CO2 Partial Pressure Research Articles

CO2 fluxes at the water-atmosphere interface in fluvial environments: an overview of studies in Brazilian rivers

Recent advances in Brazilian scientific production on CO2 fluxes at the water-atmosphere interface in rivers were reviewed, including estimates of CO2 partial pressure and fluxes. A total of 17 studies were reviewed. We compiled information regarding the location studied, the methodology used by each author, and the values of CO2 partial pressure (pCO2), CO2 fluxes (FCO2), and gas exchange coefficient (k) found in each region. The results were spatialized and synthesized. The important role of fluxes in CO2 degassing and their influence on climate change, as well as the global lack of data on these environments, were the main motivations for this study. The information was scarce, and most studies are focused on the Amazon Basin. However, high-resolution mapping of CO2 fluxes, at the scale of micro basins and streams, proved to be scarce. We emphasize, therefore, the importance of further studies in the country including other hydrographic regions, and in high resolution. These studies would add to our knowledge of how natural and anthropic processes influence CO2 flux, in addition to providing better estimates in tropical river systems.
 Keywords: climate change, CO2 emission, CO2 partial pressure.

High-pressure fermentation of CO2 and H2 by a modified Acetobacterium woodii

Global warming due to the increased atmospheric carbon dioxide concentration is the driving force for developing strategies that exploit CO2 as raw material to produce interesting compounds for industry. According to this approach, Acetobacterium woodii was modified to convert CO2 and H2 into acetone. Gas fermentation was performed at high pressure to debottleneck the issue of the low availability of gaseous substrates in the liquid medium. This work aimed to investigate the catalytic performance of a modified A. woodii strain for acetone synthesis at 10 bar providing an H2-CO2 blend. First, tests were performed to assess the ability of the biocatalyst to survive heterotrophically at high pressure. Moreover, a reference test was set up in autotrophy at atmospheric pressure to confirm that it produced both acetate and acetone. Feeding the strain at 10 bar with the H2-CO2 mix resulted in growth inhibition and formic acid production. This outcome suggested a metabolism impairment due to bicarbonate build-up in the reactor at high CO2 partial pressure. Thus, bacteria were grown at atmospheric pressure in a medium with an augmented exogenous salt concentration. Results confirmed that formic acid production and growth inhibition could be due to HCO3–. Furthermore, the modified A. woodii grown at atmospheric pressure in a sterile medium pressurized before inoculation showed the same outcomes. Finally, tests at 10 bar lowering the CO2 partial pressure indicated that this gas was responsible for formic acid production but was not the only inhibitory factor for autotrophic cell growth at high pressure.

Investigation of the acicular aragonite growth behavior in AOD stainless steel slag during slurry-phase carbonation

This study presents a novel method for producing acicular aragonite using argon oxygen decarburization (AOD) slag while controlling the reaction temperature, reaction time, stirring speed, and the magnesium-to‑calcium stoichiometric ratio. This approach provides steel plants with an opportunity to decrease their CO2 emissions and promote efficient resource utilization and CO2 storage through the production of high-quality value-added products. The experimental results showed that reaction temperature was the most significant factor affecting the carbonation efficiency of AOD slag, followed by reaction time, stirring speed, CO2 partial pressure, and the liquid-to-solid ratio (L/S). The study also found that elevated temperature and prolonged reaction duration favored the preferential precipitation of aragonite. Additionally, raising the temperature and the magnesium-to‑calcium stoichiometric ratio was shown to enhance the formation of aragonite, affecting its crystal growth orientation and dimensions. The optimal combination of reaction parameters for the preparation of acicular aragonite was found to be the reaction time of 8 h, the magnesium-to‑calcium stoichiometric ratio of 0.8, the reaction temperature of 120 °C, and the stirring speed of 200 r·min−1. Under these conditions, the resulting acicular aragonite exhibited excellent overall uniformity, a large aspect ratio, and a smooth crystal surface, with a content of 91.49 %, a single crystal length ranging from 9.86 to 32.6 μm, and a diameter ranging from 0.63 to 2.15 μm. This study provides valuable insights into the efficient production of acicular aragonite from steel slag while reducing CO2 emissions and promoting the sustainable use of resources.

CO2 absorption kinetics and equilibrium solubility measurements in potassium salts of renewable amino acids from plant‐ and animal‐protein

AbstractAqueous solutions containing alkaline salts of natural amino acids, such as those from protein in plant seeds or high protein animal‐based waste, are green CO2‐separation solvents. In the present work, potassium salts of nine such amino acids were chosen for an in‐depth study: alanine, arginine, aspartic acid, glutamic acid, glycine, leucine, proline, serine, and valine. The kinetics of CO2 absorption in aqueous solutions of these salts was studied using a stirred cell. From the measurements of the absorption rate at different salt concentrations (molarity 0.1 and higher), CO2 partial pressures (5–25 kPa), and temperatures (298–308 K), values of the reaction order, rate constant, and activation energy were determined. Additionally, the liquid‐side mass transfer coefficient (0.005 cm/s) was also found. Potassium salts of proline, glycine, and arginine were most reactive and, hence, were chosen for equilibrium study. The loading capacity of these salts was measured at 308 K in a vapour–liquid equilibrium setup at near‐ambient pressure. On the contrary, the other chosen acids were comparatively less reactive with CO2.

Impacts of Basal Melting of the Totten Ice Shelf and Biological Productivity on Marine Biogeochemical Components in Sabrina Coast, East Antarctica

AbstractTo clarify the impacts of basal melting of the Antarctic ice sheet and biological productivity on biogeochemical processes in Antarctic coastal waters, concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), inorganic nutrients, chlorophyll a, and stable oxygen isotopic ratios (δ18O) were measured from the offshore slope to the ice front of the Totten Ice Shelf (TIS) during the spring/summer of 2018, 2019, and 2020. Modified Circumpolar Deep Water (mCDW) intruded onto the continental shelf off the TIS and flowed along bathymetric troughs into the TIS cavity, where it formed a buoyant mixture with glacial meltwater from the ice shelf base. Physical oceanographic processes mostly determined the distributions of DIC, TA, and nutrient concentrations. However, photosynthesis and dilution by meltwater from sea ice and the ice shelf base decreased DIC, TA, and nutrient concentrations in surface water near the ice front. These causes also reduced the partial pressure of CO2 (pCO2) in surface water by more than 100 μatm with respect to mCDW in austral summer of 2018 and 2020, and the surface water became a strong CO2 sink for the atmosphere. Phytoplankton photosynthesis changed DIC and TA in a molar ratio of 106:16. Thus, pCO2 decreased mostly as a result of photosynthesis while dilution by glacial and sea ice meltwater had a small effect. The nutrient consumption ratio suggested that photosynthesis was stimulated by iron in the water column, supplied to the surface layer via buoyancy‐driven upwelling and basal ice shelf meltwater in addition to sea ice meltwater.

Electrochemical condition optimization and techno-economic analysis on the direct CO2 electroreduction of flue gas

Direct CO2 electroreduction of flue gas is a technology that simplifies CO2 capture and purification process and directly utilizes CO2 in flue gas. Low CO2 reduction reaction selectivity caused by the low CO2 partial pressure and side reactions competition is the challenge. In this study, a direct CO2 electroreduction system for multicomponent flue gases was established. A two-dimensional steady model was developed by considering major electrode reactions of flue gas in CuxO-based catalysts. General influence criteria and optimum operation window for the potential, temperature, and pressure were proposed. In addition, a techno-economic analysis of the flue gas electrolysis system was conducted. The results demonstrated that the CO2 electroreduction reaction performances are weak at atmospheric pressure owing to the side reaction competition and small reactant concentration. A method involving pressurization and catholyte inlet temperature declination is proposed to break the stalemate of tiny reactant concentrations and ensure the dominance of the CO2 electroreduction reaction. The selectivity and current density of the CO2 reduction reaction were 71% and − 148 mA/cm2 at −1.17 V vs. reversible hydrogen electrode potential (RHE), respectively, under the conditions of an inlet electrolyte temperature of 273 K and an operating pressure of 20 atm. C1 products with excellent yields are the dominant products. Furthermore, the techno-economic analysis showed that the flue gas electrolysis system has higher profitability and lower cost than the purified CO2 electrolysis system. The present results can be used to optimize the electrolyzer operating parameters and construct CO2 reduction systems.

Comparative analysis of artificial neural network (ANN) models: CO2 loading in MDEA and blended MDEA/PZ solvents

CO2 loading plays a vital role in gauging a solvent's capability to absorb CO2 from combustion gases and natural gas flow. Yet, the customary approaches for measuring CO2 loading hinge on laborious and costly laboratory experiments. Therefore, researchers employed artificial neural network (ANN) approaches to estimate CO2 loading using various datasets, although case-specific methods and approaches restricted their attempts. This study employed two datasets with 303 (CO2 absorption via MDEA) and 361 (CO2 absorption via MDEA/PZ) acceptable experimental data to create ANN models to estimate CO2 loading in aqueous amine solvents. The CO2 loading is evaluated using a wide range of input parameters, including temperature, CO2 partial pressure, Methyldiethanolamine (MDEA) solvent, and Piperazine (PZ) solvent for cases A and B, respectively. Twelve distinct training algorithms, four distinct activation functions, and three hidden layers with neuron variations created the models. ANN models trained with a blend of PZ and MDEA solvents generated more accurate predictions compared to models trained with solely MDEA solvent. The sigmoidal activation functions (Tansig and Logsig) generated more precise predictions than the linear activation functions (Poslin and Purelin). In addition, “Levenberg-Marquardt (lm)” with the highest coefficient of determination (R2) was selected as the best training algorithm among the twelve training functions. The best average coefficients of determination were determined to be 0.964 for the tansig activation function with [25 18 10] number of neurons in case A and 0.967 for the logsig activation function with [30 20 12] number of neurons in case B. The statistical analysis (R2, MSE, RMSE, AAD, AARD, and run time) confirmed that the network provided accurate estimates of CO2 loading for both datasets. The prediction potential of the network is then further indicated by model generalization inside the training data set.

Time‐resolved DRIFT Spectroscopy Study of Carbonaceous Intermediates during the Water Gas Shift Reaction over Au/Ceria Catalyst

AbstractChemCatChem homepage for more articles in the collection. The mechanism of the low‐temperature water gas shift reaction (LTWGS) on an Au/CeO2 catalyst was investigated by means of in situ diffuse reflectance infrared (DRIFT) spectroscopy. Under steady‐state LTWGS reaction (373–623 K), the catalyst is partially reduced, and signals from carbonate/formate dominates the infrared spectra. Time‐resolved pulse of CO experiment under a constant partial pressure of water at 423 K indicates that Ce4+ can be reduced to Ce3+ and that formate (HCOO) species cannot be directly related to the CO2 production. Further information was obtained by performing modulation excitation spectroscopy (MES) experiments coupled with a phase‐sensitive detection (PSD) method. Under periodic modulation of the CO partial pressure while keeping the H2O concentration constant, most of the intense bands of carbonate and formate remained constant, indicating that these species are only spectators. The same is observed for the concentration of Ce3+. Conversely, signals in‐phase with the conversion of CO to CO2 are observed and assigned to carboxyl [C(O)OH] and carboxylate (CO2δ−) species, while some monodentate formate (m‐HCOO) also changes but at a lower rate. A plausible associative reaction mechanism where carboxyl/carboxylate are key intermediates is postulated.

Analytical first-principles-based model for sprays-based CO2 capture

CO2 removal from flue gases or air is directly proportional to the overall contact area between the solvent and gas flow. Spraying the solvent offers possibilities for large area/volume ratios resulting from the small size of solvent droplets. The overall mass transfer (KGAv) is a crucial indicator of the performance of the system and indicates the overall CO2 capture rate per unit volume at given working pressure. The maximum capture rate of spray systems considered in this study is 608 kmol/m3-hr. This study develops an analytical model to predict mass transfer in spray-based systems for CO2 capture by evaluating KGAv and capture efficiency. Model predictions are validated using two experimental studies for a range of liquid flow rate, inlet solvent loading, different nozzle types, and inlet CO2 partial pressure. The relative importance of the incorporation of equilibrium partial pressure of CO2 (P*) into amine with respect to CO2 partial pressure is also studied. It is found that its effect on KGAv is prominent in high liquid flow rate and low solvent loading regimes where the overall CO2 capture is high. Finally, the variation of key parameters such as KGAv, total mass transfer coefficient (KG), effective area (Av), solvent loading (α), and mole fraction of CO2 in the gas stream (XCO2) along the channel height is studied, which gives insights on optimization of the channel height for specified operating conditions.

Elucidating the Performance Limits for Electrochemical CO2 Separation Using Exergy Loss Analysis and Zero-Dimensional Modeling

The use of renewable electricity to power electrochemical CO2 removal and concentration from point sources, air, and seawater is receiving considerable interest as one strategy in our portfolio of options for mitigating climate change. Two common embodiments of this idea involve CO2 separation via electrochemically reversible binding of CO2 to a nucleophilic redox mediator, or a pH swing/gradient in aqueous solution. For either embodiment to be feasible, the energetic cost of regenerating the sorbent should be low at practical separation throughputs. Consequently, there have been a number of efforts to understand how the thermodynamic minimum work input for a given separation cycle varies under different conditions using modeling. In this talk, we demonstrate that the thermodynamic minimum work input for electrochemical CO2 separation is the sum of exergy losses incurred from differences between the partial pressure of CO2 within the CO2 source/exit streams and the partial pressure of CO2 in the sorbent. This framework rationalizes minimum work inputs for pH-swing and redox-mediator-based CO2 separation cycles, and motivates the measurement or estimation of the aforementioned CO2 partial pressures in experimental studies. Applying a zero-dimensional model recently developed in our group to pH-swing-driven CO2 separation, we will then discuss how the total energetic cost of CO2 separation can be simulated under a variety of scenarios relevant to practical CO2 concentration from flue gas.

Permissive hypercapnia and oxygenation impairment in premature ventilated infants

AimIn permissive hypercapnia high levels of carbon dioxide (CO2) are tolerated in ventilated preterm infants to minimise lung injury, but hypercapnia could directly impair oxygenation. We aimed to quantify the association of elevated CO2 with oxygenation impairment in preterm infants by measuring the right-to-left shunt and the ventilation/perfusion (VA/Q) ratio. MethodsPre-existing datasets from preterm infants during the acute phase of respiratory distress syndrome or with evolving or established bronchopulmonary dysplasia were analysed. Non-invasive paired measurements of the fraction of inspired oxygen (FIO2) and transcutaneous oxygen saturation (SpO2) were used to calculate the degree of right-to-left shunt, right shift of the FIO2 versus SpO2 curve and the VA/Q. ResultsA total of 75 infants (43 male) with a median (IQR) gestational age of 26.4 (24.7–27.7) weeks were studied at 7 (2–31) days. Thirty-six infants (48 %) had an arterial partial pressure of CO2 (PaCO2) above 6 kPa. The PaCO2 was independently associated with the right shift of the curve [adjusted p < 0.001, unstandardised coefficient; 2.26, 95 % CI: 1.51–2.95] and the right-to-left shunt [adjusted p = 0.016, unstandardised coefficient; 1.86, 95 % CI: 0.36–3.36] after adjusting for confounders. An increase of the PaCO2 from 5 to 8 kPa, corresponded to a right shift of the curve of 20.2 kPa or a decrease in the VA/Q from 0.66 to 0.24. ConclusionsIncreased carbon dioxide levels were significantly associated with impaired oxygenation in preterm infants with respiratory distress syndrome or bronchopulmonary dysplasia.

Thermodynamic Analysis of Carbon Deposition on the Fuel Electrode of a Reversible Solid Oxide Cell

Fouling via carbon deposition occurs in reversable solid oxide cells (RSOCs) when it operates with carbon-based fuels or performs CO2 electrolysis. Carbon deposition is known to degrade performance and, in some cases, lead to delamination and irreversible cell damage. In this study, research was conducted using thermodynamic analysis to investigate the potential of solid carbon formation during electrolysis mode by analyzing the chemical potential of electro-neutral oxygen (O2) at the interface between the electrolyte and the fuel electrode. The chemical potential of electro-neutral oxygen is calculated based on a local chemical equilibrium assumption and addresses the isothermal transport of ions and electrons across the electrolyte. The O2 chemical potential at the fuel electrode/electrolyte interface is used to evaluate the affinity of carbon deposition reactions by the corresponding Gibbs free energy changes. Our analysis shows that regardless of the chemical makeup and physical properties of a cell an oxygen chemical potential threshold is ultimately reached as applied cell voltage during electrolysis is increased which beyond this threshold carbon deposition is inevitable. Our study is expanded to include the role of fuel electrode ionic resistance on the chemical potential of O2 at the fuel electrode/electrolyte interface and shows that an increase in ionic resistance results in more favored carbon deposition. Additional findings indicate that at 800 deg. C the electrochemical reduction of carbon monoxide is thermodynamically favored at lower local CO partial pressures over the Boudouard reaction during electrolysis mode.

Comparison of the Electrochemical and Degradation Behaviour of Ni-YSZ and Ni-GDC Electrodes Under Steam, Co- and CO2 Electrolysis

The mixed ionic and electronic conductive property of Ni-GDC has ensured that the electrochemical reaction zones of the electrode extend beyond the triple phase boundary of Ni/GDC/fuel gas to the double phase boundary of the GDC and the fuel gas [1, 2]. In addition, ceria has shown good carbon suppression properties when operated in carbon-containing fuels[3, 4]. For these reasons, Ni-GDC has emerged as a possible replacement for the conventional Ni-YSZ electrode. However, a direct comparison of the performance and long-term degradation of Ni-GDC with literature values of the Ni-YSZ would be ambiguous. On one hand, different reports utilize different fuel gas compositions, operating temperatures as well as current densities. On the other hand, the fabrication of fuel electrode-supported Ni-GDC is still a challenge due to the well-known inter-diffusion [5, 6] between the YSZ and the GDC oxide phase at a high sintering temperature (1400 °C) of YSZ electrolytes. Hence, most of the electrode fabrication has remained on electrolyte support. Thus, a direct comparison of electrolyte-supported Ni-GDC with the conventional fuel electrode-supported Ni-YSZ is ineffective due to different degradation behaviour.Therefore, this present study aims to investigate and compare the long-term stability of Ni-GDC and Ni-YSZ under three different electrolysis modes; steam-electrolysis, co-electrolysis and CO2-electrolysis. Firstly, electrolyte-supported single cells of Ni-GDC (NiO-GDC//8YSZ//GDC//LSCF) and Ni-YSZ (NiO-GDC//8YSZ//GDC//LSCF) were fabricated and investigated using electrochemical impedance spectroscopy (EIS) from 750-900 °C temperature range. Furthermore, the impedance data were also recorded under polarization (0.7 to 1.4V) as well as at OCV by varying the partial pressure of steam, CO2 and oxygen (, pH20, pCO2 and pO2). Finally, stability tests of the single cells were carried out under steam electrolysis (H2O: H2, 50:50) and co-electrolysis (H2O: CO2:H2, 40:40:20) conditions at 900 °C with 0.5 A/cm2 current density for 500 h [7]. For the CO2-electrolysis (CO2:CO, 80:20), the stability test was performed up to 1000 h. The post-test characterization of the operated cells was carried out using both SEM-EDX as well as FIB-SEM. The results reveal that Ni-GDC exhibits higher current density than Ni-YSZ in all the electrolysis modes. In the post-test analysis, loss of GDC percolation was observed and the Ni particles were observed to be covered by the GDC oxide phase. Furthermore, both electrodes demonstrate that Ni is migrating away from the electrolyte in all the electrolysis modes. The detailed electrochemical and microstructural properties of the operated cells will be presented and discussed.

The jugular venous-to-arterial difference during rebreathing and end-tidal forcing: Relationship with cerebral perfusion.

We examined two assumptions of the modified rebreathing technique for the assessment of the ventilatory central chemoreflex (CCR) and cerebrovascular CO2 reactivity (CVR), hypothesizing: (1) that rebreathing abolishes the gradient between the partial pressures of arterial and brain tissue CO2 [measured via the surrogate jugular venous and arterial difference (Pjv-a CO2 )] and (2) rebreathing eliminates the capacity of CVR to influence the Pjv-a CO2 difference, and thus affect CCR sensitivity. We also evaluated these variables during two separate dynamic end-tidal forcing (ETF) protocols (termed: ETF-1 and ETF-2), another method of assessing CCR sensitivity and CVR. Healthy participants were included in the rebreathing (n=9), ETF-1 (n=11) and ETF-2 (n=10) protocols and underwent radial artery and internal jugular vein (advanced to jugular bulb) catheterization to collect blood samples. Transcranial Doppler ultrasound was used to measure middle cerebral artery blood velocity (MCAv). The Pjv-a CO2 difference was not abolished during rebreathing (6.2± 2.6mmHg; P<0.001), ETF-1 (9.3± 1.5mmHg; P<0.001) or ETF-2 (8.6±1.4mmHg; P<0.001). The Pjv-a CO2 difference did not change during the rebreathing protocol (-0.1±1.2mmHg; P=0.83), but was reduced during the ETF-1 (-3.9±1.1mmHg; P<0.001) and ETF-2 (-3.4±1.2mmHg; P=0.001) protocols. Overall, increases in MCAv were associated with reductions in the Pjv-a CO2 difference during ETF (-0.095±0.089mmHgcm-1 s-1 ; P=0.001) but not during rebreathing (-0.028±0.045mmHg·cm-1 ·s-1 ; P=0.067). These findings suggest that, although the Pjv-a CO2 is not abolished during any chemoreflex assessment technique, hyperoxic hypercapnic rebreathing is probably more appropriate to assess CCR sensitivity independent of cerebrovascular reactivity to CO2 . KEY POINTS: Modified rebreathing is a technique used to assess the ventilatory central chemoreflex and is based on the premise that the rebreathing method eliminates the difference between arterial and brain tissue . Therefore, rebreathing is assumed to isolate the ventilatory response to central chemoreflex stimulation from the influence of cerebral blood flow. We assessed these assumptions by measuring arterial and jugular venous bulb and middle cerebral artery blood velocity during modified rebreathing and compared these data against data from another test of the ventilatory central chemoreflex using hypercapnic dynamic end-tidal forcing. The difference between arterial and jugular venous bulb remained present during both rebreathing and end-tidal forcing tests, whereas middle cerebral artery blood velocity was associated with the difference during end-tidal forcing but not rebreathing. These findings offer substantiating evidence that clarifies and refines the assumptions of modified rebreathing tests, enhancing interpretation of future findings.

Experimental Analysis of the Effect of Cathodic CO2 Supply to Industrial Solid Oxide Fuel Cells

The integration of Solid Oxide Fuel Cells (SOFCs) in hybrid power generation systems offers the opportunity to achieve higher electric efficiencies. In the SOS-CO2 cycle [1], a newly developed cycle for blue power production (i.e., power generated starting from natural gas while capturing CO2), the SOFC cathode is supplied with mixtures of CO2 and O2, up to 79% CO2 molar fraction, while the anode is supplied with a reformate feed, containing H2, CH4, CO, CO2, and water vapour. Aim of this work is to experimentally evaluate the performance and the durability of industrial 5x5 cm2 Ni-YSZ anode-supported SOFCs under the SOS-CO2 cycle conditions, focusing on the effects of the CO2-rich cathodic atmosphere. The cells mounted a LSCF-based (La0.6Sr0.4Co0.2Fe0.8O3) single phase cathode, coated by a current collection layer of LSC (La0.6Sr0.4CoO3). Laboratory tests were performed at 700°C, acquiring polarization (I/V) curves and EIS spectra by means of a Horiba – FuelCon C50 Evaluator test station. Initial investigations with 7% humidified H2 and 21/79 O2/CO2 cathodic mixture revealed 25% power loss compared to the base case with cathodic air. The test showed not only that the loss of performance was stable in time, but also that the power reduction was reversible since the initial performance in air was recovered. The EIS spectra showed an increase of the polarization resistance and of the ohmic resistance upon feeding CO2. This latter observation suggested a reduction of the electronic conductivity of the cathode, compatible with the formation of Sr carbonates on the perovskite surface [2–4]. To assess the performance of the SOFC under the operating conditions of the SOS-CO2 cycle, the anode was supplied with reformate. Compared to the base case with humidified hydrogen and air, the current density at 0.7 V decreased by 37% (490 mA/cm2). When supplying the 21/79 O2/CO2 mixture at the cathode, the current density stabilized at 420 mA/cm2 (Figure 1). Durability tests (over 300 h) at 700°C with reformate and 21/79 O2/CO2 mixture highlighted a moderate decrease of the current density at 0.7 V. After these tests, the cathode was characterized post-mortem with XRD, SEM and Raman to analyse the consequences of the prolonged exposure to CO2. To further quantify the effect of CO2 on the cathode, symmetric button cells were also characterized with EIS, measuring ohmic and polarization resistances. The results suggested that the adsorption of CO2 is reversible and indicated a better suitability of LSCF- compared to LSC-based cathodes for operations with CO2-rich mixtures. Experiments performed between 550 and 700°C at varying CO2 and O2 partial pressures allowed to describe the kinetics of the oxygen reduction reaction and extract its activation energy. Overall, the results provided key elements for the integration of SOFCs in the SOS-CO2 blue power technology.

A technique to determine the end-expiratory lung volume and dead space in a ventilated patient: Theoretical considerations

The term “dead space (VD)” refers to the volume of air/gas in the respiratory tract which does not take part in gas exchange. VD can increase in some pathological settings and has been found to be a prognostic marker in acute lung injury and respiratory distress syndrome. The end-expiratory lung volume (EELV) in a mechanically ventilated patient is the volume in the lungs at the end of passive expiration which is often influenced by disease, atelectasis, airway resistance, shunt, pulmonary vascular resistance, right heart strain, etc. Measuring EELV and VD may allow monitoring of disease state and treatment effect. VD can be derived from the arterial and exhaled CO2 partial pressures. In the intensive care unit, certain ventilators can measure EELV automatically. Unfortunately, there are no means of measuring EELV in the operating room. We herein propose a technique that may theoretically allow for measurement of the EELV and VD in the operating room setting without special equipment or an arterial blood sample.

Investigation of process parameters for solar fuel production using earth-abundant materials

Photoreduction of CO2 to solar fuels and chemicals offers a sustainable method to produce net zero energy vectors. For large-scale applications, it is crucial to develop an improved understanding of the influence of reaction conditions on the design and optimisation of the photoreactor. The performance of CuO impregnated on BaTiO3 photocatalyst was investigated and compared to pristine BaTiO3, and CuO impregnated on commercial P25 (CuO/P25) and ZnO. The influence of irradiance, CO2 and H2O flow and partial pressure, and CO2/H2O ratio on the product yield and selectivity were examined. Using Design of Experiments and Computational Fluid Dynamic modelling, the optimised reaction conditions were irradiance of 125 mW cm−2, with a CO2 flow of 0.09 mL min−1, and water bubbler temperature of 25 °C. At these conditions, a 2 and 10-fold increase of CO and CH4 production, respectively, were obtained, compared to baseline conditions as well as exhibited the highest CO and CH4 production rate compared to previous reports. Among the earth-abundant photocatalysts, CuO/P25 had the highest quantum yield for CH4 (φCH4: 0.47), whilst CuO/BaTiO3 exhibited highest φCO (0.09) and stability for CO production. The under-performing of BaTiO3 and CuO/BaTiO3 was attributed to the presence of amorphous phase in BaTiO3. This work reveals that the combination of catalyst design, reaction engineering, and modelling can improve the efficiencies of CO2 photoreduction.

Handgrip exercise does not alter CO2 -mediated cerebrovascular flow-mediated dilation.

Handgrip exercise (HG), a small muscle exercise, improves cognitive function and is expected to provide a useful exercise mode to maintain cerebral health. However, the effect of HG on cerebral blood flow regulation is not fully understood. The present study aimed to examine the effect of acute HG on cerebral endothelial function as one of the essential cerebral blood flow regulatory functions. Thirteen healthy young participants performed interval HG, consisting of 4 sets of 2min HG at 25% of maximum voluntary contraction with 3min recovery between each set. Cognitive performance was evaluated before and at 5 and 60min after interval HG using the Go/No-Go task (reaction time and accuracy). The diameter and blood velocity of the internal carotid artery (ICA) were measured using a duplex Doppler ultrasound system. To assess cerebral endothelial function, hypercapnia (30s of hypercapnia stimulation, end-tidal partial pressure of CO2 : +9mmHg)-induced cerebrovascular flow-mediated dilatation (cFMD) was induced, calculated as relative peak dilatation from baseline diameter. The shear rate (SR) was calculated using the diameter and blood velocity of the ICA. As a result, cognitive performance improved only at 5min after interval HG (reaction time, P=0.008; accuracy, P=0.186), whereas ICA SR during interval HG and cFMD after interval HG were unchanged (P=0.313 and P=0.440, respectively). These results suggest that enhancement in cerebral endothelial function is not an essential mechanism responsible for acute HG-induced cognitive improvement. NEW FINDINGS: What is the central question of this study? Does handgrip exercise, a small muscle exercise, improve cerebral endothelial function? What is the main finding and its importance? Acute interval isometric handgrip exercise (2min of exercise at 25% maximum voluntary contraction, followed by 3min of recovery, repeated for a total of 4 sets) did not improve cerebral endothelial function. Since the cerebrovascular shear rate did not change during exercise, it is possible that acute handgrip exercise is not sufficient stimulation to improve cerebral endothelial function.

Effect of borate on the corrosion behaviors of Ni11Fe10Cu anode in molten carbonate

Borates are an excellent electrolyte modifier for molten carbonate electrolyzers, which modulate electrode reactions. However, the addition of borate in molten carbonate causes the degradation of the Ni11Fe10Cu anode. Herein, the corrosion behaviors of Ni, Fe, Cu and Ni11Fe10Cu electrodes in molten Na2CO3-K2CO3 with/without borates were studied at different temperatures, gas atmospheres, and pre-oxidation conditions. The in situ formed acidic borate at the anode accelerates the dissolution of the oxide scale, which can be suppressed by increasing temperature or decreasing CO2 partial pressure. The corrosion resistance of the Ni11Fe10Cu anode can be further enhanced by preparing a NiFe2O4 scale through electrochemical pre-oxidation.

Carbon dioxide reduction by photosynthesis undetectable even during phytoplankton blooms in two lakes

Lakes located in the boreal region are generally supersaturated with carbon dioxide (CO2), which emerges from inflowing inorganic carbon from the surrounding watershed and from mineralization of allochthonous organic carbon. While these CO2 sources gained a lot of attention, processes that reduce the amount of CO2 have been less studied. We therefore examined the CO2 reduction capacity during times of phytoplankton blooms. We investigated partial pressure of CO2 (pCO2) in two lakes at times of blooms dominated by the cyanobacterium Gloeotrichia echinulata (Erken, Sweden) or by the nuisance alga Gonyostomum semen (Erssjön, Sweden) during two years. Our results showed that pCO2 and phytoplankton densities remained unrelated in the two lakes even during blooms. We suggest that physical factors, such as wind-induced water column mixing and import of inorganic carbon via inflowing waters suppressed the phytoplankton signal on pCO2. These results advance our understanding of carbon cycling in lakes and highlight the importance of detailed lake studies for more precise estimates of local, regional and global carbon budgets.