Activated 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.

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.

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.

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.

The use of natural hierarchical porous carbon from Artemia cyst shells alleviates power decay in activated carbon air-cathode

Activated carbon (AC) air-cathode is demonstrated to be promising for the energy recovery from wastewaters. However, it suffers from the performance decay after long-term operation in microbial fuel cells (MFCs). Here we add a natural hierarchical porous nitrogen-rich carbon material, carbonized Artemia cyst shells (LC), to alleviate the power decay. When the air-cathode is made of a mixture of AC and LC with a mass ratio of 1:2 (named 1AC2LC), the current densities are 28% (the beginning) and 65% (after 1 year's operation) higher than AC cathodes, and the long-term power densities increase from 0.871 ± 0.002 (AC) to 1.296 ± 0.005 W m−2 (1AC2LC) after one year's operation. The Coulombic efficiency increases by 20% than the control. This can be primarily attributed to these inerratic hierarchical pores enhancing oxygen transfer in the catalyst layer since the oxygen mass transfer coefficient is increased by 3.4 times, where the meso- and macro-pores are enlarged, showing the importance of oxygen transfer on the longevity and energy production. Our results show a novel way, addition of inexpensive carbonized Artemia cyst shells, to optimize cathodic porous structure and enhance the longevity of MFCs.

Activated carbon-supported multi-doped graphene as high-efficient catalyst to modify air cathode in microbial fuel cells

It is difficult to apply microbial fuel cells (MFCs) basing on activated carbon air cathode in practical application because of the low efficiency of oxygen reduction reaction. Thus, exploring high-efficient catalyst to improve the cathode performance is of emergent significance. Herein, we synthesize an activated carbon-supported FeAgN multi-doped graphene as the air cathode catalyst in MFCs via a simple preparation and calcination of FeAg prussian blue analogues. As proved, the designed catalyst contributes to the decrease of the cathode's diffusion resistance and charge transfer resistance; meanwhile it immensely promotes the kinetics towards ORR by accelerating the migration of electron from the encapsulated bimetals to the surrounding carbon structure, indicating that the deposit of multi-doped graphene catalyst reinforces the cathode's conductivity and expedites the electron transfer process. The output power performances indicate that a highest maximum power density reaches up to 1956.45 mW m−2, which is 7 times higher than that of the control, foreboding the catalyst's potential application in MFCs.

Metal organic framework-derived Co3O4/NiCo2O4 double-shelled nanocage modified activated carbon air-cathode for improving power generation in microbial fuel cell

To improve the power generation of the microbial fuel cell, activated carbon is modified by the Co3O4/NiCo2O4 double-shelled nanocage, which prepared via a metal-organic framework method. When tested as cathodic material, the mesoporous Co3O4/NiCo2O4 double-shelled nanocage with a large surface (112.9 m2 g−1) exhibits higher open circuit potential (0.252 V) and higher exchange current density (19.70 × 10−4 A cm−2). Moreover, the maximum power density of the air-cathode microbial fuel cell equipped with the 5% as-prepared catalyst is 1810 mW m−2, 104% higher than the control. The morphology and crystal structure of Co3O4/NiCo2O4 are investigated by the Transmission electron microscope and X-ray diffraction. X-ray photoelectron spectroscopy analysis indicates that there exists Co3+/Co2+ and Ni3+/Ni2+ redox couples in the catalyst, and divalence - trivalence - divalence redox cycles contribute to the improved oxygen reduction reaction performance and enhanced power output. Owing to the structural merits and improved electrochemical activity, the synthesized Co3O4/NiCo2O4 double-shelled nanocage would be considered as a replacement of the new material for Pt in microbial fuel cell.

Regeneration of activated carbon air-cathodes by half-wave rectified alternating fields in microbial fuel cells

The activated carbon air-cathode is promising but usually be rapidly contaminated in wastewater due to the salt accumulation and biofilm formation on the catalysis layers in microbial fuel cells (MFCs). For the first time, the half-wave rectified alternating fields (AC+) was demonstrated as a novel, efficient and energy-saving way to remove ions from porous surface and regenerate this cathode. 1.2 V AC+ treatment recovered the power generation by 50% and 43% in 12 h when the cathodes were operated in MFCs for 20 and 30 d, comparing to 12–15% recoveries of direct current (DC) treatment, but the energy needed of AC+ was only 1/4 of DC. Pores in the catalyst layer were substantially cleaned after AC+ treatment, leading to a 43% increase in cathodic oxygen diffusion coefficient. Bacteria attached to the cathode were simultaneously inactivated (65 ± 1% dead). The biofilm on cathodes was expanded from 34 ± 1 to 51 ± 1 µm by salts released from the catalyst layer. These findings provide a novel energy-saving technology to prolong the performance of activated carbon air-cathodes in MFCs, which can be also used to remove ions and biofouling from the porous surface.

Mitigating external and internal cathode fouling using a polymer bonded separator in microbial fuel cells

Microbial fuel cell (MFC) cathodes rapidly foul when treating domestic wastewater, substantially reducing power production over time. Here a wipe separator was chemically bonded to an activated carbon air cathode using polyvinylidene fluoride (PVDF) to mitigate cathode fouling and extend cathode performance over time. MFCs with separator-bonded cathodes produced a maximum power density of 190 ± 30 mW m−2 after 2 months of operation using domestic wastewater, which was ∼220% higher than controls (60 ± 50 mW m−2) with separators that were not chemically bonded to the cathode. Less biomass (protein) was measured on the bonded separator surface than the non-bonded separator, indicating chemical bonding reduced external bio-fouling. Salt precipitation that contributed to internal fouling was also reduced using separator-bonded cathodes. Overall, the separator-bonded cathodes showed better performance over time by mitigating both external bio-fouling and internal salt fouling.

Reduced graphene oxide modified activated carbon for improving power generation of air-cathode microbial fuel cells

Abstract

Electric field induced salt precipitation into activated carbon air-cathode causes power decay in microbial fuel cells

As a promising design for the real application of microbial fuel cells (MFCs) in wastewater treatment, activated carbon (AC) air-cathode is suffering from a serious power decay after long-term operation. However, the decay mechanism is still not clear because of the complex nature of contaminations. Different from previous reports, we found that local alkalinization and natural evaporation had an ignorable effect on cathode performance (∼2% decay on current densities), while electric field induced salt precipitation (∼53%) and biofouling (∼37%) were dominant according to the charge transfer resistance, which decreased power desities by 36% from 1286 ± 30 to 822 ± 23 mW m−2 in 6 months. Biofouling can be removed by scrapping, however, electric field induced salt precipitation under biofilm still clogged 37% of specific area in catalyst layer, which was even seen to penetrate through the gas diffusion layer. Our findings provided a new insight of AC air-cathode performance decay, providing important information for the improvement of cathodic longevity in the future.

Durability and regeneration of activated carbon air-cathodes in long-term operated microbial fuel cells

The performance of activated carbon catalyst in air-cathodes in microbial fuel cells was investigated over one year. A maximum power of 1722 mW m−2 was produced within the initial one-month microbial fuel cell operation. The air-cathodes produced a maximum power >1200 mW m−2 within six months, but gradually became a limiting factor for the power output in prolonged microbial fuel cell operation. The maximum power decreased by 55% when microbial fuel cells were operated over one year due to deterioration in activated carbon air-cathodes. While salt/biofilm removal from cathodes experiencing one-year operation increased a limiting performance enhancement in cathodes, a washing-drying-pressing procedure could restore the cathode performance to its original levels, although the performance restoration was temporary. Durable cathodes could be regenerated by re-pressing activated carbon catalyst, recovered from one year deteriorated air-cathodes, with new gas diffusion layer, resulting in ∼1800 mW m−2 of maximum power production. The present study indicated that activated carbon was an effective catalyst in microbial fuel cell cathodes, and could be recovered for reuse in long-term operated microbial fuel cells by simple methods.

Efficient removal of nitrobenzene and concomitant electricity production by single-chamber microbial fuel cells with activated carbon air-cathode

Single-chamber microbial fuel cells (S-MFCs) with bio-anodes and activated carbon (AC) air-cathodes showed high nitrobenzene (NB) tolerance and NB removal with concomitant electricity production. The maximum power over 25Wm−3 could be obtained when S-MFCs were operated in the NB loading range of 1.2–6.2molm−3d−1, and stable electricity production over 13.7Wm−3 could be produced in a NB loading range of 1.2–14.7molm−3d−1. The present S-MFCs exhibited high NB removal performance with NB removal efficiency over 97% even when the NB loading rate was increased to 17.2molm−3d−1. The potential NB reduced product (i.e. aniline) could also be effectively removed from influents. The findings in this study means that single-chamber MFCs assembled with pre-enriched bio-anodes and AC air-cathodes could be developed as effective bio-electrochemical systems to remove NB from wastewaters and to harvest energy instead of consuming energy.