Oxygen Evolution Rate Research Articles

Corrosion Resistant Polypyrrole Coated Lead-Alloy Positive Grids for Advanced Lead-Acid Batteries

We herein report a method for reducing lead-alloy positive grid corrosion in lead acid batteries by developing a polypyrrole (ppy) coating on to the surface of lead-alloy grids through potentiostatic polymerization technique. The experimental results demonstrate that the presence of ppy coating significantly enhances the corrosion resistance and inhibits the oxygen evolution rate as compare to bare grids. C-rate studies of 2 V/2.6 Ah lead-acid cells show ∼15–20% improvement in capacity at low charge-discharge rates (C/20- C/5) and ∼10% at high C rates (C/2 and 3C) for the cells with ppy coating grids in relation to conventional lead-acid cells.

Fabrication of a Au-loaded CaFe2O4/CoAl LDH p–n junction based architecture with stoichiometric H2& O2generation and Cr(vi) reduction under visible light

Visible-light-efficient Au-loaded CaFe2O4/CoAl LDH p–n junction for H2& O2generation and Cr(vi) reduction.

Organic/inorganic nitride heterostructure for efficient photocatalytic oxygen evolution

Given the four-electron water oxidation reaction as the rate-limiting step for water splitting, highly efficient photocatalysts for oxygen evolution have been receiving increasing research attentions. In this study, an organic/inorganic g-C3N4/CoN nitride heterostructure was developed by a facile precipitation-nitridation two-step process. With the CoN loading amounts optimized, the obtained g-C3N4/CoN composite achieves more than 4-fold increase in photocatalytic activity for oxygen evolution, as compared to the pristine g-C3N4, with a highest oxygen evolution rate reaching 607.2 μmol h−1 g−1 under visible light (λ > 420 nm). It was demonstrated that the formed g-C3N4/CoN heterostructure could promote the interfacial charge carrier separation and the loaded CoN acting as an effective cocatalyst could accelerate the water oxidation reaction kinetics, which synergistically contributes to the great enhancement in photocatalytic activity for oxygen evolution. Interestingly, by physically mixing g-C3N4/CoN and g-C3N4/Ni, acting as oxygen and hydrogen production photocatalysts, respectively, the obtained composite could stably produce oxygen and hydrogen in the stoichiometric ratio from pure water under visible light (λ > 420 nm). Although the photocatalytic overall water splitting activity is still very low, this study demonstrates a facile and promising approach to develop visible-light active photocatalysts for simultaneous hydrogen and oxygen production from water, from the perspective of surface modification and bifunctional cocatalyst loading.

The Low Molecular Mass Photosystem II Protein PsbTn Is Important for Light Acclimation.

Photosystem II (PSII) is a supramolecular complex containing over 30 protein subunits and a large set of cofactors, including various pigments and quinones as well as Mn, Ca, Cl, and Fe ions. Eukaryotic PSII complexes contain many subunits not found in their bacterial counterparts, including the proteins PsbP (PSII), PsbQ, PsbS, and PsbW, as well as the highly homologous, low-molecular-mass subunits PsbTn1 and PsbTn2 whose function is currently unknown. To determine the function of PsbTn1 and PsbTn2, we generated single and double psbTn1 and psbTn2 knockout mutants in Arabidopsis (Arabidopsis thaliana). Cross linking and reciprocal coimmunoprecipitation experiments revealed that PsbTn is a lumenal PSII protein situated next to the cytochrome b 559 subunit PsbE. The removal of the PsbTn proteins decreased the oxygen evolution rate and PSII core phosphorylation level but increased the susceptibility of PSII to photoinhibition and the production of reactive oxygen species. The assembly and stability of PSII were unaffected, indicating that the deficiencies of the psbTn1 psbTn2 double mutants are due to structural changes. Double mutants exhibited a higher rate of nonphotochemical quenching of excited states than the wild type and single mutants, as well as slower state transition kinetics and a lower quantum yield of PSII when grown in the field. Based on these results, we propose that the main function of the PsbTn proteins is to enable PSII to acclimate to light shifts or intense illumination.

Synthesis of a plasmonic CuNi bimetal modified with carbon quantum dots as a non-semiconductor-driven photocatalyst for effective water splitting

In artificial photocatalysis, attention is focused mainly on semiconductor photocatalysts, due to their long research history and excellent photocatalytic performance. Here, we demonstrate that dendrite-like plasmonic CuNi bimetal, used as a nonsemiconductor photocatalyst, produces electrons for photocatalytic water splitting by the surface plasmon resonance (SPR) effect of the CuNi bimetal. Carbon quantum dots (CQDs), by virtue of their outstanding charge transfer properties, serve as a co-catalyst that can facilitate the transfer of the photoinduced charge. The photocatalytic water splitting rate of the CuNi bimetal was significantly improved after modification with CQDs, and the highest hydrogen evolution rate was 55.19 μmol g−1h−1, with an oxygen evolution rate of 27.51 μmol g−1h−1, when the content of CQDs in the photocatalyst was 3 wt%. X-ray diffraction and X-ray photoelectron spectroscopy characterization reveal that the structure and state of the element in the photocatalyst remain unchanged after four consecutive cycles of, cumulatively, 20 h. Our findings may help in the development of a non-semiconductor-driven photocatalytic system for application in the photocatalytic field.

Characterization of TrxC, an Atypical Thioredoxin Exclusively Present in Cyanobacteria.

Cyanobacteria form a diverse group of oxygenic photosynthetic prokaryotes considered to be the antecessor of plant chloroplast. They contain four different thioredoxins isoforms, three of them corresponding to m, x and y type present in plant chloroplast, while the fourth one (named TrxC) is exclusively found in cyanobacteria. TrxC has a modified active site (WCGLC) instead of the canonical (WCGPC) present in most thioredoxins. We have purified it and assayed its activity but surprisingly TrxC lacked all the classical activities, such as insulin precipitation or activation of the fructose-1,6-bisphosphatase. Mutants lacking trxC or over-expressing it were generated in the model cyanobacterium Synechocystis sp. PCC 6803 and their phenotypes have been analyzed. The ΔtrxC mutant grew at similar rates to WT in all conditions tested although it showed an increased carotenoid content especially under low carbon conditions. Overexpression strains showed reduced growth under the same conditions and accumulated lower amounts of carotenoids. They also showed lower oxygen evolution rates at high light but higher Fv’/Fm’ and Non-photochemical-quenching (NPQ) in dark adapted cells, suggesting a more oxidized plastoquinone pool. All these data suggest that TrxC might have a role in regulating photosynthetic adaptation to low carbon and/or high light conditions.

Rapid identification of homogeneous O2 evolution catalysts and comparative studies of Ru(II)-carboxamides vs. Ru(II)-carboxylates in water-oxidation

One of the major challenges in developing sustainable energy storage systems is to discover robust oxygen evolving catalysts (OECs) that can efficiently oxidize water and produce oxygen, electrons and protons under highly oxidizing conditions. Thus, developing new screening methodologies and practical tools for OEC discovery is essential. Herein, we report a screening protocol which allows the accurate identification, benchmarking and kinetic analysis of molecular OECs using chemical oxidants, based on an oxygen-sensitive luminescent dissolved oxygen optical probe (DOOP). To demonstrate the practicality of this protocol, we screened more than 100 reactions to benchmark and evaluate the structure-activity relationship of several transition-metal complexes 1–16 based on Ru, Fe and Cu. Water-oxidation by Ru(II)-carboxylates is compared to structurally similar and less studied Ru(II)-carboxamides. A new Ru(II) complex 6 containing the doubly deprotonated N,N′-bis(aryl)pyridine-2,6-dicarboxamide was also synthesized and its oxygen evolution rate was found to be dramatically enhanced at neutral pH.

Co-deprivation of photosynthetic electron transport mineral pairs significantly enhanced antioxidant contents in a local isolate of Arthrospira (Spirulina) platensis

Co-deprivation of some photosynthetic electron transport mineral pairs is sought for enhancing antioxidant accumulation in a local isolate of Arthrospira (Spirulina) platensis, to improve their nutritional value and economic feasibility. The omitted element pairs were iron and sulfur (‑FeS), manganese and iron (‑MnFe) and nitrogen and sulfur (‑NS); chosen on the basis of their strong mediation in redox activities (Fe, Mn or S) or as sinks (N or S) of photosynthetic electrons.Antioxidant contents were estimated in 15 days old cells as growth of Arthrospira was not deteriorated by depriving the studied mineral pairs on the one hand and older cells tend to accumulate secondary compounds than younger ones whose bioenergetics are diverted into vegetative growth on the other hand. Iron‑sulfur, followed by iron‑manganese deprivation, induced the highest rates of photosynthtic oxygen evolution and respiratory oxygen uptake. Nitrogen‑sulfur starved cells, however, seem just survived as the increment of their dry mass relative to the inoculum was insignificant; they exhibited the lowest rates of photosynthesis with significantly enhanced respiration.A positive correlation between dry mass allocation and antioxidant accumulation can be deduced in the following order: ‑FeS > ‑FeMn > ‑NS. Vitamins A and tocopherols exhibited significant rise per unit dry mass (about fourfold that of the control) at ‑FeS while total antioxidants, reducing power and phenolics were more than doubled. FeMn pair deprivation sustained growth but did not enhance the accumulation of the targeted antioxidants. Under NS deprivation, neither Vitamin A nor tocopherols was enhanced although total antioxidants, reducing power and total phenolics were significantly higher than in control cultures.Soluble carbohydrates and free amino acids did not exhibit significant alterations in response to the imposed deprivations, indicating that enhancing the antioxidant accumulation did not take place at the expense of growth or primary metabolism in Arthrospira.

High-light selection produces a fast-growing Picochlorum celeri

A new species of marine algae Picochlorum celeri was obtained by enriching for fast reproductive rates under constant high irradiance in semi-continuous culture. Several rapidly-growing cell lines were isolated from the enrichment culture by bringing up cultures from single cells in very high light. Therefore, individual cells are very resilient to inhibition by light. This is a prominent characteristic of this P. celeri in all cell lines. Measured oxygen evolution rates were unusually high. One of these lines is able to double in as short as 2.0 h. Doubling times of other cell lines were between 2.4 and 3.5 h. This species is characterized by high pigment content, high absorption cross section, and an antenna size that is very responsive to irradiance becoming very small at high irradiance.

Amorphous Ta2OxNy-enwrapped TiO2 rutile nanorods for enhanced solar photoelectrochemical water splitting

This work demonstrated the 12 fold-enhanced solar water splitting over the type-II core-shell nanostructured TiO2 rutile photoanodes by orienting the charge flow and accelerating the hole transport to water-oxidation sites. Such nanoheterostructured photoanodes were designed rationally and prepared by a facile strategy to enwrapping an amorphous Ta2OxNy layer on surface of TiO2 nanorods grown on the FTO glass substrates, consequently the incident photon-to-current conversion efficiency was increased from 2.2% to 22.6% in a two-electrode system under 390 nm light irradiation. The activity results showed that under AM 1.5 G illumination, the photocurrent output of TiO2@Ta2OxNy photoanodes reached a stable density of 1.32 mA cm−2 at 1.23 V vs RHE, and which is 12 times and ca. 4.3 times than that of the pristine TiO2 and TiO2@Ta2O5 counterparts, respectively. Correspondingly, the oxygen evolution rate was improved from 20.3 to 112.7 mmol m−2 h−1. A solar-to-chemical energy conversion efficiency of ca. 1.49% was achieved at 1.23 V vs RHE.

The impact of elevated atmospheric CO2 on cadmium toxicity in Pyropia haitanensis (Rhodophyta).

Cadmium is one of the major heavy metal pollutions in coastal waters, and it is well known that cadmium at trace concentration is toxic to macroalgae. Change in marine carbonate system and ocean acidification caused by elevated atmospheric CO2 also alter physiological characteristics of macroalgae. However, less research is focused on the combined impacts of elevated CO2 and cadmium pollution on the growth and physiology in macroalgae. In this study, the maricultivated macroalga Pyropia haitanensis (Rhodophyta) was cultured at three levels of Cd2+ (control, 4 and 12mgL-1) and two concentrations of CO2, the ambient CO2 (AC, 410ppm) and elevated CO2 (HC, 1100ppm). The results showed that 12mgL-1 Cd2+ significantly suppressed the relative growth rate and superoxide dismutase activity in AC-grown P. haitanensis, while such inhibition extents by Cd2+ were alleviated in HC-grown algae. Cd2+ had no effects on efficiency of electron transport (α) and maximum electron transport rate (ETRmax), but α was increased by elevated CO2. Cd2+ dramatically suppressed the maximum net photosynthesis oxygen evolution rate (NPRm) and the minimum saturation irradiance (Ik) when the algal thalli were grown at AC, while such suppression of NPRm by Cd2+ was much decreased when the thalli were grown at HC. Collectively, our results suggested that elevated CO2 would alleviate Cd2+ toxicity on P. haitanensis.

Co-overexpression of native phospholipid-biosynthetic genes plsX and plsC enhances lipid production in Synechocystis sp. PCC 6803

The overexpression of native plsX and plsC genes involving in fatty acid/phospholipid synthesis first timely-reported the significantly enhanced lipid contents in Synechocystis sp. PCC 6803. Growth rate, intracellular pigment contents including chlorophyll a and carotenoids, and oxygen evolution rate of all overexpressing (OX) strains were normally similar as wild type. For fatty acid compositions, saturated fatty acid, in particular palmitic acid (16:0) was dominantly increased in OX strains whereas slight increases of unsaturated fatty acids were observed, specifically linoleic acid (18:2) and alpha-linolenic acid (18:3). The plsC/plsX-overexpressing (OX + XC) strain produced high lipid content of about 24.3%w/dcw under normal condition and was further enhanced up to 39.1%w/dcw by acetate induction. This OX + XC engineered strain was capable of decreasing phaA transcript level which related to poly-3-hydroxybutyrate (PHB) synthesis under acetate treatment. Moreover, the expression level of gene transcripts revealed that the plsX- and plsC/plsX-overexpression strains had also increased accA transcript amounts which involved in the irreversible carboxylation of acetyl-CoA to malonyl-CoA. Altogether, these overexpressing strains significantly augmented higher lipid contents when compared to wild type by partly overcoming the limitation of lipid production.

Oxygen vacancies modulated Bi-rich bismuth oxyiodide microspheres with tunable valence band position to boost the photocatalytic activity

How to optimize the photogenerated electron-hole pairs’ separation efficiency and redox performance of defective photocatalysts is still a concern for photocatalysis research. In this study, rich oxygen vacancy was introduced in Bi7O9I3 microsphere (Bi7O9I3-OVR) via a facile ionic liquid assisted solvothemal method to investigate the charge separation and photocatalytic performance. To demonstrate the dominant role of the introduced oxygen vacancy, partial oxygen vacancy in Bi7O9I3 microsphere was repaired by post-calcination treatment (Bi7O9I3-OVL), which was confirmed by electron paramagnetic resonance (EPR). The experimental results indicated the introduction of oxygen vacancy boosted the holes mobility and electrons reduction of Bi7O9I3, then the increased charge carriers’ separation efficiency and high concentration of produced reactive oxygen species was realized. Benefiting from these, the Bi7O9I3-OVR microsphere exhibited a better photocatalytic oxygen evolution performance than Bi7O9I3-OVL, and the oxygen evolution rate was up to 2.66 μmol m−2 h−1.

Cyanobacteria-specific algicidal mechanism of bioinspired naphthoquinone derivative, NQ 2-0

To mitigate cyanobacterial blooms, the naphthoquinone derivative, NQ 2-0, which has selective algicidal activity against cyanobacteria, has been developed. However, due to a lack of information on its algicidal mechanisms, there are significant gaps in our understanding of how this substance is capable of selectively killing cyanobacteria. Here, we investigated the selective algicidal mechanisms of NQ 2-0 using target (Microcystis aeruginosa) and non-target (Cyclotella sp. and Selenastrum capricornutum) species. NQ 2-0 showed selective algicidal activity against only M. aeruginosa, and this activity was strongly light-dependent. This NQ compound has selectively reduced the oxygen evolution rate and photosystem II (PSII) efficiency of M. aeruginosa throughout blocking electron transfer from the photosynthetic electron transport system, and significantly (p ≤ 0.05) increased levels of reactive oxygen species (ROS), resulting in membrane damage through lipid peroxidation. In ultrastructural observations, thylakoid membranes were disintegrated within 12 h after NQ 2-0 treatment, and cytoplasmic vacuolation and disintegrated cellular membrane were observed at 24 h. These findings suggest that increased ROS levels following NQ 2-0 treatment may induce cell death. Interestingly, compared to non-target eukaryotic cells, M. aeruginosa showed relatively late antioxidant response to reduce the increased ROS level, this may enhance algicidal activity against this cyanobacterium.

Enhanced photocatalytic oxygen evolution activity by formation of Ir@IrOx(OH)y core–shell heterostructure

Developing efficient catalysts to accelerate the rate of oxygen evolution reaction (OER) is critical for photocatalytic water-splitting. In this work, metallic Ir, IrOx(OH)y, and core–shell Ir@IrOx(OH)y were synthesized and employed as OER catalysts for photocatalytic water oxidation. It was found that the Ir@IrOx(OH)y core–shell heterostructure catalyst showed the best photocatalytic performance among these three catalysts, with the oxygen evolution rate as high as 59.63 mmol g−1 h−1. Detailed investigations revealed that the excellent photocatalytic activity of Ir@IrOx(OH)y could be attributed to both the outstanding intrinsic activity of IrOx(OH)y shell and the efficient electron transfer between the photosensitizer and catalyst.

Bandgap Engineering of Organic Semiconductors for Highly Efficient Photocatalytic Water Splitting

AbstractThe bandgap engineering of semiconductors, in particular low‐cost organic/polymeric photocatalysts could directly influence their behavior in visible photon harvesting. However, an effective and rational pathway to stepwise change of the bandgap of an organic/polymeric photocatalyst is still very challenging. An efficient strategy is demonstrated to tailor the bandgap from 2.7 eV to 1.9 eV of organic photocatalysts by carefully manipulating the linker/terminal atoms in the chains via innovatively designed polymerization. These polymers work in a stable and efficient manner for both H2 and O2 evolution at ambient conditions (420 nm < λ < 710 nm), exhibiting up to 18 times higher hydrogen evolution rate (HER) than a reference photocatalyst g‐C3N4 and leading to high apparent quantum yields (AQYs) of 8.6%/2.5% at 420/500 nm, respectively. For the oxygen evolution rate (OER), the optimal polymer shows 19 times higher activity compared to g‐C3N4 with excellent AQYs of 4.3%/1.0% at 420/500 nm. Both theoretical modeling and spectroscopic results indicate that such remarkable enhancement is due to the increased light harvesting and improved charge separation. This strategy thus paves a novel avenue to fabricate highly efficient organic/polymeric photocatalysts with precisely tunable operation windows and enhanced charge separation.

Strong coupling effect at the interface of cobalt phosphate-carbon dots boost photocatalytic water splitting

Hydrogen and oxygen produced by water splitting under solar energy are ideal future energy sources. At present, obtaining the efficient, stable and inexpensive photocatalyst for photocatalytic overall water splitting is still a huge challenge. Cobalt phosphate (Co3PO4, CoPi) possesses proper band positions for water splitting. However, the fast recombination of photogenerated electron and hole pairs for CoPi restricts its application. Herein, strongly coupling Co3PO4-carbon dots (CoPi-CDs) composite was constructed as an effective strategy to depress the fast recombination behavior of photogenerated electron and hole pairs. CoPi-CDs show superior photocatalytic water splitting activity than that of single CoPi. When the concentration of CDs in the composite is 0.002 gCDs/gcatalyst, the hydrogen production rate was obtained for approximately 0.592 μmol h−1, as well as the oxygen evolution rate about 0.258 μmol h−1 (with 2:1 stoichiometry), which are both nearly 33 times than that of pristine CoPi. This enhanced photocatalytic activity of CoPi-CDs should ascribe to the efficient coupling effect between CoPi and CDs, which allows fast electron transfer at the interface of CoPi and CDs and thus effectively boosts the photocatalytic water splitting. The strongly coupling nanocomposites should be inspiring for further nanocomposite building for photocatalytic overall water splitting.

Quality of supplementary LED lighting effects on growth and photosynthesis of two different Lactuca recombinant inbred lines (RILs) grown in a tropical greenhouse

LED lamps with various combinations of red (R) and blue (B) wavelengths were used to supplement sunlight for the growth of a heat-resistant (HR) and heat-sensitive (HS) recombinant inbred lines (RIL) of lettuce. The RB-LED ratios were 100R:0B (0B), 92R:8B (8B), 84R:16B (16B), and 76R:24B (24B) with an equal PPFD of 100 μmol m−2 s−1. The greatest leaf expansion rates were observed at 8B for both genotypes. All HR-RILs had similar values of growth parameters and specific leaf area (SLA). However, higher values of growth parameters were observed in HS-RIL with 0B, 8B, and 16B than that under 24B and sunlight. Furthermore, HS-RIL had higher SLA under 0B compared to other conditions. Photosynthetic light-use efficiency and maximal oxygen evolution rate were the lowest under 8B for both genotypes. The quality of LED lighting, if provided, seemed to implicate genotype dependence, probably as a result of their different sensitivities to heat stress.

Characterization of mutants expressing thermostable D1 and D2 polypeptides of photosystem II in the cyanobacterium Synechococcus elongatus PCC 7942

Photosystem II complex embedded in thylakoid membrane performs oxygenic photosynthesis where the reaction center D1/D2 heterodimer accommodates all components of the electron transport chain. To express thermostable D1/D2 heterodimer in a cyanobacterium Synechococcus elongatus PCC 7942, we constructed a series of mutant strains whose psbA1 and psbD1 genes encoding, respectively, the most highly expressed D1 and D2 polypeptides were replaced with those of a thermophilic strain, Thermosynechococcus vulcanus. Because the C-terminal 16 amino acid sequences of D1 polypeptides should be processed prior to maturation but diverge from each other, we also constructed the psbA1ΔC-replaced strain expressing a thermostable D1 polypeptide devoid of the C-terminal extension. The psbA1/psbD1-replaced strain showed decreased growth rate and oxygen evolution rate, suggesting inefficient photosystem II. Immunoblot analyses for thermostable D1, D2 polypeptides revealed that the heterologous D1 protein was absent in thylakoid membrane from any mutant strains with psbA1, psbA1ΔC, and psbA1/psbD1-replacements, whereas the heterologous D2 protein was present in thylakoid membrane as well as purified photosystem II complex from the psbA1/psbD1-replaced strain. In the latter strain, the compensatory expression of psbA3 and psbD2 genes was elevated. These data suggest that heterologous D2 polypeptide could be combined with the host D1 polypeptide to form chimeric D1/D2 heterodimer, whereas heterologous D1 polypeptide even without the C-terminal extension was unable to make complex with the host D2 polypeptide. Since the heterologous D1 could not be detected even in the whole cells of psbA1/psbD1-replaced strain, the rapid degradation of unprocessed or unassembled heterologous D1 was implicated.

Kinetin alleviates chromium toxicity on growth and PS II photochemistry in Nostoc muscorum by regulating antioxidant system

The present study was undertaken to evaluate the metal toxicity alleviating effects of kinetin (KN, 10 nM) on growth, photosynthetic pigments and photochemistry of PS II in the cyanobacterium Nostoc muscorum exposed to chromium (CrVI) stress (100 and 150 µM). Chromium declined growth, photosynthetic pigments (chlorophyll a, phycocyanin and carotenoids), photosynthetic oxygen evolution rate and parameters of fluorescence kinetics (ϕP0, FV/F0, ϕE0, Ψ0 and PIABS except F0/FV) in concentration dependent manner, while stimulating effects on respiration, energy flux parameters (ABS/RC, TR0/RC, ET0/RC and DI0/RC), oxidative stress biomarkers i.e., superoxide radical (SOR), hydrogen peroxide (H2O2) and lipid peroxidation (TBARS contents) and antioxidative enzymes: superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and glutathione-S-transferase (GST), were observed. However, upon addition of KN in the growth medium an alleviating effect against chromium induced toxicity on growth, photosynthetic pigments and photochemistry of PS II was recorded. This had occurred due to substantial reduction in levels of oxidative stress biomarkers: SOR, H2O2 and TBARS contents with concomitant rise in activity of antioxidative enzymes: SOD, POD, CAT and GST and appreciable lowering in the cellular accumulation of chromium. The overall results demonstrate that KN application significantly alleviated chromium induced toxicity on growth performance of the cyanobacterium N. muscorum due to significant improvement in photosynthetic pigments and photochemistry of PS II by up-regulating the activity of antioxidative enzymes, and declining cellular accumulation of chromium. Furthermore, Cr induced toxicity at lower dose (100 µM) was found to be ameliorated more efficiently in N. muscorum following supplementation of KN.