Carbon Air Cathode Research Articles

Flexible Aluminum-Air Batteries

Wearable and flexible electronics have a wide range of applications. Making a flexible power source for them is essential. Aluminum-air batteries are attractive for powering portable, lightweight devices due to their inexpensive, light, and powerful energy source. In this project, the Al-air battery was made using activated carbon and aluminum electrodes, chloride-based electrolytes with ionic liquid additives. Various mixtures of 1-ethyl-3-methylimidazolium chloride, aluminum chloride, sodium hydroxide, and sodium chloride were studied. Fundamental properties of room-temperature ionic liquids, such as lower conductivity and density, improved the performance of aluminum-air batteries. Cell capacity, cyclic voltammetry behavior, and cell interfacial impedance with various electrolytes were optimized using the design of experiments. The battery's electrical power output and cell capacity were lower than those obtained using an activated carbon air cathode. The cell capacity over repeated electrochemical reactions was stable. The Al-air battery had regular cyclic voltammetry behavior. Aluminum hydroxide was not found on the anode electrode when an ionic liquid electrolyte was used. The interfacial cell impedance did not decrease after electrochemical reactions over a long time.

Inhibiting effects of humic acid on iron flocculation hindered As removal by electro-flocculation on air cathode iron anode

Activated carbon air cathode combined with iron anode oxidation-flocculation synergistic Arsenic (As) removal was a new groundwater purification technology with low energy consumption and high efficiency for groundwater with high As concentration. The presence of organic matter such as humic acid (HA) had ambiguous effects on formation of organic colloids in the system. The effects of the particle size distribution characteristics of these colloids on the formation characteristics of flocs and the efficiency of As purification was not clear. In this work, we used five different pore size alumina filter membranes to separate mixed phase solutions and studied the corresponding changes in iron and arsenic concentrations in the presence and absence of humic acid conditions. In the presence of HA, the arsenic concentration of < 0.05 µm particle size components was 1.01, 1.28, 3.07, 7.69, 2.85 and 1.24 times of that in the absence of HA. At the same time, the arsenic content in 0.05–0.1 µm and 0.1–0.45 µm particle size components was also higher than that in the system without HA, which revealed that the presence of HA hindered the flocculation behavior of As distribution to higher particle sizes in the early stage of the reaction. The presence of HA affected the flocculation rate of iron flocs from small to large particle size fractions and it had limited effect on the behavior of large-size flocs in adsorption of As. These results provide a theoretical basis for targeted, rapid, and low consumption synergistic removal of arsenic and organic compounds in high arsenic groundwater.

Preparation of 3‐D Porous Pure Al Electrode for Al‐Air Battery Anode and Comparison of its Electrochemical Performance with a Smooth Surface Electrode

AbstractThis study compared the electrochemical performances of porous surface electrodes obtained by the salt casting process against a smooth surface electrode. Potentiodynamic polarization test, linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) tests of porous and smooth Al electrodes were performed using 0.5 M NaOH solution. According to the Tafel analysis, the Jcor value of the Al‐porous electrode was measured as 3.23 mA cm−2, which is approximately 55 % higher than the Al‐smooth electrode. The Ecor value was more negative for the Al‐porous electrode. Results of the low charge transfer resistance (2.2 Ω) of the Al‐porous electrode compared to the Al‐smooth electrode (2.8 Ω) concluded that the porous surface was increased the current density by increasing charge transport due to higher surface area. The galvanostatic discharge tests of the electrodes were carried out in an Al‐air battery test cell using a graphite carbon air cathode. As a result, the power density of the Al‐porous electrode was approximately 42 % higher than the Al‐smooth surface electrode.

Electrodeposited Ionomer Protection Layer for Negative Electrodes in Zinc-Air Batteries.

The protection of zinc anodes in zinc-air batteries (ZABs) is an efficient way to reduce corrosion and Zn dendrite formation and improve cyclability and battery efficiency. Anion-conducting poly(N-vinylbenzyl N,N,N-trimethylammonium)chloride (PVBTMA) thin films were electrodeposited directly on zinc metal using cyclic voltammetry. This deposition process presents a combination of advantages, including selective anion transport in PVBTMA reducing zinc crossover, high interface quality by electrodeposition improving the corrosion protection of zinc and high ionomer stiffness opposing zinc dendrite perforation. The PVBTMA layer was observed by optical and electron microscopy, and the wettability of the ionomer-coated surface was investigated by contact angle measurements. ZABs with PVBTMA-coated Zn showed an appreciable and stable open-circuit voltage both in alkaline electrolyte (1.55 V with a Pt cathode) and in miniaturized batteries (1.31 V with a carbon paper cathode). Cycling tests at 0.5 mA/cm2 within voltage limits of 2.1 and 0.8 V gave a stable discharge capacity for nearly 100 cycles with a liquid electrolyte and more than 20 cycles in miniaturized batteries. The faster degradation of the latter ZAB was attributed to the clogging of the carbon air cathode and drying or carbonation of the electrolyte sorbed in a Whatman paper.

Transitional trimetallic alloy embedded polyacrylamide hydrogel derived nitrogen-doped carbon air-cathode for bioenergy generation in microbial fuel cell

Heterometallic carbons are popular materials for application in energy devices due to their high oxygen reduction reaction (ORR) activity and good catalytic stability. Particularly in microbial fuel cells (MFCs), Fe group metal alloys are efficient ORR catalysts. This work has embedded different metallic alloy nanoparticles in polyacrylamide hydrogel derived in-situ nitrogen-doped carbon. All the catalysts (Fe@NC, FeCo@NC, FeNi@NC, and FeCoNi@NC) are used as air cathodes and examined for power generation in single chamber MFCs. Trimetallic composite (FeCoNi@NC) performed better than Pt/C. FeCoNi@NC exhibited superior electrocatalytic activity with an oxygen reduction peak at 0.394 V (vs RHE) and a corresponding peak current density of −0.159 mA. FeCoNi@NC records maximum power output of 963.5 mW m−2 at 2483.2 mA m−2, 3.287 and 1.136 times higher than NC and 10 wt% Pt/C, respectively. This could be due to the uniformly distributed alloy nanoparticles, abundant pyridinic-N, and M−Nx sites that enhance the durability, charge transfer, and power generation in MFCs. These findings suggest that the trimetallic transition metal-carbon (MNC) electrodes could be promising ORR catalysts, justifying their application for energy devices.

Dual functions of activated carbon air‐cathode: Nitrobenzene removal and electricity production in microbial fuel cells

AbstractThe removal of nitrobenzene (NB) in microbial electrochemical systems generally requires electrical power to operate systems in the mode of microbial electrolysis cells (MECs). The present study demonstrates that single‐chamber microbial fuel cells (S‐MFCs) assembled with a bioanode and an activated carbon (AC) air cathode could simultaneously remove NB and generate electricity. S‐MFCs with 1 mM NB exhibit long term NB tolerance and stable electricity production, with NB removal up to 98% in an operation cycle and a maximum power of 16.2 ± 1.3 W m−3. High NB loadings significantly inhibited the activity of anodic biofilms, but the inhibition was reversible. Investigating the removal of NB and its reduction product aniline (AN) in different operations supported the fact that the adsorption at the AC air cathode is the main pathway for the removal of NB and AN from solution, except for the partial conversion of NB to AN by anaerobic reduction in solution. In S‐MFCs, the activated carbon in the cathode plays both functions: catalyzing the oxygen reduction reaction and adsorbing NB and AN, so that the S‐MFC assembled with the AC air cathode, unlike most NB removing MECs, functions as a system with both NB removal and electricity production.

Defect free rolling phase inversion activated carbon air cathodes for scale-up electrochemical applications

Scalable production of air cathodes is crucial for applying electrochemical technologies in practical water treatment applications. However, existing fabrication procedures of air cathodes for microbial fuel cells (MFCs) are either complicated or not sufficiently waterproof for larger-scale processes. In this study, an easily implemented low-pressure rolling phase inversion method was developed for preparing scalable, waterproof activated carbon air cathodes. An aminated PVDF (NH2-PVDF) membrane was synthesized as a new gas diffusion layer (GDL) to avoid defect formation from contacting organic solvent during cathode fabrication. The cathode was easily enlarged to 1000 cm2 with a high pressure resistance of 13 ± 0.7 m H2O height (∼137 kPa), exceeding the waterproof capability of previously reported air cathodes. The electrochemical performance of the fabricated air cathode was not affected by the additional membrane. MFCs with the NH2-PVDF cathodes produced a maximum power density of 1010 ± 40 mW m−2, consistent with literature values. The cathode was used to generate H2O2 at a rate of 420 ± 40 mg L−1 h−1 (25 mA cm−2), and nickel catalyst modification further increased the rate to 760 ± 60 mg L−1 h−1 (25 mA cm−2). Overall, the highly waterproof rolling phase inversion activated carbon air cathodes showed great promise for scaling up biotic and abiotic electrochemical systems for practical applications.

Enhanced Performance of Microbial Fuel Cells Using PVDF Activated Carbon Air Cathode and Electrochemically and Chemically Treated Carbon Felt Anode

Microbial fuel cells (MFCs) harness the metabolism of microorganisms, converting chemical energy into electrical energy. Improving both Anode and Cathode design is thus of great significance to enhance the MFC performance and its commercial application. For the performance improvement of MFCs, the anode becomes a breakthrough point due to its influence on bacterial attachment and extracellular electron transfer (EET). On the other hand, air cathodes have considerable influence on the maximum power of air-driven MFCs. The cathodes used in MFCs need to have high catalytic activity for oxygen reduction, but they should be inexpensive watertight,and easy to manufacture.As the first part of this work, carbon felt was electrochemically and chemically treated by electrolyzing in nitric acid and phosphate buffer followed by soaking in aqueous ammonia. The treated and untreated carbon felts were utilized as anodes in MFCs, and current production was compared while the cathode was stainless steel mesh (SS-316L) in both cases. The treated carbon felt displays strong interaction with the microbial biofilm of Shewanella baltica 20 facilitating electron transfer from exoelectrogens to the anode. An MFC equipped with a treated carbon felt as anode has significantly lower charge-transfer resistance and achieves considerably better performance than one equipped with an untreated carbon felt anode. The enhanced electron transfer is attributed to newly generated carboxyl containing functional groups on the treated carbon felt.In the second part of the present study, SS-316L as a cathode was modified using phase inversion process to construct a poly vinylidenefluoride (PVDF) binder and an activated carbon catalyst according to the procedure reported previously.Finally, the MFC with treated carbon felt anode and PVDF air cathode was tested. The MFC with both modified anode and cathode achieves considerably better performance than one with a traditional carbon felt anode and SS-316L cathode. The maximum current density, power density, and energy recovery, and sensitivity of the biofilm to the heavy metals are significantly improved.

Amplifying anti-flooding electrode to fabricate modular electro-fenton system for degradation of antiviral drug lamivudine in wastewater

The advanced oxidation based on in-situ hydrogen peroxide production using carbon air cathode is very potential for wastewater treatment. However, catalyst flooding and complex assembly patterns are the bottleneck limiting the air cathode to the long-term and large-scale application. In this work, a novel anti-flooding air-breathing cathode (ABC) was prepared by a simple rolling-spraying method with relatively low price commercial materials. The novel method changed the morphology of gas diffusion layer as well as adjusted the hydrophobicity of air side of the catalyst layer. As a result, water-air distribution management was achieved and TPI disequilibrium was prevented. Compare with traditional ABC, the H2O2 yield and current efficiency (CE) of optimized anti-flooding ABC (ABC0.9) increased by 13.5% (941 ± 10 mg·L−1·h−1 with CE of 84% at 30 mA·cm−2), the material cost and fabrication time decreased by 10.1% (2.32 ¥·dm−2, ~0.36 $·dm−2) and 40%. Amplified ABC coupled with Ti/IrO2 anodes were integrated into a modular electrode used for H2O2generation. When the current density (j) increased from 10 to 30 mA·cm−2, the energy cost increased from 0.19 to 0.43 ¥·mol−1 H2O2 (from 0.03 to 0.07 $·mol−1 H2O2). The modular electrode was utilized in a 2 L pre-pilot scale reactor for antiviral drug lamivudine degradation by electro-Fenton (EF) process. 100% of lamivudine and 78.1% of total organic carbon (TOC) were removed within 60 min at 20 mA·cm−2. The susceptible sites on the lamivudine toward hydroxyl radicals were investigated and transformation products (TP) as well as degradation pathway were studied.

Development and Demonstration of Pilot Scale Metal-Air Flow Battery for Ultra-Large Capacity Energy Storage System

Recently, novel concepts of electrochemical cells have been spotlighted for ultra-charge energy storage system. Among these cells, magnesium alloy (AZ31) air batteries have attracted much attention as promising energy conversion devices due to their high theoretical energy density, eco-friendly materials and low fabrication cost. Although AZ31–air battery is a primary battery, the AZ31–air battery can be re-used or recharged mechanically by replacing the consumed AZ31 anode and turbid electrolyte with a fresh AZ31 anode and electrolyte, refering to “re-fuelable” During the discharge process, the AZ31 anode is oxidized to ionized Mg, producing two electrons, while at the opposite carbon air-cathode, oxygen molecules pass through the gas diffusion layer and is then reduced to OH− by reaction with H2O and electrons. The theoretical voltage of the AZ31–air battery is 1.2 V and the specific energy density is 2.2 kW h kg−1. Though AZ31–air batteries have a relative high voltage and energy density, there are still scientific problems limiting their pilot scale application. The main issue of cell is the high polarization and low coulombic efficiency. These problems are caused by the corrosion of the metal anode arising from the reaction of metal ions and the electrolyte, and the sluggish by-product kinetics in the air-cathode. In this work, we combined Mg-air batteries with electrolyte flow system, called metal-air flow battery (MAFB) in order to enhance the discharge properties and lifetime by solving the sluggish by-product problems. The components of anode and electrolyte were AZ31 (magnesium alloy) as a fuel and 18wt% saline aqueous solution. The circulation of electrolyte flow efficiently reduces the coagulation of Mg(OH)2 by-product in the unit-cells. As a result, the anode surface efficiency has increased from 72 to above 90 % after the use of flow system. In addition, we have successfully design and developed the metal-air flow battery from unit-cell to rack system. The rack system is made up of 25 series of electrically wired unit-cells for modules and 4-level of modules with electrolyte flow system. The flow system conducted simultaneously in each unit-cells by electrolyte supply tank in the top and by-product filter tank in the bottom. From the rack system, a pilot scale MAFB with 400 pieces of unit-cells was developed and fabricated for ultra-large energy storage system. The 704 kWh of energy storage system demonstrated by 25s-16p electrical wiring with 4-rack flow systems. As a result, it is the first report about the MAFB using AZ31 anodes in pilot-scale energy storage system. It has shown a large potential for future energy conversion devices for smart grid applications. Figure 1

Co2P embedded in nitrogen-doped carbon nanoframework derived from Co-based metal-organic framework as efficient oxygen reduction reaction electrocatalyst for enhanced performance of activated carbon air-cathode microbial fuel cell

• The MPD of optimized MFC was 2001 ± 48 mW m −2 , 123% higher than that of control. • The electronic interaction between embedded Co 2 P and N -C improved ORR activity. • Co 2 PNC-NF electrocatalyst exhibited a desired four-electron pathway for ORR. • The double Co site of 001 face of Co 2 P could boost the cracking of OOH* group. A kind of Co 2 P embedded in nitrogen-doped carbon nanoframework (Co 2 PNC-NF) synthesized from directly carbonized Co-based metal-organic framework (ZIF-67) combined with phosphorus was utilized in the microbial fuel cell (MFC) to modify the active carbon air-cathode for the first time. Various techniques involving XRD, FESEM, TEM/EDS, BET and XPS were used to characterize the microstructure, morphology and surface chemical composition belonging to as-synthesized Co 2 PNC-NF. The electrochemical measurements revealed that the active carbon cathode modified by Co 2 PNC-NF got reduced resistance and optimized catalytic behavior in oxygen reduction reaction (ORR) process. The optimized MFC had a high maximum power density reaching 2001 mW m −2 , increasing by 123% compared with the bare active carbon cathode MFC. This result showed that combination between transition-metals phosphide and heteroatom-doped carbon matrices was beneficial to the improvement of MFC performance. Moreover, density functional theory calculations indicated that the special structure of double Co site of 001 face of Co 2 P can accelerate the ORR by boosting the cracking of OOH* group. Therefore, the Co 2 PNC-NF could be applied as an economical and efficient electrocatalyst in MFC to replace noble metal catalyst.

Leaf-like carbon frameworks dotted with carbon nanotubes and cobalt nanoparticles as robust catalyst for oxygen reduction in microbial fuel cell

In this investigation, a double Zeolitic Imidazolate Frameworks (ZIF) precursor is used to synthesize a leaf-like cobalt/nitrogen co-doped porous carbon embedded with carbon nanotubes (Co–N–PC@CNTs), as a catalyst to modify an activated carbon air cathode microbial fuel cell (MFC). The unique leaf structure of carbon frameworks, which is rich in carbon nanotubes and cobalt nanoparticles on the surface, is confirmed to accelerate the oxygen reduction reaction (ORR) through a four-electron pathway similar to Pt/C. The time-current test reveals the remarkable stability of indicated by the retain of around 92% current after 12 h. The electrochemical reactions with Co–N–PC@CNTs are far superior to the control group. What's more, the best improved MFC exhibits outstanding exchange current density (27.83 × 10−4 A cm−2), and the optimized power density of MFC reaches 2479 ± 70 mW m−2, which is 247.2% higher than that of the control group (714 ± 59 mW m−2). In addition, Co–N–PC@CNTs modified activated carbon cathode MFC has an excellent chemical oxygen demand (COD) removal rate of 86.52%, which is significantly better than the control group (50.51%). Therefore, Co–N–PC@CNTs is considered to be a promising MFC cathode catalyst.

Cobalt phosphide embedded N-doped carbon nanopolyhedral as an efficient cathode electrocatalyst in microbial fuel cells

Design and synthesis of effective and low-cost electrocatalysts for oxygen reduction reaction (ORR) is of great significance for the performance of microbial fuel cells (MFCs). Herein, we fabricated a cobalt phosphide embedded N-doped carbon nanopolyhedral (CoP@N-C) by simultaneous phosphidation and carbonization of ZIF-67 under N2 atmosphere. The physical and chemical properties of the electrocatalysts were analyzed in detail by scanning electron microscope, transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy and N2 adsorption–desorption isotherms. Results showed that the CoP@N-C had a dodecahedral shape with cobalt, nitrogen and phosphorus incorporating in porous graphical carbon. CoP compound which had a strong electron capture capability and ORR activity was embedded within the electrocatalysts. Introducing of P increased the contents of pyridinic-N, Co2+/Co3+ couples and oxygen vacancies, which provided sufficient catalytic active sites for ORR. The increased metallic Co content and mesoporous/macroporous surface area ensured efficient electron and mass transfer during ORR. Rotating disk electrode measurement revealed that the CoP@N-C exhibited a high ORR catalytic activity comparable to Pt/C, and an efficient four-electron pathway during ORR. When fabricated into activated carbon air cathode, the optimized CoP@N-C produced a maximum power density of 2236.8 mW m−2 in MFCs, which was about 2 times that of the bare activated carbon control. In addition to the superb ORR performance, the cost of the CoP@N-C was only ∼1/3 of commercial Pt/C. This study suggests that CoP@N-C could be an attractive non-precious metal ORR electrocatalyst for the application in high-performance MFCs.

Enhanced electricity production in single-chamber MFCs with air cathodes decorated by Fe–N–C catalysts derived from 5H-dibenz [b,f] azepine-5-carboxamide (Carbamazepine)

For practical applications of microbial fuel cells (MFCs), 5H-dibenz [b,f] azepine-5-carboxamide (Carbamazepine, CBZ) was used as the organic precursor for the synthesis of catalysts composed of Fe–N–C complexes (named as Fe-CBZ-Cats) through a sacrificial support method. Characterizations by SEM, XPS and TEM-EDS elemental mapping show that the synthesized Fe-CBZ-Cats have porous structure and uniformly dispersed Fe/N/C complex centers which could play key roles in effective ORR. Linear scanning voltammetry (LSV) measurements show that the synthesized Fe-CBZ-Cats exhibits ORR activity comparable to commercial Pt/C catalysts under the same catalyst loading (2 mg cm−2). The maximum power density produced by cathode-limiting MFCs with Fe-CBZ-Cats air cathodes was 431 ± 23 μW cm−2, higher than those in the control MFCs with Pt/C air cathodes (403 ± 13 μW cm−2) and activated carbon air cathodes (296 ± 24 μW cm−2). In addition, the toxicity tolerance of the synthesized Fe-CBZ-Cats is much higher than Pt/C.

Simultaneously enhancing power density and coulombic efficiency with a hydrophobic Fe–N4/activated carbon air cathode for microbial fuel cells

The application of microbial fuel cells (MFCs) for electricity generation is still hindered by relatively low power densities and coulombic efficiencies. Here a hydrophobic Fe–N4 macromolecule catalyst was directly immobilized on the activated carbon (AC) surface to fabricate a hydrophobic Fe–N4/AC air cathode. With a 10 wt% Fe–N4/AC cathode, a maximum power density of 2.5 ± 0.1 W m−2 was obtained, which was 25% higher than plain AC cathodes (2.0 ± 0.01 W m−2). The additional hydrophobicity due to the Fe–N4 macromolecule catalyst simultaneously reduced water electrolyte evaporation and oxygen intrusion for improved coulombic efficiency. The coulombic efficiency was increased to 20 ± 0.5% for the 10 wt% Fe–N4/AC cathode, which was ~54% higher than that of the AC cathodes (13 ± 0.2%) at an external resistance of 1000 Ω. The use of hydrophobic Fe–N4 macromolecule catalyst is the first attempt to simultaneously improve the power density and coulombic efficiency by tuning the catalyst hydrophobicity, which also explores a new direction of catalyst engineering for the advancement of MFCs.

An investigation of commercial carbon air cathode structure in ionic liquid based sodium oxygen batteries

In order to bridge the gap between theoretical and practical energy density in sodium oxygen batteries challenges need to be overcome. In this work, four commercial air cathodes were selected, and the impacts of their morphologies, structure and chemistry on their performance with a pyrrolidinium-based ionic liquid electrolyte are evaluated. The highest discharge capacity was found for a cathode with a pore size ca. 6 nm; this was over 100 times greater than that delivered by a cathode with a pore size less than 2 nm. The air cathode with the highest specific surface area and the presence of a microporous layer (BC39) exhibited the highest specific capacity (0.53 mAh cm−2).

Interfacial integration and roll forming of quasi-solid-state Li–O2 battery through solidification and gelation of ionic liquid

The development of solid-state lithium-oxygen batteries is currently limited primarily by the high solid-solid interfacial resistance and the lack of efficient assembly of electrolyte and electrode. In this work, noncovalent interactions between the cations of an ammonium ionic liquid and both solid electrolytes and carbon air cathodes are introduced. The ionic liquid-based electrolytes (ILE) are solidified on Li6·40La3Zr1·40Ta0·60O12 (LLZTO) nanoparticles and gelated by multi-wall carbon nanotubes (MWCNTs), respectively, to construct LLZTO@ILE quasi-solid-state electrolyte (QSSE) and MWCNTs-LLZTO/ILE gel cathode (GC). The QSSE exhibits a high ionic conductivity of 1.71 × 10−3 S cm−1 at 60 °C, high Li-ion transference number of 0.56, broad electrochemical window of ~4.8 V and good thermal stability. The GC shows outstanding compatibility with QSSE. Quasi-solid-state Li–O2 batteries are assembled by integrating QSSE and GC films with a facile roll forming method, showing a low total interfacial resistance (~87 Ω cm2), and excellent reversible cycles (70 cycles) with low charge overpotential (<0.44 V) and quite high electrical energy efficiency (>70%) at 60 °C and 200 mA g−1. A 0.12 Ah pouch-type Li–O2 battery was achieved by this method. These results suggest that the noncovalent interactions initiated by IL cations could be an effective approach to solve the solid-solid interface issue and achieve high discharge capacity in solid-state energy storage devices.

Performance and inorganic fouling of a submergible 255 L prototype microbial fuel cell module during continuous long-term operation with real municipal wastewater under practical conditions

A submergible 255 L prototype MFC module was operated under practical conditions with municipal wastewater having a large share in industrial discharges for 98 days to investigate the performance of two of the largest, ever investigated multi-panel stainless steel/activated carbon air cathodes (85 × 85 cm). At a flow rate of 144 L/d, power density of 78 mW/m2Cat (317 mW/m3) and COD, TSS and TN removal of 41 ± 16 %, 36 ± 16 % and 18 ± 14 %, respectively, were reached. Observed Coulombic efficiency and substrate-specific energy recovery were 29.5 ± 14 % and 0.184 ± 0.125 kWhel/kgCOD,deg, respectively. High salt content of wastewater (TDS = 2.8 g/L) led to severe inorganic fouling causing a drastic decline in power output and energy recovery of more than 90 % in the course of experiments. Mechanical cleaning of the cathodes restored only 22 % (17 mW/m2Cat) of the power output and did not improve nutrient removal or energy recovery.

Nanorod β-Ga2O3 semiconductor modified activated carbon as catalyst for improving power generation of microbial fuel cell

Nanorod monoclinic β-Ga2O3 semiconductor, synthesized by a facile hydrothermal method, was firstly researched as a catalyst to modify activated carbon air cathode in microbial fuel cells (MFCs). The maximum power density of modified MFC reaching 1843 ± 40 mW m−2 was 3 times higher than the control. The Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), and X-ray diffraction (XRD) results revealed the larger surface area and porous structure could provide more active sites to improve the performance of MFCs. The result of X-ray photoelectron spectroscopy (XPS) confirmed that plenty of oxygen vacancy existed in the synthesized β-Ga2O3. Tafel curve and rotating disk electrode (RDE) results illustrated the high exchange current density of β-Ga2O3 and the four-electron pathway at the cathode during the oxygen reduction reaction (ORR), respectively. The cathode modified with β-Ga2O3 displayed excellent improvement towards ORR and therefore improved the performance of MFCs.

Domestic wastewater treatment and energy harvesting by serpentine up-flow MFCs equipped with PVDF-based activated carbon air-cathodes and a low voltage booster

Microbial fuel cells (MFCs) exhibit high capital cost and low energy output, which are major issues of the expected practical application of MFCs in wastewater treatment. Here, we have developed serpentine up-flow MFCs equipped with polyvinylidene fluoride (PVDF)-based activated carbon (AC) air-cathode (MFC-PVDF/AC) and continuously operated for more than 6 months with real domestic wastewater as a substrate. The MFC-PVDF/ACs achieved average total COD removal rates (5.11 ± 0.94 kg tCOD/m3/d) and power densities (3.96 ± 3.01 W/m3) without major water leakage, which were even higher than those of MFCs equipped with Pt-based air-cathode (MFC-Pts). The MFC-PVDF/ACs also achieved high and stable suspended solid (SS) removal efficiency (>90%) at 1.5-h HRT without any clogging event during the entire operation period. Since the PVDF-based AC air-cathode is less expensive, more durable, and easy to manufacture, expensive Pt cathodes are not necessary for MFCs treating low strength domestic wastewater. Furthermore, we have developed a low voltage booster (LVB) to increase low output voltage of MFC-PVDF/ACs (i.e., <0.4 V). Connecting a single LVB with a single MFC-PVDF/AC increased the voltage from <0.4 V to 4.35–5.2 V without the voltage reversal, which was enough to turn on three LED bulbs for >12 days. Taken together, the MFC-PVDF/AC with a LVB circuit exhibits excellent and stable performance of domestic wastewater treatment and usable power generation, suggesting that it could be used as a cost- and energy-saving primary wastewater treatment system.