Low-level CO2 Research Articles

Carbon monoxide exposure inside UK road vehicles: a pilot study

Environmental CO presents a risk to public health. The effects of chronic low-level CO exposure are well-documented, with pregnant women, the unborn and children being particularly vulnerable. Although a number of studies have investigated the phenomenon, its current prevalence in the UK has not been examined. To address this, this study sampled CO levels from 33 vehicles driven by 28 participants. Drivers were members of the public using their cars for purposes including commutes and personal use. The study excluded vehicles carrying smokers. In all, 20 vehicles logged (60.6 per cent) logged non-zero CO at least once. Mean average ppm CO exceeded the WHO target limit of 4mg/m3 (3.49 ppm) in 4 vehicles; peak ppm CO exceeded this limit in 13 vehicles. Peak single-journey mean CO was 192.17 ppm and overall mean all-journey CO was 6.63 ppm, median 0.02 ppm. Patterns of detected CO, in some cars, were suggestive of internal fume leakage. There was a significant positive correlation between vehicle age and in-cabin CO levels. While the sample size was small, these results give grounds to consider that vehicle drivers and passengers in the UK may be exposed to CO within the passenger cabin due to leakage from the exhaust system. Wider investigation of the issue, in order to determine an appropriate public health policy response, is warranted.

In Situ Fourier Transform Infrared Investigation on the Low-Level Carbon Dioxide Conversion over a Nickel/Titanium Dioxide Catalyst.

Efficiently converting atmospheric carbon dioxide (CO2) is crucial for sustainable human development. In this study, we conducted systematic in situ Fourier transform infrared tests to examine how hydrogen (H2) partial pressure affects the conversion of low-level CO2 (around 400 ppm) using nickel/titanium dioxide (Ni/TiO2). Results show that increasing H2 partial pressure significantly increases surface monodentate formate species, leading to enhanced methane (CH4) production at both 250 and 400 °C. Conversely, on Ni's surface, the key species are formyls and bidentate formate at 250 °C, but these decrease significantly at 400 °C. These findings indicate that low-level CO2 is more easily converted to CH4 over Ni/TiO2 than Ni, regardless of temperature. Additionally, the strong Ni-TiO2 interaction gives Ni/TiO2 an advantage in converting low CO2 concentrations, with excellent durability even at 400 °C. This study enhances our understanding of direct CO2 conversion and aids in the development of advanced CO2 emission reduction technologies.

Engineering hydrophobicity and high-index planes of gold nanostructures for highly selective electrochemical CO2 reduction to CO and efficient CO2 capture

In current study, we demonstrate a strategy for improving the catalytic performance of gold (Au) for carbon dioxide reduction reaction (CO2RR), specifically enhancing selectivity for CO over hydrogen evolution reaction (HER) and increasing low-level CO2 capture efficiency. This involved controlling nanostructures without any further modification. Au nanostructures having four different morphologies (i.e., degree of roughness) were fabricated via electrodeposition at varied deposition potential, resulting in different intrinsic surface hydrophobicity and exposure of high-index planes depending on the actual morphology. The roughest Au, with its combination of the most hydrophobic feature and abundant high-index planes, generated greater partial current density (jCO) and faradaic efficiency for CO (FECO) than the other Au deposits within a tested potential region: The roughest Au showed 6-fold higher FECO (95.8 %) and 327-fold higher jCO (normalized to electrode geometric surface area) at −0.75 VRHE compared to the smoothest Au. Moreover, the roughest Au exhibited excellent CO2 capture ability even at low CO2 concentration, confirmed with scanning electrochemical microscopy. These improvement at hierarchical Au for CO2RR could be ascribed to two factors. Firstly, the morphology-driven hydrophobicity provides an optimal gas–liquid-solid triple-phase interfaces, increasing the local CO2 concentration near the Au catalyst surface due to its superb CO2 capture ability. Secondly, the abundant high-index planes serve as stable active sites for CO2RR, expediting the reaction rates. Remarkably, Au with the highest hydrophobicity and enriched high-index planes, even without any chemical modification, showed excellent CO2RR catalytic performance comparable to or even better than the other previously reported Au-based catalysts.

Fabrication of Bamboo-Based Activated Carbon for Low-Level CO2 Adsorption toward Sustainable Indoor Air

This study fabricated a low-cost activated carbon (AC) adsorbent from readily available bamboo trees to control indoor CO2 levels and reduce energy costs associated with sustaining clean indoor air. Bamboo is naturally high in potassium content and has narrow fibrous channels that could enhance selective CO2 adsorption. The prepared bamboo-based activated carbon (BAC) exhibits predominantly micropores with an average pore size of 0.17 nm and a specific surface area of 984 m2/g. Upon amination, amine functionalities, such as pyridine, pyrrole, and quaternary N, were formed on its surface, enhancing its CO2 adsorption capacity of 0.98 and 1.80 mmol/g for low-level (3000 ppm) and pure CO2 flows at the ambient condition, respectively. In addition, the 0.3% CO2/N2 selectivity (αs,g) of the prepared sorbents revealed a superior affinity of CO2 by BAC (8.60) over coconut shell-based adsorbents (1.16–1.38). Furthermore, amination enhanced BAC’s CO2αs,g to 13.4. These results exhibit this sustainable approach’s potential capabilities to ensure the control of indoor CO2 levels, thereby reducing the cost associated with mechanical ventilation systems. Further research should test the new sorbent’s adsorption properties (isotherm, kinetics, and thermodynamics) for real-life applicability.

Low level CO2 supplementation maintains isocapnia and reveals ventilatory long-term facilitation in rats

Acute, intermittent hypoxia (AIH) induces ventilatory long-term facilitation (vLTF) in awake, freely behaving rats under poikilocapnic and isocapnic experimental conditions. Establishing pre-clinical methods for vLTF induction that more closely align with successful protocols in humans and anesthetized rats would minimize dissonance in experimental findings and improve translational aspects of vLTF. Here, we tested several levels of low-dose CO2 supplementation during and after AIH to determine 1) the lowest amount of inspired CO2 that would maintain isocapnia in rats during a vLTF protocol, and 2) the net impact of supplemental CO2 on vLTF expression. Rats received one of four levels of inspired CO2 (0%, 0.5%, 1% or 2%) administered during AIH and for the 60 min following AIH to quantify vLTF. Our findings indicated that 2% inspired CO2 was sufficient to maintain isocapnia across the AIH protocol and reveal significant vLTF. These findings provide evidence-based support for using 2% supplemental CO2 during and after AIH when assessing vLTF in rats.

Atmospheric CO2 controls on the MIS 6 glaciation: 10Be chronology of moraines in the Haizishan area, southeastern Tibetan Plateau

A unifying theory interpreting the cause of ice-age cycles remains elusive, in view of the near-synchronous interhemispheric major climate shifts but anti-phased summer solar insolation signatures between hemispheres. Determining the timing and magnitude of mountain glaciations helps in shedding new light on this long-standing unsolved puzzle. Yet, robust glacial chronologies are limited for the pre-Last Glaciation time periods, impeding a full understanding of glacial histories and climatic mechanisms behind them in mountainous regions, such as the Tibetan Plateau (TP). Here, we report thirty-five new 10Be exposure-ages from moraine boulders in the Niqingqu Valley, eastern Haizishan Plateau, which adds to the existing glacial chronologies of the Hengduan Mountains, southeastern TP. The dating results indicate that four centennial to millennial-scale glacial activities occurred around 168.4 ka in the studied valley. Despite being indistinguishable in age, these high-frequency glacial fluctuations allow us to draw a conclusion that glaciers in the studied valley achieved the marine isotope stage 6 (MIS 6) glacial maximum prior to the Penultimate Glacial Maximum (PGM), inconsistent with Northern Hemisphere. We attribute the MIS 6 glacial maximum identified here to the response of glaciers to a combination of low-level atmospheric CO2 content and low northern high-latitude summer solar insolation/high summer-monsoon precipitation. The consistent local PGM and low CO2 levels suggest that low atmospheric CO2 contents are likely a necessary prerequisite for the MIS 6 glaciation.

Effect of supercharging in neat biodiesel fuelled naturally aspirated diesel engine combustion, vibration and emission analysis

Diesel engines are the most efficient internal combustion engines widely used in automotive, agriculture and industry applications. However, their harmful exhaust emissions contribute to an increase in environmental air pollution. Therefore, different green fuels, often called biodiesels, have inspired researchers to examine. In this work, neat palm methyl ester (PME) is used as an alternative fuel to examine the combustion performance, engine cylinder vibration and exhaust emissions. The experiments are conducted on a single-cylinder diesel engine at naturally aspirated and supercharged modes. The combustion results at three-fourth and full loads reveal that maximum in-cylinder combustion pressures are attained for Supercharged PME (S-PME), which helps to produce high power with better torque conversion. The brake thermal efficiency (BTE) of 33.06% and 32.87% at 0.45 and 0.54 equivalency ratios is attained for naturally operated PME (N-PME). The FFT vibrations measured vertically on the cylinder head reveal that the high-frequency vibrations are attenuated and better combustion with low-frequency vibrations (<50 dB) is achieved with the implementation of S-PME. Furthermore, low-level CO, NOx, UHC and smoke emissions are reported for S-PME. Supercharging is found to be beneficial by achieving low exhaust emissions and vibrations.

Low Level Carbon Dioxide Indoors—A Pollution Indicator or a Pollutant? A Health-Based Perspective

With modern populations in developed countries spending approximately 90% of their time indoors, and with carbon dioxide (CO2) concentrations inside being able to accumulate to much greater concentrations than outdoors, it is important to identify the health effects associated with the exposure to low-level CO2 concentrations (&lt;5000 ppm) typically seen in indoor environments in buildings (non-industrial environments). Although other reviews have summarised the effects of CO2 exposure on health, none have considered the individual study designs of investigations and factored that into the level of confidence with which CO2 and health effects can be associated, nor commented on how the reported health effects of exposure correspond to existing guideline concentrations. This investigation aimed to (a) evaluate the reported health effects and physiological responses associated with exposure to less than 5000 parts per million (ppm) of CO2 and (b) to assess the CO2 guideline and limit concentrations in the context of (a). Of the 51 human investigations assessed, many did not account for confounding factors, the prior health of participants or cross-over effects. Although there is some evidence linking CO2 exposures with health outcomes, such as reductions in cognitive performance or sick building syndrome (SBS) symptoms, much of the evidence is conflicting. Therefore, given the shortcomings in study designs and conflicting results, it is difficult to say with confidence whether low-level CO2 exposures indoors can be linked to health outcomes. To improve the epidemiological value of future investigations linking CO2 with health, studies should aim to control or measure confounding variables, collect comprehensive accounts of participants’ prior health and avoid cross-over effects. Although it is difficult to link CO2 itself with health effects at exposures less than 5000 ppm, the existing guideline concentrations (usually reported for 8 h, for schools and offices), which suggest that CO2 levels &lt;1000 ppm represent good indoor air quality and &lt;1500 ppm are acceptable for the general population, appear consistent with the current research.

Hydrogen-rich gas with low-level CO produced with autothermal methanol reforming providing a real-time supply used to drive a kW-scale PEMFC system

An integrated system was developed to produce hydrogen-rich gas with low-level CO via autothermal reforming (ATR) of methanol for the purpose of real-time use in a kW-scale proton exchange membrane fuel cell (PEMFC) system. Methanol was converted into a hydrogen-rich gas through ATR in conjunction with water gas shifting (WGS) and preferential oxidation (PrOX) reactors to reduce the CO concentration. A 29.5% hydrogen-rich gas with a CO concentration of approximately 20 ppm was achieved under the optimal parameter settings (i.e., an H2O/CH3OH ratio = 0.5 and an O2/CH3OH ratio = 0.55 for the ATR reaction, an H2O/CO ratio = 5.6 for the WGS reaction, and an O2/CO ratio = 1.08 for the PrOX reaction). Specifically, the reformer system steadily produced low CO, hydrogen-rich gas after 4 h of durability testing. This system was then combined with 40-cell fuel cell stacks with air bleeding and tested for its durability over a period of 6 h. It was verified that the hydrogen-rich gas produced by the reformer system enabled the fuel cell to steadily generate 1040 W of power. Notably, the hydrogen-rich gas (the actual reformate gas) produced herein could generate better performance than the simulated reformate gas reported in the literature.

Effects of Adding CO2 to Low Level H2S Containing Aqueous Environments on the Corrosion and Hydrogen Penetration Behaviors of High-Strength Steel

The effects of adding CO2 to low level H2S containing aqueous environment on the corrosion and hydrogen penetration behaviors of high-strength steel were evaluated using a range of experimental and analytical methods. The corrosion rate of the steel sample exposed to a low level of H2S dissolved in an aqueous solution was comparatively higher than the one exposed to a mixture of low concentrations of H2S with CO2 dissolved in the aqueous solution. The higher corrosion resistance of the steel in the mixture of low concentrations of H2S and CO2 was attributed primarily to the three-layer structure of corrosion scale, comprised of an outer Fe-oxide, middle FeS1-X, and inner FeCO3, which formed on the steel sample. In particular, the formation of a thin FeCO3 layer with protective and non-conductive nature may serve as an effective barrier against the penetration of aggressive ionic species in solution, as well as hydrogen atoms formed by cathodic reduction or hydrolysis reactions. Consequently, the hydrogen permeation level, which was measured in a mixture of low-level H2S and CO2, was controlled to a comparatively lower value. Nevertheless, the higher level of hydrogen permeation in a mixture of low levels of H2S and CO2 at the early corrosion stage might increase the potential risk of pre-mature failure by hydrogen-assisted cracking.

Sequential improvement of activated carbon fiber properties for enhanced removal efficiency of indoor CO2

For effective capture of low-level indoor CO2, a polyacrylonitrile (PAN) solution was doped with potassium hydroxide (KOH) before electrospinning to increase the specific surface area and microporosity of the resulting activated carbon nanofiber (ANF). Additionally, the KOH-doped ANF was treated with tetraethylenepentamine (TEPA) in ethanol to introduce nitrogen functionalities favorable for CO2 adsorption on the surface. The sequential improvements of the physical and chemical properties of ANF were carried out at a PAN: KOH mass ratio of 1:0−0.05 and TEPA solution concentrations of 1, 2, and 3%. The effects of KOH and TEPA on the structure and chemical properties were investigated using a Monosorb instrument, a field-emission scanning electron microscope, a thermogravimetric analyzer, and an x-ray photoelectron spectrometer. In terms of the textural improvements resulting from KOH doping, a sample of 0.03-ANF showed a significant increase in specific surface area: from 94.59 for pristine ANF to 469.09m2/g after treatment. The XPS(X-ray photoelectron spectroscopy) examinations also showed a large increase in the content of the nitrogen-containing functional groups on the sample treated with TEPA, thereby increasing the selective adsorption capacity of 0.3% CO2 by 21-fold. The combination of textural enhancement by KOH impregnation and surface chemistry enhancement provided by the TEPA doping improved the low-level CO2 capture capability of ANF.

Efficient removal of triclosan via peroxymonosulfate activated by a ppb level dosage of Co(II) in water: Reaction kinetics, mechanisms and detoxification.

Triclosan (TCS), an extensively used broad-spectrum antimicrobial agent, has raised significant environmental concerns regarding its widespread occurrence in waters. In this study, the removal of TCS in aqueous solution via peroxymonosulfate (PMS) activated by an extremely low-level Co2+ (0.02μM) was systematically investigated. During preliminary test, TCS (10μM) was totally degraded in 30min by using 0.1μM Co2+ and 40μM PMS at pH 7.0 with a degradation rate constant of 0.1219 min-1. A first-order apparent degradation rate of TCS was found with respect to the PMS concentrations. At extremely low dosage of Co2+ (0.02μM), the presence of NO3-, HCO3-, PLFA, and SRHA within test concentrations significantly inhibited TCS removal, while a dual effect of Cl- on the degradation rate of TCS was observed. The quenching experiments verified that SO4- was the dominant reactive oxygen species (ROS) rather than OH. Six major intermediates were identified using TOF-LC-MS, based on which we proposed three associated reaction pathways including hydroxylation, ether bond breakage, and dechlorination. Toxicity predictions by ECOSAR software exhibited aquatic toxicity reduction of TCS after Co2+/PMS treatment. We outlook these findings to advance the feasibility of organic contaminants removal via Co2+/PMS system with Co2+ at extremely low levels.

TEPA impregnation of electrospun carbon nanofibers for enhanced low-level CO2 adsorption

The CO2 adsorption selectivity of plain activated carbon nanofibers (ANF) is generally low. For enhancement, nitrogen functionalities favorable for CO2 adsorption are usually tethered to the ANF. In the current study, we adopted chemical impregnation using 0.5 wt% tetraethylenepentamine (TEPA) solution as an impregnant. To enhance the impregnation of TEPA further, preliminary oxidation of the nanofibers with 70% HNO3 was conducted. The effects of HNO3 and TEPA treatments on the modified ANFs were investigated for physical (using N2 monosorb, thermogravimetric analyzer, scanning electron microscopy) and chemical (X-ray photoelectron spectrometer) changes. From the results, we found that although TEPA impregnation reduced the specific surface area and pore volume of the ANFs (from 673.7 and 15.61 to 278.8 m2/g and 0.284 cm3/g, respectively), whereas the HNO3 pre-oxidation increased the number of carboxylic groups on the ANF. Upon TEPA loading, pyridinic nitrogen was tethered and further enhanced by pre-oxidation. The surface treatment cumulatively increased the amine content from 5.81% to 13.31%. Consequently, the final adsorption capacity for low (0.3%) and pure CO2 levels were enhanced from 0.20 and 1.89 to 0.33 and 2.96 mmol/g, respectively. Hence, the two-step pre-oxidation and TEPA treatments were efficient for improved CO2 affinity.

CO2 leakage detection in the near-surface above natural CO2-rich water aquifer using soil gas monitoring

Conventional soil gas monitoring methods were applied above a natural low-level CO2 reservoir to locate natural CO2 leakage and assess effectiveness in monitoring geological carbon storage sites. The concentrations of the soil gas (N2, O2, and CO2) and carbon-13 isotopes of soil CO2 (δ13CCO2) were determined for ninety-four soil gas samples that were collected at a depth of ∼60 cm. The CO2 flux was also measured at the same sampling locations. The 93 soil gas samples were divided into two groups: Group A with low soil CO2 concentrations and high δ13CCO2, which was influenced by the atmospheric air, and Group B with high soil CO2 concentrations and low δ13CCO2, which originated from microbial processes. Sample M17, which was close to a CO2-rich water well, had an exceptionally high soil CO2 (36.0% v/v), δ13CCO2 (-5.7‰), and flux (546.2 g/m2/d), indicating geogenic CO2 inflow to the soil layer and discharge through the surface. This study shows that conventional soil gas monitoring methods are useful for locating CO2 leakage. A dense grid soil CO2 sampling near wells and periodic investigations are crucial for further understanding of the CO2 flow paths in the soil layer.

Efficient degradation of organic pollutants by low-level Co2+ catalyzed homogeneous activation of peroxymonosulfate.

Dissolved cobalt ions (Co2+) are an excellent catalyst for activating peroxymonosulfate (PMS) to generate SO4- for the degradation of organic pollutants, but fairly high level of Co2+ is generally required, which may cause secondary pollution due to its toxicity. Herein, we demonstrate a novel strategy for this catalytic oxidation treatment in which the required Co2+ addition is very small, being much less than the emission limit of 17 μmol L-1. This new strategy is based on the much enhanced catalytic effect by the addition of small organic acids (SOAs). In a typical case, all the added diclofenac (30 μmol L-1) was degraded in 20 min by using 2 μmol L-1 Co2+, 0.15 mmol L-1 PMS and 0.5 mmol L-1 acetate with a degradation rate constant of 0.482 min-1, which was about 10 times higher than that (0.048 min-1) of equivalent Co2+-PMS system without acetate. The formation of SO4- was greatly enhanced by introducing acetate, and this novel system is universal for enhanced degradation of various organic pollutants. Similarly, formate, propionate, and butyrate also exhibited enhancing effects on the catalytic ability of Co2+. The enhancement mechanism of SOAs on catalytic activation of PMS by low-level Co2+ was also proposed.

Besides Photothermal Effects, Low-Level CO2 Laser Irradiation Can Potentiate Skin Microcirculation Through Photobiomodulation Mechanisms.

Background: Improvement of microcirculation is one of the important mechanisms of low-level laser therapy (LLLT) to treat some diseases such as wound healing. Most previous studies have been carried out with multiple lasers other than the 10,600-nm CO2 laser. Recently, the CO2 laser has been used not only as a tool for excision of soft tissues but also for therapeutic applications. Objective: To study whether low-level CO2 laser irradiation can influence microcirculation and further explore the underlying mechanisms. Methods: Seventy-milliwatt (70-mW) CO2 lasers irradiated the forearms of 12 participants and skin blood perfusion (SkBP) was measured with a laser speckle imager. The thermal effect of irradiation was evaluated by measuring the irradiated skin in vivo and the exposed cell suspensions in vitro. Extracellular adenosine triphosphate (eATP) of the human mast cell line (HMC-1) is assessed by luciferin-luciferase assay to explore the potential mechanisms. Results: Irradiation caused dose-dependent increase in SkBP. At a medium dose of 262 J/cm2, SkBP reached its maximum value at 195.8% ± 18.6% of the baseline (n = 12, p < 0.01). Such laser irradiation had a mild thermal effect, heating local skin temperature (SkT) by 6.1°C ± 0.3°C (n = 10) and warming cell suspensions by 4.5°C ± 0.8°C (n = 6). Irradiation dose-dependently lowered eATP levels of HMC-1 cells in vitro. At a medium dose of 262 J/cm2, eATP levels declined to the minimum at 74.8% ± 5.5% of the baseline (n = 12, p < 0.01). This downregulation effect could be significantly inhibited by 100-μM ARL67156, a nonspecific ecto-ATPase inhibitor. On the contrary, heating itself slightly raised the level of eATP. Conclusions: Low-level CO2 laser irradiation can improve microcirculation. Besides the thermal effect, regulation of extravascular eATP by the photobiomodulation mechanism may be involved. This implies that CO2 lasers might be used in LLLT.

Effects of low-level inhalation exposure to carbon dioxide in indoor environments: A short review on human health and psychomotor performance

Scientific literature and documents pertaining to the effects of inhalation exposure to carbon dioxide (CO2) on human health and psychomotor performance were reviewed. Linear physiological changes in circulatory, cardiovascular, and autonomic systems on exposure to CO2 at concentrations ranging from 500 to 5000 ppm were evident. Human experimental studies have suggested that short-term CO2 exposure beginning at 1000 ppm affects cognitive performances including decision making and problem resolution. Changes in autonomic systems due to low-level exposure to CO2 may involve these effects. Further research on the long-term effects of low-level CO2 exposure on the autonomic system is required. Numerous epidemiological studies indicate an association between low-level exposure to CO2 beginning at 700 ppm and building-related symptoms. Respiratory symptoms have been indicated in children exposed to indoor CO2 concentrations higher than 1000 ppm. However, other indoor comorbid pollutants are possibly involved in such effects. In the context of significant linear increase of globally ambient CO2 concentration caused by anthropogenic activities and sources, reducing indoor CO2 levels by ventilation with ambient air represents an increase in energy consumption in an air-conditioned building. For the efficient energy control of CO2 intruding a building from ambient air, the rise of atmospheric CO2 concentration needs to be urgently suppressed.

Clinical and Histological Evaluations of Enlarged Facial Skin Pores After Low Energy Level Treatments With Fractional Carbon Dioxide Laser in Korean Patients.

Enlarged facial pores can be an early manifestation of skin aging and they are a common aesthetic concern for Asians. However, studies of improving the appearance of enlarged pores have been limited. The authors aimed to study the application of CO2 fractional laser treatment in patients with enlarged facial pores. A total of 32 patients with dilated facial pores completed 3 consecutive sessions of low energy level treatments with a fractional CO2 laser at 4-week intervals. Image analysis was performed to calculate the number of enlarged pores before each treatment session and 12 weeks after the final treatment. After application of laser treatments, there was a significant decrease in the number of enlarged pores. The mean number of enlarged pores was decreased by 28.8% after the second session and by 54.5% at post-treatment evaluation. Post-treatment side effects were mild and transitory. Histological and immunohistochemical analyses demonstrated clear increases in the number of collagen fibers and the expression of transforming growth factor-β1. The short-term results showed that treatment with low energy level CO2 fractional laser therapy could be a safe and effective option for patients with Fitzpatrick skin Types III and IV who are concerned with enlarged pores.

Continuous Monitoring of Natural CO2 Emissions Near Rome – Lessons for Low-level CO2 Leakage Detection

Continuous monitoring has been carried out at a fluvial flood-plain site near Rome for over a year. There is a mix of biogenic CO2 and deep geogenic CO2 at the site at relatively low concentrations and fluxes compared with other natural CO2 seepage sites studied previously. Factors such as temperature and soil moisture clearly affect the CO2 concentration and flux and seasonal and diurnal influences are apparent. Statistical approaches are being used to try to define these relationships and separate out the two gas components, which would be necessary in any quantification of leakage from CO2 storage.

Understand the Hydrogen Electrode Reaction for Proton Conducting SOFC Via Controlled Poisoning Experiments Using Hydrogen Sulfide and Carbon Dioxide

The hydrogen electrode reaction for conventional solid oxide fuel cells (SOFC) has been widely studied and well understood. In comparison, electrochemical behaviors for hydrogen electrode reaction of proton conducting SOFC are often distinctly different and there are still many unknowns about the fundamental kinetics and mechanism for such reaction. For example, it is well known that the hydrogen electrodes for conventional oxide ion SOFC, which consist of oxygen ion conducting oxides and Ni, are susceptible to poisoning by even sub-ppm level hydrogen sulfide (H2S). On the other hand, literature suggests that the hydrogen electrodes for proton conducting SOFC, which contains proton conducting oxides and Ni, show much better resistance against H2S. By understanding the origin of differences like this, new insights of the fundamental reaction mechanism for the hydrogen electrode of proton conducting SOFC can be obtained. In this study, electrochemical tests based on the concept of “controlled poisoning”, which is to selectively poison specific parts of the hydrogen electrode using low concentration of either H2S as a “Ni poison” or CO2 as a “proton conducting oxide poison”, are carried out to understand the fundamentals about the hydrogen electrode reaction for proton-conducting SOFCs. In particular, anode-supported cell with the configuration of Ni-BaZe0.1Ce0.7Y0.1Yb0.1O3 (BZCYYb)/BZCYYb/LSCF and anode symmetrical cell with the configuration of Ni-BZCYYb/BZCYYb/BZCYYb were subject to ppm-level H2S and low percentage level CO2, and the electrochemical responses for both types of cells are characterized. Preliminary results show that, contrary to the Ni-based hydrogen electrode for conventional SOFC, the Ni-BZCYYb hydrogen electrode for proton conducting SOFC shows much better resistance against “sulfur poisoning” while gets poisoned by CO2 at low percentage level. Results for experiments aimed at understanding such differences will be presented and the implications on what the electrocatalytic roles of proton conducting oxides play in the hydrogen electrode reaction for proton conducting SOFC will be discussed.