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2 L stirred bioreactor (VSF 2000, Bioengineering AG, CH) with an electrochemical carbon dioxide sensor (KSI).
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In this review the basic principles of carbon dioxide sensors and their manifold applications in environmental control, biotechnology, biology, medicine and food industry are reported. Electrochemical CO2 sensors based on the Severinghaus principle and solid electrolyte sensors operating at high temperatures have been manufactured and widely applie...
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... [12,13] Nevertheless, in alkaline environments, the majority of dissolved CO 2 transforms to HCO 3 À at pH 7À 10, with a shift toward CO 3 2À at higher pH values (Figure 1a). [14] This transformation occurs rapidly and thermodynamically favorably through reactions with bulk or locally electrogenerated hydroxide ions, resulting in (bi)carbonate at the cathode (2OH À (aq) + CO 2(g) !CO 3 2À (aq) + H 2 O (l) , ΔG°= À 56 kJ/mol), [15][16][17] as displayed in Figure 1b. This process, called salt precipitation, obstructs the gas diffusion channel for CO 2 transport and results in cathode flooding, thus drastically reducing the CO 2 single-pass conversion efficiency (SPCE) and causing premature device death. ...
... [103,104] The changes in the bulk pH and the carbonaceous species (CO 2 , H 2 CO 3 , HCO 3 À , and CO 3 2À ) distribution in different electrolytes indicate that the real active CO 2 source during the CO 2 RR is dependent on the pH rather than the widely accepted dissolved CO 2 . [14,105] Alkaline electrolytes are considered to be optimal for activating CO 2 while hampering the HER; however, the low CO 2 utilization rate and electrocatalytic instability initiated by the simultaneous generation of (bi)carbonate severely decrease the economic feasibility of this technology. The above issues can be mitigated by carrying out the CO 2 RR in acidic media. ...
The electrocatalytic CO2 reduction reaction (CO2RR) is a sustainable route for converting CO2 into value‐added fuels and feedstocks, advancing a carbon‐neutral economy. The electrolyte critically influences CO2 utilization, reaction rate and product selectivity. While typically conducted in neutral/alkaline aqueous electrolytes, the CO2RR faces challenges due to (bi)carbonate formation and its crossover to the anolyte, reducing efficiency and stability. Acidic media offer promise by suppressing these processes, but the low Faradaic efficiency, especially for multicarbon (C2+) products, and poor electrocatalyst stability persist. The effective regulation of the reaction environment at the cathode is essential to favor the CO2RR over the competitive hydrogen evolution reaction (HER) and improve long‐term stability. This review examines progress in the acidic CO2RR, focusing on reaction environment regulation strategies such as electrocatalyst design, electrode modification and electrolyte engineering to promote the CO2RR. Insights into the reaction mechanisms via in situ/operando techniques and theoretical calculations are discussed, along with critical challenges and future directions in acidic CO2RR technology, offering guidance for developing practical systems for the carbon‐neutral community.
... Typically, the electrolyte's pH remains relatively stable in the absence of electrode reactions. As shown in Fig. 10, illustrated by the example of a bicarbonate solution, a dynamic equilibrium among various ions prevails within the system [97]. When the pH levels are excessively high, CO 2 gets excessively absorbed, while low pH leads to heightened concentrations of hydronium ions, causing aggressive HER. ...
... Apart from the effect of pH, this curve is also slightly dependent on the temperature (T), salinity (S), and pressure (P). Reproduced with permission from Ref. [97]. Copyright 2011, IOP Publishing Understanding the inhibition of HER necessitates consideration of the significant shift in local pH, which stems from the depletion of protons and the generation of hydroxide ions due to water reduction. ...
The electrochemical reduction of carbon dioxide (CO2RR) stands as an enticing approach for the production of essential chemicals and feedstocks, storing clean electric energy and mitigating greenhouse gas emissions. Recent years have witnessed remarkable breakthroughs in CO2RR, enhancing its performance and transitioning related research from laboratory settings toward industrial realization. However, the journey of CO2RR development is not devoid of challenges, including issues like mass transfer limitation, salt accumulation, and flooding phenomena. Remarkably, recent studies have unveiled a promising avenue by conducting CO2RR in an acidic environment, effectively circumventing these challenges and presenting novel opportunities. In this review, we embark on a reassessment of H-cells and flow cells, delving into their opportunities, challenges, strengths, and weaknesses. Additionally, we compile recent advancements in CO2RR under acidic conditions, elucidating the performance metrics and strategies embraced by pertinent research. Subsequently, we propose three pivotal concerns in acidic CO2RR: ① balancing the competition between CO2RR and hydrogen evolution reaction (HER), ② enhancing the selectivity, and ③ exploring industrial applications. And finally, we delve into the core factors influencing the performance of CO2RR in acid: local pH, cation effects, and catalyst design. Building upon these strategies, challenges, and insights, prospects are proposed for the future trajectory of CO2RR development.
... Proper assessment of GHG emissions may therefore require self-monitoring and reporting by the farmers, but the farmers usually lack the time, skills or equipment to do rigorous gas measurements. Between the two gases, CO 2 can be measured relatively easily using inexpensive sensors (e.g., Zosel et al., 2011). By developing simple algorithms to estimate CH 4 from CO 2 data, we can greatly expand the nation's ability to assess the combined carbon emission from the fast-growing aquaculture sector. ...
... Therefore, simple and practical methods for estimating GHG emissions will be highly desirable. Automated or handheld dataloggers for dissolved CO 2 are relatively inexpensive and low maintenance (e.g., Zosel et al., 2011), and F CO2 can be calculated from C CO2 using easily obtained wind (from weather station) and water temperature data (stand-alone sensor or integrated into CO 2 sensor). We therefore attempted to derive useful algorithms to predict F CH4 from F CO2 , and compared the outcomes by binning the data at different time resolutions. ...
Aquaculture ponds are potential hotspots for carbon cycling and emission of greenhouse gases (GHGs) like CO2 and CH4, but they are often poorly assessed in the global GHG budget. This study determined the temporal variations of CO2 and CH4 concentrations and diffusive fluxes and their environmental drivers in coastal aquaculture ponds in southeastern China over a five-year period (2017–2021). The findings indicated that CH4 flux from aquaculture ponds fluctuated markedly year-to-year, and CO2 flux varied between positive and negative between years. The coefficient of inter-annual variation of CO2 and CH4 diffusive fluxes was 168% and 127%, respectively, highlighting the importance of long-term observations to improve GHG assessment from aquaculture ponds. In addition to chlorophyll-a and dissolved oxygen as the common environmental drivers, CO2 was further regulated by total dissolved phosphorus and CH4 by dissolved organic carbon. Feed conversion ratio correlated positively with both CO2 and CH4 concentrations and fluxes, showing that unconsumed feeds fueled microbial GHG production. A linear regression based on binned (averaged) monthly CO2 diffusive flux data, calculated from CO2 concentrations, can be used to estimate CH4 diffusive flux with a fair degree of confidence (r2 = 0.66; p < 0.001). This algorithm provides a simple and practical way to assess the total carbon diffusive flux from aquaculture ponds. Overall, this study provides new insights into mitigating the carbon footprint of aquaculture production and assessing the impact of aquaculture ponds on the regional and global scales.
... Various physical and chemical sensors have been introduced for detecting toxic, flammable, or explosive gases. Numerous gas sensors have been reported, such as fluorescent, chemosensors (Cicek et al. 2019;Guo et al. 2012;Liu et al. 2010;Xu et al. 2013a), infrared (IR), nondispersive infrared (NDIR) (Zosel et al. 2011), electrochemical (Gassensmith et al. 2014), thin films having porous silicon and mesoporous silica (Karthik et al. 2018;Lee et al. 2012), Raman spectroscopy (Petrov et al. 2018), two-dimensional (2D) materials like Graphene (Kim et al. 2018) and acoustic (Cicek et al. 2019;Zosel et al. 2011;Butt et al. 2021). FET and MOSFET-based gas sensors have been reported by researchers for a long time. ...
... Various physical and chemical sensors have been introduced for detecting toxic, flammable, or explosive gases. Numerous gas sensors have been reported, such as fluorescent, chemosensors (Cicek et al. 2019;Guo et al. 2012;Liu et al. 2010;Xu et al. 2013a), infrared (IR), nondispersive infrared (NDIR) (Zosel et al. 2011), electrochemical (Gassensmith et al. 2014), thin films having porous silicon and mesoporous silica (Karthik et al. 2018;Lee et al. 2012), Raman spectroscopy (Petrov et al. 2018), two-dimensional (2D) materials like Graphene (Kim et al. 2018) and acoustic (Cicek et al. 2019;Zosel et al. 2011;Butt et al. 2021). FET and MOSFET-based gas sensors have been reported by researchers for a long time. ...
In this paper, we introduce a micro-ring resonator-based highly sensitive carbon dioxide sensor. For this purpose, a valley is created in the core of the ring, and then PbSe quantum dots (QDs) are deposited in the valley and the sensor is exposed to CO2 gas. In this way, the refractive index of the PbSe QDs increases with an increase in the concentration of CO2 gas flow, which shifts the resonant frequency of the micro-ring resonator accordingly. The designed sensor operates almost linearly over a wide range of CO2 gas concentrations and shows a high shift in resonance frequency at different concentrations of CO2 gas. The detection limit for the designed sensor is 10 ppm of CO2 gas, which is more sensitive than previously reported sensors based on microring resonators. The resonance frequency shifts are investigated by changing the width of the valley. The minimum width of the valley was determined for the evanescent field in which only the outer core of the ring affects the resonant frequency. Also, the modal analysis of the waveguide of the designed micro-ring resonator is investigated to determine the core width. The radius of the micro-ring resonator is also investigated to determine the length of the straight waveguide at 193.41 THz.
... Several review papers on capnometry have been published [5][6][7][8][9][10]. The standard technology to measure carbon dioxide transcutaneous pressure is based on Severinghaus's electrochemical principle [11]. ...
The development of a capnometry wristband is of great interest for monitoring patients at home. We consider a new architecture in which a non-dispersive infrared (NDIR) optical measurement is located close to the skin surface and is combined with an open chamber principle with a continuous circulation of air flow in the collection cell. We propose a model for the temporal dynamics of the carbon dioxide exchange between the blood and the gas channel inside the device. The transport of carbon dioxide is modeled by convection–diffusion equations. We consider four compartments: blood, skin, the measurement cell and the collection cell. We introduce the state-space equations and the associated transition matrix associated with a Markovian model. We define an augmented system by combining a first-order autoregressive model describing the supply of carbon dioxide concentration in the blood compartment and its inertial resistance to change. We propose to use a Kalman filter to estimate the carbon dioxide concentration in the blood vessels recursively over time and thus monitor arterial carbon dioxide blood pressure in real time. Four performance factors with respect to the dynamic quantification of the CO2 blood concentration are considered, and a simulation is carried out based on data from a previous clinical study. These demonstrate the feasibility of such a technological concept.
... Dagılmayan kızılötesi (NDIR) gaz algılama, en yaygın kullanılan optik gaz algılama tekniklerinden biridir ve ticari üretimde çok çeşitli sensör tasarımları bulunmaktadır [8]. Bu NDIR gaz sensörleri, kızılötesi radyasyon kaynagı, algılayıcı ve optik sensör kapsülü olmak üzere üç ana kısımdan oluşmaktadır. ...
... Non-dispersive infrared (NDIR) detection is one of the gas detection methods used in flammable and explosive gas detection systems. NDIR gas detection method, used in detecting hydrocarbon gases, is widely used today because it allows the detection of a specific gas and is a fast and accurate gas analysis technology [1], [2]. ...
Non-dispersive infrared (NDIR) gas sensor capsules have holes for gas inlet-outlet. The volumetric flow rate of the target gas into the sensor capsule is a significant factor affecting the fast and accurate measurement of gas concentration. The structure and dimensions of the holes in the capsule affect the volumetric flow rate of the target gas. If cylindrical holes are preferred in sensor capsules, it is necessary to enlarge the hole diameter to increase the volumetric flow rate of the gas. However, enlarging the hole diameter in NDIR gas sensors increases IR rays exiting the sensor capsule. This energy loss reduces the light concentration reaching the detector and adversely affects sensor performance. One of the ways to increase the volumetric flow of gas passing through the barrier without enlarging the hole diameter is the use of a convergent nozzle structure. Convergent nozzles increase the gas inlet velocity by increasing the pressure difference between the inner and outer points of the barrier, thanks to their structure. In this study, fluid dynamics analysis was conducted in a sensor capsule with cylindrical holes of different diameters 1mm and 1.5 mm, and convergent nozzles of two different sizes 1.5 mm to 1mm and 2 mm to 1 mm. According to the results obtained, when 1.5 mm to 1 mm convergent nozzles are used, the gas’s volumetric flow rate is approximately the same as when using cylindrical holes with a diameter of 1.5 mm. Thus, the same result is obtained without increasing the hole area in the capsule by 2.25 times by using convergent nozzles, and additional IR rays are prevented from exiting the sensor capsule. Even higher volumetric flow rate values have been achieved using 2 mm to 1 mm convergent nozzles. With this study, the importance of the structure of the holes where the gas enters the capsule is emphasized for the fast and accurate operation of NDIR gas sensors.
... Non-dispersive infrared (NDIR) optical gas sensing is increasingly used technique in gas sensing technologies. The infrared gas sensing method is simple and economical for long-term work and enables detection of a specific gas [1]. Besides, NDIR sensors technology provides fast and accurate gas analysis as seen in the sensors and actuators book [2]. ...
... [3][4]. Depending on the infrared light intensity before and after gas absorption, the gas concentration is calculated through Beer- (1) Where indicates the intensity of incident radiation; indicates the intensity of transmitted radiation; indicates the correlation coefficient of gas absorption; indicates the effective optical path length for infrared light absorption, and indicates the gas concentration for absorbing infrared light. ...
In non-dispersive infrared (NDIR) gas sensors, one of the factors affecting sensor performance is the light concentration reaching the detector. In these NDIR gas sensors, which consist of an IR light source, an optical gas chamber, and a detector, the scattered rays from the infrared light source spread in all directions, resulting in a low concentration of light reaching the detector. The low concentration of light reaching the detector reduces the measurement accuracy. This situation creates the necessity of directing the scattered rays from the IR light source. A reflector to be placed behind the light source in the optical gas chamber will ensure that the rays falling on it are directed towards they come from. This will increase the light concentration reaching the detector. However, depending on the geometric shape of the reflectors, the direction of reflected rays falling on them varies. In this paper, studies have been carried out on the effect of different reflector geometries in NDIR gas sensors, in order to increase the light concentration reaching the detector, which is one of the methods of improving the performance of the NDIR gas sensor. To observe the effect of this situation on the light concentration, three types of reflector structures circular, elliptical, and parabolic were added to the sensor and their effect was investigated. As a result of the parallel reflection of the rays falling on a circular or parabolic reflector used in the sensor, it was obtained that the light concentration increased by approximately 1.14-1.15 times.
... Humans indirectly produce CO 2 , where all human activities release 70 million tonnes of CO 2 into the atmosphere daily (Driessen, 2013) . CO 2 has been widely used in various aspects of human life, such as CO 2 use for re extinguishers, pneumatic applications (Binions and Naik, 2013) , laser (Oh and Kim, 2012) , important reagents in the manufacture of many products, and carbonated drinks (Zosel et al., 2011) . CO 2 concentration is one parameter that is widely used in various elds, such as controlling air quality (Kaneyasu et al., 2000;Daisey et al., 2003), and used to reduce energy consumption in heating, ventilation, and air con-ditioning (HVAC) system (Apte, 2006) , controlling industrial processes (Trapp et al., 1998) , health diagnostics, and analysis in the eld of chemistry (Zhang et al., 2010) . ...
... On the other hand, CO 2 concentrations are increasing due to human activities, such as hydrocarbon combustion, industrial processes (Zosel et al., 2011) , and carbon-containing fuels (Binions and Naik, 2013) . CO 2 is also produced by volcanic activity, where volcanic gases usually contain 10-40% CO 2 . ...
In this research, improvisation was carried out by modifying the market IR thermopile which functions as a thermal conductivity detector to measure the concentration of CO2 gas in the gas mixture. Four thermopiles are configured with a Wheatstone bridge with the aim of increasing the accuracy of the measurement system in detecting changes in CO2 concentration in the gas mixture (N2 and CO2). Using the bridge configuration of these four thermopiles, this measurement system can measure changes in CO2 concentration in small orders. The sensor developed is easy to manufacture, low cost, and has high linearity as evidenced by a correlation coefficient of 0.9943. From the experiments carried out, the sensor works quite accurately in detecting CO2 concentrations with the sensor’s sensitivity of -88.19 Volt/%, the detection range is 0% to 100%, and the RMS error value is 2.25.
... On the base of the conducted literature review [52][53][54] several CO2 sensors were selected that possibly would be applicable in the designed test rig. They are as follows: Potentiometric sensors-Severinghaus, Potentiometric sensors-Solid electrolyte sensors, Non-dispersive infrared (NDIR) CO2 sensors. ...
The paper deals with the problem of accurate measuring techniques and experimental research methods for performance evaluation of direct contact jet-type flow condensers. The nominal conditions and range of temperature, pressure and flow rate in all characteristic points of novel test rig installation were calculated using the developed model. Next, the devices for measurement of temperature, pressure and flow rate in a novel test rig designed for testing the two-phase flow spray ejector condensers system (SEC) were studied. The SEC can find application in gas power cycles as the device dedicated to condensing steam in exhaust gases without decreasing or even increasing exhaust gas pressure. The paper presents the design assumptions of the test rig, its layout and results of simulations of characteristic points using developed test rig models. Based on the initial thermal and flow conditions, the main assumptions for thermal and flow process monitoring were formulated. Then, the discussion on commercially available measurement solutions was presented. The basic technical parameters of available sensors and devices were given, discussed with details.
