CO2 Supply Research Articles

Rubisco deactivation and chloroplast electron transport rates co-limit photosynthesis above optimal leaf temperature in terrestrial plants

Net photosynthetic CO2 assimilation rate (An) decreases at leaf temperatures above a relatively mild optimum (Topt) in most higher plants. This decline is often attributed to reduced CO2 conductance, increased CO2 loss from photorespiration and respiration, reduced chloroplast electron transport rate (J), or deactivation of Ribulose-1,5-bisphosphate Carboxylase Oxygenase (Rubisco). However, it is unclear which of these factors can best predict species independent declines in An at high temperature. We show that independent of species, and on a global scale, the observed decline in An with rising temperatures can be effectively accounted for by Rubisco deactivation and declines in J. Our finding that An declines with Rubisco deactivation and J supports a coordinated down-regulation of Rubisco and chloroplast electron transport rates to heat stress. We provide a model that, in the absence of CO2 supply limitations, can predict the response of photosynthesis to short-term increases in leaf temperature.

Towards a European supply chain for CO2 capture, utilization, and storage by mineralization: Insights from cost-optimal design

Carbon dioxide (CO2) capture, utilization, and storage (CCUS) by mineralization has been shown to reduce greenhouse gas (GHG) emissions not only in stand-alone plants but also in large-scale climate-optimal supply chains. Yet, implementing the large-scale supply chain for CCUS by mineralization requires a substantial financial investment and, thus, a deep understanding of its economics. The current literature estimates the economics of CO2 mineralization for stand-alone plants. While CO2 mineralization plants have their specific a) CO2 supply, b) solid feedstock supply, c) energy supply, and d) product market, the plant-level cost estimation does not account for a large and potentially shared supply chain. In our study, we assess the economics of mineralization by designing and analyzing cost-optimal supply chains for CCUS by mineralization in Europe. Our results show that the CO2e abatement costs of individual mineralization plants in a supply chain range from 110 to 312 €/ton CO2e avoided. The proposed supply chains for CCUS by mineralization can avoid 60 Mt CO2e/year in Europe at CO2e abatement costs comparable to CO2 capture and geological storage. Furthermore, we identify five locations that could offer a robust business case for CO2 mineralization. The analysis thus shows pathways on how to add CO2 mineralization to the GHG mitigation portfolio of Europe.

Interacting Effects of CO2, Temperature, and Nitrogen Supply on Photosynthetic, Root Growth, and Nitrogen Allocation of Strawberry at the Fruiting Stage

To efficiently improve the productivity of strawberries under growing environmental change, the photosynthesis, root growth, and nitrogen allocation of strawberries (Fragaria × ananassa Duch. cv. Toyonoka) were investigated in a factorial design of CO2, temperature, and nitrogen supply. Elevated CO2 decreased the maximum CO2 assimilation rate (Amax), maximum CO2 carboxylation capacity per unit leaf area (Vcmax), and maximum CO2 carboxylation capacity per unit leaf mass (Vcm-m) by 20%, 24%, and 44%, respectively. Meanwhile, it reduced the SPAD value, maximal fluorescence level in the dark-adapted state (Fm), and maximal photochemical efficiency of PSII (Fv/Fm). Moreover, root branches, root number, root dry weight, and nitrogen-use efficiency were further increased in response to elevated CO2 under low nitrogen. When elevated CO2 was applied together with nitrogen nutrients, the Vcm-m and root nitrogen concentration (RNC) declined by 32% and 12%, respectively, but the total root dry weight (TRDW) increased by 88%. If the nitrogen nutrient was individually applied, the TRDW decreased by 16%, while the RNC increased by 21%. When the high temperature was individually applied, the TRDW increased by 104%, but the RNC decreased by 5%. Overall, elevated CO2 exacerbated photosynthetic down-regulation and significantly affected nitrogen redistribution among strawberry organs, reducing leaf nitrogen concentration and accelerating leaf senescence. However, it could increase seed quantity and improve its quality as well. In other words, under nitrogen-deficient conditions, elevated CO2 could improve the survival of offspring via the cost of the mother plant’s growth capacity.

Re-purposing onshore and offshore infrastructure for CCUS in Gippsland

With the race to decarbonise in full swing how do carbon capture utilisation and storage (CCUS) projects get a head start? This paper explores the journey the Gippsland Basin Joint Venture has gone through to identify and exploit the advantages that its existing infrastructure presents in order to progress world-class CCUS opportunities. Drawing on examples across the full CO2 supply chain it details how re-use of existing infrastructures can achieve positive results in terms of cost, schedule and the environment. Hydrocarbon production from the Bream Field ceased in 2020. Normally this would put the platform and associated infrastructure on the path to decommissioning and removal. Instead Bream will continue to have a bright future storing CO2 supplied via a re-used gas export pipeline. Technical evaluations have considered how to safely handle CO2, what parts of the asset could be re-used, what new kit is required and what should be decommissioned. Powered by a hybrid renewables system the new-look injection platform will be remotely operated storing up to 2 MTA. At the Longford Gas Plant the focus has been how to efficiently capture CO2 in order to meet the requirements of multiple purification plants and the Bream sequestration project. Plant trials and testing have determined how to optimise gas processing for integrated CCUS operations. Opportunities to leverage existing power, utilities and process equipment have been included in design through careful brownfield assessment. Supporting this is a cross-functional team rapidly enhancing their hydrocarbon toolkit with the opportunities that CCUS integration presents.

Combined effect of elevated CO2 and Fe deficiency on common bean metabolism and mineral profile

Abstract Aims Elevated atmospheric CO2 (eCO2) and restricted iron (Fe) supply are known to impact plant growth and nutritional quality of food crops. However, studies aimed at understanding how eCO2 will interact with Fe deficiency are scarce. Changes in the nutritional status of the common bean (Phaseolus vulgaris L.) may significantly impact the nutritional status of populations that rely heavily on this crop. Methods To understand the combined effects of eCO2 and Fe deficiency on mechanisms relevant to plant nutrient uptake and accumulation, common bean plants were grown under Fe sufficiency (Fe+, 20 mM Fe-EDDHA) and Fe deficiency (Fe-, 0 mM Fe-EDDHA) combined with eCO2 (800 ppm) or ambient CO2 (aCO2, 400 ppm) in hydroponics until maturity. Results Elevated CO2, besides stimulating photosynthesis and stomatal closure, highly affected plant Fe metabolism: stimulated root ferric chelate reductase (FCR) activity by 6-fold and downregulated the expression of root FRO1 and IRT1 expressions by about 4-fold. In leaves, citrate and oxalate increased, but ferritin expression decreased by 9-fold. Such changes may have determined the differences on mineral accumulation patterns particularly the lower levels of Fe in roots (62%), leaves (38%) and seeds (50%). The combination of Fe deficiency and eCO2 doubled the effect of a single factor on FCR up-regulation, balanced the internal pH of Fe deficient plants, and resulted in the lowest Fe accumulation in all plant parts. Conclusions These results suggest that eCO2 directly affects the Fe uptake mechanism of common bean plants, decreasing plant Fe content.

Implementation of particle swarm optimization strategy in Venlo‐type greenhouse climate to make energy‐efficient process

AbstractThis study appears to be the first to use a MATLAB simulator to illustrate Particle Swarm Optimization with multiple input–output restrictions. This proposed study's overarching objective was to make the entire process energy efficient, which provides improved performance with high accuracy and minimizes the operating cost by incorporating energy, ventilation, and CO2. Further, to reduce the complexity of the system, the optimization technique was divided into control and controlled variables. Meanwhile, to define state constraints for variables used in the objective function was to make the overall process cost‐effective, composing energy, CO2 supply, and ventilation cost. The chosen technique effectively decreased operating costs while maintaining the appropriate ranges for temperature (14–26°C), relative humidity (0–90%), and CO2 concentration (400–2000 ppm), according to simulation results. Off‐peak, standard, and peak energy cost levels were R1080.26, R748.56, and R7078.4, respectively. On the other hand, it was found through comparative analysis that the standard and off‐peak energy consumption figures decreased by 65.4 and 8.1%, respectively, as compared to the peak tariff (2279.9 kWh). The suggested PSO technique is implied to be a viable means of increasing greenhouse energy efficiency and achieving sustainable, cleaner manufacturing.

Bio-Succinic Acid Production from Palm Oil Mill Effluent Using Enterococcus gallinarum with Sequential Purification of Biogas

Bio-succinic acid production using microorganisms has been interesting as an environmentally friendly process. Palm oil mill effluent (POME) was considered as a cheap substrate to lower the cost of production. It was revealed that 2-fold diluted POME produced more succinic acid than undiluted and 5-fold diluted POME. In addition, the effects of various neutralizing agents on succinic acid production utilized to manage pH and CO2 supply indicated that the utilization of MgCO3 as a neutralizing agent produced succinic acid of 11.5 g/L with a small amount of by-product synthesis. Plackett–Burman Design (PBD) was used to screen the most significant nutrients for bio-succinic acid production from 2-fold diluted POME using E. gallinarum. From the Pareto chart, MgCO3 and peptone presented the highest positive effect on the production of succinic acid. In addition, Box–Behnken Design (BBD) was conducted to increase bio-succinic acid production. Experiments showed the highest production of succinic acid of 23.7 g/L with the addition of 22.5 g/L MgCO3 and 12.0 g/L peptone in 2-fold diluted POME. Moreover, the experiment of replacing MgCO3 with CO2 from biogas resulted in 19.1 g/L of succinic acid, simultaneously creating the high purity of biogas and a higher CH4 content.

The effect of increasing temperature and pCO2 on experimental pelagic freshwater communities

AbstractAs the global climate is changing, average water temperatures and the supply of CO2 to water bodies are increasing. To determine how the effects of these changes on freshwater communities interact, we ran a month‐long factorial mesocosm experiment, in which we manipulated water temperature (heated, ambient) and pCO2 (preindustrial, ambient, future). We found that the total phytoplankton biomass responded positively to the pCO2 and temperature treatments but no interactive effects were detected. Green algae were positively affected by temperature and, over the course of the experiment, responded to pCO2 first positively, then negatively. Heterokonts, on the other hand, were unaffected by temperature but responded positively to pCO2. pCO2 enrichment also led to increases in seston C : N stoichiometry, although the experiment ended before we could observe any effects of pCO2 on the zooplankton community composition. Warming caused shifts in zooplankton community composition, primarily through higher abundances of the cladoceran Bosmina longirostris and the rotifer Conochilus unicornis, and lower abundances of the rotifer Polyarthra vulgaris. We found that, in contrast to the effects of temperature, which can be explained by temperature‐dependent plankton growth curves, the responses of algal groups to pCO2 enrichment were difficult to anticipate, despite the availability of priors from previous pCO2 enrichment experiments in the same lake mesocosms. We conclude that climate change‐induced increases in aquatic pCO2 and temperatures are likely to affect pelagic ecosystems, though further research in freshwater systems is needed before generalized claims regarding the simple and interactive effects of pCO2 can be made.

Carbon emissions of prefabricated steel structure components: A case study in China

China has been vigorously promoting the use of prefabricated steel structure buildings (PSSBs)1 in recent years. However, owing to the deficit in carbon emission (CE) research and the lack of basic CE parameters for PSSB components (PSCs), it is not feasible to conduct reliable CE calculations or develop scientific strategies for CE reduction. Based on the actual situation in China, this study investigated the CE of upstream raw steel sheet production (CEA1-A3), measured the CEs of PSC prefabrication (CEA3+), and obtained a carbon emission factor (CEF) for PSCs in the “cradle-to-gate” stage. The CEF of PSCs was found to be 2175.7 kgCO2e/t; CEA1-A3 contributed 1959 kgCO2e/t (90.0%), while CEA3+ contributed 216.7 kgCO2e/t (10.0%). Previous studies focused almost exclusively on CEA1-A3, whereas this study systematically investigated the direct, indirect, and embodied CEs for the A3+ stage of PSCs. The sources of CEA3+ were quantified; this showed that the CEs for energy and material consumption accounted for 59.6% and 40.4%, respectively. Compared with CEA1-A3, the CE types of CEA3+ were more diverse, with indirect CE (52.4%) > embodied CE (38.4%) > direct CE (9.2%). For this reason, CE calculation methods suitable for these characteristics were discussed, mainly based on consumption–production (CP) and process analysis (PA). In the CO2 gas-shielded welding test, it was found that the CO2 shielding gas decomposed in large quantities during the welding process, and the degree of decomposition was positively correlated with the welding power; the CP method regarded the CO2 supply as the direct CE and overestimated the CEA3+. In this study, the CE parameters of the main prefabrication processes were measured and the corresponding empirical formulas were fitted, which made the PA-based CE calculations feasible. Finally, the temporal and spatial ranges of the results were clarified, and the CEF trends for PSCs were predicted according to the expected CEs for crude steel and power grids in China. The results show that the scrap proportion in the production of raw steel sheets has a major impact on the CEFs of PSCs, whereas low-carbon electricity offers considerable CE reduction potential for PSC prefabrication.

Metabolic flexibility during a trophic transition reveals the phenotypic plasticity of greater duckweed (Spirodela polyrhiza 7498).

The greater duckweed (Spirodela polyrhiza 7498) exhibits trophic diversity (photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic growth) depending on the availability of exogenous organic carbon sources and light. Here, we show that the ability to transition between various trophic growth conditions is an advantageous trait, providing great phenotypic plasticity and metabolic flexibility in S. polyrhiza 7498. By comparing S. polyrhiza 7498 growth characteristics, metabolic acclimation, and cellular ultrastructure across these trophic modes, we show that mixotrophy decreases photosynthetic performance and relieves the CO2 limitation of photosynthesis by enhancing the CO2 supply through the active respiration pathway. Proteomic and metabolomic analyses corroborated that S. polyrhiza 7498 increases its intracellular CO2 and decreases reactive oxygen species under mixotrophic and heterotrophic conditions, which substantially suppressed the wasteful photorespiration and oxidative-damage pathways. As a consequence, mixotrophy resulted in a higher biomass yield than the sum of photoautotrophy and heterotrophy. Our work provides a basis for using trophic transitions in S. polyrhiza 7498 for the enhanced accumulation of value-added products.

OsαCA1 Affects Photosynthesis, Yield Potential, and Water Use Efficiency in Rice.

Plant growth and crop yield are essentially determined by photosynthesis when considering carbon dioxide (CO2) availability. CO2 diffusion inside a leaf is one of the factors that dictate the CO2 concentrations in chloroplasts. Carbonic anhydrases (CAs) are zinc-containing enzymes that interconvert CO2 and bicarbonate ions (HCO3-), which, consequently, affect CO2 diffusion and thus play a fundamental role in all photosynthetic organisms. Recently, the great progress in the research in this field has immensely contributed to our understanding of the function of the β-type CAs; however, the analysis of α-type CAs in plants is still in its infancy. In this study, we identified and characterized the OsαCA1 gene in rice via the analysis of OsαCAs expression in flag leaves and the subcellular localization of its encoding protein. OsαCA1 encodes an α-type CA, whose protein is located in chloroplasts with a high abundance in photosynthetic tissues, including flag leaves, mature leaves, and panicles. OsαCA1 deficiency caused a significant reduction in assimilation rate, biomass accumulation, and grain yield. The growth and photosynthetic defects of the OsαCA1 mutant were attributable to the restricted CO2 supply at the chloroplast carboxylation sites, which could be partially rescued by the application of an elevated concentration of CO2 but not that of HCO3-. Furthermore, we have provided evidence that OsαCA1 positively regulates water use efficiency (WUE) in rice. In summary, our results reveal that the function of OsαCA1 is integral to rice photosynthesis and yield potential, underscoring the importance of α-type CAs in determining plant physiology and crop yield and providing genetic resources and new ideas for breeding high-yielding rice varieties.

Variation of coal quantity accumulated in the Mississippian to Pennsylvanian coal seams (Upper Silesia and Lublin Coal basins, Poland): a reflection of changes in climate and CO2 availability

Many coal seams of varied thickness and aerial extent occur in the Upper Silesia and Lublin basins within Mississippian and Pennsylvanian coal-bearing deposits. Well-documented data on coal quantity in the seams identified allows visualization of their variation within the stratigraphic succession and analysis of the time-dependent coal accumulation process. Some characteristic features of this variation were observed. Coal seams of the Mississippian age (Serpukhovian, Paralic Series), formed within a near-shore environment, most often constitute small resources. There were only two intervals of increased coal accumulation in seams of >100 million tons, in the lower and uppermost parts of the Paralic Series. Within the Pennsylvanian coal-bearing succession of terrestrial fluvio-lacustrine origin, a specific, wave-like pattern of seam resource variations and four intervals of increased coal accumulation are observed. In the Lublin Coal Basin, the Lublin Beds only, deposited during the Late Bashkirian, are coal-bearing, in which a bell-shaped pattern of seam resource variation in the stratigraphic succession is observed. The location of enhanced coal accumulation events in the stratigraphic succession suggests their repetition at ~1–4 My intervals. The characteristic features of the quantitative variation in these coal seams may be correlated with glacial-interglacial and climate humidity changes, and interpreted as a response to variable volcanogenic CO2 supply.

Combination of non-sterilized wastewater purification and high-level CO2 bio-capture with substantial biomass yield of an indigenous Chlorella strain

The indigenous microalga Chlorella sorokiniana NBU-3 grown under air, 5 %, 15 %, and 25 % CO2 supply was evaluated to determine its potential for flue gas bio-capture, nutrient removal capacity and biomass yield using non-sterilized wastewater as growth medium. The results indicated that C. sorokiniana NBU-3 exhibited high nutrient removal efficiency (>95 % for NH4+-N, TN and TP) with either air or CO2 aeration. 5 %–15 % CO2 supplies promote biomass yield, nutrient utilization and CO2 biofixation of C. sorokiniana NBU-3. In particular, 15 % CO2 promotes C. sorokiniana NBU-3 growth in non-sterilized MW, but inhibits its growth in BG11 medium, indicating the importance of non-sterilized MW and high CO2 aeration concurrence for C. sorokiniana NBU-3 economically practical cultivation. Moreover, the highest values of lipid (27.84 ± 2.12 %) and protein (32.65 ± 4.11 %) contents were obtained in MW with 15 % CO2 aeration. Conceivably, microalgal-bacterial symbiosis may help C. sorokiniana NBU-3 tolerate high concentration of CO2 and promote microalga growth. The succession of the community diversity toward the specific functional bacterial species such as Methylobacillus and Methylophilus (Proteobacteria) which were predicted to possess the function of methylotroph, methanol oxidation and ureolysis would help facilitate the microalgal-bacterial symbiosis and promote the microalgae biomass accumulation with high dosage of CO2 aeration. Overall, these findings clearly highlight the potential of this indigenous microalga C. sorokiniana NBU-3 for industrial-emission level CO2 mitigation and commercial microalga biomass production in MW.

Sustainable Use of CO2 and Wastewater from Mushroom Farm for Chlorella vulgaris Cultivation: Experimental and Kinetic Studies on Algal Growth and Pollutant Removal

The potential use of carbon dioxide (CO2) and wastewater released from a mushroom farm for the cultivation of Chlorella vulgaris microalga was investigated in this study. For this purpose, a microcontroller-based aided CO2 capture and mixing prototype was constructed for the cultivation of C. vulgaris under varying concentrations of mushroom farm wastewater (0 as control, 50 and 100%). The results showed that the constructed prototype was helpful to maintain desirable CO2 levels (6000 ppm) in the mushroom cultivation chamber with constant CO2 supply to algal culture, i.e., 0.6% at an airflow rate of 50 mL/min. After 16 days of algal cultivation, it was observed that the maximum significant (p < 0.05) algal biomass production of 2.550 ± 0.073 mg/L was recorded in 50% wastewater concentration followed by 100% and control. Also, the maximum removal of selected mushroom farm wastewater pollutants, such as total dissolved solids (84.00 ± 1.37%), biochemical oxygen demand (90.17 ± 2.42%), chemical oxygen demand (91.53 ± 0.97%), total nitrogen (86.27 ± 1.60%) and total phosphorus (94.19 ± 2.33%), was achieved in 50% concentration of wastewater treatment with maximum first-order rate constant (k) values. In addition, the algal growth kinetics results showed that the logistic model fit best compared to the modified Gompertz model, based on selected validation tools, such as experimental vs. predicted values, coefficient of determination (R2 > 0.9938), model efficiency (ME > 0.98) and root mean square error (RMSE < 0.03). The post-harvest characterization of algal biomass revealed that the proximate, biochemical, ultimate elements (carbon, oxygen and nitrogen) and structural properties were significantly higher in 50% treatment than those in 100% and control treatments. Therefore, the findings of this study are novel and provide significant insight into the synergistic use of CO2 and wastewater produced by mushroom farms for algal cultivation and biological wastewater treatment.

Optimal Design of Hybrid Renewable Systems, Including Grid, PV, Bio Generator, Diesel Generator, and Battery

Renewable energies are the best solutions to reduce CO2 emissions and supply reliable electricity. This study aims to find the best combination of various components considering economic, environmental, and technical factors together. The most important consideration factors are the limitation of using PV panels due to the land constraints and applying CO2 penalties where diesel generators and the grid are generating electricity. Findings show that providing electricity by hybrid systems would be useful even in the well-provided electricity regions by the grid with the least blackouts. The best combination of the proposed components, including PV, bio generator, diesel generator, batteries, and grid for the case study region where the load demand is 890 kWh/day and peak load is 167.2 kW, would be an off-grid hybrid system including PV, bio generator, diesel generator, and battery. The optimization results show an NPC (present value of the costs of investment and operation of a system over its lifetime) of $1.02 million and a COE (the average cost per capital of useful electricity produced by the system) of 0.188 $/kWh. Finally, due to the showing of the effect of different conditions on the optimization results and making the study usable for other circumstances of the case study region, some sensitivity analyses have been carried out.

Effects of concentration and frequency of CO2 supply on productivity of marine microalga Isochrysis galbana

Demand for the high fucoxanthin and docosahexaenoic acid (DHA) content found in the marine microalga Isochrysis galbana is rising annually, and it is essential to devise large-scale cultivation systems that are low in energy and cost. Continuous CO2 supply occupies a considerable portion of total electricity consumption for microalgae cultivation. While an intermittent, high-concentration CO2 supply/agitation has the potential to reduce the electricity consumption required for aeration, it may cause carbon starvation and sedimentation of cells when the supply frequency is insufficient. This study investigated the effects of concentration and frequency of CO2 supply on productivity of I. galbana. Semi-continuous cultivation was conducted under different conditions of CO2 supply (0.04 (air) to 10 % concentration and continuous or intermittent (1 min every 9 min) supply). Under continuous air supply (control), biomass productivity reached 0.18 g L−1 day−1. A continuous supply of CO2 at 5 % showed the highest biomass productivity (0.33 g L−1 day−1). Productivity was only 0.12 g L−1 day−1 with a continuous CO2 supply at 10 % concentration. It was confirmed that growth was suppressed under conditions of a continuous supply of CO2 at high concentrations. The study found that intermittent CO2 concentrations of 5 % and 10 % showed productivity of 0.29 and 0.24 g L−1 day−1, respectively. These productivities were higher than that in the control. Under conditions of continuous CO2 supply, 0.61 mg/g dry weight (DW) of a higher fucoxanthin content was achieved with air supply than was found at concentrations of 5 % and 10 % (0.18 and 0.11 mg/g DW, respectively). However, under intermittent supply conditions, the fucoxanthin reached the higher content of 0.56 mg/g DW under 5% supply. Under conditions of high CO2 concentrations, continuous supply inhibited the accumulation of fucoxanthin, while an intermittent supply promoted its accumulation.

CO2 sequestration and biodiesel production from Volvox aureus a newly isolated green microalgal species from industrial wastewater

Recently, large-scale biofuel production is mainly dependent on third-generation feedstock, especially microalgae. Since most microalgae can sequester carbon dioxide and utilize it for the enhancement of their growth parameter. In the present study, CO2 sequestration and Biodiesel production from Volvox aureus a newly isolated green microalgal species from industrial wastewater. Volvox aureus was isolated from the wastewater sample collected from the sewage treatment plant. The isolated V.aureus was grown in the BBM culture containing excess nutrients along with Artificial CO2 supply to the bioreactor. The addition of an external carbon dioxide source enhanced the total lipid content by up to 27.95%. Further, the lipid was extracted using soxhlet extraction from the isolated microalgal biomass. The extracted lipid was converted into biodiesel using a base catalyst potassium hydroxide. The produced biodiesel was analyzed to test their fuel properties and compared with the diesel standard. This study approach investigated the potential of a future possible environmental pollution reduction and significant potential for a viable biofuel production from microalgae.

Effects of RuBisCO and CO2 concentration on cyanobacterial growth and carbon isotope fractionation.

Carbon isotope biosignatures preserved in the Precambrian geologic record are primarily interpreted to reflect ancient cyanobacterial carbon fixation catalyzed by Form I RuBisCO enzymes. The average range of isotopic biosignatures generally follows that produced by extant cyanobacteria. However, this observation is difficult to reconcile with several environmental (e.g., temperature, pH, and CO2 concentrations), molecular, and physiological factors that likely would have differed during the Precambrian and can produce fractionation variability in contemporary organisms that meets or exceeds that observed in the geologic record. To test a specific range of genetic and environmental factors that may impact ancient carbon isotope biosignatures, we engineered a mutant strain of the model cyanobacterium Synechococcus elongatus PCC 7942 that overexpresses RuBisCO across varying atmospheric CO2 concentrations. We hypothesized that changes in RuBisCO expression would impact the net rates of intracellular CO2 fixation versus CO2 supply, and thus whole-cell carbon isotope discrimination. In particular, we investigated the impacts of RuBisCO overexpression under changing CO2 concentrations on both carbon isotope biosignatures and cyanobacterial physiology, including cell growth and oxygen evolution rates. We found that an increased pool of active RuBisCO does not significantly affect the 13 C/12 C isotopic discrimination (εp ) at all tested CO2 concentrations, yielding εp of ≈ 23‰ for both wild-type and mutant strains at elevated CO2 . We therefore suggest that expected variation in cyanobacterial RuBisCO expression patterns should not confound carbon isotope biosignature interpretation. A deeper understanding of environmental, evolutionary, and intracellular factors that impact cyanobacterial physiology and isotope discrimination is crucial for reconciling microbially driven carbon biosignatures with those preserved in the geologic record.

Toward a Stackable CO2-to-CO Electrolyzer Cell Design─Impact of Media Flow Optimization

Aqueous CO2-to-CO electrolysis is a promising technology for closing the carbon cycle and defossilizing industrial processes. Considering the technological readiness, consensus has been achieved about using silver as a stable and selective electrocatalyst for the CO2-to-CO reduction reaction in aqueous electrolyte. On the other hand, challenges such as media flow management, component stability, and force distribution are still associated with improving the process performance and developing a stackable cell concept to meet industrially relevant levels. We therefore report on a promising stack concept with continuous flowcells operated with gas diffusion electrodes (GDEs). To enhance the CO2-to-CO conversion efficiency, dedicated media flow chambers were developed on two levels. In the gas chamber, which touches the GDE from the far side of the anode, the feed gas flow and distribution over the GDE were controlled by introducing various gas path architectures in a modular flowcell. In addition, an ionically conductive spacer was implemented in the catholyte chamber, which is adjacent to the opposite side of the GDE. The effect of these modifications on the cell voltage, selectivity, and overall conversion was investigated at 100 mA/cm2 with varying CO2 feed gas flow and concentration. Noteworthy, an optimized feed gas distribution generated an increase of the Faraday efficiency for CO under reduced CO2 supply. Furthermore, the implementation of the spacer enhanced the process stability by suppressing gas-bubble-induced noise in the cell voltage measurements. By functioning as support structures to the GDE, the combined modifications provided the cell with mechanical integrity and allowed an ionic and electric contact over the full active cell area, which is required for both stacking and upscaling of the cell. The corresponding performance was demonstrated by a two-cell short-stack.

Research Progress in Cathode Catalysts for Li-CO2 Batteries

The need for environmentally friendly and effective energy storage technologies is growing urgently in response to the rising energy demand and the seriousness of the environmental issues, in order to meet the Double Carbon objective. Li-CO2 batteries are a newer battery technology that has drawn a lot of interest. Its distinctiveness comes from the utilization of CO2 as a key component in energy storage, which can efficiently transform CO2 supplies into energy preservation and potentially be sustainable and environmentally friendly. This article examines the Li-CO2 battery's internal working mechanisms, delves into the selection and development of positive electrode catalysts, and contrasts several materials to list their benefits and drawbacks. Carbon-based materials, precious metals, and their compounds, and transition metals and their complexes are the main areas of emphasis. Carbon materials' exceptional conductivity, enormous specific surface area, and high commercial viability are underlined. The performances of precious metals and transition metals paired with carbon materials are compared in detail. Finally, suggestions for further research into potential cathode catalytic materials for Li-CO2 batteries are provided based on the effectiveness and practical utility of various materials. In an attempt to combat global warming and environmental pollution, new methods for converting waste gases, such as carbon dioxide, into energy will be developed thanks to research on Li-CO2 batteries. The features of this battery technology, such as its high density of energy and lengthy cycle life, are projected to make it more practical to store and use renewable energy.