Activated Carbon Air Cathode Research Articles

Addition of conductive particles to improve the performance of activated carbon air-cathodes in microbial fuel cells

Inexpensive carbon black combined with heat-treatment produced the most effective activated carbon catalyst for improving microbial fuel cell cathode performance.

Waterproof Breathable Membrane Used as Gas Diffusion Layer in Activated Carbon Air Cathode Microbial Fuel Cells

AbstractOne of the main limiting factors for scaling up microbial fuel cells (MFCs) technology is to develop low‐cost and high‐efficiency cathode. A new and simplified approach was developed by using a commercial waterproof breathable membrane (WBM) as gas diffusion layer (GDL) material as substitution for conventional polytetrafluoroethylene (PTFE) GDL. Air‐cathode with the WBM pasted (AC‐P) onto the stainless steel mesh (SSM) achieved a maximum power density of 611 ± 10 mWm−2, which was similar to that using a PTFE GDL by rolling method (645 ± 12 mWm−2, AC‐R). Physical and electrochemical techniques were employed to investigate the morphology and electrochemical characteristics of the cathode. The result demonstrated that AC‐P had a higher current density and internal resistance than AC‐R. Besides, the WBM had a higher porosity and uniform texture. The study showed that the WBM was a kind of good GDL material for easy preparation, low cost and stable performance of cathode construction.

Temperature-depended Cu0.92Co2.08O4 modified activated carbon air cathode improves power output in microbial fuel cell

Temperature-depended Cu0.92Co2.08O4 catalyst doped activated carbon (AC) air cathode for microbial fuel cells (MFCs) was studied for the first time. The Cu0.92Co2.08O4 was compounded via hydrothermal method followed by calcinated at 400, 500, 600 and 700 °C, respectively. The maximum power density (MPD) with the catalyst calcinated at 600 °C was 1895 mW m−2, 113% higher than the control. Besides, the resistances including total resistance and charge transfer resistance were remarkably decreased compared to the bare AC. Tafel curve also showed the fastest electro-transfer kinetics with exchange current density of 2.38347 × 10−3 A cm−2, 4.2 times higher than the bare. The oxygen reduction reaction pathway of Cu0.92Co2.08O4 was via four electrons. The mechanism of improved oxygen reduction reaction performance of Cu0.92Co2.08O4 was researched by XRD, SEM, TEM and XPS. Thus Cu0.92Co2.08O4 would be a promising electrocatalyst alternative to Pt for the ORR in microbial fuel cell.

Influence of Micropore and Mesoporous in Activated Carbon Air-cathode Catalysts on Oxygen Reduction Reaction in Microbial Fuel Cells

In this study, carbon samples with different micropore and mesoporous structures are prepared as air-cathode catalyst layer to explore the role of pore structure on oxygen reduction reaction. The results of linear sweep voltammetry and power density show that the commercially-produced activated carbon (CAC) has the best electrochemical performance, and carbon samples with only micropore or mesoporous show lower performance than CAC. Nitrogen adsorption-desorption isotherms analysis confirm that CAC has highest surface area (1616m2g−1) and a certain amount of micropore and mesoporous. According to Tafel plot and rotating disk electrode, CAC behaves the highest kinetic activity and electron transfer number, leading to the improvement of oxygen reduction reaction. The air permeability test proves that mesoporous structure enhance oxygen permeation. Carbon materials are also analyzed by In situ Fourier Transform Infrared Spectroscopy and H2 temperature programmed reduction, which indicate that micropore provide active sites for catalysis. In a word, micropore and mesoporous together would improve the electrochemical performance of carbon materials.

The Addition of Ortho-Hexagon Nano Spinel Co3O4 to Improve the Performance of Activated Carbon Air Cathode Microbial Fuel Cell

Commercial Co3O4 and ortho-hexagon spinel nano-Co3O4 (OHSNC) were doped in the AC at a different percentage (5%, 10% and 15%) respectively to enhance the performance of microbial fuel cell (MFC). The maximum power density of MFC with 10% OHSNC doped cathode was 1500 ± 14 mW m-2, which was 97.36% and 41.24% higher than the bare AC air cathode and commercial Co3O4 respectively. The electrocatalytic behavior for their better performance was discussed in detail with the help of various structural and electrochemical techniques. The OHSNC was characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The results showed that the improved performance owed to both the enhancement of kinetics activity and the number of electron transfer in the ORR, and the internal resistance was largely reduced. Therefore, OHSNC was proved to be an excellent cathodic catalyst in AC air cathode MFC.

The excellent performance and mechanism of activated carbon air cathode doped with different type of cobalt for microbial fuel cells

A novel cobalt decorated activated carbon (AC) air cathode with facilitated oxygen reduction activity is developed for microbial fuel cells (MFCs). Two kinds of cobalt modified cathodes Co(OH)2/AC and Co3O4/AC were prepared via a simple electrodeposition. The electrodeposition process was optimized to achieve high a surface area and pore volume structure. Transmission electron spectroscopy (TEM) analyses confirmed that Co3O4 and Co(OH)2 nanosheets were homogeneously distributed on the AC. Compared to raw AC. Electrochemical evaluation showed that the onset potentials towards oxygen reduction reaction (ORR) of Co(OH)2/AC and Co3O4/AC shifted to higher potential and the exchange current densities were increased by 2.6 times and 1.6 times, respectively. The MFCs with Co3O4/AC reached a maximum power density of 1420.8±54mWm−2, significantly improved performance by 64% in relative raw AC.

Energy efficient electrocoagulation using an air-breathing cathode to remove nutrients from wastewater

Electrocoagulation (EC) can be used to remove nutrients as well as suspended solids and organic carbon from wastewaters, but the high energy requirements (pumping air) and the use of precious metals in some processes has hindered widespread application of EC technologies. The use of a thermodynamically favorable activated carbon air cathode and a sacrificial aluminum anode was examined to reduce the energy needed for EC for nutrient removal. Performance of the air cathode electrocoagulation (ACEC) process was tested using raw wastewater, and a carbon-free synthetic solution (nitrogen:phosphorus ratio of 1:10 in deionized water) to simulate nutrient removal of a wastewater treated for organic matter removal. ACEC treatment of wastewater removed up to 99% of both ammonia and phosphorus, along with 72–81% COD and 78–89% TSS in 4h (1.5cm electrode spacing, current density of 8Am−2). Nearly total removal of the nutrients required 1.8kWhm−3, which is lower than that previously reported for some EC processes for this application (0.4–22kWhm−3). Nutrient removals using synthetic solutions (no organic matter) ranged from 74% to 93% for nitrogen (47–370mg-N/L) and 44–76% for phosphorus. These results indicate that the ACEC can achieve good levels of nutrient removal with reduced energy demands compared to previous EC systems.

Iron–nitrogen–activated carbon as cathode catalyst to improve the power generation of single-chamber air-cathode microbial fuel cells

In order to improve the performance of microbial fuel cell (MFC), iron–nitrogen–activated carbon (Fe–N–C) as an excellent oxygen reduction reaction (ORR) catalyst was prepared here using commercial activated carbon (AC) as matrix and employed in single chamber MFC. In MFC, the maximum power density increased to 2437±55mWm−2, which was 2 times of that with AC. The open circuit potential (OCP) of Fe–N–C cathode (0.47) was much higher than that of AC cathode (0.21V). The R0 of Fe–N–C decreased by 47% from 14.36Ω (AC) to 7.6Ω (Fe–N–C). From X-ray photoelectron spectroscopy (XPS), pyridinic nitrogen, quaternary nitrogen and iron species were present, which played an important role in the ORR performance of Fe–N–C. These results demonstrated that the as-prepared Fe–N–C material provided a potential alternative to Pt in AC air cathode MFC for relatively desirable energy generation and wastewater treatment.

Diffusion layer characteristics for increasing the performance of activated carbon air cathodes in microbial fuel cells

Air cathode characteristics significantly affected power production of microbial fuel cells during wastewater treatment.

Development of carbon free diffusion layer for activated carbon air cathode of microbial fuel cells

The fabrication of activated carbon air cathodes for larger-scale microbial fuel cells requires a diffusion layer (DL) that is highly resistant to water leakage, oxygen permeable, and made using inexpensive materials. A hydrophobic polyvinylidene fluoride (PVDF) membrane synthesized using a simple phase inversion process was examined as a low cost ($0.9/m2), carbon-free DL that prevented water leakage at high pressure heads compared to a polytetrafluoroethylene/carbon black DL ($11/m2). The power density produced with a PVDF (20%, w/v) DL membrane of 1400±7mW/m2 was similar to that obtained using a wipe DL [cloth coated with poly(dimethylsiloxane)]. Water head tolerance reached 1.9m (∼19kPa) with no mesh supporter, and 2.1m (∼21kPa, maximum testing pressure) with a mesh supporter, compared to 0.2±0.05m for the wipe DL. The elimination of carbon black from the DL greatly simplified the fabrication procedure and further reduced overall cathode costs.

The performance and mechanism of modified activated carbon air cathode by non-stoichiometric nano Fe3O4 in the microbial fuel cell

Cathodic catalyst is one of the key materials in microbial fuel cell (MFC). The addition of non-stoichiometric nano Fe3O4 in activated carbon (NSFe3O4/AC) air cathode was beneficial to boosting the charge transfer of the cathode accompanying with the enhancement of power performance in MFC. The air cathode modified by NSFe3O4 (5%, Wt%) increased the maximum power density by 83.3% from 780 mW/m(2) to 1430 mW/m(2) compared with bare air cathode. The modified cathodes showed enhanced electrochemical properties and appeared the maximum exchange current density of 18.71×10(-4) A/cm(2) for oxygen reduction reaction. The mechanism of oxygen reduction for the NSFe3O4/AC catalyst was a 4-electron pathway. The oxygen vacancy of the NSFe3O4 played a crucial role in electrochemical catalytic activity. The great catalytic performance made NSFe3O4 have a promising outlook applied in MFC.

Influence of different morphology of three-dimensional CuxO with mixed facets modified air–cathodes on microbial fuel cell

Three kinds of three-dimensional (3D) CuxO catalysts were prepared to modify activated carbon air–cathode using a facile electrochemical method with addition of surfactants. The maximum power density of MFC using SC-Cu air cathode (added sodium citrate into the electrolyte solution in electrodeposition process) was 1550±47mWm−2, almost 77% higher than AC cathode. Specifically, the charge transfer resistance significantly decreased by 89% from 9.3980Ω to 1.0640Ω compared to the control. Lumphy and mutually embedded filmy sheet structure were observed in SEM, which provided sufficient active sites for oxygen adsorption and diffusion. In XRD and TEM result, CuxO with mixed facets showed special structure which had a better performance. Crystallization condition of electrodeposited materials played a significant role in their nature electrochemical properties, morphology controlled by surfactant of CuxO exhibited high properties on the air–cathode MFC.

The addition of ortho-hexagon nano spinel Co3O4 to improve the performance of activated carbon air cathode microbial fuel cell

Commercial Co3O4 and ortho-hexagon spinel nano-Co3O4 (OHSNC) were doped in the AC at a different percentage (5%, 10% and 15%) to enhance the performance of microbial fuel cell (MFC). The maximum power density of MFC with 10% OHSNC doped cathode was 1500±14mWm−2, which was 97.36% and 41.24% higher than that with the bare AC air cathode and commercial Co3O4 respectively. The electrocatalytic behavior for their better performance was discussed in detail with the help of various structural and electrochemical techniques. The OHSNC was characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The results showed that the improved performance owed to the enhancement of both kinetics activity and the number of electron transfer in the ORR, and the internal resistance was largely reduced. Therefore, OHSNC was proved to be an excellent cathodic catalyst in AC air cathode MFC.

Effects of Catalyst Layer and Gas Diffusion Layer Thickness on the Performance of Activated Carbon Air-cathode for Microbial Fuel Cells

Effects of Catalyst Layer and Gas Diffusion Layer Thickness on the Performance of Activated Carbon Air-cathode for Microbial Fuel Cells

Inhibition of microbial growth on air cathodes of single chamber microbial fuel cells by incorporating enrofloxacin into the catalyst layer.

The inevitable growth of aerobic bacteria on the surface of air cathodes is an important factor reducing the performance stability of air cathode single-chamber membrane-free microbial fuel cells (MFCs). Thus searching for effective methods to inhibit the cathodic microbial growth is critical for the practical application of MFCs. In this study, enrofloxacin (ENR), a broad spectrum fluoroquinolone antibiotic, was incorporated into the catalyst layer of activated carbon air cathodes (ACACs) to inhibit the cathodic microbial growth. The biomass content on ACACs was substantially reduced by 60.2% with ENR treatment after 91 days of MFCs operation. As a result of the inhibited microbial growth, the oxygen reduction catalytic performance of the ENR treated ACACs was much stable compared to the fast performance decline of the untreated control. Consequently, a quite stable electricity production was obtained for the MFCs with the ENR treated ACACs, in contrast with a 22.5% decrease in maximum power density of the MFCs with the untreated cathode. ENR treatment of ACACs showed minimal effects on the anode performance. These results indicate that incorporating antibiotics into ACACs should be a simple and effective strategy to inhibit the microbial growth and improve the long-term stability of the performance of air cathode and the electricity production of MFCs.

N-type Cu2O doped activated carbon as catalyst for improving power generation of air cathode microbial fuel cells

A novel n-type Cu2O doped activated carbon (AC) air cathode (Cu/AC) was developed as an alternative to Pt electrode for oxygen reduction in microbial fuel cells (MFCs). The maximum power density of MFCs using this novel air cathode was as high as 1390±76mWm−2, almost 59% higher than the bare AC air cathode. Specifically, the resistance including total resistance and charge transfer resistance significantly decreased comparing to the control. Tafel curve also showed the faster electro-transfer kinetics of Cu/AC with exchange current density of 1.03×10−3Acm−2, which was 69% higher than the control. Ribbon-like Cu2O was deposited on the surface of AC with the mesopore surface area increasing. Cubic Cu2O crystals exclusively expose (111) planes with the interplanar crystal spacing of 2.48Å, which was the dominate active sites for oxygen reduction reaction (ORR). N-type Cu2O with oxygen vacancies played crucial roles in electrochemical catalytic activity.

Optimization of Fabrication Parameters to Enhance the Performance of Activated Carbon Air-Cathode

The aim of this work was to investigate the effect of three key fabrication factors (i.e. pressure, AC/PTFE mass ratio, and AC load) on the performance of activated carbon air-cathode (ACAC). The design of experiment work was performed with the response surface methodology (RSM) using the central composite design. 20 combinations of the three variables were optimized based on the responses evaluated by linear sweep voltammetry (LSV). The results showed that the proposed mathematical model in the RSM could be used adequately for prediction and optimization within the factor levels investigated. The combined optimum fabrication parameters that gave the highest performance of ACAC were pressure 10 MPa, AC/PTFE mass ratio 6 and AC load 0.3 g. The fabricated ACACs were characterized by Electrochemical Impedance Spectroscopy (EIS), Brunauer-Emmett-Teller (BET) test and fuel cell test. The characterization results demonstrated that the improved performance of ACAC owed to the increase of both specific surface area and conductivity, and the controlled surface hydrophilicity/hydrophobicity.

Bifunctional quaternary ammonium compounds to inhibit biofilm growth and enhance performance for activated carbon air-cathode in microbial fuel cells

The slow diffusion of hydroxyl out of the catalyst layer as well as the biofouling on the surface of cathode are two problems affecting power for membrane-less air-cathode microbial fuel cells (MFCs). In order to solve both of them simultaneously, here we simply modify activated carbon air-cathode using a bifunctional quaternary ammonium compound (QAC) by forced evaporation. The maximum power density reaches 1041 ± 12 mW m−2 in an unbuffered medium (0.5 g L−1 NaCl), which is 17% higher than the control, probably due to the accelerated anion transport in the catalyst layer. After 2 months, the protein content reduced by a factor of 26 and the power density increases by 33%, indicating that the QAC modification can effectively inhibit the growth of cathodic biofilm and improve the stability of performance. The addition of NaOH and QAC epoxy have a negative effect on power production due to the clogging of pores in catalyst layer.

A novel and high performance activated carbon air-cathode with decreased volume density and catalyst layer invasion for microbial fuel cells

To enhance the performance of activated carbon air cathodes for microbial fuel cells (MFCs), scattered and dense air-cathodes are fabricated by the rolling-press method with the gas diffusion layer or the catalyst layer (CL) invaded to stainless steel meshes (SSM). The maximum power density with scattered cathodes (2503 ± 61 mW m−2) is 29% higher than those of dense cathodes because of the decreased internal resistance and increased oxygen reduction reaction activity. The decrease in the electrode volume density and invasion of CL into SSM has been demonstrated to be an optimal structure, with the highest exchange current density up to 1.26 A m−2 and the lowest charge transfer resistance as low as 1.5 Ω. The increase in performance is believed to result from the enhanced mass transport through extra pores and the contact of activated carbon to the current collector. This novel structure of an air-cathode has a promising future as an application in MFCs.

Silver electrodeposition on the activated carbon air cathode for performance improvement in microbial fuel cells

The present work was to study silver electrodeposition on the activated carbon (AC) air cathode for performance improvement in microbial fuel cells (MFCs). The treated cathodes were proved to be effective to enhance the performance of MFCs. The maximum power density of MFC with silver electrodeposition time of 50 s (Ag-50) cathode was 1080 ± 60 mW m−2, 69% higher than the bare AC air cathode. X-ray photoelectron spectroscopy (XPS) results showed that zero-valent, monovalent and divalent silver were present to transform mutually, which illustrated that the oxygen reduction reaction (ORR) at the cathode took place through four-electron pathway. From electrochemical impedance spectroscopy (EIS) analysis, the electrodeposition method made the total resistance of the electrodes largely reduced. Meanwhile the deposited silver had no toxic effects on anode culture but inhibited the biofilm growth of the cathodes. This kind of antimicrobial efficient cathode, prepared with a simple, fast and economical method, was of good benefit to the performance improvement of MFCs.