Cell Reactor Research Articles

Contributions of Pulsed Operation Along with Proper Choice of the Substrate for Stabilizing the Catalyst Performance in Electrochemical Reduction of CO2 Toward Ethylene in Gas Diffusion Electrode Based Flow Cell Reactors

Electrochemical reduction of CO2 is a promising method to close the carbon cycle and thereby contribute to counteracting climate change. A large share of the research is going into the development of new high‐performance catalysts. Often, these catalysts are expensive and difficult to synthesize, especially if considering scaling up to the industrial application. The catalyst is, however, only one factor within the complex system of a CO2‐electrolyzer with numerous parameters to explore and optimize. Herein, an optimization process relying on a commercial copper nanopowder as a catalyst is reported. By replacing conductive carbon with polytetrafluoroethylene as the base material of the gas diffusion electrode (GDE) and applying a pulsed potential during electrolysis, the average faradaic efficiency for ethylene could be increased from 38% over 20 h to 50% over 100 h. In addition to the five times increased stability of the process, the ethylene‐producing current density rises from 106 to 152 mA cm−2, respectively, while hydrogen evolution was simultaneously reduced. Additionally, further investigations on the interplay of GDE base material, binder, current collector, and catalyst on the electrode performance are presented.

A New Approach to Modeling Solid Oxide Cell Reactors with Multiple Stacks for Process System Simulation

Reactors with solid oxide cells (SOC) are highly efficient electrochemical energy converters, which can be used for electricity generation and production of chemical feedstocks. The technology is in an upscaling phase. Thereby demanding development of strategies for robust and efficient operation or large SOC reactors and plants. The present state of technology requires reactors with multiple stacks to achieve the appropriate power. This study aims to establish and apply a simulation framework to investigate process systems containing SOC reactors with multiple stacks. Focusing especially on the operating behavior of SOC reactors under transient conditions, by observing the performance of all cells in the reactor. For this purpose, a simulation model of the entire SOC reactor consisting of multiple stacks, pipes, manifolds, and thermal insulation was developed. After validation on stack and reactor level, the model was used to investigate the fundamental behavior of the SOC reactors and the individual stacks in various operation modes. Additionally, the influences of local degradation and reactor scaling on the performance were examined. The results show that detailed investigation of the reactors is necessary to ensure operability and to increase efficiency and robustness. Furthermore, the computing performance is sufficient to develop and validate system controls.

Development of miniature self-powered single-chamber microbial fuel cell and its response mechanism to copper ions in high and trace concentration

Copper ions are widely present in water environment and are involved in various biochemical reaction processes, causing irreversible damage to the human body. In this study, we design and establish a self-powered miniature single-chamber microbial fuel cell (SCMFC) reactor using xurography technology. Optimal volume of 188 μL is obtained by controlling the distance between the anode and cathode. Copper ions in two concentration gradients are tested and good linear response curves are obtained. The opposite responses to copper ions in the trace concentration range (0–0.4 mg/L) and high concentration range (1.0–8.0 mg/L) are observed. The results show that at trace concentration range, the inhibitory effect of copper ions on the biofilm activity of micro-SCMFC is dominant; while high concentration copper ions are involved in chemical reactions that produce Cu2O, which may act as a catalyst and promote electron transfer. A good linear response to trace concentration (0–0.4 mg/L) of copper ions with detection limits of 0.05 mg/L is obtained in this study. It could be used in drinking water for trace copper ion detection. The investigation of the mechanisms provides the scientific basis for the design of the efficient detection of copper ions by SCMFC.

Enhancement of nitrogen removal and energy recovery from low C/N ratio sewage by multi-electrode electrochemical technology and tidal flow via siphon aeration

In view of the difficulty in denitrification of low C/N ratio wastewater, electrochemical technology with multiple electrodes and tidal flow method via siphon aeration were used to enhance the denitrification process. At the same time, because of the low phosphorus removal efficiency in traditional activated sludge process, the constructed wetland and microbial fuel cell (CW-MFC) reactor with dewatered alum sludge (DAS) as substrate were constructed. In addition, the REDOX conditions of the reactor were changed by siphon, which significantly improved the removal efficiency of N and P and the energy recovery capacity of the reactor. In the 172 d, the Tidal Flow Constructed Wetland-Microbial Fuel Cell (TF CW-MFC) had the highest removal efficiency of COD and total nitrogen (TN), which were 97.4% and 83.4%, respectively. Although the removal rate of total phosphorus (TP) by TF CW-MFC was lower than artificial aeration, it can still reached 89.0%. The removal effect of aromatic protein substances in water was also significant. The amount of electrons generated by the artificial aeration anode and the amount of oxygen generated by the cathode were not enough to match. The voltage of TF CW-MFC was significantly higher than artificial aeration, around 350 mV, and the maximum power density was 98.16 mW m−3. In addition, MFC had an inhibitory effect on CW methane emissions. The analysis of the microbial community structure showed that most of the dominant bacteria of TF CW-MFC belonged to the Proteobacteria, Actinobacteria and Chloroflexi. These results showed that the TF CW-MFC technology as a zero-energy oxygen supply mode had high efficiency in the treatment of low C/N ratio wastewater and also had the environmental effect of reducing methane emissions. This study suggests that this green wastewater treatment technology has potential application value.

Controllable fabrication of atomic dispersed low-coordination nickel-nitrogen sites for highly efficient electrocatalytic CO2 reduction

Single-atom catalysis has been considered as a powerful approach for CO2 reduction reaction (CO2RR) to achieve efficient resource conversion and carbon neutrality. The electrocatalytic activity of single-atom catalysts (SACs) is closely related to the local coordination environment. Herein, Ni SACs with well-defined low-coordination nickel-nitrogen sites (denoted as NiSA@N3-C) have been successfully developed via a facile sacrificial template method. XAS results reveal that the coordination environment of the atomically dispersed Ni active sites can be controlled by the pyrolysis temperature. Significantly, NiSA@N3-C displays remarkably excellent activity toward electrocatalytic CO2RR with CO Faradaic efficiency (FECO) of 96.0% at −0.83 V vs. RHE and remains high FECO exceeding 90% over a broad potential range from −0.63 to −0.93 V vs. RHE, outperforming those of NiSA@N4-C and NiNP@NC. More importantly, NiSA@N3-C exhibits an excellent CO selectivity of 99.2% with a considerable current density of −160 mA cm−2 in the flow cell reactor. Density functional theory (DFT) calculations further suggest that the Ni single atoms coordinated by three N atoms possesses a suitable free energy barrier for *COOH formation and *CO desorption, thereby exhibiting the most excellent CO2RR performance. This study sheds a new light on the design of SACs with controllable coordination structures for CO2RR.

An investigation of photoelectrocatalytic disinfection of water using titania nanotube photoanodes with carbon cathodes and determination of the radicals produced

In photoelectrocatalysis (PEC) a considerable amount of research has been focused on improving the photoelectrode; however, cathodic reactions are essential to PEC disinfection. In this work, a TiO2 nanotube (TiNT) array was used as the photoanode with various cathode electrodes materials, including gas diffusion electrodes (GDE) modified with different Pt nanoparticle loadings. The highest rate of E.coli inactivation was achieved with the non-modified GDE (2.51 log) compared to Pt mesh paddle (0.79 log reduction). This was explained by the examining reactive oxygen species generated at the counter electrode, where the non-modified GDE had the highest Faradaic efficiency of 15.5% for the formation of H2O2. Modification with Pt inhibited the formation of H2O2 to below the detection limit. The TiNT photoanode was shown to generate hydroxyl radicals, but importantly, there was reduction of molecular oxygen to superoxide radical at the anode. A thin cell reactor was then constructed using the identified optimal materials and a 5.0 log reduction in E.coli was in 20 min under UVA irradiation.

Kinetics study of CO2 absorption into methyldiethanolamine, potassium lysinate, and their blends in aqueous solution

AbstractIn this work, the kinetics for the reaction of CO2 with three chemical solvents were studied experimentally and theoretically. The CO2 absorption flux into the potassium lysinate (K‐Lys), methyldiethanolamine (MDEA), and their blends was measured over the CO2 partial pressure range of 50–500 kPa, and at temperatures 298.15, 303.15, and 313.15 K using a stirred cell reactor. The effect of the addition of K‐Lys on the absorption flux of CO2 into MDEA solution at low and high pressure was investigated. The reaction kinetics of CO2 absorption in CO2‐loaded MDEA, K‐Lys, and MDEA + K‐Lys solutions were also examined and absorption flux of CO2 as a function of CO2 loading was determined. The values of CO2 diffusivity, viscosity, the liquid mass transfer coefficient, the overall reaction rate constant, and the physical solubility of CO2 into MDEA + K‐Lys solution were reported. Furthermore, a standard kinetics model was developed to describe the CO2 absorption behavior in the solution at low and high pressures, for both unloaded and CO2‐loaded systems.

Operation of a Solid Oxide Fuel Cell Reactor with Multiple Stacks in a Pressured System with Fuel Gas Recirculation

Large‐scale modular solid oxide fuel cell (SOFC) reactors composed of multiple stacks are regarded as an efficient form of power generation and important for the global energy transition. However, such an arrangement leads to several operational challenges, and methods are required for handling such challenges and understanding their sources. Hence, a test rig for the examination of a 30 kW SOFC reactor with multiple stacks, for operation near real system conditions, is built. The test rig, which allows operation at elevated pressure, is equipped with a high‐temperature blower that recirculates the fuel gas at SOFC reactor temperature. In a measurement campaign, fuel gas, reactant conversion, and pressure are varied in stationary and transient experiments. The experimental results showed that the operating conditions of the individual stacks of large SOFC reactors vary largely due to flow distribution and heat losses. Methods for the investigation of these critical characteristic parameters are derived from the experimental results. Furthermore, the impact of pressurization and fuel gas recirculation on the SOFC reactor is analyzed. This publication shows the need to understand the behavior of large SOFC reactors with multiple stacks to increase the performance and robustness of complete process systems.

Effective toxicity assessment of synthetic dye in microbial fuel cell biosensor with spinel nanofiber anode

Textile dyes are one of the most commonly found contaminants in wastewater requiring their insitu real-time monitoring and biotreatment. In the present study, two different microbial fuel cells with plain and magnesium ferrite coated stainless steel mesh (PBS/SS and PBS/MF-SS) bioanodes were tested for the simultaneous biosensing and biotreatment of three different concentrations of Ponceau BS dye with mixed microbial community as biological sensing elements. The study revealed the direct correlation of added toxicant and the performance of microbial fuel cell biosensor and observed an almost perfect linear fit for concentration vs. voltage output graph corroborating the potential of microbial fuel cell as a toxicity detector. The cyclic voltammetry confirmed the bioactivity of microbial fuel cell reactor with reference to the unacclimated system. In addition, the cyclic voltammetry analysis of microbial fuel cells at different dye concentration suggested its promising toxicity sensing potential. Electrochemical Impedance Spectroscopy data confirmed that biofouling affected the internal resistances of microbial fuel cells. In addition, the effect of extended run-time (of a year) on the performance of microbial fuel cell was established by comparing the voltage outputs of this study with our previous work. As compared to the previous study, the voltage output for microbial fuel cells with plain and magnesium ferrite coated stainless steel mesh showed a decline by nearly 53% and 41% respectively suggesting the fouling of system. The lesser drop in the performance for microbial fuel cell with modified electrode showed the potential of modified electrode in more efficient electron transfer in the long run. The results conclude that the microbial fuel cell biosensor provides a quick and effective approach for real-time monitoring of hazardous and recalcitrant contaminants such as dyes in environmental samples; nevertheless, fouling of the system is a significant impediment to the long-term practical implementation of microbial fuel cells.

Recent advance in microbial fuel cell reactor configuration and coupling technologies for removal of antibiotic pollutants

Microbial fuel cell (MFC) technology, as a biological treatment model that can convert antibiotic pollutants into electrical energy, has attracted extensive attention in recent years. Reactor configuration and coupling process play an important role in the treatment of antibiotic wastewater by the MFC, which will affect microbial activity, pollutant removal, and electricity generation. In this review, recent advances of reactor configuration (single chamber, double chamber, and cylinder) and coupling technology (wetland-MFC, sediment-MFC and membrane-MFC, and so on) of the MFC on treating of antibiotics are summarized, and their characteristics in the aspects of pollutant removal and power output are analyzed. Finally, through comparing removal quantity (mg antibiotics per day), the double chamber MFC as the individual treatment unit and the membrane-MFC exhibit better removal quantity.

CO2 absorption/desorption rates in aqueous DEEA/MDEA and sulfolane-contained hybrid solutions: effects of physical properties and reaction rate.

The rates of CO2 absorption into fresh and regenerated aqueous solutions of N,N-diethylethanolamine (DEEA), N-methyldiethanolamine (MDEA), and their mixture with sulfolane are investigated in a batch stirred cell reactor. The data are obtained in the temperature range of 293.15-313.15K, pressures up to 800kPa, and different concentrations of alkanolamines and sulfolane. The diffusion coefficients and Henry's law constants for all the solutions are obtained. The absorption rate of DEEA solutions increased by increasing component concentrations and pressure, but the effects of temperature on the absorption rates of hybrid and aqueous DEEA solutions are different. Comparison of absorption rates in aqueous and hybrid solutions under the same conditions can determine the role of sulfolane as the physical solvent. It has been found that sulfolane acts as an effective absorption activator in the hybrid DEEA solutions. However, in the MDEA solutions, in all experimental conditions except for high pressure ([Formula: see text] 400kPa) and certain MDEA concentration (20 wt%), sulfolane has a negative effect on the absorption rate. The absorption rates of regenerated aqueous DEEA solutions are in the range of 50.5-87.7% of fresh ones, while these values for the hybrid DEEA solution are in the range of 75-90.5%. These values for the aqueous and hybrid MDEA solutions are almost equal. Based on the values of Hatta number and enhancement factor, the CO2 absorption regime in the DEEA solutions is determined as the fast second-order reaction. The absorption rate can be interpreted considering the tradeoff between kinetics and thermodynamics of CO2 absorption in the aqueous and hybrid DEEA/MDEA solutions. The desorption rates in hybrid DEEA/MDEA solutions are higher than those in aqueous solutions.

Substrate loading rates conducive to nitritation in entrapped cell reactors: performance and microbial community structure.

This study aimed to elucidate the boundaries of ammonia and organic loading rates that allow for nitritation in continuous flow phosphorylated-polyvinyl alcohol entrapped cell reactors and to clarify the community structure of microorganisms involving nitrogen transformation in the gel bead matrices. At operating bulk dissolved oxygen concentration of 2mg/L, nitritation was accomplished when the total ammonia nitrogen (TAN) loading rate was ≥ 0.3 kgN/m3/d. At TAN loading rates of ≤ 0.2 kgN/m3 /d, complete oxidation of ammonia to nitrate took place. Nitritation performance dropped with increased chemical oxygen demand (COD) loading rates indicating limitation of nitritation reactor operation at some COD loading conditions. 16S rRNA gene amplicon sequencing revealed that the uncultured Cytophagaceae bacterium, Arenimonas, Truepera, Nitrosomonas, Comamonas, unclassified Soil Crenarchaeotic Group, and uncultured Chitinophagaceae bacterium were highly abundant taxa in the reactors' gel bead matrices. qPCR with specific primers targeting amoA genes demonstrated the coexistence of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea, and Comammox in the gel bead matrices. AOB was likely the main functioning ammonia-oxidizing microorganisms due to the amoA gene being of highest abundance in most of the studied conditions. Nitrite-oxidizing microorganisms presented in less relative abundance than ammonia-oxidizing microorganisms, with Nitrobacter rather than Nitrospira dominating in the group. Results obtained from this study are expected to further the application of nitritation entrapped cell reactors to real wastewater treatment processes.

Effect of physical properties of synthesized protic ionic liquid on carbon dioxide absorption rate.

The concentration of carbon dioxide gas has accelerated over the last two decades which cause drastic changes in the climatic conditions. In industries, carbon capture plants use a volatile organic solvent which causes many environmental threats. So, a low-cost green absorbent has been formulated with nontoxicity and high selectivity properties for absorbing carbon dioxide gas. This paper contains the synthesis process along with the structure confirmation using 1H NMR, 13C NMR, FT-IR, and mass spectroscopy. Density, viscosity, and diffusivity are measured at different ranges with standard instruments. The kinetic studies were also conducted in a standard predefined-interface stirred cell reactor. The kinetic parameters were calculated at different parameters like agitation speeds, absorption temperature, initial concentrations of ionic liquid, and partial pressure of carbon dioxide. The reaction regime of carbon dioxide absorption is found to be in fast reaction kinetics with pseudo-first-order. The reaction rate and the activation energy of CO2 absorption are experimentally determined in the range of 299 to 333K with different initial concentrations of ionic liquid (0.1-1.1 kmol/m3). The second-order rate constant and activation energy of carbon dioxide absorption in the synthesized ionic liquid is found to be 9.48 × 103m3mol-1s-1 and 16.61kJmol-1 respectively. On increasing the viscosity of the reacting solvent, the diffusivity of CO2 gas molecules decreases, and thus the rate of absorption decreases. This solvent has shown great potential to absorb CO2 at a large scale.

Optimization of catalyst dosage and total volume for extendible stacked microbial fuel cell reactors using spacer

Reactors stack may be one of the most viable methods for microbial fuel cells (MFCs) scaling up. Optimization of catalyst and total reactor volume is necessary for stacked MFCs. Optimization of active carbon dosage (10 mg/cm 2 ) or adding a small amount of Pt/C (1/10 of the common quantity) into active carbon can both improve reactor performances with relative low catalyst cost. One stacked unit set up with four cubic MFCs is built in this research, which spacers are used to minimize the distance of cathodes and two anodes share mutual chambers. The total volume of stacked unit is reduced by 23.8%, without adversely affecting performance, including start up, power density and columbic efficiency. Theoretically, more stacked units can be extended using similar stack structures in this study. • Dosage optimization is important for active carbon catalyst. • One stacked unit set up with four cubic microbial fuel cells. • Spacers minimize the cathodes distance and two anodes share mutual chamber. • Total volume is reduced by 23.8% without adversely affecting performance. • The stack structure can be further extended horizontally.

Coupling of Desorption of Phenanthrene from Marine Sediments and Biodegradation of the Sediment Washing Solution in a Novel Biochar Immobilized–Cell Reactor

Coupling of Desorption of Phenanthrene from Marine Sediments and Biodegradation of the Sediment Washing Solution in a Novel Biochar Immobilized–Cell Reactor

A Review on the Design and Performance of Enzyme-Aided Catalysis of Carbon Dioxide in Membrane, Electrochemical Cell and Photocatalytic Reactors.

Multi-enzyme cascade catalysis involved three types of dehydrogenase enzymes, namely, formate dehydrogenase (FDH), formaldehyde dehydrogenase (FaldDH), alcohol dehydrogenase (ADH), and an equimolar electron donor, nicotinamide adenine dinucleotide (NADH), assisting the reaction is an interesting pathway to reduce thermodynamically stable molecules of CO2 from the atmosphere. The biocatalytic sequence is interesting because it operates under mild reaction conditions (low temperature and pressure) and all the enzymes are highly selective, which allows the reaction to produce three basic chemicals (formic acid, formaldehyde, and methanol) in just one pot. There are various challenges, however, in applying the enzymatic conversion of CO2, namely, to obtain high productivity, increase reusability of the enzymes and cofactors, and to design a simple, facile, and efficient reactor setup that will sustain the multi-enzymatic cascade catalysis. This review reports on enzyme-aided reactor systems that support the reduction of CO2 to methanol. Such systems include enzyme membrane reactors, electrochemical cells, and photocatalytic reactor systems. Existing reactor setups are described, product yields and biocatalytic productivities are evaluated, and effective enzyme immobilization methods are discussed.

Restructuring of copper catalysts by potential cycling and enhanced two-carbon production for electroreduction of carbon dioxide

The activity and selectivity of electrocatalytic CO2 reduction (CO2R) is strongly dependent on the structure of the catalyst. Structural engineering is always at the heart of preparing the high-performance catalysts. Herein, mixed copper oxide catalysts were prepared by a hydrothermal method, which consisted of Cu4O3, CuO and Cu2O. The potential cycling of this Cu oxide catalyst in 1 M KHCO3 electrolyte resulted in metallic state of smaller particles and Cu nanowires, as manifested by scanning electron microscopy and X-ray diffraction. The catalytic performance of the restructured Cu catalysts towards two carbon products in CO2R were much enhanced compared to the pristine catalyst, as explored in flow cell reactor on gas diffusion electrode. In 1 M KOH solution, the Faradaic efficiency of two-carbon products is 34.1 % at –0.8 V vs. reversible hydrogen electrode, and the partial current density reaches 80 mA/cm2 on gas diffusion electrode.

Strategies to achieve high productivity, high conversion, and high yield in yeast fermentation of algal biomass hydrolysate.

The conversion of carbohydrates in biomass via fermentation is an important component of an overall strategy to decarbonize the production of fuels and chemicals. Owing to the cost and resources required to produce biomass hydrolysates, the economic and environmental sustainability of these fermentation processes requires that they operate with high yields, sugar conversion, and productivity. Immobilized‐cell technology in a continuous bioprocess can achieve significantly higher volumetric productivities than is possible from standard batch fermentation using free cells. Here, we demonstrate approaches for improvement of ethanol yield from algal hydrolysates and a mock hydrolysate medium. Saccharomyces cerevisiae was immobilized in alginate and incorporated into a two‐column immobilized cell reactor system. Furthermore, the yeast quorum‐sensing molecule, 2‐phenylethanol, was added to improve ethanol yield by restricting growth and diverting sugar to ethanol. The bioreactor system could achieve high ethanol volumetric productivity (>20 g/Lreactor·h) and high glucose conversion (>99%) in mock hydrolysate, while the addition of 0.2% 2‐phenylethanol resulted in 4.9% higher ethanol yield. With an algal hydrolysate of <10 g/L sugar, the ethanol volumetric productivity reached 9.8 g/Lreactor·h, and the addition of 0.2% 2‐phenylethanol increased the ethanol yield by up to 7.4%. These results demonstrate the feasibility of novel strategies to achieve sustainability goals in biomass conversions.

Autothermal reforming of methane over an integrated solid oxide fuel cell reactor for power and syngas co-generation

Autothermal reforming of methane couples exothermal partial oxidation of methane and endothermal steam or dry reforming of methane to achieve high energy efficiency, which can be operated through solid oxide fuel cells (SOFCs) so that expensive oxygen is not required and safety issue caused by CH4/O2 mixture is avoided. In addition, electric power is simultaneously generated. This study has demonstrated the efficient electrochemical autothermal reforming of methane over a SOFC reactor integrated with catalyst beds within anode channel structure. The catalyst bed reformer increases syngas yield by a factor of about 6 owing to the increased methane conversion and syngas selectivity. By numerical assessment, enhanced mass transportation is well validated by high fuel accessibility at the electrode-electrolyte interface benefiting from the integrated catalyst beds. Compared with conventional catalyst layer on anode surface, the catalyst beds are more efficient for conducting methane reforming. After the initial stabilization of cell microstructure, the SOFC reactor has demonstrated stable cell performance and syngas yield during the test for 120 h. The integrated SOFC reactor has demonstrated a promising application in performing catalytic reforming reactions.

Efficient CO2 Electroreduction via Au-Complex Derived Carbon Nanotube Supported Au Nanoclusters.

The production of value-added chemicals from CO2 electroreduction, using renewable energy, provides an appealing route to achieve the goal of carbon neutrality. Challenges remain in designing and understanding of high-performance catalysts with restructuring behavior under electrochemical conditions. Here, the intrinsic performance enhancement of an Au-complex derived carbon nanotube-supported Au nanoclusters catalyst was demonstrated for CO2 reduction. This catalyst exhibited impressive activity for yielding CO in both H-cell and flow cell reactors. Experimental results revealed that the synthesis procedure via metal complex reconstructing on proper support induced charge transfer between Au nanoclusters and carbon nanotubes, forming a rather electron-rich state for Au active sites, which greatly contributed to the CO2 activation pathway.