 3 and 5 wt.% of ruthenium were subjected to a characterization study with the help of X-ray diffraction, Raman, X-ray photoelectron spectroscopy, photoluminescence, morphology as well as scanning and transmission electron microscopy. Through the measurement of the optical properties of the suspension of the catalysts and the hydrogen photo-production reaction rate we calculate the true quantum efficiency. Optimum activity is presented by the catalyst with a 3 wt.% of Ru component, which shows quantum efficiency values of ca. 3.1 and 0.6% under, respectively, UV and visible light illumination. Careful examination of the physico-chemical properties of the solid allows to establish a correlation between the ruthenium surface exposed and the quantum efficiency. The implications of such result to justify chemical activity of the ruthenium supported samples are discussed both for UV and visible illumination conditions.

Photohydrogen production from dark-fermented palm oil mill effluent (DPOME) and statistical optimization: Renewable substrate for hydrogen

Biological hydrogen production through photo-fermentative process using dark fermented palm oil effluent (DPOME) is a cost effective and environmentally benign process. In this study, effect of various factors like light intensity, agitation rate and dilution of DPOME on the hydrogen productivity of Rhodopseudomanas palustris were investigated using batch system. Investigation methods like response surface methodology (RSM) and Box-Behnken design were employed to investigate the optimum conditions for enhanced photo-fermentative hydrogen production. The regression analysis suggested that hydrogen yield was well fitted by a quadratic polynomial equation (R2 = 0.92). The hydrogen production was investigated by varying the intensity levels of these three independent variables, in which all have significant influences on hydrogen yield. The set of 19 experimental runs were conducted to optimize these variables. The highest hydrogen yield of 3.07 ± 0.66 H2 yield mol-H2/mol-acetate was obtained under the optimum condition of light intensity 250 W/m2, agitation rate 200 rpm, and 30% dilution of DPOME. The experimentally obtained hydrogen yield found out to be in a good agreement with predicted yield which was about 2.80 mol-H2/mol-acetate. In short, results suggest that experimental strategy using RSM approach along with Box-Behnken design can be a promising approach to achieve enhanced biological hydrogen production.

Overcoming the expression barrier of the ferredoxin‑hydrogenase chimera in Chlamydomonas reinhardtii supports a linear increment in photosynthetic hydrogen output

While the prospect of producing hydrogen from photosynthetic microalgae has long been described as one of the promising directions towards achieving a renewable fuel source, current endeavors towards this goal face serious limitations including the inefficient electron supply to hydrogenase and the enzyme's sensitivity to molecular oxygen. In this work we express our ferredoxin‑hydrogenase (fd-hyd) fusion enzyme in a hydrogenase knockout Chlamydomonas reinhardtii mutant and compare its hydrogen production traits to those of wild-type strains. We found that the active enzyme abundance in both systems is in linear correlation with photosynthetic hydrogen production, thus establishing that protein abundance is an additional important bottleneck in the process of hydrogen photo-production. We report here the isolation of two clones with high expression of fd-hyd; OP68 and R2D2, created by either nuclear or chloroplast transformation, respectively. The study of these clones shows that fd-hyd's roughly 4.5-fold higher H2 production efficiency, compared to the native hydrogenase, is maintained in high expression regimes. By comparing a strain's active enzyme pool to its total protein amount, we observed that the engineered clones harbor a large non-mature enzyme pool, indicating that natural maturation of the fd-hyd saturates at a lower level than the native hydrogenase. Subsequently, we measured mRNA levels by quantitative PCR and observed that while the two clones express roughly the same amount of protein, R2D2 has considerably more mRNA. Thus improving transcription rates in nuclear transformants or translation efficiency in chloroplast transformants are both potential routes towards further increasing protein abundance. Finally, we show that these clones are able to continuously produce H2 in sealed bioreactors for five days, significantly outcompeting their parental wild-type strain.

Green Algal Hydrogenase Activity Is Outcompeted by Carbon Fixation before Inactivation by Oxygen Takes Place.

Photoproduction of hydrogen by green algae is considered a transitory release valve of excess reducing power and a potential carbon-free source of sustainable energy. It is generally accepted that the transitory production of hydrogen is governed by fast inactivation of hydrogenase by oxygen. However, our data suggest that photosynthetic electron loss to competing processes, mainly carbon fixation, stops hydrogen production, supports hydrogen uptake, and precedes the inevitable inactivation by oxygen. Here, we show that when transitioning from dark anaerobiosis to light, hydrogen production ceases within 2 min, regardless of the presence of oxygen. Simultaneous monitoring of the active hydrogenase pool size shows that it remains entirely intact up to 4 min after illumination and is inactivated only later. Thus, our data reveal a window of 4 min in which the hydrogenase pool is not being degraded by oxygen. Furthermore, we show that electron loss, prominently to carbon fixation, outcompetes hydrogen production and leads to hydrogen uptake. Indeed, supplying additional reducing power to hydrogenase at the cessation point regenerates the accumulation of hydrogen. Our results imply the fast cessation of hydrogen production is governed by electron loss rather than oxygen inactivation, which takes place minutes later.

An endogenous microRNA (miRNA1166.1) can regulate photobio-H2 production in eukaryotic green alga Chlamydomonas reinhardtii

BackgroundHydrogen photoproduction from green microalgae is regarded as a promising alternative solution for energy problems. However, the simultaneous oxygen evolution from microalgae can prevent continuous hydrogen production due to the hypersensitivity of hydrogenases to oxygen. Sulfur deprivation can extend the duration of algal hydrogen production, but it is uneconomical to alternately culture algal cells in sulfur-sufficient and sulfur-deprived media.ResultsIn this study, we developed a novel way to simulate sulfur-deprivation treatment while constantly maintaining microalgal cells in sulfur-sufficient culture medium by overexpressing an endogenous microRNA (miR1166.1). Based on our previous RNA-seq analysis in the model green alga Chlamydomonas reinhardtii, three endogenous miRNAs responsive to sulfur deprivation (cre-miR1166.1, cre-miR1150.3, and cre-miR1158) were selected. Heat-inducible expression vectors containing the selected miRNAs were constructed and transformed into C. reinhardtii. Comparison of H2 production following heat induction in the three transgenic strains and untransformed control group identified miR1166.1 as the best candidate for H2 production regulation. Moreover, enhanced photobio-H2 production was observed with repeated induction of miR1166.1 expression.ConclusionsThis study is the first to identify a physiological function of endogenous miR1166.1 and to show that a natural miRNA can regulate hydrogen photoproduction in the unicellular model organism C. reinhardtii.

Photobiological hydrogen production via immobilization: understanding the nature of the immobilization and investigation on various conventional photobioreactors.

Hydrogen photoproduction from microalgae has been an emerging topic for biofuel development. However, low yield for large-scale cultivations seems to be the main challenge. Immobilization seems to be an alternative method for sustainable hydrogen generation. In this study we examined the bead stability, bead diameter and immobilization method in accordance with photobioreactors (PBR). 2.1mm diameter beads were selected for PBR experiments. CSTR, tubular and panel type PBRs give important results to develop suitable immobilization matrixes and techniques for mass production in scalable PBR systems. In conclusion, we suggest to develop techniques specific for the design and operation characteristic of the PBR for a yield efficient hydrogen generation.

In-vivo turnover frequency of the cyanobacterial NiFe-hydrogenase during photohydrogen production outperforms in-vitro systems

Cyanobacteria provide all components for sunlight driven biohydrogen production. Their bidirectional NiFe-hydrogenase is resistant against low levels of oxygen with a preference for hydrogen evolution. However, until now it was unclear if its catalytic efficiency can keep pace with the photosynthetic electron transfer rate. We identified NikKLMQO (sll0381-sll0385) as a nickel transporter, which is required for hydrogen production. ICP-MS measurements were used to quantify hydrogenase molecules per cell. We found 400 to 2000 hydrogenase molecules per cell depending on the conditions. In-vivo turnover frequencies of the enzyme ranged from 62 H2/s in the wild type to 120 H2/s in a mutant during photohydrogen production. These frequencies are above maximum in-vivo photosynthetic electron transfer rates of 47 e−/s (equivalent to 24 H2/s). They are also above those of existing in-vitro systems working with unlimited electron supply and show that in-vivo photohydrogen production is limited by electron delivery to the enzyme.

Effect of temperature on the gas-phase photocatalytic H2 generation using microreactors under UVA and sunlight irradiation

The effect of temperature on the photocatalytic hydrogen generation from a gaseous water-ethanol mixture has been tested in a silicone microreactor containing nine microchannels of 500 μm (width) × 1 mm (depth) × 47 mm (length) coated with Au/TiO2 photocatalyst under UVA irradiation. Kinetic analyses have indicated that the hydrogen production rate follows the Langmuir-Hinshelwood model. The effect of temperature from 298 to 348 K has been determined by thermodynamic parameters, such as enthalpy (ΔH≠), entropy (ΔS≠) and Gibbs free energy (ΔG≠) of activation, using the transition state theory (TST). The apparent rate constants (kapp) are higher by increasing the temperature, and the activation energy has been determined to be 24 ± 1 kJ·mol−1. In order to evaluate if solar concentration could be used to enhance the photoproduction of hydrogen, the reaction has also been conducted under direct sunlight using a solar concentrator of about 1 m in diameter. Finally, the microreactor has been scaled out by a factor of ca. 10 to a device containing thirty-two microchannels of 500 μm (width) × 1 mm (depth) × 117.5 mm (length). The specific (i.e. per irradiated area of catalyst) hydrogen production rates of both microreactors using sunlight are very similar suggesting that this technology could lead to viable solar hydrogen production.

Impact of cultural conditions on photoproduction of hydrogen by Allochromatium sp. GSKRLMBKU-01 isolated from marine water of Visakhapatnam

In the present study, photoproduction of hydrogen by Allochromatium sp. strain GSKRLMBKU-01 isolated from marine water was measured under different cultural conditions. Hydrogen production was measured by using a Gas chromatography using argon gas as a carrier. Among different carbon and nitrogen sources used, succinate induced maximum hydrogen (5.68 ± 0.27 mL) production by immobilized cells, while free cells recorded 4.24 ± 0.30 mL of hydrogen under anaerobic light conditions. Immobilization of cells resulted in increased production of hydrogen. Ammonium chloride promoted more amounts of hydrogen production (2.68 ± 0.29 mL) by free cells, whereas glycine enhanced the hydrogen production upto 4.82 ± 0.36 mL in immobilized cells. In formic acid and urea, less hydrogen production was observed in both free and immobilized cells compared to other sources. Cumulative hydrogen production by the bacterium was recorded with the progress in incubation period. Incubation period of 192 h, pH of 7.0 and temperature at 30 °C were found to be optimum for the maximum hydrogen production. Significance of the above results was discussed in light of existing literature.

Photosynthetic biohydrogen production in a wastewater environment and its potential as renewable energy

Oxygen (O2) is a strong inhibitor of hydrogenase (HydA) activity and expression and altering the sulfur (S) oxidizing transitions in photosystem II (PSII) often allows algal photohydrogen production; however, this may not be practical in a wastewater environment. To counteract natural mechanisms of oxygen evolution in PSII, we utilized acetic acid and butyric acid, which are main volatile fatty acids (VFAs) found in anaerobic bacterial digestion in wastewater treatment, as oxygen regulators for photosynthetic biohydrogen production using Chlorella vulgaris. It was found that a VFA-containing synthetic wastewater promotes oxygen depletion in a photobioreactor (PBR), producing maximum hydrogen yield of 65.4 ± 0.3 μmoL H2 L−1 mM−1 acetate without artificial sulfur or chloride deprivation. Butyric acids showed no significant effect on oxygen depletion and biohydrogen production in the PBR. The measurements of both relative expression level of mRNA and specific activities of reactivate HydA revealed that repetitive algal H2 photo-evolution was possible by HydA synthesis in C. vulgaris followed by complete oxygen depletion controlled by acetic acid levels in the PBR. This emerging understanding of the role of VFAs on oxygen regulation in PSII in natural environments is expected to lead algal-driven bioenergy production technologies to the next level.

H2 photo-production from methanol, ethanol and 2-propanol: Pt-(Nb)TiO2 performance under UV and visible light

In this work we analyzed the photo-production of hydrogen using titania-based systems able to profit from UV and visible light photons. For this purpose, we prepared Niobium-doped titania and a titania reference by a microemulsion method, subjected these oxide precursors to calcination and subsequently introduced Pt as co-catalyst by a chemical reduction method. These materials were characterized in terms of the structural and morphological properties of the oxide and metal phases. Using these materials, we measured the reaction rate and quantum efficiency of the hydrogen photo-production using methanol, ethanol, and 2-propanol as sacrificial agents. Significant activity enhancement was observed in the Niobium-doped material with respect to the titania reference material. The study focuses on interpreting the differences presented (between the two samples) among the three alcohols in the hydrogen yield and provides a physico-chemical study to understand the roots of the activity. Such study was mainly based on the analysis of the reaction mechanism using in-situ infrared spectroscopy together with the analysis of the energetics of the reaction taking into account the fate of the sacrificial alcohol during reaction.