Felt Cathode Research Articles

Degradation of antiviral drug molnupiravir using a dual function FeIIFeIIILDH@carbon felt cathode in the heterogeneous electro-Fenton process: Kinetics and mineralization study

Pharmaceuticals constitute one of the more widely reported anthropogenic micropollutants, and their removal usually requires a specific treatment method. The oxidative degradation and mineralization of molnupiravir (MNP), a novel antiviral drug used for COVID treatment, were investigated for the first time by EF processes using both raw carbon felt (CF) and modified dual-function CF cathodes. The classical electro-Fenton (CEF) process using CF cathode has significant challenges, including a narrow pH range and a lack of ability to reuse the catalyst. To overcome these limitations, a dual-function FeIIFeIII layered double hydroxide modified carbon felt (FeIIFeIIILDH@CF) cathode was developed using a hydrothermal method. The FeIIFeIIILDH@CF cathode was characterized using BET, FTIR, SEM, cyclic, and linear sweep voltammetry. The efficiency of FeIIFeIIILDH@CF cathode for the removal of MNP compared with that of raw carbon felt (CF) cathode, including the effects of operating parameters. The heterogeneous electro-Fenton (HEF) process with FeIIFeIIILDH@CF cathode allowed an almost complete mineralization (98.08 % TOC removal) of 0.1 mM MNP solution. The mineralization ability of the FeIIFeIIILDH@CF cathode was more than 95 % after 5 cycles, suggesting a good reusability of the synthesized cathode. The absolute rate constant for the oxidation of MNP with ●OH (2.22 ± 0.03 ×109 M−1 s−1) was also determined for the first time. In addition, the modified LDH cathode has the advantage of being effective over a wide pH range while avoiding the use of an iron salt as a catalyst.

A solid-diffusion-free hydronium-ion battery with ultra-long cycle life over 8000 cycles

Hydronium-ion batteries possess the advantages of high conductivity, good economic benefits and environmental friendliness. However, inorganic solid electrode materials always suffer from structure collapse because of their insertion mechanism, while organic solid electrode materials always face dissolution challenges. Herein, a hydronium-ion battery with a soluble methylene blue (MB) anode and a MnO2@graphite felt cathode is proposed, involving a -C=N / -C-NH group transition at the anode and MnO2/Mn2+ at the cathode. The anode exhibits a maximum capacity of 1324 μAh cm−2 at 2 mA cm−2 and excellent cycle stability over 7500 cycles with a retention of 93 %. In- and ex-situ characterizations uncover that MB possesses a highly reversible interfacial redox reaction and excellent ring skeleton stability. By coupling with MnO2@graphite felt cathode, the MB//MnO2 batteries deliver an energy density of 198 μWh cm−2 and outstanding long cycle stability over 8000 cycles. Moreover, the batteries exhibit an excellent electrochemical performance at a low temperature of -20 °C with a capacity of 220 μAh cm−2 at 0.4 mA cm−2 and a remarkable capacity retention of 80 % over 5500 cycles. The achieved results provide a path for high-stability hydronium-ion batteries.

Proton Intercalation/De-intercalation Chemistry in Phenazine-based Anode for Hydronium-ion Batteries.

Hydronium-ion batteries have received significant attention owing to the merits of extraordinary sustainability and excellent rate abilities. However, achieving high-performance hydronium-ion batteries remains a challenge due to the inferior properties of anode materials in strong acid electrolyte. Herein, a hydronium-ion battery is constructed which is based on a diquinoxalino [2,3-a:2',3'-c] phenazine (HATN) anode and a MnO2@graphite felt cathode in a hybrid acidic electrolyte. The fast kinetics of hydronium-ion insertion/extraction into HATN electrode endows the HATN//MnO2@GF battery with enhanced electrochemical performance. This battery exhibits an excellent rate performance (266 mAh g-1 at 0.5 A g-1, 97 mAh g-1 at 50 A g-1), attractive energy density (182.1 Wh kg-1) and power density (31.2 kW kg-1), along with long-term cycle stability. These results shed light on the development of advanced hydronium-ion batteries.

Proton Intercalation/De‐intercalation Chemistry in Phenazine‐based Anode for Hydronium‐ion Batteries

AbstractHydronium‐ion batteries have received significant attention owing to the merits of extraordinary sustainability and excellent rate abilities. However, achieving high‐performance hydronium‐ion batteries remains a challenge due to the inferior properties of anode materials in strong acid electrolyte. Herein, a hydronium‐ion battery is constructed which is based on a diquinoxalino [2,3‐a:2’,3’‐c] phenazine (HATN) anode and a MnO2@graphite felt cathode in a hybrid acidic electrolyte. The fast kinetics of hydronium‐ion insertion/extraction into HATN electrode endows the HATN//MnO2@GF battery with enhanced electrochemical performance. This battery exhibits an excellent rate performance (266 mAh g−1 at 0.5 A g−1, 97 mAh g−1 at 50 A g−1), attractive energy density (182.1 Wh kg−1) and power density (31.2 kW kg−1), along with long‐term cycle stability. These results shed light on the development of advanced hydronium‐ion batteries.

Efficient rifampicin degradation and simultaneous energy recovery in photocatalytic fuel cell based on the enhanced PMS and H2O2 synergistic activation on sulfur-doped CuMnO/carbon felt cathode

Photocatalytic fuel cells (PFC) as a potential green technology has been widely reported. In this study, a PFC/peroxymonosulfate (PMS) system with sulfur-doped CuMnO/carbon felt as the cathode to promote the co-activation of PMS and H2O2 was constructed for efficient rifampicin (RIF) wastewater purification and synchronous power generation. The experimental results demonstrate that sulfur introduction makes the specific surface area of CuMnO increase and the stability of the system improve. Compared with the PFC system alone, PFC/PMS system exhibited excellent RIF degradation performance in 15 min with a removal ratio of 96.9 % and a TOC removal ratio of 78.12 %. Free radical quenching experiment and EPR test results give certification of the fact that •OH, 1O2, O2•−, and SO4·- played a crucial part in RIF degradation. Furthermore, the constructed system demonstrated stable electricity generation performance during the degradation process with a short-circuit current density of 0.57 mA cm−2, open-circuit voltage of 2.75 V, and maximum power output of 0.78 mW cm−2. This work provides a sustainable approach for organic wastewater purification with high mineralization ratio.

Degradation of emerging pollutants on bifunctional ZnFeV LDH@graphite felt cathode through prominent catalytic activity in heterogeneous electrocatalytic processes

The heterogeneous Electro-Fenton (EF) process is a promising wastewater treatment technology that can generate onsite H2O2, and operate in a wide pH range without generating a metal sludge. However, the heterogeneous EF process needs bifunctional cathode electrodes that can have high activity in 2e− oxygen reduction reaction and H2O2 decomposition. Herein, ZnFeV layered double hydroxide (LDH), as a heterogeneous catalyst, was coated on the graphite felt (ZnFeV LDH@GF) cathode using the electrophoretic deposition method. ZnFeV LDH@GF cathode was able to generate 59.8 ± 5.9 mg L−1 H2O2 in 90 min under a constant supply of O2. EF process with ZnFeV LDH@GF cathode exhibited 89.8 ± 6.8% removal efficiency for pharmaceutical (ciprofloxacin) at neutral pH. Remarkably, the apparent reaction rate constant (kapp) of the ZnFeV LDH@GF-EF was 2.14 times that of the EF process with pristine GF. ZnFeV LDH coating increased the hydroxyl radical (•OH) production of the EF process from 1.74 mM to 3.65 mM. The pathway of •OH production is thought to be a single electron transfer from redox couples of Fe2+/Fe3+ and V4+/V5+ to H2O2. After 10 reuse cycles, the ZnFeV LDH@GF cathode retained 90.2% of its efficiency. Eight intermediate compounds were identified by GC-MS including cyclic compounds and aliphatic compounds.

Novel self-sustained flow-through electrochemical advanced oxidation processes using nano-Fe0 confined B, N co-doped carbon nanotubes/graphite felt cathode: Higher mineralization efficiency under wider pH

To improve the mineralization efficiency of pollutants under wide pH ranges by self-sustained electrochemical advanced oxidation processes (EAOPs) without any reagent addition, a flow-through system based on the bifunctional cathode of B, N-doped carbon nanotubes embedded with nano-Fe0 particles that loaded on graphite felt (Fe@BN-C/GF) was developed. Dominant by 1O2 oxidation, the sulfamethazine (SMT) degradation rate and TOC removal in this recirculated flow-through system were 2.6 ∼ 3.3-folds and 1.4 ∼ 2.4-folds that of the batch system under the pH ranges of 3 ∼ 11, respectively. The SMT degradation performance was found not affected in the presence of HCO3–, NO3–, Cl-, K+, or humic acid (HA). The Fe@BN-C/GF cathode had more potential to treat enlarged wastewater by 5-folds during 10 h operation, and the SMT and TOC removal was 99% and 70.31%, respectively. The total phosphorus (TP), ammonia nitrogen (NH3-N) and TOC in reverse osmosis concentrate and secondary wastewater effluent could be simultaneously removed to <0.01 mg L-1 and 8 mg L-1 by this flow-through system with a low electric energy consumption (EEC) of 0.022 and 0.18 kWh gTOC-1, respectively. This EAOPs based on the flow-through Fe@BN-C/GF cathode was self-sustained, and had very promising application prospect of high mineralization of pollutants even for low-conductivity wastewater.

Application of electro-Fenton and photoelectro-Fenton processes for the degradation of contaminants in landfill leachate

Worldwide, most solid waste ends its life in landfill sites, which have a significant environmental impact in several respects. In particular, rainfall over landfill sites results in the production of an aqueous leachate containing compounds having low biodegradability, high toxicity, and a high organic load. For this reason, this study aims to investigate the applicability of electro-Fenton (EF) and photoelectro-Fenton (PEF) processes as alternative for treating a local landfill effluent with high organic content (chemical oxygen demand (COD) = 2684.7 mg-O2 L −1) in a continuous-flow reactor (using, for first time, this kind of system with higher electrodes area of 35 cm2) using boron-doped diamond anode (Nb/BDD) and a carbon felt cathode (FC) electrodes. The effects of current density j (30, 60 and 90 mA cm−2) and UV radiation wavelength (UVA and UVC) were studied to evaluate the treatment efficiency as well as the energy consumption. Results clearly showed that, the best efficiencies removing organic matter, in terms of COD, were about 66%, 68% and 89% with an energy consumption of only 19.41, 17.61 and 17.59 kWh kg COD−1 for EF, PEF-UVA and PEF-UVC respectively, at 90 mA cm−2 after 4 h of operation. The treatment of this kind of effluent produced organic and inorganic by-products, the acetic and formic acids as well as NO2−, NO3−, and NH4+, being assessed their concentrations.

Bioelectrochemical regulation accelerates biomethane production from waste activated sludge: Focusing on operational performance and microbial community

Bioelectrochemical regulation represents a newly emerging strategy to enhance anaerobic digestion (AD) of biowastes. Herein, a novel microbial electrolysis cell (MEC) system, equipped with a pair of carbon brush anode and hybrid Ti/RuO2-graphite felt cathode, was developed to explore the role of bioelectrochemical regulation in the proliferation/enrichment of functional microbes and methanation of waste activated sludge. The methane production was significantly improved by applying bioelectrochemical regulation. The maximum methane yield was 16.4 mL/L-reactor at the applied external voltage 1.2 V and solids retention time 15 d, 8.6-time higher than that of a single AD. Further analysis demonstrated that bioelectrochemical regulation selectively enriched electroactive fermentative partners and methanogens (especially Thermincola, Methanobacterium) in the MEC-AD system and built up a robust syntrophic interaction. This drove the decomposition of complex organics and concurrent bioelectroreduction of CO2 in biogas and subsequently enhanced methane generation. Besides, bioelectrochemical simulation attenuated N2O emissions and enhanced the dewaterability of digested sludge.

A comprehensive study on the heterogeneous electro-Fenton degradation of tartrazine in water using CoFe2O4/carbon felt cathode

In this study, cobalt ferrite coated carbon felt (CoFe2O4/CF) was synthesized by solvothermal method and applied as cathode for electro-Fenton (EF) treatment of tartrazine (TTZ) in water. The materials were characterized by SEM, XRD, FTIR, CV, and EIS to explore their physical, chemical, and electrical properties. The effects of solvothermal temperature and metal content on the TTZ removal were examined, showing that 220 °C with 2 mM of Co and 4 mM of Fe precursors were the best synthesis condition. Various influencing factors such as applied current density, pH, TTZ concentration, and electrolytes were investigated, and the optimal condition was found at 8.33 mA cm−2, pH 3, 50 mgTTZ L−1, and 50 mM of Na2SO4, respectively. By radical quenching test, ▪, 1O2, and HO were recognized as the key reactive oxygen species and the reaction mechanism was proposed for the EF decolorization of TTZ using CoFe2O4/CF cathode. The reusability and stability test showed that the highly efficient CoFe2O4/CF cathode is very promising for practical application in wastewater treatment, especially for dyes and other recalcitrant organic compounds to improve its biodegradability.

An organic/inorganic electrode-based hydronium-ion battery

Hydronium-ion batteries are regarded as one of the most promising energy technologies as next-generation power sources, benefiting from their cost effectivity and sustainability merits. Herein, we propose a hydronium-ion battery which is based on an organic pyrene-4,5,9,10-tetraone anode and an inorganic MnO2@graphite felt cathode in an acid electrolyte. Its operation involves a quinone/hydroquinone redox reaction on anode and a MnO2/Mn2+ conversion reaction on cathode, in parallel with the transfer of H3O+ between two electrodes. The distinct operation mechanism affords this hydronium-ion battery an energy density up to 132.6 Wh kg−1 and a supercapacitor-comparable power density of 30.8 kW kg−1, along with a long-term cycling life over 5000 cycles. Furthermore, surprisingly, this hydronium-ion battery works well even with a frozen electrolyte under −40 °C, and superior rate performance and cycle stability remain at −70 °C.

Electro-Fenton degradation of antibiotic ciprofloxacin (CIP): Formation of Fe3+-CIP chelate and its effect on catalytic behavior of Fe2+/Fe3+ and CIP mineralization

This work investigated the effect of the chelation of Fe3+ with a fluoroquinolone (FQ) antibiotic ciprofloxacin (CIP) on the catalytic behavior of Fe3+/Fe2+ and the degradation and mineralization of CIP in electro-Fenton (EF) process using activated carbon fiber (ACF) felt cathode. First of all, effect of initial Fe2+ and Fe3+ concentrations on the degradation and mineralization of CIP in EF process was compared, while the optimal initial Fe2+ and Fe3+ contents were both verified to be 1.50mmoldm−3, in which 73% and 72% of initial TOC were eliminated after 360min electrolysis, respectively. Secondly, Fe3+-CIP chelate was produced during CIP degradation in EF process, whose predominant form was confirmed as 1:2 metal-ligand stoichiometry. The formation of Fe3+-CIP chelate had no obvious inhibition on the degradation and mineralization of CIP due to the efficient Fe3+ reduction on the ACF cathode with excellent catalytic feature. About 17% and 35% of initial 1.50mmoldm−3 Fe3+ were reduced to Fe2+ at 18mAcm−2 in ultrapure water and 200mgdm−3 CIP solutions during 30min pre-aeration of EF process, respectively, while higher Fe2+ concentration was maintained for initial 1.50mmoldm−3 Fe3+ during CIP degradation. Finally, the evolution of F−, NH4+ and NO3− ions released to the acidic medium were determined, as well as the formation of short-chain carboxylic acid (oxalic, oxamic and formic acids). Eight aromatic intermediates were identified using UPLC-QTOF-MS/MS, and a feasible mineralization pathway was proposed.

Effect of oxygen sparging into packed-bed electrode on production rate of hydrogen peroxide.

Production of hydrogen peroxide by electroreduction of oxygen in alkaline solutions was experimentally carried out using a packed-bed electrode of graphite particles or graphite felts. Oxygen sparging into the bed was found to increase overall yield of hydrogen peroxide for a one-pass operation because of the increase in concentration of dissolved oxygen. The current efficiency decreased with increasing concentration of hydrogen peroxide. Effects of packing materials, sparging rate of oxygen and operational conditions on production rate were analysed by measuring potential distribution within the bed. The production rate for the electrolysis using graphite felts was found to be larger than that using graphite particles. The felt cathode had a large electrode surface area and a large volumetric ratio of gas to electrolyte, which might enhance the mass transfer rate of dissolving oxygen. The consumption of electric power for producing hydrogen peroxide was found to range from 2 to 6 kWh·kg–1-H2O2 in the packed-bed electrode with graphite felts.