H2 Photoproduction Research Articles

Red Absorbing Cyclometalated Ir(III) Diimine Photosensitizers Competent for Hydrogen Photocatalysis.

Two new cyclometalated Ir(III) diimine complexes were used as photosensitizers for homogeneous hydrogen evolution reaction (HER). These complexes were characterized by electrochemistry, ultraviolet-visible absorption, time-resolved and steady-state photoluminescence spectroscopy as well as by theoretical methods. The metal-ligand-to-ligand charge transfer character of their lowest excited state was shown to be competent for efficient H2 photoproduction in the presence of [Co(dmgH)2(py)Cl] as the hydrogen evolution catalyst, triethanolamine as the sacrificial electron donor, and HBF4 as the proton source. Under optimized experimental conditions, both complexes displayed HER over a period of more than 90 h, with turnover numbers reaching up to 11,650, 10,600, and 174 molH2 molPS-1 under blue-, green-, and red-light irradiation, respectively. Both complexes showed higher stability and efficiency vs HER than most of the previously described systems of the same kind.

Photosystem I light-harvesting proteins regulate photosynthetic electron transfer and hydrogen production.

Linear electron flow (LEF) and cyclic electron flow (CEF) compete for light-driven electrons transferred from the acceptor side of photosystem I (PSI). Under anoxic conditions, such highly reducing electrons also could be used for hydrogen (H2) production via electron transfer between ferredoxin and hydrogenase in the green alga Chlamydomonas reinhardtii. Partitioning between LEF and CEF is regulated through PROTON-GRADIENT REGULATION5 (PGR5). There is evidence that partitioning of electrons also could be mediated via PSI remodeling processes. This plasticity is linked to the dynamics of PSI-associated light-harvesting proteins (LHCAs) LHCA2 and LHCA9. These two unique light-harvesting proteins are distinct from all other LHCAs because they are loosely bound at the PSAL pole. Here, we investigated photosynthetic electron transfer and H2 production in single, double, and triple mutants deficient in PGR5, LHCA2, and LHCA9. Our data indicate that lhca2 and lhca9 mutants are efficient in photosynthetic electron transfer, that LHCA2 impacts the pgr5 phenotype, and that pgr5/lhca2 is a potent H2 photo-producer. In addition, pgr5/lhca2 and pgr5/lhca9 mutants displayed substantially different H2 photo-production kinetics. This indicates that the absence of LHCA2 or LHCA9 impacts H2 photo-production independently, despite both being attached at the PSAL pole, pointing to distinct regulatory capacities.

Preparation and photoelectrochemical characterization of the Ca2Co2O5, as novel photocatalyst for the H2 photo-production

Preparation and photoelectrochemical characterization of the Ca2Co2O5, as novel photocatalyst for the H2 photo-production

Photochemical hydrogen evolution using Pt/titania nanosheet catalysts prepared by chemical-reduction and photo-deposition methods

Photocatalysts where platinum nanoparticles are loaded on titania nanosheets (TNS) were synthesized by the chemical reduction with sodium borohydride (CR-Pt/TNS) and the photo-deposition (PD-Pt/TNS). In the case of UV light irradiation to Pt/TNS, H2 production activity of PD-Pt/TNS was about 3 times higher than that of CR-Pt/TNS. Visible light (455 nm) induced H2 photoproduction using Pt/TNS and Zn(II)5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (Zn(II)TMPyP4+) adsorbed on TNS was carried out in the presence of an electron donor (ascorbic acid). In the case of visible light irradiation to Pt/TNS-Zn(II)TMPyP4+, H2 production activity of PD-Pt/TNS-Zn(II)TMPyP4+ was about 20 times higher than that of CR-Pt/TNS- Zn(II)TMPyP4+. Because TNS has an anisotropy in the direction of carrier migration, the excited electrons tend to move to the edge of nanosheet. It is known that metal nanoparticles tend to be loaded at the edge of nanosheet for PD-Pt/TNS. Therefore, the difference in hydrogen evolution activity between CR- and PD-Pt/TNS is expected to be due to the selective loading of Pt at the edge of nanosheet and the efficient electron transfer to Pt at the edge for PD-Pt/TNS.

Photosynthetic hydrogen production: Novel protocols, promising engineering approaches and application of semi-synthetic hydrogenases.

Photosynthetic production of molecular hydrogen (H2 ) by cyanobacteria and green algae is a potential source of renewable energy. These organisms are capable of water biophotolysis by taking advantage of photosynthetic apparatus that links water oxidation at Photosystem II and reduction of protons to H2 downstream of Photosystem I. Although the process has a theoretical potential to displace fossil fuels, photosynthetic H2 production in its current state is not yet efficient enough for industrial applications due to a number of physiological, biochemical, and engineering barriers. This article presents a short overview of the metabolic pathways and enzymes involved in H2 photoproduction in cyanobacteria and green algae and our present understanding of the mechanisms of this process. We also summarize recent advances in engineering photosynthetic cell factories capable of overcoming the major barriers to efficient and sustainable H2 production.

The prospects of alcohol industry wastes application in photoproduction of hydrogen by the purple bacteria Rhodobacter sphaeroides

The possibilities of using various industrial wastes to produce biofuel are currently being considered. It will provide not only novel, efficient and cheap sources of hydrogen (H2), but will also help to solve the problem of waste disposal. The current work presents the prospects of application of alcohol industry wastes, such as distillers grains and brewery spent grains, for production of H2 by the purple bacteria Rhodobacter sphaeroides MDC6522. The data obtained showed the possibility of using distillers grains and brewery spent grains as effective carbon sources for producing H2. It was shown that pre-treatment of wastes, their dilution and neutralization are necessary to ensure the effective bacterial growth and H2 production by R. sphaeroides. The growth rate and H2 yield during the cultivation of bacteria on a 2-fold diluted distillers grains medium increased 2- and 4-fold, respectively, compared with a culture, grown on standard Ormerod medium. At the same time, the growth rate and photoproduction of H2 on a 10-fold diluted brewery spent grains medium were 2-fold higher, in comparison with the control. Thus, the results obtained indicate that these alcohol industry wastes can be used as promising substrates for biohydrogen production.

Photochemistry and photoinhibition of the H-cluster of FeFe hydrogenases

The photosensitivity of the active site of hydrogenases is an opportunity for studying its reactivity. However, the photoinhibition of certain hydrogenases may have a negative impact on H2 photoproduction.

Charge storage of carbon dot enhances photo-production of H2 and H2O2 over Ni2P/carbon dot catalyst under normal pressure

Photo-production of hydrogen (H2) and hydrogen peroxide (H2O2) simultaneously from water catalytic-splitting has received widespread attention. Most photocatalysts suffer from H2O2 poisoning and rapid recombination of photogenerated electrons and holes. Although photocatalysts against H2O2 poisoning have been prepared, the long-time stability of photogenerated electrons is still a great challenge. Here, we demonstrate that carbon dots (CDs) can stabilize and store the photogenerated electrons, promote the effective separation of photo-generated charges, and improve the photocatalytic activity and stability of the catalyst. The Ni2P/CDs composite photocatalyst synthesized in this work can produce H2 and H2O2 simultaneously under atmosphere, and the yields of H2 and H2O2 can reach 258.6 μmol/h/g and 1281.4 μmol/h/g, respectively. It represents the highest yield of H2O2 ever reported in photocatalysts capable of producing both H2 and H2O2 simultaneously under normal pressure. This work provides some deep insight on the storage and stability of photogenerated electrons, and open up a new way for the high efficient photocatalyst design based on the regulation of the interface charge dynamics.

Water oxidation by photosystem II is the primary source of electrons for sustained H2 photoproduction in nutrient-replete green algae

The unicellular green alga Chlamydomonas reinhardtii is capable of photosynthetic H2 production. H2 evolution occurs under anaerobic conditions and is difficult to sustain due to 1) competition between [FeFe]-hydrogenase (H2ase), the key enzyme responsible for H2 metabolism in algae, and the Calvin-Benson-Bassham (CBB) cycle for photosynthetic reductants and 2) inactivation of H2ase by O2 coevolved in photosynthesis. Recently, we achieved sustainable H2 photoproduction by shifting algae from continuous illumination to a train of short (1 s) light pulses, interrupted by longer (9 s) dark periods. This illumination regime prevents activation of the CBB cycle and redirects photosynthetic electrons to H2ase. Employing membrane-inlet mass spectrometry and [Formula: see text], we now present clear evidence that efficient H2 photoproduction in pulse-illuminated algae depends primarily on direct water biophotolysis, where water oxidation at the donor side of photosystem II (PSII) provides electrons for the reduction of protons by H2ase downstream of photosystem I. This occurs exclusively in the absence of CO2 fixation, while with the activation of the CBB cycle by longer (8 s) light pulses the H2 photoproduction ceases and instead a slow overall H2 uptake is observed. We also demonstrate that the loss of PSII activity in DCMU-treated algae or in PSII-deficient mutant cells can be partly compensated for by the indirect (PSII-independent) H2 photoproduction pathway, but only for a short (<1 h) period. Thus, PSII activity is indispensable for a sustained process, where it is responsible for more than 92% of the final H2 yield.

Promoting H2 photoproduction of TiO2-based materials by surface decoration with Pt nanoparticles and SnS2 nanoplatelets

The production of hydrogen from the photoreforming of sacrificial alcohols was essayed using an anatase-based ternary system having Pt nanoparticles and SnS2 nanoplatelets at the surface of the oxide support. Contact between phases was optimized to achieve optimum functional properties under UV and visible illumination, providing the basis for an excellent profit of solar light as measured by the evaluation of the quantum efficiency of the process. The study of the charge carrier fate using photoluminescence and the reactants under reaction conditions using infrared spectroscopy demonstrated that the outstanding photoactivity is connected with the occurrence of multiple cooperative effects between the components of the ternary system, taking place under all (UV and visible) illumination conditions and: i) facilitating charge carrier separation as well as ii) driving the evolution of the carbon-containing intermediates and concomitant hydrogen production.

Mechanistic insights into pH-dependent H2 photoproduction in bisulfite-treated Chlamydomonas cells

BackgroundBisulfite addition is an important H2 photoproduction strategy that removes O2 and activates hydrogenase. The pH values of cell cultures can change the ratio of bisulfite to sulfite, which may affect H2 photoproduction. However, little is known regarding the pH effect of bisulfite addition on H2 photoproduction and relevant underlying mechanism.ResultsHere, changes in H2 photoproduction with different initial extracellular pH values showed a parabolic distribution and a pH of 8.0 is an optimal value for H2 photoproduction in Chlamydomonas reinhardtii cells treated with bisulfite. Compared to the growth pH (pH 7.3), increased photoproduction of H2 at this optimal pH was primarily caused by a relatively high residual activity of photosystem II (PSII), which provides a relatively plentiful source of electrons for H2 photoproduction. Such increased H2 photoproduction was most likely a result of decreased the ratio of bisulfite to sulfite, consistent with the result that the toxicity of bisulfite on PSII was much more than that of sulfite. This possibility was corroborated by the result that treatment with a combination of 7 mM bisulfite and 6 mM sulfite further enhanced H2 photoproduction compared with 13 mM bisulfite alone.ConclusionsCollectively, our findings provide novel mechanistic insights into pH-dependent H2 photoproduction in C. reinhardtii cells treated with bisulfite, and demonstrate that sulfite addition is another important strategy for H2 photoproduction, just like bisulfite addition.

Overproduction of the Flv3B flavodiiron, enhances the photobiological hydrogen production by the nitrogen-fixing cyanobacterium Nostoc PCC 7120

BackgroundThe ability of some photosynthetic microorganisms, particularly cyanobacteria and microalgae, to produce hydrogen (H2) is a promising alternative for renewable, clean-energy production. However, the most recent, related studies point out that much improvement is needed for sustainable cyanobacterial-based H2 production to become economically viable. In this study, we investigated the impact of induced O2-consumption on H2 photoproduction yields in the heterocyte-forming, N2-fixing cyanobacterium Nostoc PCC7120.ResultsThe flv3B gene, encoding a flavodiiron protein naturally expressed in Nostoc heterocytes, was overexpressed. Under aerobic and phototrophic growth conditions, the recombinant strain displayed a significantly higher H2 production than the wild type. Nitrogenase activity assays indicated that flv3B overexpression did not enhance the nitrogen fixation rates. Interestingly, the transcription of the hox genes, encoding the NiFe Hox hydrogenase, was significantly elevated, as shown by the quantitative RT-PCR analyses.ConclusionWe conclude that the overproduced Flv3B protein might have enhanced O2-consumption, thus creating conditions inducing hox genes and facilitating H2 production. The present study clearly demonstrates the potential to use metabolic engineered cyanobacteria for photosynthesis driven H2 production.

Transcriptomic analysis of hydrogen photoproduction in Chlorella pyrenoidosa under nitrogen deprivation

H2 photoproduction by green algae is a very attractive way to produce clean and renewable energy. In our previous study, Chlorella pyrenoidosa strain IOAC707S was found to produce hydrogen under nitrogen deprivation in seawater medium; however the mechanism is not entirely clear. In this work, it was found that under nitrogen deprivation, the efficiency of photosystem II photochemical activity and the photosynthetic O2 evolution rate of C. pyrenoidosa strain IOAC707S decreased, while the respiratory rate increased, which were favorable for the establishment of anoxia and H2 photoproduction. Transcriptomic analysis indicated that photosynthetic activity did not simply decline but underwent a complex adjustment to prepare for H2 photoproduction. The activities of glycolysis and the pentose phosphate pathway were up-regulated, suggesting more electron transport from endogenous substrate to H2 photoproduction. The decrease of the tricarboxylic acid cycle activity resulted in decreased levels of CO2, which would limit Calvin cycle activity, and subsequently lead to the accumulation of NADPH and a reduction of the photosynthetic electron transport chain. Under these conditions, the induced hydrogenase served as an electron valve, and H2 was produced.

Elimination of the flavodiiron electron sink facilitates long-term H2 photoproduction in green algae

BackgroundThe development of renewable and sustainable biofuels to cover the future energy demand is one of the most challenging issues of our time. Biohydrogen, produced by photosynthetic microorganisms, has the potential to become a green biofuel and energy carrier for the future sustainable world, since it provides energy without CO2 emission. The recent development of two alternative protocols to induce hydrogen photoproduction in green algae enables the function of the O2-sensitive [FeFe]-hydrogenases, located at the acceptor side of photosystem I, to produce H2 for several days. These protocols prevent carbon fixation and redirect electrons toward H2 production. In the present work, we employed these protocols to a knockout Chlamydomonas reinhardtii mutant lacking flavodiiron proteins (FDPs), thus removing another possible electron competitor with H2 production.ResultsThe deletion of the FDP electron sink resulted in the enhancement of H2 photoproduction relative to wild-type C. reinhardtii. Additionally, the lack of FDPs leads to a more effective obstruction of carbon fixation even under elongated light pulses.ConclusionsWe demonstrated that the rather simple adjustment of cultivation conditions together with genetic manipulation of alternative electron pathways of photosynthesis results in efficient re-routing of electrons toward H2 photoproduction. Furthermore, the introduction of a short recovery phase by regular switching from H2 photoproduction to biomass accumulation phase allows to maintain cell fitness and use photosynthetic cells as long-term H2-producing biocatalysts.

Photochemical characteristics of Chlamydomonas mutant hpm91 lacking proton gradient regulation 5 (PGR5) during sustained H2 photoproduction under sulfur deprivation

Renewable H2 photoproduction by Chlamydomonas reinhardtii offers a desirable bio-system for solar fuels. However, its large-scale application is hindered mainly due to lack of ideal strains. We previously isolated a mutant hpm91 which lacks PGR5 and sustains H2 photoproduction for 25 days. To understand the photosynthetic basis for this remarkable phenotype, we hereby investigated its photochemical characteristics during sulfur-deprived H2 photoproduction using in vivo chlorophyll fluorescence spectroscopy. Compared to wild type, effective quantum yield of PSII and PSI of hpm91 increased upto 78.9% and 147.6%, respectively. Electron transport rate of each photosystem is closely correlated with the increase of quantum yield, suggesting overall enhanced photochemistry of hpm91 under such condition. Moreover, ATP synthase activity decays slower and remains higher in this mutant. These are in vivo evidence demonstrating increased photosynthetic efficiency of hpm91 promotes its H2 photoproduction. Together with its competent photoheterotrophic growth in a larger photobioreactor, we propose that hpm91 is a valuable strain for re-engineering Chlamydomonas towards improving light energy efficiency in a large-scale system.

Optimization of Hydrogen Gas Production Conditions from Egyptian Chlamydomonas Sp

Hydrogen gas could provide attractive options as ideal fuel for a world, in which environmental friendly and economically sustainable manner. Microalgae have the ability to bio-synthesis hydrogen gas. Algal H2 does do not generate any toxic or polluting bi-products and could potentially offer value-added products derived from algal biomass. In this work, the feasibility of coupling sulfur deprivation and light on hydrogen production by Chlamydomonas sp grown in photobioreactor was investigated. The cells growth, hydrogen production, total carbohydrate and chlorophyll content were determined. The results showed that, under optimum condition, algae cells were required 168 hr (7days) to reach the late logarithmic phase (the algal dry weight 4.11 g/L). Whereas the algae cells were needed about 18~22 days to reach this value (3.55 g/ L) when grow in optimum medium. The concentration of Chlorophyll (5.65%) and carbohydrate (39.46%) were accumulated in algae cells grow in S-deprives medium coupled with dark condition over that did in algae cells cultured in optimum medium. After about a 24 h of cultivation, photo-production of H2 was observed for C. sp either in absence or presence of sulfate. But under sulfur deprivation coupled with dark condition, higher H2 gas was obtained after 16 hr (7 several days) of incubation period. In new design photobioreactors (PhBRs), after 18 days of cultivation, the volume of H2 gas in was found to be 450 ml in cells grow in sulfur-deprived culture). This value was 360 ml in cells grow under optimal condition.

Improvement of photobiological hydrogen production by suspended and immobilized cells of the N2-fixing cyanobacterium Fischerella muscicola TISTR 8215

To develop H2 photoproduction by using the N2-fixing cyanobacterium Fischerella muscicola TISTR 8215, a novel strain isolated from soil in Thailand, the factors affecting H2 production were investigated in this study. Enhanced H2 production in suspension culture was obtained when adapting the cells under N2-fixing condition (modified AA medium) with continuous illumination of 250 μmol photons m−2 s−1 under aerobic condition for 24 h, followed by further incubation under anaerobic condition for 9 h for production phase. The maximum H2 production rate was 38.5 μmol mg−1 chl a h−1. Low concentration of Fe2+ and Mo6+, essential elements for nitrogenase, enhanced H2 production. The enhanced H2 production was accompanied by the upregulation of nifD. On the other hand, an increased hupL transcript level was observed when there was a decrease of H2 production. In cells immobilization, 1.5% (w/v) agar-immobilized cells had a 23-fold increase in maximum H2 yield compared with that using free cell suspension at the same cell concentration, i.e., 7.48 mmol H2 L−1 by immobilized cells and 0.32 mmol H2 L−1 by suspended cells. Moreover, cell immobilization in agar could prolong H2 production up to 108 h. This study underlines the strategies toward enhanced and sustained H2 production from cyanobacteria. Furthermore, it will pave the way for large-scale production of biohydrogen to be used as an eco-friendly energy resource.

Whey and molasses as inexpensive raw materials for parallel production of biohydrogen and polyesters via a two-stage bioprocess: New routes towards a circular bioeconomy

Consecutive dark-fermentation and photo-fermentation stages were investigated for a profitable circular bio-economy. H2 photo-production versus poly(3-hydroxybutyrate) (P3HB) accumulation is a modern biotechnological approach to use agro-food industrial byproducts as no-cost rich-nutrient medium in eco-sustainable biological processes. Whey and molasses are very important byproducts rich in nutrients that lactic acid bacteria can convert, by dark-fermentation, in dark fermented effluents of whey (DFEW) and molasses (DFEM). These effluents are proper media for culturing purple non-sulfur bacteria, which are profitable producers of P3HB and H2. The results of the present study show that Lactobacillus sp. and Rhodopseudomonas sp. S16-VOGS3 are two representative genera for mitigation of environmental impact. The highest productivity of P3HB (4.445 mg/(L·h)) was achieved culturing Rhodopseudomonas sp. S16-VOGS3, when feeding the bacterium with 20% of DFEM; the highest H2 production rate of 4.46 mL/(L·h) was achieved when feeding the bacterium with 30% of DFEM.

Effects of the Photosystem II Inhibitors CCCP and DCMU on Hydrogen Production by the Unicellular Halotolerant Cyanobacterium Aphanothece halophytica.

The unicellular halotolerant cyanobacterium Aphanothece halophytica is a potential dark fermentative producer of molecular hydrogen (H2) that produces very little H2 under illumination. One factor limiting the H2 photoproduction of this cyanobacterium is an inhibition of bidirectional hydrogenase activity by oxygen (O2) obtained from splitting water molecules via photosystem II activity. The present study aimed to investigate the effects of the photosystem II inhibitors carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on H2 production of A. halophytica under light and dark conditions and on photosynthetic and respiratory activities. The results showed that A. halophytica treated with CCCP and DCMU produced H2 at three to five times the rate of untreated cells, when exposed to light. The highest H2 photoproduction rates, 2.26 ± 0.24 and 3.63 ± 0.26 μmol H2 g−1 dry weight h−1, were found in cells treated with 0.5 μM CCCP and 50 μM DCMU, respectively. Without inhibitor treatment, A. halophytica incubated in the dark showed a significant increase in H2 production compared with cells that were incubated in the light. Only CCCP treatment increased H2 production of A. halophytica during dark incubation, because CCCP functions as an uncoupling agent of oxidative phosphorylation. The highest dark fermentative H2 production rate of 39.50 ± 2.13 μmol H2 g−1 dry weight h−1 was found in cells treated with 0.5 μM CCCP after 2 h of dark incubation. Under illumination, CCCP and DCMU inhibited chlorophyll fluorescence, resulting in a low level of O2, which promoted bidirectional hydrogenase activity in A. halophytica cells. In addition, only CCCP enhanced the respiration rate, further reducing the O2 level. In contrast, DCMU reduced the respiration rate in A. halophytica.

A new approach for improving microalgal biohydrogen photoproduction based on safe & fast oxygen consumption

Microalgal H2 photoproduction has the potential of being an affordable method for producing this alternative fuel; however extreme sensitivity of hydrogenase enzyme to photosynthetic O2 naturally prevents large-scale H2 production upon illumination. Although a two-phase sulfur deficiency method has been established to deal with this incompatibility, its time and cost demanding, so that this model is not commercially scalable. Despite much research has been conducted, no proper economic alternative for the sulfur deprivation model, with higher or even same productivity and sustainability, has been presented till now. Herein we propose a simple and viable alternative, through introducing a chemical O2 scavenger system, called oxysorb, to algal cultures.Oxysorb, in non-cytotoxic concentrations (including 50 or 100 mM sodium ascorbate and 5 ppm cupric sulfate) for CC124 as well as pgr5 cultures (containing 30 μg/ml chlorophyll) showed a fast, safe and persisted O2 removal capacity, initiating H2 production in the sulfur-containing cultures, either in photoheterotrophic or in autotrophic conditions. Total H2 production obtained with CC124 and pgr5 cultures, containing 100 mM oxysorb, was 2–5.5 times higher than sulfur-deprived ones (measured in a small closed system). This higher H2 productivity in the oxysorb approach was achieved due to anoxia establishment with no ROS production and without impacting PSII activity.