Anodic Membranes Research Articles

A High Flux Electrochemical Filtration System Based on Electrospun Carbon Nanofiber Membrane for Efficient Tetracycline Degradation

In this work, an electrochemical filter using an electrospun carbon nanofiber membrane (ECNFM) anode fabricated by electrospinning, stabilization and carbonization was developed for the removal of antibiotic tetracycline (TC). ECNFM with 2.5 wt% terephthalic acid (PTA) carbonized at 1000 °C (ECNFM-2.5%-1000) exhibited higher tensile stress (0.75 MPa) and porosity (92.8%), more graphitic structures and lower electron transfer resistance (23.52 Ω). Under the optimal condition of applied voltage 2.0 V, pH 6.1, 0.1 mol L−1 Na2SO4, initial TC concentration 10 ppm and membrane flux 425 LMH, the TC removal efficiency of the electrochemical filter of ECNFM-2.5%-1000 reached 99.8%, and no obvious performance loss was observed after 8 h of continuous operation. The pseudo-first-order reaction rate constant in flow-through mode was 2.28 min−1, which was 10.53 times higher than that in batch mode. Meanwhile, the energy demand for 90% TC removal was only 0.017 kWh m−3. TC could be converted to intermediates with lower developmental toxicity and mutagenicity via the loss of functional groups (-CONH2, -CH3, -OH, -N(CH3)2) and ring opening reaction, which was mainly achieved by direct anodic oxidation. This study highlights the potential of ECNFM-based electrochemical filtration for efficient and economical drinking water purification.

Photothermal Optimization of Quantum Dot Converters for High‐Power Solid‐State Light Sources

AbstractQuantum dots (QDs) exhibit remarkable photoelectric performance. However, the conversion efficiency and thermal performance of QD converters so far is not satisfactory for high‐power solid‐state light (SSL) applications owing to the serious reabsorption loss of QDs and the poor thermal diffusion of polymer materials. Here, an efficient QD converter based on an anodic aluminum membrane (AAM), with high light enhancement and thermal diffusion, is introduced for high‐power SSL applications. Nanoporous AAMs are utilized as templates for confining the QD deposition into the nanowire (NW) shape by incorporating inkjet printing and vacuum‐deposition methods, forming vertical QD NW arrays. Compared with conventional converters, QD‐AAM yields nearly twofold photoluminescence intensity. Three‐dimensional finite‐difference (FDTD) simulations attribute the fluorescence‐enhancement mechanism to the enhancement of QD conversions and boosting of the waveguide effect in QD‐AAM. Furthermore, QD‐AAM exhibits excellent thermal diffusion performance under high‐power excitation, owing to the inner heat conduction path in the AAM framework. This study provides a practical and efficient strategy to comprehensively enhance the optical and thermal performance of QD converters for high‐power SSL applications.

Fatty Amines Embedded Carbon Membranes with Aligned Nanochannels Network: A Device with Extremely High Photothermal Conversion Efficiency toward Solar Energy Harvesting and Storage

The development of phase change materials (PCMs) composites with high light‐to‐thermal energy conversion efficiency is of great importance for solar energy storage. Herein, the preparation of novel PCMs composites by incorporation of fatty amines (FAs) into the carbon membranes (CMs) with aligned nanochannels network is first reported, which is obtained by employing an anodic alumina oxidation membrane as sacrificing template and using polypyrrole and asphalt as carbon precursor via a simple carbonization treatment. The carbonized membranes possess abundant porosity and aligned nanochannels, which is beneficial to harvest solar light combined with their carbon in nature. In addition, organic PCMs, i.e. 1‐Hexadecanamine (HDA, ΔH = 311.1 kJ/kg) and 1‐Aminoheptadecane (AHD, ΔH = 293.0 kJ/kg) can be spontaneously loaded into the nanochannels of CMs by the capillary action and surface tension. The fabricated FAs/CMs composites present an enhanced thermal conductivity ranging from 0.291 to 0.525 W m−1 K−1. Compared to pure FAs, the thermal conductivities of the PCMs composites are 144.8–357.1% higher than that of the control. Meanwhile, the as‐synthesized FAs/CMs composites also exhibit a remarkable high photothermal energy storage efficiency of up to 93.8%, which is one of the highest values reported to date, making them promising candidates for a broad range of applications in solar energy harvesting, conversion, and storage.

Study of the dynamics of heating anode units in a maskless nanolithograph based on an array of microfocus X-ray tubes

In this paper, we study the dynamics of heating the matrix of anode nodes membrane with a transmission-type target under the action of a field emission current generated in the electronic system of a maskless X-ray nanolithograph. The promising membrane materials that provide the most efficient heat removal from the matrix have been determined, among which diamond-like films have shown the best thermal stability. At the calculated power of soft X-ray radiation P_X=2.5 nW, scattered by a pixel with a size of 20 nm and an X-ray resist irradiation dose D=100 J/m2, the exposure time was 25 μs. It is shown that during the exposure of a 150 mm plate, a diamond-like anode membrane with a size of 300x300 elements heats up from 20 to 62oC, which is 15-25 times lower than the heating temperature of alternative anode materials (Cu, Fe, Ni, Si, Al). The technological route for the fabrication of the matrix of anode nodes is described, taking into account the proposed methods for optimizing its design, aimed at reducing the thermal effects of heating during X-ray nanolithography processes. The results obtained can be applied in the development of a thermostable system of microfocus X-ray tubes as part of a maskless X-ray nanolithograph. Keywords: X-ray nanolithography, microfocus X-ray tube, transmission-type target, matrix of anode nodes, electron bombardment heating, thermal expansion, Bosch-process.

Performance deterioration of Sb-SnO2/C membrane anode treating phenolic wastewater and anode regeneration: Adsorption and physicochemical change of catalysts

• The removal performance of Sb-SnO 2 /C for phenol deteriorated with time. • The adsorption of benzoquinone had a significant impact on phenol degradation. • Sn(OH) 4 and decreased crystallinity of SnO 2 also led to performance deterioration. • The degradation performance was fully restored after cleaning and recalcination. Stability of anodes is the core of electrochemical oxidation (EO), but there still lacks systematic investigation on the stability of anodes under the conditions of long-term wastewater treatment. Sb-SnO 2 anode was selected for investigation in this study due to its outstanding electrocatalytic activity. The sol–gel method was utilized to coat the Sb-SnO 2 onto a carbon membrane to form the Sb-SnO 2 /C membrane anode, and its stability during long-term treatment of phenol was studied in an electrocatalytic membrane reactor. The results showed that the COD removal efficiency of Sb-SnO 2 /C dropped from 80.6% to 41.3% after 6 days. Carbonaceous intermediates were found to be adsorbed onto Sb-SnO 2 /C, mainly including aromatic intermediates and fatty acids. The adsorption of benzoquinone had a significant adverse impact on the phenol degradation of Sb-SnO 2 /C, leading to a decreased COD removal efficiency. The formation of Sn(OH) 4 , decreased crystallinity of Sb-SnO 2 , and the reduced Sb/Sn of the used Sb-SnO 2 /C were also proposed to lead to the performance deterioration. NaOH cleaning (pH = 11.9) was able to remove the adsorbed carbonaceous intermediates and improved the COD removal from 41.3% to 64.3%. Recalcination after chemical cleaning could further improve the COD removal efficiency to 89.7%, close to the initial value.

Novel analytic method of membrane electrode assembly parameters for fuel cell consistency evaluation by micro-current excitation

Consistency evaluation and degradation diagnosis of membrane electrode assemblies (MEAs) in a large-scale fuel cell stack remain critical problems despite the accelerated commercialization. In this paper, a novel analytic method of MEA parameters is proposed with high accuracy and stability, which does not require high sampling frequency and data filtering of voltage signals anymore. By means of micro-current excitation, regardless of whether it is galvanostatic or not, four key parameters of each MEA can be calculated simultaneously based on complete excitation model, including hydrogen crossover current density, electrochemical surface area (ECSA), double-layer capacitance, and short-circuit resistance. The universality of the method is demonstrated by the high consistency between galvanostatic and non-constant current excitation results. Effects of condition parameters, including operating temperature, relative humidity, and back pressure, on MEA parameters are further investigated. Low temperature, high relative humidity, and high back pressure make high ECSA. Elevated temperature and back pressure increase hydrogen crossover. Relative humidity is proved to determine the hydrogen crossover by affecting both anodic hydrogen partial pressure and membrane water content. Finally, the method is applied to evaluate the MEA consistency of a long-time-stored seven-cell stack and recognizes part of the membranes ineffective. This method shows a promising prospect in consistency-based MEA screening, aging evaluation of MEAs in a stack, and recombination of old and broken stacks.

Degradation of tetracycline/oxytetracycline by electrospun aligned polyacrylonitrile-based carbon nanofibers as anodic electrocatalysis microfiltration membrane

The treatment of antibiotic wastewater is a hot research topic now. To achieve a fast and efficient degradation effect, aligned polyacrylonitrile-based carbon nanofibrous (ACFs) membrane as anodic electrocatalysis microfiltration membrane was fabricated by high-speed electrospinning technology in this work. The morphology, structure, electrochemical performance and mechanical properties of ACFs membrane as anode filter were characterized. The high degrees of nanofiber alignment and carbonization are obtained at the rotating speed of 1500 r/min and the temperature of 900 ℃, respectively, which provides the ACFs membrane with good electrical conductivity and mechanical properties. The highest removal rate (nearly 80%) of tetracycline/oxytetracycline (TC/OTC) in mixture solution was obtained with 4 layers of ACFs membranes under the potential of 2.5 V at the initial concentration of 40 mg/L within the reaction time of 120 min. A decrease of removal rate by only 5% after 5 cycles of repeated experiments indicated good electrocatalytic activity and cycling stability of ACFs membrane. These results indicated that more than one antibiotic could be treated rapidly by ACFs membranes with a high removal rate in a short reaction time, and has great application prospects in the treatment of refractory antibiotic wastewater.

Is HFPO-DA (GenX) a suitable substitute for PFOA? A comprehensive degradation comparison of PFOA and GenX via electrooxidation

Due to the potential hazard of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid (HFPO-DA, GenX) has become a typical alternative since 2009. However, GenX has recently been reported to have equal or even greater toxicity and bioaccumulation than PFOA. Considering the suitability of alternatives, it is quite essential to study and compare the degradation degree between PFOA and GenX in water. Therefore, in the present study, a comprehensive degradation comparison between them via electrooxidation with a titanium suboxide membrane anode was conducted. The degradation rate decreased throughout for PFOA, while it first increased and then decreased for GenX when the permeate flux increased from 17.3 L to 100.3 L m−2·h−1. The different responses of PFOA and GenX to flux might be attributed to their different solubilities. In addition, the higher kobs of PFOA demonstrated that it had a better degradability than GenX by 2.4-fold in a mixed solution. The fluorinated byproduct perfluoropropanoic acid (PFPrA) was detected as a GenX intermediate, suggesting that ether bridge splitting was needed for GenX electrooxidation. This study provides a reference for assessing the degradability of GenX and PFOA and indicates that it is worth reconsidering whether GenX is a suitable alternative for PFOA from the point of view of environmental protection.

Advancing the Anode Compartment for Energy Efficient CO2 Reduction at Neutral pH

AbstractEnergy efficient CO2 reduction in neutral pH requires the development of electrochemical devices operating with minimal energy input. To reach this objective, we propose an original approach focused on the anode compartment where the oxygen evolution reaction (OER) takes place. Different anode catalysts, anolytes and membranes were tested, and the components resulting in the most energy efficient and stable CO2 reduction reaction device were selected. A stainless‐steel‐based anode with significant OER activity and stability in a wide pH range was used to compare symmetric (neutral catholyte and anolyte) and asymmetric (neutral catholyte and alkaline anolyte) configurations. The gain in energy efficiency for carbon products of 6–8 % in the asymmetric configuration highlighted the advantages of a pH gradient. Although a Nafion membrane gave the highest energy efficiencies, the pH was unstable. Therefore, bipolar membranes that can maintain a pH gradient emerge as the best option for long‐term electrolysis. This work paves the way for the development of highly energy efficient CO2‐reduction devices with cathodes operating in low pH conditions.

Tailoring spatial structure of electroactive biofilm for enhanced activity and direct electron transfer on iron phthalocyanine modified anode in microbial fuel cells

Electroactive biofilm (EAB) has been considered as the core determining electricity generation in microbial fuel cells (MFCs), and its spatial structure regulation for enhanced activity and selectivity is of great concern. In this study, iron phthalocyanine (FePc) was introduced into a carbon cloth (CC) electrode, aiming at improving the affinity between the anode and outer membrane c-type cytochromes (OM c-Cyts) and achieving a highly active EAB. The FePc modified CC anode (FePc-CC) effectively improved the viability of EAB and enriched the Geobacter species up to 44.83% (FePc-CC) from 6.97% (CC). The FePc-CC anode achieved a much higher power density of 2419 mW m−2 than the CC (560 mW m−2) and a remarkable higher biomass loading of 2477.2 ± 84.5 μg cm−2 than the CC (749.3 ± 31.3 μg cm−2). As the charge transfer resistance was decreased by 58.6 times from 395.2 Ω (CC) to 6.74 Ω (FePc-CC), the interfacial reaction rate was accelerated and the direct electron transfer via OM c-Cyts was promoted. This work provides an effective method to improve the EAB activity by regulating its spatial structure, and opens the door toward the development of highly active EAB using metal phthalocyanines in MFCs.

Field-emission electron gun for a MEMS electron microscope

This article presents a field-emission electron gun intended for use in a MEMS (microelectromechanical system) electron microscope. Its fabrication process follows the technology of a miniature device under development built from silicon electrodes and glass spacers. The electron gun contains a silicon cathode with a single very sharp protrusion and a bundle of disordered CNTs deposited on its end (called a sharp silicon/CNT cathode). It was tested in diode and triode configurations. For the diode configuration, a low threshold voltage <1000 V and a high emission current that reached 90 µA were obtained. After 30 min of operation at 900 V, the emission current decreased to 1.6 µA and was stable for at least 40 min, with RMS fluctuation in the anode current lower than 10%. The electron beam spot of the source was observed on the phosphor screen. In the diode configuration, the spot size was the same as the emission area (~10 µm), which is a satisfactory result. In the triode configuration, an extraction electrode (gate) control function was reported. The gate limited the emission current and elongated the lifetime of the gun when the current limit was set. Moreover, the electron beam current fluctuations at the anode could be reduced to ~1% by using a feedback loop circuit that controls the gate voltage, regulating the anode current. The developed sharp silicon/CNT cathodes were used to test the MEMS electron source demonstrator, a key component of the MEMS electron microscope, operating under atmospheric pressure conditions. Cathodoluminescence of the phosphor layer (ZnS:Ag) deposited on the thin silicon nitride membrane (anode) was observed.

Optimization of MnOx/Ti composite membrane anode in the electrocatalytic membrane reactor by acidification for phenolic wastewater treatment

Optimization of MnOx/Ti composite membrane anode in the electrocatalytic membrane reactor by acidification for phenolic wastewater treatment

Designing a Tubular Electrochemical Membrane Apparatus with Efficient Mixing of Solutions to be Separated and a Procedure for Calculating Such Apparatus

A tubular electrochemical membrane apparatus that enables efficient mixing of chemical plant solutions to be separated and of colloidal process solutions is designed and a procedure for calculating the total working area of the membranes in a tubular electrobaromembrane apparatus is developed. The areas of the cathodic and anodic membranes are calculated.

Electrosynthesis of Electrochromic Polymer Membranes Based on 3,6-Di(2-thienyl)carbazole and Thiophene Derivatives.

Five carbazole-containing polymeric membranes (PDTC, P(DTC-co-BTP), P(DTC-co-BTP2), P(DTC-co-TF), and P(DTC-co-TF2)) were electrodeposited on transparent conductive electrodes. P(DTC-co-BTP2) shows a high ΔT (68.4%) at 855 nm. The multichromic properties of P(DTC-co-TF2) membrane range between dark yellow, yellowish-green, gunmetal gray, and dark gray in various reduced and oxidized states. Polymer-based organic electrochromic devices are assembled using 2,2′-bithiophene- and 2-(2-thienyl)furan-based copolymers as anodic membranes, and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT-PSS) as the cathodic membrane. P(DTC-co-TF)/PEDOT-PSS electrochromic device (ECD) displays a high transmittance change (ΔT%) (43.4%) at 627 nm as well as a rapid switching time (less than 0.6 s) from a colored to a bleached state. Moreover, P(DTC-co-TF2)/PEDOT-PSS ECD shows satisfactory optical memory (the transmittance change is less than 2.9% in the colored state) and high coloration efficiency (512.6 cm2 C−1) at 627 nm.

Electro-catalytic membrane reactors for the degradation of organic pollutants – a review

Electro-catalytic membrane reactor exhibiting electro-oxidation degradation of organic pollutants on anodic membrane.

Nanochannel-based sensor for the detection of lead ions in traditional Chinese medicine.

Lead ions (Pb2+) are used in the quality control of traditional Chinese medicine (TCM) preparations because they are highly toxic to human health. At present, sophisticated analytical instrumentation and complicated procedures for sample analysis are needed for the determination of Pb2+. Herein, a simple, fast, and sensitive peptide-modified nanochannel sensor to detect Pb2+ in TCM is reported, which is based on a Pb2+-specific peptide modified porous anodized aluminum membrane (PAAM). This peptide-based nanochannel clearly has the highest selectivity for Pb2+ when compared to other heavy metal ions, including As2+, Cd3+, Co2+, Cr2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, and Zn2+. Based on linear ranges from 0.01 to 0.16 μM and 10 to 100 μM, the detection limit was calculated to be 0.005 μM. Moreover, this peptide-based nanochannel sensor was successfully used to detect Pb2+ in complex TCM samples. In addition, when compared with the gold standard atomic absorption spectrophotometry (AAS) method, the recovery of the peptide-modified nanochannel sensor was between 87.7% and 116.8%. The experimental results prove that this new sensor is able to achieve accurate detection of Pb2+ in TCM samples. Thus, this sensor system could provide a simple assay for sensitive and selective detection of Pb2+ in TCM, thereby showing great potential in the practical application for the quality control of heavy metals in TCM.

Constructing a graphene-contained layer in anode to improve the performance of direct methanol fuel cells using high-concentration fuel

ABSTRACT A novel membrane-electrode structure is conceived and prepared in this work, where a graphene-contained layer is constructed between anode catalyst layer and membrane, also the material composition in this layer is optimized to improve the performance of a direct methanol fuel cell (DMFC) with high-concentration fuel. The polarization test shows that the pristine graphene layer could reduce the methanol crossover, while causing a slight decrease in performance. After adding Nafion ionomer binder in the graphene layer, the peak power density of the electrode fed with 8 M methanol reaches 17.75 mW cm−2, which is increased by 12.36% and 82.69% compared with the conventional electrode and the electrode without any binder in the graphene layer, respectively. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results show that for the graphene-contained layer including Nafion ionomer binder, the charge transfer resistance is only one-fifth of that without binder in the graphene layer, and the anode electrochemical active surface area (ECSA) is increased by 40.16%. These results indicate that the anode electrode with a graphene-contained layer using Nafion ionomer as the binder can effectively improve the cell performance with high-concentration fuel, which is beneficial to increase the energy density of a DMFC system.

Finite Element Analysis and Techno-economic Modeling of Solar Silicon Molten Salt Electrolysis

A new process is presented for low-cost one-step production of pure solid silicon from natural quartzite by molten salt electrolysis. At a process temperature of 1100°C, a techno-economic model including detailed mass and energy balances estimates energy consumption below 15 kWh/kg, with operating cost of $1.74/kg and capital cost around $10,500 per t/a (tonne annually) of production capacity for a 160,000 t/a plant. Use of an inert solid oxide membrane anode results in a pure oxygen by-product and no direct emissions. Finite element analysis estimates the current density distribution and total current to inform the design of slab-shaped solid silicon cathodes.

Janus electrocatalytic flow-through membrane enables highly selective singlet oxygen production

The importance of singlet oxygen (1O2) in the environmental and biomedical fields has motivated research for effective 1O2 production. Electrocatalytic processes hold great potential for highly-automated and scalable 1O2 synthesis, but they are energy- and chemical-intensive. Herein, we present a Janus electrocatalytic membrane realizing ultra-efficient 1O2 production (6.9 mmol per m3 of permeate) and very low energy consumption (13.3 Wh per m3 of permeate) via a fast, flow-through electro-filtration process without the addition of chemical precursors. We confirm that a superoxide-mediated chain reaction, initiated by electrocatalytic oxygen reduction on the cathodic membrane side and subsequently terminated by H2O2 oxidation on the anodic membrane side, is crucial for 1O2 generation. We further demonstrate that the high 1O2 production efficiency is mainly attributable to the enhanced mass and charge transfer imparted by nano- and micro-confinement effects within the porous membrane structure. Our findings highlight a new electro-filtration strategy and an innovative reactive membrane design for synthesizing 1O2 for a broad range of potential applications including environmental remediation.

Durability Analysis on PEM Water Electrolyzers against the Voltage Fluctuation of Wind Power

Introduction Utilizing of hydrogen as an energy carrier is drawing attention as one of the efficient uses of renewable energy. Water electrolysis becomes a key technology. Polymer electrolyte membrane (PEM) water electrolyzers can be operated from room temperature and can be compact owing to the thin electrolyte membrane, leading to low ohmic resistance. Such characteristics will be advantages when water electrolyzers are combined with renewable energy power plants.While the combination between renewable energy and water electrolyzers is important, one of the problems on renewable energy is the fluctuation of the output voltage. Durability of PEM water electorlyzers against such voltage fluctuation has not been well studied. In our previous study, our group have tried durability analyses of a PEM water electrolysis cell against the voltage fluctuation simulating the wind and solar power fluctuation.[1] As a result, degradation of the water electrolysis cell according to the change in the anode catalyst layer was found. In this study, in order to further understand the durability against the voltage fluctuation of renewable energy, an actual voltage fluctuation of wind power was applied a PEM water electrolysis cell, and changes in electrochemical characteristic were analyzed. Experimental method A PEM water electrolysis cell was prepared using a method of preparing a membrane electrode assembly (MEA). MEAs were made with IrO2 anode, Pt/KB cathode, and Nafion117 membrane. The size of electrode was 1 cm2, and the anode loading and cathode loading were 0.5 mg IrO2/cm2 and 0.3 mg Pt/cm2, respectively. The actual 24-hour voltage fluctuation of wind power used in this study is shown in Figure 1. Since a single water electrolysis cell was tested in this study, the voltage was reduced into one hundredth and applied to a MEA. MEAs were electrochemically evaluated before and after applying the voltage fluctuation using impedance and current-voltage (I-V) measurements. Then, each overvoltage was separately analyzed. In addition, for the purpose of evaluating the change in the anode individually, CV measurements were conducted using the cathode as a reference electrode. Results and discussion The change in the current density at 2.0 V before and after every 24 hours of the voltage fluctuation is shown in Figure 2. In Figure 2, the current density increased in the initial term of the durability test, which means I-V performance was improved. After 96 hours, where the current density reached the highest value, the current density declined. Regarding to the initial improvement in I-V performance, each overvoltage was separately analyzed. As a result, ohmic overvoltage, concentration overvoltage, and activation overvoltage were all reduced. In order to study the decrease in activation overvoltage more deeply, the change in the electric double layer of the anode was evaluated by obtaining CV on the anode side. Accordingly, the increase in the electric double layer, leading to increase in active surface area was observed. Regarding to the decrease in I-V performance after 96 hours, it was just temporary decline and not owing to the degradation of a water electrolysis cell. The difference in results in our previous study and this study will be deeply discussed. Reference [1] Marika Muto et al, ECS Transactions, 13, 719-726 (2018). Figure 1