Graphite Felt Cathode Research Articles

Nitrogen moieties -dominated Co–N-doped nanoparticle-modified cathodes in heterogeneous-electro-Fenton-like system for catalytic decontamination of EDTA-Ni(II)

Ethylenediaminetetraacetic acid (EDTA) could form stable complexes with toxic metals such as nickel due to its strong chelation. In this study, with the same doping level of Co and N, MoO2 and ZIF-67 were used as precursors to prepare MoO2@Co/N and FeC@Co/N electrocatalysts for the modified graphite felt cathodes in heterogeneous-electro-Fenton-like reaction (HEFL) system. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that both of the catalysts are dominated with pyridinic N (2.42% and 2.82%) upon co-doping Co/N, and FeC@Co/N exhibited an obviously higher additional sp-hybridized nitrogen (sp-N) peak. The co-doping of Co/N induced the lattice modifications to produce more lattice defects, where pyridinic N and sp-N, related with the active sites (C–N, Co-Nx), were formed at near-ring defects along sheet edges through the nitrogen replacement of CC groups. FeC@Co/N demonstrated superior oxygen reduction reaction catalytic activity in terms of Cyclic Voltammetry and Rotating Ring-disk Electrode, and exhibited the remarkably higher current density (30 mA) and lower onset potential (−0.208 V) in Linear Sweep Voltammetry analysis. In the FeC@Co/N/CF modified HEFL system, despite the generated H2O2 concentrations (62.5 mg L−1) is not very high, the reducing reaction of ≡Fe(III)/Co(III)–OH could get the electron directly from the cathode, which would greatly reduce the consumption of H2O2, high utilization efficiency of H2O2 (η: 87.63%) could greatly improve the EDTA-Ni removal (97.5%) and TOC (92.6%). This work demonstrates the feasibility of utilizing FeC@Co/N/CF as a cathode for breaking metal-complex in HEFL process.

Self-powered electrochemical system by combining Fenton reaction and active chlorine generation for organic contaminant treatment

Environmental deterioration, especially water pollution, is widely dispersed and could affect the quality of people’s life at large. Though the sewage treatment plants are constructed to meet the demands of cities, distributed treatment units are still in request for the supplementary of centralized purification beyond the range of plants. Electrochemical degradation can reduce organic pollution to some degree, but it has to be powered. Triboelectric nanogenerator (TENG) is a newly-invented technology for low-frequency mechanical energy harvesting. Here, by integrating a rotary TENG (R-TENG) as electric power source with an electrochemical cell containing a modified graphite felt cathode for hydrogen peroxide (H2O2) along with hydroxyl radical (•OH) generation by Fenton reaction and a platinum sheet anode for active chlorine generation, a self-powered electrochemical system (SPECS) was constructed. Under the driven of mechanical energy or wind flow, such SPECS can efficiently degrade dyes after power management in neutral condition without any O2 aeration. This work not only provides a guideline for optimizing self-powered electrochemical reaction, but also displays a strategy based on the conversion from distributed mechanical energy to chemical energy for environmental remediation.

Novel electrodes for cathode electro-Fenton oxidation coupled with anodic oxidation system for advanced treatment of livestock wastewater

With the rapid development of livestock industry, a large amount of livestock wastewater generates in China in recent years. The conventional treatment process for livestock wastewater, including anaerobic digestion and anoxic-oxic treatment, is very common in China for the low operational cost. However, the very low BOD5/CODCr ratio (<0.1) in the associated effluent renders the further treatment process very difficult. In this study, a PbO2 anode coupled with a 2-ethylanthraquinone (EAQ)-modified graphite felt cathode was used to treat the livestock wastewater (BOD5/CODCr < 0.1) discharged from the conventional two-stage anoxic/oxic (A/O) process. The results of scan electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fourier transforminfrared spectroscopy (FTIR) show that the prepared PbO2 electrode has a smaller crystal size, higher oxygen evolution reaction (OER) potential and an excellent electro-catalytic performance compared to a purchased PbO2 electrode, and the EAQ-modified graphite felt cathode has a higher content of oxygen-containing functional groups and higher oxygen reduction reaction (ORR) electro-catalytic performance than pristine graphite felt. The results of the electrolysis experiment showed that the BOD5/CODCr ratio was increased from 0.084 to 0.42 with 71.5% CODCr removal after 80 min of electrolysis, when the Fe2+ concentration was 0.3 mM. The .OH produced in the electrolysis system was captured successfully by electron paramagnetic resonance (EPR).

Self-Powered Photosynthetic Biosensor for Pesticide Detection in Water

The excessive and uncontrolled use of pesticides seriously compromises the ecological status of water bodies worldwide. The fate and impact of these compounds in the environment is uncertain, due to the lack of appropriate sensing technologies for in situ and real time monitoring of the water quality. Such devices would allow a better assessment of the impact of pesticides on the biodiversity and human health in alternative to lab-based analytical techniques. To this end, algae-based sensors hold great potential, due to the sensitivity and rapid response to environmental changes of algae. Yet, practical applications of this type of biosensors are limited by the long-term stability of the biological sensing element and the actual portability of the device. Photosynthetic biological fuel cells (pBFC) could solve some of the issues associated with traditional algae-based electrochemical biosensors. pBFCs are a specific type of fuel cells, in which the electrochemical reactions are catalysed by photosynthetic microorganisms. In this context, we propose a simple, cost-effective photosynthetic biological fuel cell as a biosensor, for in situ monitoring of water quality. The aim of this study is to assess the ability of an algae biocathode to detect pesticides in water. The biosensor, based on a double chamber biological fuel cell design, was inoculated on the algae Scenedesmus obliquus at the cathode and anaerobic sludge at the anode. Two cathode materials were tested, graphite felt and ITO/PET, to assess relevance of the electrode morphology and transparency on the system performance. In both cases, the current output generated by the system exhibited a characteristic photosynthetic cyclic pattern, with current increasing during the day and decreasing during the night. The best performance was, however, observed with the graphite felt cathode, with a maximum value of 80 mA m-2 during the day and minimum value of 27 mA m-2, observed during the night. A linear relationship was observed between the dissolved oxygen in the catholyte and the current output, suggesting that this system can be used as dissolved oxygen sensor. When the catholyte was exposed to a herbicide, such as atrazine, the output current was reduced. Yet, the high porosity of the carbon felt was detrimental for the sensitivity and response time of the sensor, in the sub ppm range. Overall, our results suggest that the system could be used as an early warning sensor for water contamination. Keywords: biosensor, biological fuel cell, atrazine, water quality. Figure 1

Unraveling different mechanisms of persulfate activation by graphite felt anode and cathode to destruct contaminants of emerging concern

The electro-activation of persulfate (PS) by graphite felt (GF) electrode is a novel advanced oxidation process applied for the degradation of contaminants of emerging concern (CECs). Both GF anode and cathode can electro-activate PS to degrade CECs, including atrazine (ATZ), bisphenol S, ethinylestradiol, and ibuprofen. The study examines the removal performance of ATZ in sulfate, nitrate, and perchlorate electrolyte. The degradation of ATZ followed the order of sulfate (36.3 L (Ah)−1) > perchlorate (22.2 L (Ah)−1) > nitrate (5.8 L (Ah)−1) in GF anode/PS system, while electrolytes had little influence on the degradation of ATZ (15.8–21.3 L (Ah)−1) in GF cathode/PS system. The mechanisms of PS electro-activation by GF anode and GF cathode were compared and investigated for the first time, through kinetic experiments, radical identification, and products analysis. Quenching experiments demonstrated that O2− and 1O2 were generated in GF cathode/PS and GF anode/PS systems respectively, besides HO and SO4−. Degradation pathways of ATZ in these two systems showed slight difference, and a total of eight transformation products of ATZ were identified. Acute toxicity of the treated ATZ solution decreased at the beginning and then increased in both systems at electric charge of 0.11 Ah L−1. Furthermore, both GF electrodes/PS systems exhibited satisfactory performance for actual effluent from wastewater treatment plants in the presence of 30 mM perchlorate (with ATZ removal of 78% at electric charge of 0.11 Ah L−1), leaving a potential possibility for its practical application.

Cost-efficient improvement of coking wastewater biodegradability by multi-stages flow through peroxi-coagulation under low current load

Cost-effective pretreatment of the highly concentrated and biorefractory coking wastewater to improve biodegradability is of significant importance, while green electrochemical technologies without external chemicals addition are charming but still challenging due to its high energy consumption. In this work, a novel multi-stages flow through peroxi-coagulation (PC) was for the first time developed with graphite felt cathode modified by graphene, showing an excellent performance in removal of 71.5% COD, 72.3% phenol and 59.4% NH3-N and significant biodegradability enhancement with a low energy consumption as 1.2 kWh/m3. Compared with conventional flow PC, this process was more cost-effective due to more intensive .OH production and higher utilization of generated active species. Through UV spectrophotometry and GC-MS analysis, the improvement of biodegradability was attributed to the reduction of both low and high molecular weight compounds content in the coking wastewater. Comparing to the electro-Fenton, electrocoagulation and ozonation process, the proposed PC process was highly cost-effective, providing a promising and new alternative for pretreatment of coking wastewater.

Simultaneous sulfadiazines degradation and disinfection from municipal secondary effluent by a flow-through electro-Fenton process with graphene-modified cathode.

Conventionally the deep treatment and disinfection are fulfilled by different processes for municipal wastewater treatment, this work verified a breakthrough by one process of novel flow-through electro-Fenton (EF) with graphene-modified cathode, which is usually seemed to be ineffective. This process was firstly confirmed to be cost-effective for simultaneous sulfadiazines (SDZs) degradation and disinfection from municipal secondary effluent with a very low electrical energy consumption (EEC) of 0.21 kW h/m3, attributed to the high H2O2 production of 4.41 mg/h/cm2 on the novel graphite felt cathode modified by electrochemically exfoliated graphene (EEGr) with a low EEC of 3.08 kW h/(kg H2O2). Compared with the ineffective SDZs degradation by the conventional flow EF, this process was more cost-effective and overcame the harsh requirements on electrolyte concentration. It also showed good effectiveness in the degradation of different antibiotics, and the graphene-modified cathode still kept stable performance after eight consecutive runs. Account for the combined action of OH and active chlorine, the formation of hydroxylated and chlorine containing by-products was confirmed, and a possible degradation mechanism for SDZs was proposed. This flow-through EF process provided an alternative method for the disinfection and antibiotics degradation by one process for the treatment and reuse of municipal secondary effluent.

Sequential anaerobic and electro-Fenton processes mediated by W and Mo oxides for degradation/mineralization of azo dye methyl orange in photo assisted microbial fuel cells

The intensification of the degradation and mineralization of the azo dye methyl orange (MO) in contaminated water with simultaneous production of renewable electrical energy was achieved in photo-assisted microbial fuel cells (MFCs) operated sequentially under anaerobic - aerobic processes, in the presence of Fe(III) and W and Mo oxides catalytic species. In this novel process, the W and Mo oxides deposited on the graphite felt cathodes accelerated electron transfer and the reductive decolorization of MO. Simultaneously, the mineralization of MO and intermediate products was intensified by the production of hydroxyl radicals (HO) produced by (i) the photoreduction of Fe(III) to Fe(II), and by (ii) the reaction of the photochemically and electrochemically produced Fe(II) with hydrogen peroxide, which was produced in-situ during the aerobic stage. Under anaerobic conditions, the reductive decolorization of MO was driven by cathodic electrons, while the partial oxidation of the intermediates proceeded through holes oxidation, producing N,N-dimethyl-p-phenylenediamine. In contrast, under aerobic conditions superoxide radicals (O2−) were predominant to HO, forming 4-hydroxy-N,N-dimethylaniline. In the presence of Fe(III) and under aerobic conditions, the oxidation of the intermediate products driven by HO superseded that of O2−, yielding phenol and amines, via the oxidation of 4-hydroxy-N,N-dimethylaniline and N,N-dimethyl-p-phenylenediamine. These sequential anaerobic and electro-Fenton processes led to the production of benzene and significantly faster oxidation reactions, compared to either the anaerobic or the aerobic operation in the presence of Fe(III). Complete degradation and mineralization (96.8 ± 3.5%) of MO (20 mg/L) with simultaneous electricity production (0.0002 kW h/kg MO) was therefore achieved with sequential anaerobic (20 min) - aerobic (100 min) operation in the presence of Fe(III) (10 mg/L). This study demonstrates an alternative and environmentally benign approach for efficient remediation of azo dye contaminated water with simultaneous production of renewable energy.

Enhanced activation of hydrogen peroxide using nitrogen doped graphene for effective removal of herbicide 2,4-D from water by iron-free electrochemical advanced oxidation

Degradation of the herbicide 2,4-dichlorophenoxiacetic acid (2,4-D) in aqueous solutions has been studied by electrochemical oxidation process using N-doped graphene modified graphite felt cathode with ammonium nitrate as nitrogen source. The graphene was obtained via electrochemically exfoliated method (EEGr). Different ratios of EEGr/ammonium nitrate (1:0, 1:1, 1:3, 1:7) modified cathodes (N0-EEGr-GF, N1-EEGr-GF, N3-EEGr-GF, N7-EEGr-GF) were explored with electrochemical characterizations, and it was verified that N1-EEGr had the most significant catalytic performance for accelerating the activation of in-situ generated H2O2 into hydroxyl radicals. The effects of operating parameters such as applied potential, solution pH and initial concentration of 2,4-D on the degradation efficiency with N1-EEGr-GF were investigated. A fairly high mineralization rate (88%) was attained at pH 7 after 480 min electrolysis of 20 mg L−12,4-D solution. The N-doped graphene as catalyst was found to be more efficient in degradation performance compared with the unmodified graphite felt cathode. The electrochemical advanced oxidation process using this modified cathode allows extension of the working pH range compared to electro-Fenton process which is optimal at pH 3. Finally, a plausible pathway for 2,4-D mineralization was proposed according to the identified intermediated products.

“Floating” cathode for efficient H2O2 electrogeneration applied to degradation of ibuprofen as a model pollutant

The performance of the Electro-Fenton (EF) process for contaminant degradation depends on the rate of H2O2 production at the cathode via 2-electron dissolved O2 reduction. However, the low solubility of O2 (≈1 × 10−3 mol dm−3) limits H2O2 production. Herein, a novel and practical strategy that enables the synergistic utilization of O2 from the bulk electrolyte and ambient air for efficient H2O2 production is proposed. Compared with a conventional “submerged” cathode, the H2O2 concentration obtained using the “floating” cathode is 4.3 and 1.5 times higher using porous graphite felt (GF) and reticulated vitreous carbon (RVC) foam electrodes, respectively. This surprising enhancement results from the formation of a three-phase interface inside the porous cathode, where the O2 from ambient air is also utilized for H2O2 production. The contribution of O2 from ambient air varies depending on the cathode material and is calculated to be 76.7% for the GF cathode and 35.6% for the RVC foam cathode. The effects of pH, current, and mixing on H2O2 production are evaluated. Finally, the EF process enhanced by the “floating” cathode degraded 78.3% of the anti-inflammatory drug ibuprofen after 120 min compared to only 25.4% using a conventional “submerged” electrode, without any increase in the cost.

Intensified degradation and mineralization of antibiotic metronidazole in photo-assisted microbial fuel cells with Mo-W catalytic cathodes under anaerobic or aerobic conditions in the presence of Fe(III)

A novel strategy to intensify the degradation and mineralization of the antibiotic drug metronidazole (MNZ) in water with simultaneous production of renewable electrical energy was achieved in photo-assisted microbial fuel cells (MFCs). In this system Mo and W catalytic species immobilized onto a graphite felt cathode intensified the cathodic reduction of MNZ under anaerobic conditions and the oxidation of MNZ under aerobic conditions. The aerobic oxidation process was further accelerated in the presence of Fe(III), realizing a combined photo-assisted MFCs and Fenton-MFCs process. The highest rates of MNZ degradation (94.5 ± 1.4%; 75.6 ± 1.1 mg/L/h) and mineralization (89.5 ± 1.1%; 71.6 ± 0.9 mg/L/h), and power production (251 mW/m2; 0.015 kWh/m3; 0.22 kWh/kg COD) were achieved at a Mo/W loading of 0.18 mg/cm2 with a Mo/W ratio of 0.17:1.0, in the presence of 10 mg/L of Fe(III) and at an incident photon flux of 23.3 mW/cm2. Photo-generated holes were directly involved into the oxidation of MNZ under anaerobic conditions. Conversely, under aerobic conditions, the photo-generated electrons favored the production of O2− over OH, while in the presence of Fe(III), OH was predominant over O2−, explaining the intensification of the MNZ mineralization observed. This study demonstrates an alternative and environmentally benign approach for the intensification of the removal of the antibiotic MNZ in water and possibly other contaminants of emerging concern by combining photo-assisted MFCs and Fenton-MFCs in a single process with simultaneous production of renewable electrical energy.

Modification of Graphite Felt Surface for Electrochemical and Magnetic Treatment of Aqueous Contaminants

Iron nanoparticles (Fe NPs) are known to be applied efficiently to remove organic and inorganic pollutants from wastewater effluents, particularly by means of advanced oxidation processes (AOPs) such as in Fenton and electro-Fenton treatments.1,2 In these systems, surface-modified graphite felt electrodes were used either as anodes or as cathodes. Among other procedures, the surface modification of graphite felt cathodes has been achieved through the self-assembly of magnetite nanoparticles (Fe3O4 NPs).2 As for the modification of graphite felt anodes, the electrodeposition of gold nanoparticles (Au NPs) has been found to minimize the overall consumption of energy during electro-Fenton treatment operations, as opposed to most wastewater treament methods.3 In our research we are modifying the surface of graphite felt electrodes, by depositing Fe3O4 NPs on the cathode and Au NPs on the anode, in order to achieve high oxidation rates of organic compounds in aqueous systems. According to our calculations, a cell containing these combined electrodes are meant to operate under favourable energetic conditions in a range close to 200 mV and 18.1 mW m-2. These results are currently being optimized by controlling the electric charge distributed on the modified surface of these electrodes. On the other hand, we are also studying the use of magnetic interactions to remove paramagnetic probe species from aqueous phase in contact with graphite felt surfaces containing Fe3O4 NPs. Our preliminary results show that above 60% of such paramagnetic species can be removed by applying this method, which would enhance the efficiency in wastewater treatment processes. References Shahwan, T., Sirriah, S. A., Nairat, M., Boyacı, E., Eroğlu, A. E., Scott, T. B., & Hallam, K. R. (2011). Green synthesis of iron nanoparticles and their application as a Fenton-like catalyst for the degradation of aqueous cationic and anionic dyes. Chemical Engineering Journal, 172(1), 258-266.Do, T. M., Byun, J. Y., & Kim, S. H. (2017). An electro-Fenton system using magnetite coated metallic foams as cathode for dye degradation. Catalysis Today, 295, 48-55.Le, T. X. H., Esmilaire, R., Drobek, M., Bechelany, M., Vallicari, C., Nguyen, D. L., & Cretin, M. (2016). Design of a novel fuel cell-Fenton system: a smart approach to zero energy depollution. Journal of Materials Chemistry A, 4(45), 17686-17693. Figure 1

Structure-based synergistic mechanism for the degradation of typical antibiotics in electro-Fenton process using Pd–Fe3O4 model catalyst: Theoretical and experimental study

The electro-Fenton process with a dimensionally stable anode and a graphite felt cathode was applied to the oxidative degradation of the antibiotics levofloxacin and trimethoprim. The comparison of electron spin resonance spectra for the catalysts Pd-Fe3O4 and Fe3O4 verified that Pd loading contributed to the coexistence of OH and atomic H∗ in the electro-Fenton process. The use of Pd-Fe3O4 instead of Fe3O4 showed evident superiority for the degradation of levofloxacin according to the increased apparent rate constant value from 0.156 to 0.243 min−1, whereas it was almost unchanged (0.041 min−1) for trimethoprim. Moreover, the total organic carbon abatement after 8 h treatment confirmed the superiority of Pd-Fe3O4 attaining the almost complete mineralization of levofloxacin, and the mineralization current efficiency suggested that atomic H∗ weaken the recalcitrant intermediate of levofloxacin more efficiently compared to trimethoprim. The modelling study indicated that the dispersion of Pd particles on the surface of Fe3O4 promoted the d-band center due to more exposure active sites. The structure calculation of antibiotic and typical intermediates is in agreement with the comparison of experimental results, proposing a theoretical approach to evaluate antibiotic wastewater. The calculation of antibiotic structure and modelling study of catalyst were firstly combined to clarify the structure-based synergistic mechanism between the nucleophilic and electrophilic radicals.

Synergistic effect of pyrrolic N and graphitic N for the enhanced nitrophenol reduction of nitrogen-doped graphene-modified cathode in the bioelectrochemical system

The application of bioelectrochemical system (BES) for recalcitrant contaminant removal is a promising strategy for wastewater treatment but is limited to the low cathodic reduction efficiency. In this paper, a new approach using polypyrrole as nitrogen source has been utilized for the fabrication of nitrogen-doping graphene (NG) modified graphite felt (GF) electrodes. The results of the Raman spectrum and X-ray photoelectron spectroscopy confirmed that the nitrogen species, i.e., pyridinic N, pyrrolic N and graphitic N, in the NG sheets could be conveniently controlled by tuning the pyrolysis temperature from 300 to 600 °C during carbonization process. Cyclic voltammetry and electrochemical impedance spectra measurements verified that the catalytic activity and electron transfer efficiency of the ‘as prepared’ electrodes were greatly improved. Due to the synergistic effect of pyrrolic N and graphitic N, the 4-nitrophenol reduction efficiency of the modified cathode increased 2.1 times higher than that of blank GF cathode in the BES system.

Persulfate enhanced photoelectrocatalytic degradation of cyanide using a CuFe2O4 modified graphite felt cathode

In order to remove cyanide (CN−) from wastewater, a photoelectrocatalytic (PEC) system was constructed using TiO2 nanorods (NRs) anode and CuFe2O4 modified graphite felt (CuFe2O4/GF) cathode. With the addition of persulfate (PS), the performance of PEC for the removal of CN− with an initial concentration of 0.9 mM was increased from 31.10% to 98.21% in 120 min and the pseudo-first-order rate constant was calculated to be 0.0314 min−1. The removal rate of CN− was accelerated with the decrease of initial CN− concentration and the increase of PS dose. The optimal bias potential for the removal of CN− and the recovery of Cu was 1.00 V. Results of radical quenching experiments and electron spin resonance analysis suggested that OH and SO4− were generated by a Fenton-like process in the PEC/PS system. As proved by the XPS analysis, Cu(II) in CuFe2O4 cathode was dissolved by CN− into solution and then partially transformed to Cu(I). When CN− was removed, dissolved Cu ions were deposited onto the surface of CuFe2O4 cathode forming Cu2O. In addition, the dissolved Cu ions can also be deposited on TiO2 photoanode forming CuO. Cu(I) ions reacted with PS through a Fenton-like reaction, generating SO4−, which enhanced the oxidation ability of the PEC/PS system. The results provided a promising way to treat the industrial cyanide effluents efficiently.

Tuning the Composition of Bimetallic Electrodeposited Sn-Pb Catalysts for Enhanced Activity and Durability in CO2 Electroreduction to Formate

Efficient and durable catalysts are needed to convert CO2 to value added products. In recent years, extensive research has been done on tin (Sn) because of its high faradaic efficiency for producing formate (HCOO-) from CO2 [1–5] and lead (Pb) because of its high hydrogen evolution (HER) overpotential [4, 6]. In our recent study [7], bimetallic Sn-Pb catalysts with five different Sn/Pb atomic ratios were electrodeposited on Teflonated carbon paper and non-Teflonated carbon cloth using both metal fluoroborate- and metal oxide-containing deposition media to produce catalysts for electrochemical reduction of CO2 (ERC) to HCOO-. The interaction between catalyst composition, morphology, substrate and deposition media was investigated by cyclic voltammetry followed by chronoamperometry at -2.0 V vs. Ag/AgCl for 2 h in 0.5 M KHCO3. Sn majority catalysts with 15 to 35 atomic % Pb generated faradaic efficiencies up to 95% with stable performance. Pure Sn catalysts on the other hand, in spite of high initial stage formate production rates, experienced extensive (up to 30%) decrease of the faradaic efficiency. The decrease in faradaic efficiency is most likely due to the reduction of the SnO2 layer to metallic Sn0 during formate production. This newly formed Sn0 surface is no longer active for CO2 reduction to formate but instead preferentially produces parasitic H2. XRD results demonstrated the presence of polycrystalline SnO2 after electrolysis using Sn-Pb catalysts with 35 atomic % Pb and its absence in case of pure Sn. It is proposed that the presence of Pb (15 to 35 at %) in Sn majority catalysts stabilized SnO2, which is responsible for the enhanced faradaic efficiency and catalytic durability in ERC. Our results point to a promising strategy for increasing the durability of Sn based catalyst materials for ERC. Oloman C, Li H (2008) Electrochemical Processing of Carbon Dioxide. ChemSusChem 1:385–391. doi: 10.1002/cssc.200800015Li H, Oloman C (2005) The Electro-Reduction of Carbon Dioxide in a Continuous Reactor. J Appl Electrochem 35:955–965. doi: 10.1007/s10800-005-7173-4Bumroongsakulsawat P, Kelsall GH (2015) Tinned graphite felt cathodes for scale-up of electrochemical reduction of aqueous CO2. Electrochimica Acta 159:242–251. doi: 10.1016/j.electacta.2015.01.209Alvarez-Guerra M, Del Castillo A, Irabien A (2014) Continuous electrochemical reduction of carbon dioxide into formate using a tin cathode: Comparison with lead cathode. Chem Eng Res Des 92:692–701. doi: 10.1016/j.cherd.2013.11.002Chen Y, Kanan MW (2012) Tin Oxide Dependence of the CO2 Reduction Efficiency on Tin Electrodes and Enhanced Activity for Tin/Tin Oxide Thin-Film Catalysts. J Am Chem Soc 134:1986–1989. doi: 10.1021/ja2108799Innocent B, Liaigre D, Pasquier D, Ropital F, Léger J-M, Kokoh KB (2009) Electro-reduction of carbon dioxide to formate on lead electrode in aqueous medium. J Appl Electrochem 39:227–232. doi: 10.1007/s10800-008-9658-4Gyenge EL, Moore CE (2017) Tuning the Composition of Bimetallic Electrodeposited Sn-Pb Catalysts for Enhanced Activity and Durability in CO2 Electroreduction to Formate. ChemSusChem 17:3512-3519 . doi: 10.1002/cssc.201700761 Figure 1. Cumulative formate production faradaic efficiency (FE) (a, c) and total moles of formate synthesized (b, d) for catalysts produced by electrodeposition using the fluoroborate bath. Chronoamperometry at -2.0 V vs Ag/AgCl in 0.5 M KHCO3 at 293 K for 2 hours. Substrates: (a, b) teflonated carbon paper and (c, d) carbon cloth. Figure 1

Electrochemical treatment of bio-treated landfill leachate: Influence of electrode arrangement, potential, and characteristics

The integration of electrocoagulation and electrooxidation process was employed to treat residual organic pollutants, ammonia, and total phosphorus for bio-treated landfill leachate. Electrochemical processes with dimensional stable anode, iron electrode and graphite felt cathode were studied under different electrode arrangement of bipolar electrode, dual anodes, and monopolar anode systems. Their performance for removal of pollutants and characteristics of the precipitates was evaluated. The effects of applied voltage from 7 V to 14 V, flow direction, and contents of suspended solids on removal performance were investigated. The best performance of simultaneous removal was recorded at the bipolar system, with the removal efficiency of 65%, 100%, and 91% for organic pollutants, ammonia, and phosphorus at 1.5 Ah L−1. The fluorophore distributions in the fractions of organic pollutants revealed that humic and fulvic acid-like substances were removed after the bipolar electrode process. Different compositions of Fe and O identified as FeO(OH) and γ-Fe2O3 were found in precipitates generated in bipolar and dual electrodes system. An applied voltage of 10 V and the cathode inflow mode facilitated the simultaneous removal process. Suspended solids served as the core of colloidal coagulant, was of great importance in integrated process to remove organic pollutants, but had no obvious effect to remove ammonia. These results indicate that this integrated bipolar system is an efficient approach for the treatment of residual pollutants from a bio-treated landfill leachate.

Highly energy-efficient removal of acrylonitrile by peroxi-coagulation with modified graphite felt cathode: Influence factors, possible mechanism

A highly energy-efficient peroxi-coagulation (PC) process was developed based on modified graphite felt, and the acrylonitrile removal efficiency was also comparatively studied by electro-Fenton (EF) and electrocoagulation (EC). The results showed that acrylonitrile was slowly and ineffectively removed by EC and EF, whereas by PC it was not only more rapid, but also effective at wide pH ranges of 3.0–9.0, which overcame the pH limitations for EC and EF. In addition, the electric energy consumption (EEC) of EF, EC and PC was 36.01, 14.43 and 3.08 kWh/kg respectively, suggesting PC was more economical. The influence of important operating factors such as pH, applied current and initial concentration were investigated for these three processes. The production of OH and transformation of iron ions were analyzed to explore the mechanisms of PC process. Compared to conventional treatment methods, PC was more cost-effective due to the combined action of OH as well as the coagulation with the formed Fe(OH)3 precipitate. Primary intermediates were identified by GC–MS analysis, and a possible pathway was proposed by the action of OH in EF and the hydrogenation in EC. This work demonstrated that PC is cost-effective and has potential for the degradation of acrylonitrile.

A metal-free visible light active photo-electro-Fenton-like cell for organic pollutants degradation

To avoid the potential secondary metal pollution leached from Fenton-like catalysts and use less or no external chemicals supply, we develop an all-carbon based visible light active photo-electro-Fenton-like (PEF) cell to in-situ generate highly active •OH radical for environmental remediation. In this cell, the mesoporous carbon coated graphite felt (MesoC/GF) cathode could effectively produce H2O2 by electrochemical reduction of oxygen. Graphitic carbon nitride (g-C3N4) with visible light photocatalytic activities acts as an efficient metal-free Fenton-catalyst for H2O2 activation to produce •OH radical under visible light irradiation. The different cell parameters such as applied voltage, photocatalysts dosage and pH condition have been investigated for phenol removal in aqueous solution. This metal-free visible light active PEF cell shows excellent mineralization efficiency of stubborn phenol with high stability and its performance of phenol removal efficiency is much higher than that of the g-C3N4 only photocatalysis cell and MesoC/GF only electrolysis cell. Moreover, our PEF cell presents comparable or even better Fenton-catalytic activities than the similar electro-Fenton cell using MesoC/GF and homogeneous Fe2+ ion. These results demonstrate our all-carbon based PEF cell without external chemicals supply is promising for environmental remediation.

Effect of Start-Up Strategies and Electrode Materials on Carbon Dioxide Reduction on Biocathodes.

ABSTRACTThe enrichment of CO2-reducing microbial biocathodes is challenging. Previous research has shown that a promising approach could be to first enrich bioanodes and then lower the potential so the electrodes are converted into biocathodes. However, the effect of such a transition on the microbial community on the electrode has not been studied. The goal of this study was thus to compare the start-up of biocathodes from preenriched anodes with direct start-up from bare electrodes and to investigate changes in microbial community composition. The effect of three electrode materials on the long-term performance of the biocathodes was also investigated. In this study, preenrichment of acetate-oxidizing bioanodes did not facilitate the start-up of biocathodes. It took about 170 days for the preenriched electrodes to generate substantial cathodic current, compared to 83 days for the bare electrodes. Graphite foil and carbon felt cathodes produced higher current at the beginning of the experiment than did graphite rods. However, all electrodes produced similar current densities at the end of the over 1-year-long study (2.5 A/m2). Methane was the only product detected during operation of the biocathodes. Acetate was the only product detected after inhibition of the methanogens. Microbial community analysis showed that Geobacter sp. dominated the bioanodes. On the biocathodes, the Geobacter sp. was succeeded by Methanobacterium spp., which made up more than 80% of the population. After inhibition of the methanogens, Acetobacterium sp. became dominant on the electrodes (40% relative abundance). The results suggested that bioelectrochemically generated H2 acted as an electron donor for CO2 reduction.IMPORTANCE In microbial electrochemical systems, living microorganisms function as catalysts for reactions on the anode and/or the cathode. There is a variety of potential applications, ranging from wastewater treatment and biogas generation to production of chemicals. Systems with biocathodes could be used to reduce CO2 to methane, acetate, or other high-value chemicals. The technique can be used to convert solar energy to chemicals. However, enriching biocathodes that are capable of CO2 reduction is more difficult and less studied than enriching bioanodes. The effect of different start-up strategies and electrode materials on the microbial communities that are enriched on biocathodes has not been studied. The purpose of this study was to investigate two different start-up strategies and three different electrode materials for start-up and long-term operation of biocathodes capable of reducing CO2 to valuable biochemicals.