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•Bi-based catalysts were used in a continuous process for CO2 electroreduction.•The process developed offers the best trade-off among relevant figures of merit.•FE of 90% and ...concentrations of 340 g·L−1 of HCOO− were achieved.•At 45 mA·cm−2, energy consumption of only 180 kWh·kmol−1 was required.
The electrochemical conversion of CO2 is gaining increasing attention because it could be considered as an appealing strategy for making value-added products at mild conditions from CO2 captured. In this work, we report a process for the electrocatalytic reduction of CO2 to formate (HCOO−) operating in a continuous way, employing a single pass of the reactants through the electrochemical reactor and using Bi carbon supported nanoparticles in the form of a membrane electrode assembly composed by a Gas Diffusion Electrode, a current collector and a cationic exchange membrane. This contribution presents the best trade-off between HCOO− concentration, Faradaic Efficiency and energy consumption in the literature. We also show noteworthy values of energy consumption required of only 180 kWh·kmol−1 of HCOO−, lower than previous approaches, working at current densities that allow achieving formate concentration higher than 300 g·L−1 and simultaneously, a Faradaic Efficiency close to 90%. The results here displayed make the electrochemical approach closer for future implementation at the industrial scale.
Water contamination from ammonia has recently became a global concern. Herein, a chloride-radical-mediated electrochemical filtration system has been developed towards effective and rapid conversion ...of ammonia to nitrogen (N2). This continuous-flow system consists of a nanoscale tin oxide modified carbon nanotube (SnO2-CNT) anode and a Pd−Cu co-modified Ni foam (Pd−Cu/NF) cathode. The SnO2-CNT anode enables the Cl− oxidation to a chloride radical (Cl) at a proper anode potential (e.g., 2.5 V vs. Ag/AgCl) without severe self-oxidation. The macro-porous Pd−Cu/NF cathode further reduces anodic by-products (e.g., NO3− and NO2−) to N2. EPR and scavenging tests indicate that Cl was the dominant radical specie responsible for ammonia conversion. Anode potentials, chloride concentration, flow rate and solution pH were identified as key parameters affecting the overall conversion performance. The proposed continuous-flow system showed enhanced conversion kinetics as compared to the conventional batch reactor due to the convectively enhanced mass transport. This study provides new insight for the rational design of advanced continuous-flow systems towards ammonia decontamination from water bodies.
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•A continuous flow chloride-radical-mediated electrochemical system were rationally designed.•This system consists of a SnO2-CNT filter anode and a Pd−Cu/NF cathode.•EPR studies and scavenging tests suggest that Cl. was the dominant radical specie.•N2 was identified as a major product under optimal conditions.•Rapid and effective transformation of ammonia to nitrogen was achieved.
Electrochemical technology is promising for the selective removal of nitrate from recirculating aquaculture saltwater. For commonly used sequential batch or flowing by reactor, the electrostatic ...repulsion of electric double layer near cathodic surface to NO3‾ anions brings essential adsorption limit, which suppresses the efficiency of NO3‾ reduction. In order to solve this problem, an electrochemical filter was created by installing mesh electrodes with regulated thickness. During saltwater flowing through the filter, NO3‾ have to flow through cathodic holes with diameter of one and half hundred micrometers. Compared with centimeter-scale electrode gap of commonly used reactors, this micrometer-scale diffusion distance increases the concentration gradient, which intensifies NO3‾ diffusion to the cathode surface and counteracts electrostatic repulsion. In line with expectations, for 50.0 mg/L of initial nitrate-N, nitrate-N in effluent of this filter was only 2.0 mg/L, no ammonia-N and nitrite-N were detected, which met Chinese standard of water quality for aquatic mammals in aquariums (SC/T 9411-2012). While for batch process and flow-by process, the effluent concentration of nitrate-N was 60.6% and 47.6% higher than that of flow-through process, respectively. In addition, the filter displayed low energy consumption and wide availability for real recirculating aquaculture saltwater, RO wastewater and metallurgical wastewater. Furthermore, a scale-up reactor was assembled by connecting seventeen filters in series. Its water treatment capacity (5 L/h) exceeded most reported data. These results support the practicability of this novel electrochemical filter in denitrification from saltwater.
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•✓ A novel electrochemical filter was built using mesh electrodes with regulated thickness.•✓ NO3‾ anion was reduced efficiently in micropores of mesh cathode.•✓ The filter achieved excellent denitrification performance compared to data in literatures.•✓ The water treatment capacity is easily scaled up by connecting filters in series.
In this work, a novel porous-structure electrochemical PbO2 filter (PEF-PbO2) was developed to achieve the reuse of bio-treated textile wastewater. The characterization of PEF-PbO2 confirmed that its ...coating has a variable pore size that increases with depth from the substrate, and the pores with a size of 5 μm account for the largest proportion. The study on the role of this unique structure illustrated that PEF-PbO2 possesses a larger electroactive area (4.09 times) than the conventional electrochemical PbO2 filter (EF-PbO2) and enhanced mass transfer (1.39 times) in flow mode. The investigation of operating parameters with a special discussion of electric energy consumption suggested that the optimal conditions were a current density of 3 mA cm−2, Na2SO4 concentration of 10 g L−1 and pH value of 3, which resulted in 99.07% and 53.3% removal of Rhodamine B and TOC, respectively, together with an MCETOC of 24.6%. A stable removal of 65.9% COD and 99.5% Rhodamine B with a low electric energy consumption of 5.19 kWh kg−1 COD under long-term reuse of bio-treated textile wastewater indicated that PEF-PbO2 was durable and energy-efficient in practical applications. Mechanism study by simulation calculation illustrated that the part of the pore of the PEF-PbO2's coating with small size (5 μm) plays an important role in this excellent performance which provides the advantage of rich ·OH concentration, short pollutant diffusion distance and high contact possibility.
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•A novel porous-structure electrochemical PbO2 filter (PEF-PbO2) was developed.•PEF-PbO2 showed excellent performance on electrochemical experiments.•The treated bio-treated textile wastewater has met the reuse standard under a low electric energy consumption.•Mechanism of the excellent performance was discussed by simulation calculation.
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•The hybrid O3-ECF process was successfully applied to remove phenol.•Two different carbon nanotube (CNT) networks were used as anode material.•Ozone-CNT functionalization and ...potential O3-ECF mechanisms were discussed.•Residual mass on the CNT electrode was considerably reduced with O3-ECF hybrid process.•Improved kinetic performance was achieved for O3-ECF as compared to the sum of the individual processes.
Here, we investigated the synergistic effect towards phenol degradation and mineralization between ozonation (O3) and electrochemical filtration (ECF) using perforated titanium as cathode and porous carbon nanotube (CNT) networks as anode. A flow rate of 1.6 mL min−1, 10 mM of sodium sulfate electrolyte, 1.0 mM of phenol (model aromatic compound), and an ozone dose of 12 mgO3 L−1 were used. Insight into the synergistic mechanism was achieved via carbon anode morphology characterization and phenol degradation kinetics analysis. Improved kinetic performance was observed for the combined process (O3-ECF) as compared to the sum of the individual processes, not only towards phenol degradation (3.2-fold increase), but also towards phenol mineralization (2.2-fold increase). Scanning electron microscopy revealed a significant decrease of polymer formation and deposition on CNT after the hybrid O3-ECF process as compared to the ECF alone. Voltage-dependent (0–2.5 V) ozone CNT functionalization was investigated at pH 7–11 to assist in elucidation of the synergistic mechanism. X-Ray photoelectron spectroscopy indicated increases up to 26-fold in CNT oxygen content post-ozonation at pH 7 comparing to fresh CNT. Various potential O3-ECF synergistic reaction mechanisms for organic aromatic oxidation and mineralization are discussed.
Carbon nanotube (CNT) membrane electrochemical filtration has been found to provide effective solutions for water contaminant removal. However, bubble elimination, water flux increase, and CNT ...membrane robustness enhancement still remain great challenges for CNT electrochemical filtration technologies. To improve the performance of the electrochemical CNT filter, a ceramic flat membrane is used as the CNT electrode support. Aniline (AN) is chosen as the target pollutant to investigate the effects of water quality (initial pH, initial AN concentration, and support electrolyte concentration) and running conditions (anode potential and water flux). In addition, the current efficiencies (CE) of the two different modes (single-pass filtration and recirculated filtration) are also estimated. The results showed that the effects of various impact factors on the AN degradation were generally similar in both modes. Overall, the CEs of the sing-pass filtration mode with the stable influent conditions were higher than those of the recirculation filtration mode. Increasing the flux and applied anode potential did increase the AN degradation rate. The maximum water flux density of the high-flux CNT electrochemical filter reached 83.9 mL/(cm2·h), 4.0–16.1 fold of that of a typical CNT electrochemical filter, addressing the defects of bubble formation and CNT fragility of the free-standing BUCKYPAPER membrane in a conventional electrochemical filter. The configuration with a ceramic membrane support greatly improved the practicability of CNT-based electrochemical filtration technology for real wastewater treatment.
This study examined the electrocatalytic activity of multi-walled carbon nanotube (CNT) filters for remediation of aqueous phenol in a sodium sulfate electrolyte. CNT filters were loaded with ...antimony-doped tin oxide (Sb-SnO
2
; SS) and bismuth- and antimony-codoped tin oxide (Bi-Sb-SnO
2
; BSS) via electrosorption at 2 V for 1 h and then assembled into a flow-through batch reactor as anode–cathode couples with perforated titanium foils. The as-synthesized pristine CNT filters were composed of 50–60-nm-thick tubular carbons with smooth surfaces, whereas the tubes composing the SS-CNT and BSS-CNT filters were slightly thicker and bumpy, because they were coated with SS and BSS particles ~50 nm in size. Electrochemical characterization of the samples indicated a positive shift in the onset potential and a decrease in the current magnitude in the modified CNT filters due to passivation and oxidation inhibition of the bare CNT filters. These filters exhibited a similar adsorption capacity for phenol (5–8%), whereas loadings of SS and BSS enhanced the degradation rate of phenol by ~1.5 and 2.1 times, respectively. In particular, the total organic carbon removal performance and mineralization efficiency of the BSS-CNT filters were approximately twice those of the bare CNT filters. The BSS-CNT filters also exhibited an enhanced oxidation of ferrocyanide Fe
II
(CN)
6
4−
, which was not adsorbed onto the CNT filters. The enhanced electrocatalytic performance of the modified CNT filters was attributed to an effective generation of OH radicals. The surfaces of the filters were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy.
The study is aimed at improving a methodology to purify nickel or cobalt ion containing effluents by an electrochemical filter. Consequently, a cell with reticulated vitreous carbon (RVC) cathode for ...Ni and Co depletion was designed to analyze, at room temperature and pH equal to 6, flowrates and cathodic potentials able to affect the electrochemical process. Starting with Ni and Co initial concentration of 150ppm, it is possible to reach a concentration lower than 0.1ppm for both metals in less than 1h, with a flowrate of about 1300ml/min and for a catholyte volume of 1000ml, under mass transport control conditions (for Ni −1.1V and for Co −1.2V cathodic potential versus Standard Calomel Electrode (SCE)). Moreover, the proposed work studied the process kinetics and fluid dynamics through the use of dimensionless relations such as Reynolds and Sherwood numbers. In addition considerations on current efficiency for reduction of both metal ions were done.
•Purification of effluents by electrowinning of nickel or cobalt ion•Characterization of the metal deposition on reticulated vitreous carbon•Dimensionless analysis for each ionic species electrodeposited•Efficiency analysis and cost estimation of a scale-up of the electrochemical system
SO2, a pollutant in air, can cause a serious degradation of the proton exchange membrane fuel cell (PEMFC) performance. After direct exposure to 1ppm SO2-air for 50h, the cell voltage degraded by ...28%. In order to cope with this problem, an electrochemical filter was fabricated and used for SO2 removal on-board in this study. The modified carbon felt was used as the filter anode. The effect of the applied voltages on the SO2 removal was investigated, and the cell performance was further tested both with and without the filter. When an external voltage of 0.5V was applied across the filter, the cell voltage had no obvious decrease during the 240h test, and cycle voltammery (CV) measurements showed that SO2 was not adsorbed on the cell cathode. The electrochemical filter successfully protected a single cell from being poisoned by 1ppm SO2-air for more than 240h.
► An electrochemical filter is designed and fabricated for the PEMFC application. ► The mechanism of SO2 removal at the filter anode is investigated with linear sweep operations. ► The filter successfully protects a single cell from being poisoned by 1ppm SO2-air for more than 240h.
Development of systems with reduced emission of pollutants is one of the major challenges of this century. Fuel cells promise to provide clean and renewable source of energy, which can operate on ...many fuels. They are promising candidates for transportation and portable power source applications. These applications include battery replacement for potable telephones and computers, power sources in remote areas, etc. Fuel cells can also work using other fuels such as hydrocarbons including methanol either directly or indirectly. Since there is plenty of hydrocarbons resources available in the Gulf region such as gasoline, naphtha, and methane/natural gas etc., they can be utilized in the fuel cell to produce clean power without combustion. There has been tremendous research effort in other parts of the world, especially the Western world for the development of fuel cells. Research at KFUPM is focused on two different aspects, fuel for fuel cells (reformat feed) and PEM fuel cell system. Our research group at KFUPM is actively involved in fuel cell research since 1980s. Current focus is to develop PEM fuel cell system emphasizing three different aspects: (A) developing novel low cost proton conducting membranes, (B) developing multifunctional catalyst system and (C) development of hydrocarbon based fuel processing systems. In this communication research activities and/ongoing projects undertaken at KFUPM for fuel cell development will be presented.
