O2 Evolution Rate Research Articles

Synthesis of PDI/Zn0.8Cd0.2S composites for efficient visible light-driven photocatalytic overall water splitting

BackgroundOverall water splitting based on particulate photocatalysts under visible light irradiation is a cost-effective technology for the conversion of solar energy into renewable energy (hydrogen and oxygen). MethodsHerein, the perylene diimide (PDI)/Zn0.8Cd0.2S composite photocatalyst is synthesized for application in visible light driven photocatalytic overall water splitting. Significant findingsThe PDI/Zn0.8Cd0.2S composite with 10 wt% PDI loading exhibits superior H2-evolution rate of 71.98 μmol·g−1·h−1 and O2-evolution rate of 32.44 μmol·g−1·h−1, which in a perfect stoichiometric ratio close to 2:1. The PDI/Zn0.8Cd0.2S with remarkable enhanced photocatalytic activity have the advantages of high charge separation efficiency and strong redox capacity. This work provided a new approach for the design of new type composite photocatalysts with efficient photocatalytic overall water splitting.

Dark fermentative hydrogen production and transcriptional analysis of genes involved in the unicellular halotolerant cyanobacterium Aphanothece halophytica under nitrogen and potassium deprivation.

The unicellular halotolerant cyanobacterium Aphanothece halophytica is known as a potential hydrogen (H2) producer. This study aimed to investigate the enhancement of H2 production under nutrient deprivation. The results showed that nitrogen and potassium deprivation induced dark fermentative H2 production by A. halophytica, while no differences in H2 production were found under sulfur and phosphorus deprivation. In addition, deprivation of nitrogen and potassium resulted in the highest H2 production in A. halophytica due to the stimulation of hydrogenase activity. The effect of adaptation time under nitrogen and potassium deprivation on H2 production was investigated. The results showed that the highest H2 accumulation of 1,261.96 ± 96.99µmol H2 g dry wt-1 and maximum hydrogenase activity of 179.39 ± 8.18µmol H2 g dry wt-1 min-1 were obtained from A. halophytica cells adapted in the nitrogen- and potassium-deprived BG11 medium supplemented with Turk Island salt solution (BG110-K) for 48h. An increase in hydrogenase activity was attributed to the decreased O2 concentration in the system, due to a reduction of photosynthetic O2 evolution rate and a promotion of dark respiration rate. Moreover, nitrogen and potassium deprivation stimulated glycogen accumulation and decreased specific activity of pyruvate kinase. Transcriptional analysis of genes involved in H2 metabolism using RNA-seq confirmed the above results. Several genes involved in glycogen biosynthesis (glgA, glgB, and glgP) were upregulated under both nitrogen and potassium deprivation, but genes regulating enzymes in the glycolytic pathway were downregulated, especially pyk encoding pyruvate kinase. Interestingly, genes involved in the oxidative pentose phosphate pathway (OPP) were upregulated. Thus, OPP became the favored pathway for glycogen catabolism and the generation of reduced nicotinamide adenine dinucleotide phosphate (NADPH), which resulted in an increase in H2 production under dark anaerobic condition in both nitrogen- and potassium-deprived cells.

Engineering a molecular ruthenium catalyst into three-dimensional metal covalent organic frameworks for efficient water oxidation.

The water oxidation reaction plays an important role in clean energy conversion, utilization, and storage, but mimicking the oxygen-evolving complex of photosystem II for designing active and stable water oxidation catalysts (WOCs) is still an appealing challenge. Here, we innovatively engineered a molecular ruthenium WOC as a metal complex building unit to construct a series of three-dimensional metal covalent organic frameworks (3D MCOFs) for realizing efficient oxidation catalysis. The resultant MCOFs possessed rare 3D interlocking structures with inclined interpenetration of two-dimensional covalent rhombic nets, and the Ru sites were periodically arranged in the crystalline porous frameworks. Impressively, these MCOFs showed excellent performance towards water oxidation (the O2 evolution rate is as high as 2830 nmol g-1 s-1) via the water nucleophilic attack pathway. Besides, the MCOFs were also reactive for oxidizing organic substrates. This work highlights the potential of MCOFs as a designable platform in integrating molecular catalysts for various applications.

Defect engineering of two-dimensional Nb-based oxynitrides for visible-light-driven water splitting to produce H2 and O2.

Two-dimensional (2D) Nb-based oxynitrides are promising visible-light-responsive photocatalysts for the water splitting reaction, but their photocatalytic activity is degraded by the formation of reduced Nb5+ species and O2- vacancies. To understand the influence of nitridation on the formation of crystal defects, this study synthesized a series of Nb-based oxynitrides through the nitridation of LaKNaNb1-xTaxO5 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). During nitridation, K and Na species volatilized, which helped transform the exterior of LaKNaNb1-xTaxO5 into a lattice-matched oxynitride shell. Ta inhibited defect formation, yielding Nb-based oxynitrides with a tunable bandgap between 1.77 and 2.12 eV, straddling the H2 and O2 evolution potentials. After loading with Rh and CoOx cocatalysts, these oxynitrides exhibited good photocatalytic activity for H2 and O2 evolution in visible light (650-750 nm). The nitrided LaKNaTaO5 and LaKNaNb0.8Ta0.2O5 delivered the maximum H2 (19.37 μmol h-1) and O2 (22.81 μmol h-1) evolution rates, respectively. This work provides a strategy for preparing oxynitrides with low defect densities and demonstrates the promising performance of Nb-based oxynitrides for water splitting.

Effects of n-butanol production on metabolism and the photosystem in Synecococcus elongatus PCC 7942 based on metabolic flux and target proteome analyses.

Although n-butanol (BuOH) is an ideal fuel because of its superior physical properties, it has toxicity to microbes. Previously, a Synechococcus elongatus PCC 7942 derivative strain that produces BuOH from CO2 was developed by introducing six heterologous genes (BUOH-SE strain). To identify the bottleneck in BuOH production, the effects of BuOH production and its toxicity on central metabolism and the photosystem were investigated. Parental (WT) and BUOH-SE strains were cultured under autotrophic conditions. Consistent with the results of a previous study, BuOH production was observed only in the BUOH-SE strain. Isotopically non-stationary 13C-metabolic flux analysis revealed that the CO2 fixation rate was much larger than the BuOH production rate in the BUOH-SE strain (1.70 vs 0.03 mmol gDCW-1 h-1), implying that the carbon flow for BuOH biosynthesis was less affected by the entire flux distribution. No large difference was observed in the flux of metabolism between the WT and BUOH-SE strains. Contrastingly, in the photosystem, the chlorophyll content and maximum O2 evolution rate per dry cell weight of the BUOH-SE strain were decreased to 81% and 43% of the WT strain, respectively. Target proteome analysis revealed that the amounts of some proteins related to antennae (ApcA, ApcD, ApcE, and CpcC), photosystem II (PsbB, PsbU, and Psb28-2), and cytochrome b6f complex (PetB and PetC) in photosystems decreased in the BUOH-SE strain. The activation of photosynthesis would be a novel approach for further enhancing BuOH production in S. elongatus PCC 7942.

Tight relationship between two photosystems is robust in rice leaves under various nitrogen conditions.

Leaf nitrogen (N) level affects not only photosynthetic CO2 assimilation, but also two photosystems of the photosynthetic electron transport. The quantum yield of photosystem II [Y(II)] and the non-photochemical yield due to the donor side limitation of photosystem I [Y(ND)], which denotes the fraction of oxidized P700 (P700+) to total P700, oppositely change depending on leaf N level, and the negative correlation between these two parameters has been reported in leaves of plants cultivated at various N levels in growth chambers. Here, we aimed to clarify whether this correlation is maintained after short-term changes in leaf N level, and what parameters are the most responsive to the changes in leaf N level under field conditions. We cultivated rice varieties at two N fertilization levels in paddy fields, treated additional N fertilization to plants grown at low N, and measured parameters of two photosystems of mature leaves. In rice leaves under low N condition, the Y(ND) increased and the photosynthetic linear electron flow was suppressed. In this situation, the accumulation of P700+ can function as excess energy dissipation. After the N addition, both Y(ND) and Y(II) changed, and the negative correlation between them was maintained. We used a newly-developed device to assess the photosystems. This device detected the similar changes in Y(ND) after the N addition, and the negative correlation between Y(ND) and photosynthetic O2 evolution rates was observed in plants under various N conditions. This study has provided strong field evidence that the Y(ND) largely changes depending on leaf N level, and that the Y(II) and Y(ND) are negatively correlated with each other irrespective of leaf N level, varieties and annual variation. The Y(ND) can stably monitor the leaf N status and the linear electron flow under field conditions.

Ruthenium Complexes of Rigid, Dianionic, Tetradentate N‐Donor Ligands and their Potential as Catalysts for Water Oxidation

AbstractTwo mononuclear ruthenium(II) complexes based on dianionic {N4} ligands and with axial pyridines have been prepared and characterized crystallographically (1) or by 2D NMR spectroscopy using residual dipolar couplings (2). The {N4} ligands provide a constrained equatorial coordination with one large N−Ru−N angle, and additional non‐coordinating N atoms in case of 2. Their redox properties have been investigated (spectro)electrochemically, and their potential to serve as water oxidation catalysts has been probed using cerium ammonium nitrate (CAN) at pH 1.0. Complex 1 undergoes rapid degradation, likely via ligand oxidation, whereas 2 is more rugged and exhibits 80 % efficiency in the CeIV‐driven water oxidation, with a high initial turnover frequency (TOFi) of 3.07×10−2 s−1 (at 100 equiv. CAN). The initial rate of O2 evolution exhibits 1st order dependence on catalyst concentration, suggesting a water nucleophilic attack mechanism. Repeated addition of CAN and control experiments show that high ionic strength conditions (both NO3− and CeIII) significantly decrease the TOF.

Oxygen vacancy-mediated WO3 phase junction to steering photogenerated charge separation for enhanced water splitting

Effective charge separation and transfer is deemed to be the contributing factor to achieve high photoelectrochemical (PEC) water splitting performance on photoelectrodes. Building a phase junction structure with controllable phase transition of WO3 can further improve the photocatalytic performance. In this work, we realized the transition from orthorhombic to monoclinic by regulating the annealing temperatures, and constructed an orthorhombic-monoclinic WO3 (o-WO3/m-WO3) phase junction. The formation of oxygen vacancies causes an imbalance of the charge distribution in the crystal structure, which changes the W-O bond length and bond angle, accelerating the phase transition. As expected, an optimum PEC activity was achieved over the o-WO3/m-WO3 phase junction in WO3-450 photoelectrode, yielding the maximum O2 evolution rate roughly 32 times higher than that of pure WO3-250 without any sacrificial agents under visible light irradiation. The enhancement of catalytic activity is attributed to the atomically smooth interface with a highly matched lattice and robust built-in electric field around the phase junction, which leads to a less-defective and abrupt interface and provides a smooth interfacial charge separation and transfer path, leading to improved charge separation and transfer efficiency and a great enhancement in photocatalytic activity. This work strikes out on new paths in the formation of an oxygen vacancy-induced phase transition and provides new ideas for the design of catalysts.

Anchoring Co3O4 on CdZnS to accelerate hole migration for highly stable photocatalytic overall water splitting

Photocatalytic overall water splitting represents a promising strategy to achieve the renewable hydrogen energy. Although Cd1−xZnxS catalysts show high photocatalytic hydrogen evolution efficiency in pure water, severe photocorrosion problems limit their applications. Herein, photocatalytic system composed of Co3O4 nanoparticles anchored one-dimensional Cd0.6Zn0.4S nanorods (CZS/Co3O4) is designed and prepared by a simple hydrothermal method. Transient photovoltage tests and continuous wavelet transform analyses demonstrate that Co3O4 nanoparticles efficiently capture the photogenerated holes to inhibit photocorrosion of CZS nanorods, accelerate surface charge transfer and prolong the lifetime of photogenerated carriers. The CZS/Co3O4 photocatalyst exhibits high H2 and O2 evolution rates of 83.48 and 40.48 μmol h−1 g−1, respectively. The stability is maintained over four reaction cycles without significant decrease in the absence of sacrificial agents. This work provides insight into metal sulfides against photocorrosion and extends the range of metal sulfides in solar water splitting.

Molten salt-assisted synthesis of nitrogen-vacancy crystalline graphitic carbon nitride with tunable band structures for efficient photocatalytic overall water splitting

The photocatalytic overall water splitting performance of graphitic carbon nitride (g-C3N4) has still been restricted by its inefficient charge separation efficiency. Herein, nitrogen-vacancy crystalline g-C3N4 nanosheets (g-C3N4-D) with tunable band structures were successfully prepared by the alkali-molten salt-assisted method for efficient photocatalytic overall water splitting. Among them, g-C3N4-D2 not only combines the advantages of the amorphous and crystalline state of two-dimensional g-C3N4 nanosheets, but also introduces nitrogen vacancy to adjust the bandgap structures of crystalline g-C3N4 by an alkali etching, thus improving the light energy utilization and charge separation efficiency. TEM and EPR spectrum prove the existence of N defects in the crystalline g-C3N4. The excellent and stable photocatalytic overall water splitting activity with H2 and O2 evolution rate of 49.60 μmol g−1 h−1 and 24.71 μmol g−1 h−1 was obtained over g-C3N4-D2 with Pt and Co3O4 nanorods as cocatalysts (Pt/g-C3N4-D2/3%Co3O4 NRs) under AM 1.5G simulated light irradiation. In the half-reaction experiments, the maximum H2 evolution rate of Pt/g-C3N4-D2/3%Co3O4 NRs is 3.78 mmol g−1 h−1 with a significant quantum efficiency of 11.94 % at 400 nm, and the solar-hydrogen conversion efficiency (STH) is 1.48 %. The photocatalytic water oxidation activity of Pt/g-C3N4-D2/5%Co3O4 NRs is 42.34 μmol g−1 h−1. Additionally, the potential mechanism of photocatalytic overall water splitting was testified by in-situ XPS. This work provides a simple strategy for further advancing the potential application of g-C3N4 by molten salt-assisted alkali etching to introduce N vacancies to regulate the band gap of crystalline g-C3N4 for photocatalytic overall water splitting.

Powdered MnySb1–yOx Catalysts for Cerium-Mediated Oxygen Evolution in Acidic Environments

MnySb1–yOx powders with a series of compositions were evaluated as catalysts for chemical water oxidation in aqueous perchloric, sulfuric, or methanesulfonic acid. O2(g) evolved spontaneously over MnySb1–yOx catalyst powders that had been suspended in solutions that were pre-loaded with Ce4+ ions. The rate of O2 evolution depended on the amount, as well as the oxidation state, of the Mn in the powder. The highest O2 evolution rate was observed from the most Mn-rich catalyst, which had an effective surface oxidation state of Mn2.9+ in its rest state. The facile synthetic accessibility of such catalysts in powder form constitutes a step toward replacing Ir or Ru in Ce-mediated oxygen evolution in decoupled water splitting systems, as well as toward developing inks of earth-abundant catalysts for preparation of catalyst-coated membranes used in conventional proton-exchange membrane electrolyzers.

Effect of Mycotoxin Cytochalasin A on Photosystem II in Ageratina adenophora.

Biological herbicides have received much attention due to their abundant resources, low development cost, unique targets and environmental friendliness. This study reveals some interesting effects of mycotoxin cytochalasin A (CA) on photosystem II (PSII). Our results suggested that CA causes leaf lesions on Ageratina adenophora due to its multiple effects on PSII. At a half-inhibitory concentration of 58.5 μΜ (I50, 58.5 μΜ), the rate of O2 evolution of PSII was significantly inhibited by CA. This indicates that CA possesses excellent phytotoxicity and exhibits potential herbicidal activity. Based on the increase in the J-step of the chlorophyll fluorescence rise OJIP curve and the analysis of some JIP-test parameters, similar to the classical herbicide diuron, CA interrupted PSII electron transfer beyond QA at the acceptor side, leading to damage to the PSII antenna structure and inactivation of reaction centers. Molecular docking model of CA and D1 protein of A. adenophora further suggests that CA directly targets the QB site of D1 protein. The potential hydrogen bonds are formed between CA and residues D1-His215, D1-Ala263 and D1-Ser264, respectively. The binding of CA to residue D1-Ala263 is novel. Thus, CA is a new natural PSII inhibitor. These results clarify the mode of action of CA in photosynthesis, providing valuable information and potential implications for the design of novel bioherbicides.

Bismuth Gadolinium Oxychloride with a Remarkable Visible-Light-Responsive O2 Evolution Activity Promoted by Iodine Doping.

Visible-light-responsive bismuth-based oxyhalide has recently attracted extensive attention, however, the promotion of its charge separation is still challenging. Herein, we introduce iodine into Bi2 GdO4 Cl to synthetize I-doped Bi2 GdO4 Cl (denoted as yI-Bi2 GdO4 Cl, 0≤y≤2). The incorporation of I- ions is found to enhance light absorption and to accelerate charge separation by combining various characterizations such as density functional theory calculation, photoelectrochemical test, electrochemical impedance spectroscopy, photoluminescence spectrum, and open-circuit voltage decay. The O2 -evolving performances of 1I-Bi2 GdO4 Cl with optimized dopant concentration of I- ion and IrO2 loaded 1I-Bi2 GdO4 Cl are tremendously enhanced by ca. 4 and 45 times compared to pristine Bi2 GdO4 Cl. Notably, The O2 evolution rate reaches as high as 154.8 μmol ⋅ h-1 with an apparent quantum efficiency of ∼1.1 % at 420 nm. The synthetic iodine-doped photocatalyst remains stable after long-term photoreaction, demonstrating its potential in the field of photocatalysis.

Orthogonal Charge Transfer by Precise Positioning of Silver Single Atoms and Clusters on Carbon Nitride for Efficient Piezocatalytic Pure Water Splitting.

Developing efficient piezocatalytic systems for two-electron water splitting (TEWS) with producing H2 and H2 O2 shows great promise to meet the industrial demand. Herein, Ag single atoms (SAs) and clusters are co-anchored on carbon nitride (AgSA+C -CN) to serve as the multifunctional sites for efficient TEWS. The Ag SAs enhance the in-plane piezoelectric polarization of CN that is intimately modulated by the atomic coordination induced charge redistribution, and Ag clusters afford strong interfacial electric field to remarkably promote the out-of-plane migration of piezoelectrons from CN. Moreover, AgSA+C -CN yields a larger piezoresistive effect that elevates carrier mobility under strain. Consequently, a superior H2 and H2 O2 evolution rate of 7.90 mmol g-1 h-1 and 5.84 mmol g-1 h-1 is delivered by AgSA+C -CN, respectively, far exceeding that of the previously reported piezocatalysts. This work not only presents the SAs decoration as an available polarization enhancement strategy, but also sheds light on the superiority of multi-sites engineering in piezocatalysis.

Efficiently photocatalytic H2O overall splitting within the strengthened polarized field by reassembling surface single atoms

Surface single atom Ni-coordinated carbon nitride fibers (Ni/C3N4Fs) were reassembled into tiny NiP nanoparticle-integrated C3N4Fs (NiP/C3N4Fs) with the strengthened polarized electric fields accompanied by a weakened interface barrier. Photogenerated e- and h+ dynamically transfer to the convex-integrated NiP and concave of C3N4Fs under the synergetic electric fields via inner single atoms of Ni as charge transfer bridges within C3N4Fs interlayers, which is confirmed by high-angle annular dark field scanning transmission electron microscopy, K-edge extended X-ray absorption fine structure, X-ray photoelectron spectroscopy and theoretical prediction. H2- and O2-evolution rates of 1.89 and 0.92 mmol g−1 h−1 with solar-to-hydrogen efficiency of 2.33% are obtained over NiP/C3N4Fs system under visible light irradiation. This research provides a rational strategy for constructing the connection of H2 fuel production with its practical application.

Bay‐Monosubstitution with Electron‐Donating Group as an Efficiently Strategy to Functionalize Perylene Imide Polymer for Enhancing Photocatalytic Oxygen Evolution Activity

AbstractIt is still a challenge to develop an organic conjugated photocatalyst with a high O2 evolution rate. Functionalization organic polymer photocatalysts is an effective way to enhance photocatalytic performance. In this study, a series of perylene imide polymers (PDIs) are prepared by introducing different number of phenyl groups at bay position of PDI, and the influence of the number of substituents on charge separation and photocatalytic activity is investigated. It reveals that monosubstituted PDI exhibits the highest O2 evolution rate of 2524.88 µmol g–1 h–1 under visible light illumination without any cocatalyst. The excellent performance ascribes to the push–pull intramolecular charge transfer and the high crystallinity, which significantly promote separation and transfer of photoinduced charge. However, the O2 evolution rate dramatically drops with the number of substituent groups increase because introducing more groups at the bay position of PDI decreased charge local excitation of the PDI core and occupied the O2 evolution active site. In addition, it is found that increasing the number of electron–donor substituent groups would seriously destroy the crystallinity, leading to a decrease in the O2 evolution rate. This study highlights a reasonably structural modification strategy to enhance the O2 evolution rate of the PDI polymer by electron‐donating group monosubstitution.

Photoelectrochemical Water Oxidation over Novel Semiconducting Zinc-Based Metal–Thiolate Framework

Designing an efficient catalyst for a sustainable photoelectrochemical water oxidation reaction is very challenging in the context of renewable energy research. Here, we have introduced a new semiconducting porous zinc-thiolate framework via successful stitching of an "N" donor linker with a triazine-based tristhiolate secondary building unit in the overall architecture. The introduction of both linker and tristhiolate ligand synergistically modifies the architecture by making it a rigid, crystalline, three-dimensional, thermally stable, and porous framework. Our novel zinc-thiolate framework is used as an n-type semiconductor as revealed from the solid-state UV-vis DRS spectroscopic analysis, ac and dc conductivity analysis, and Mott-Schottky plot. This n-type semiconductor-based zinc-thiolate framework is utilized in the photoelectrochemical water oxidation reaction. It displayed a very high efficiency for a visible-light-driven oxygen evolution reaction (OER) in a KOH medium using standard Ag/AgCl as the reference electrode. The superiority of this material was further revealed from the low onset potential (0.822 mV vs RHE), high photocurrent density (0.204 mA cm-2), good stability, and high O2 evolution rate (77 μmol g-1 of oxygen evolution within 2 h), and a good efficiency (ABPE 0.42%, IPCE 29.6% and APCE 34.5%). Furthermore, the porosity in the overall framework seems to be a blessing to the photoelectrochemical performance due to better mass diffusion of the electrolyte. A detailed mechanism for the OER reaction was analyzed through density functional theory analysis suggesting the potential future of this Zn-thiolate framework for achieving a high efficiency in the sustainable water oxidation reaction.

Highly Dispersion Cu2O QDs Decorated Bi2WO6 S-Scheme Heterojunction for Enhanced Photocatalytic Water Oxidation.

Developing suitable photocatalysts for the oxygen evolution reaction (OER) is still a challenging issue for efficient water splitting due to the high requirements to create a significant impact on water splitting reaction kinetics. Herein, n-type Bi2WO6 with flower-like hierarchical structure and p-type Cu2O quantum dots (QDs) are coupled together to construct an efficient S-scheme heterojunction, which could enhance the migration efficiency of photogenerated charge carriers. The electrochemical properties are investigated to explore the transportation features and donor density of charge carriers in the S-scheme heterojunction system. Meanwhile, the as-prepared S-scheme heterojunction presents improved photocatalytic activity towards water oxidation in comparison with the sole Bi2WO6 and Cu2O QDs systems under simulated solar light irradiation. Moreover, the initial O2 evolution rate of the Cu2O QDs/Bi2WO6 heterojunction system is 2.3 and 9.7 fold that of sole Bi2WO6 and Cu2O QDs systems, respectively.

Microrods-evolved WO3 nanospheres with enriched oxygen-vacancies anchored on dodecahedronal CoO(Co2+)@carbon as durable catalysts for oxygen reduction/evolution reactions

Oxygen reduction/evolution reactions (ORR/OER) play the vital roles in energy-conversion devices, especially for Zn-air batteries (ZABs). However, it is always a challenge to explore a stable bifunctional catalyst. Here, WO3-anchored ZIF-67-derived CoO@graphitized carbon is wrapped by a thin carbon-layer to obtain CoO@GC/WO3@CL catalysts. The well-crystallized WO3 nanospheres are evolved from WO3 microrods via an intra-particle maturation. For ORR, the peak-potential of CoO@GC/WO3@CL-800 (800 ℃) (0.81 V vs. RHE) is higher than that of Pt/C (0.79 V). Synergies between WO3 (oxygen vacancies) and CoO (Co2+) improve mass/charge transfer to boost the 4e− pathway. For OER, CoO@GC/WO3@CL-800 has a lower overpotential (330 mV) than RuO2 (490 mV) at 10 mA cm−2. The O2 evolution rate can reach 0.125 mmol s−1 with a high Faraday efficiency of 96.7 %. Cooperation between CoOOH and oxygen vacancies promotes the H2O-oxidation to boost the O2-generation. A relatively low ΔE [Ej=10(OER)-E1/2(ORR)] of 0.72 V confirms the highly-stable ORR/OER activities of CoO@GC/WO3@CL-800, which obtains a higher power density (138 mW cm−2) than Pt/C + RuO2 cathode in primary ZABs. This study indicates a new direction to build a multilayer-structured ORR/OER catalyst by using ZIFs as templates.

Toxic mechanism of two cyanobacterial volatiles β-cyclocitral and β-ionone on the photosynthesis in duckweed by altering gene expression

Volatile organic compounds (VOCs) promote cyanobacteria dominating eutrophicated waters, with aquatic plant decrease and even disappearance. To uncover the toxic mechanism of cyanobacterial VOCs on aquatic plants, we investigated the growth, photosynthetic pigment levels, photosynthetic abilities and related gene expression in duckweed treated with β-cyclocitral and β-ionone, 2 main components in the VOCs. The levels of chlorophylls and carotenoids gradually declined with raising the concentration of the 2 compounds and prolonging the treatment time. Their decline should result from the down-regulation of 8 genes associated with photosynthetic pigment biosynthesis and up-regulation of 2 genes involved in carotenoid degradation. The reduction was also found in the photosystem II (PSII) efficiency and O2 evolution rate, which should result from the lowered photosynthetic pigment levels and down-regulation of 38 genes related with photosynthetic process. The frond numbers, total frond area and fresh weight gradually decreased with raising the 2 compound concentration, which may result from the lowered photosynthetic abilities as well as down-regulated expression of 7 genes associated with growth-promoting hormone biosynthesis and signal transduction. It can be speculated that cyanobacterial VOCs may poison aquatic plants by lowering the photosynthesis and growth through altering related gene expression.