SiOC-based polymer derived-ceramic porous anodes for microbial fuel cells

PDA-Fe3O4 decorated carbon felt anode enhancing electrochemical performance of microbial fuel cells: Effect of electrode materials on electroactive biofilm

Anode modification is an effective strategy for enhancing the electrochemical performance of microbial fuel cell (MFC). However, the impacts of the modified materials on anode biofilm development during MFC operation have been less studied. We prepared a novel PDA-Fe3O4-CF composite anode by coating original carbon felt anode (CF) with polydopamine (PDA) and Fe3O4 nanoparticles. The composite anode material was characterized by excellent hydrophilicity and electrical conductivity, and the anodic biofilm exhibited fast start-up, higher biomass, and more uniform biofilm layer after MFC operation. The MFC reactor assembled with the composite anode achieved a maximum power density of 608 mW m-2 and an output voltage of 586 mV, which were 316.4% and 72.4% higher than the MFC with the original CF anode, respectively. Microbial community analysis indicated that the modified anode biofilm had a higher relative abundance of exoelectrogen species in comparison to the unmodified anode. The PICRUSt data revealed that the anodic materials may affect the bioelectrochemical performance of the biofilm by influencing the expression levels of key enzyme genes involved in biofilm extracellular polymer (EPS) secretion and extracellular electron transfer (EET). The growth of the anodic biofilm would exert positive or negative influences on the efficiency of electricity production and electron transfer of the MFCs at different operating stages. This work expands the knowledge of the role that anodic materials play in the development and electrochemical performance of anodic biofilm in MFCs.

N-Doped Carbon Nanowire-Modified Macroporous Carbon Foam Microbial Fuel Cell Anode: Enrichment of Exoelectrogens and Enhancement of Extracellular Electron Transfer

Microbial fuel cell (MFC) performance is affected by the metabolic activity of bacteria and the extracellular electron transfer (EET) process. The deficiency of nanostructures on macroporous anode obstructs the enrichment of exoelectrogens and the EET. Herein, a N-doped carbon nanowire-modified macroporous carbon foam was prepared and served as an anode in MFCs. The anode has a hierarchical porous structure, which can solve the problem of biofilm blockage, ensure mass transport, favor exoelectrogen enrichment, and enhance the metabolic activity of bacteria. The microscopic morphology, spectroscopy, and electrochemical characterization of the anode confirm that carbon nanowires can penetrate biofilm, decrease charge resistance, and enhance long-distance electron transfer efficiency. In addition, pyrrolic N can effectively reduce the binding energy and electron transfer distance of bacterial outer membrane hemin. With this hierarchical anode, a maximum power density of 5.32 W/m3 was obtained, about 2.5-fold that of bare carbon cloth. The one-dimensional nanomaterial-modified macroporous anodes in this study are a promising strategy to improve the exoelectrogen enrichment and EET for MFCs.

Investigating the Performance of a Zinc Oxide Impregnated Polyvinyl Alcohol-Based Low-Cost Cation Exchange Membrane in Microbial Fuel Cells

The current study investigated the development and application of lithium (Li)-doped zinc oxide (ZnO)-impregnated polyvinyl alcohol (PVA) proton exchange membrane separator in a single chambered microbial fuel cell (MFC). Physiochemical analysis was performed via FT-IR, XRD, TEM, and AC impedance analysis to characterize thus synthesized Li-doped ZnO. PVA-ZnO-Li with 2.0% Li incorporation showed higher power generation in MFC. Using coulombic efficiency and current density, the impact of oxygen crossing on the membrane cathode assembly (MCA) area was evaluated. Different amounts of Li were incorporated into the membrane to optimize its electrochemical behavior and to increase proton conductivity while reducing biofouling. When acetate wastewater was treated in MFC using a PVA-ZnO-Li-based MCA, the maximum power density of 6.3 W/m³ was achieved. These observations strongly support our hypothesis that PVA-ZnO-Li can be an efficient and affordable separator for MFC.

Ceramic-microbial fuel cell (C-MFC) for waste water treatment: A mini review

Microbial fuel cell (MFC) is a bio-electrochemical system that utilizes the activity of electrogenic bacteria to generate electricity. When wastewater is used as feed in MFC, its organic constituents are hydrolyzed and oxidized by the bacteria. Hence, this technology is a source of clean electricity while simultaneously treating wastewater. Over the years much research has been done to improve its efficiency as well as to reduce the cost of implementation and functioning. However, scalability and commercialization of this technology still faces several challenges. This mini review discusses the use of ceramics in MFCs using wastewater feed as a method of overcoming the current technological challenges. Ceramics can be used as separators, chassis or electrode, conferring facile chemical and structural stability. The material is low-cost, environment-friendly and easily available. Studies reporting stacked configurations have been mentioned, and those that have reported field studies and technology oriented practical applications. Critical analysis of the scalability of the use of ceramics for the dual purpose of electricity generation as well as wastewater treatment has been done in this review. Future research directives towards potential sustainable commercialization have also been mentioned. C-MFC is a promising technology and the primary aim of this review is to help enhance the knowledge base for the optimization of use of ceramics in MFC to achieve large-scale clean electricity generation and sewage treatment.

Degradation of pyrene using single-chamber air-cathode microbial fuel cells: Electrochemical parameters and bacterial community changes

Pyrene, a typical four-ring polycyclic aromatic hydrocarbon, is abundantly present in the environment and is potentially harmful to the human body. In this study, single-chamber air-cathode microbial fuel cells (MFCs) were used to treat pyrene, and the ensuing degradation, electrical parameters, and microbial changes were analyzed. The results showed that MFCs could degrade pyrene, and the maximum degradation rate for 30 mg/L reached 88.1 ± 5.4%. The addition of pyrene reduced the electrical performance of the MFCs and suppressed the power output. Analysis of the anodic microbial community showed that the proportion of Alcaligenes and Stenotrophomonas increased with an increase in pyrene concentration, which may explain the high degradation rate of pyrene.

Tuning of Electrode Surface for Enhanced Bacterial Adhesion and Reactions: A Review on Recent Approaches

The study of bacterial adhesion and its consequences has great significance in different fields such as marine science, renewable energy sectors, soil and plant ecology, food industry, and the biomedical field. Generally, the adverse effects of microbial surface interactions have attained wide visibility. However, herein, we present distinct approaches to highlight the beneficial aspects of microbial surface interactions for various applications rather than deal with the conventional negative aspects or prevention strategies. The surface microbial reactions can be tuned for useful biochemical or bio-electrochemical applications, which are otherwise unattainable through conventional routes. In this context, the present review is a comprehensive approach to highlight the basic principles and signature parameters that are responsible for the useful microbial-electrode interactions. It also proposes various surface tuning strategies, which are useful for tuning the electrode characteristics particularly suitable for the enhanced bacterial adhesion and reactions. The tuning of surface characteristics of electrodes is discussed with a special reference to the Microbial Fuel Cell as an example.

Carbon-Based Composites as Anodes for Microbial Fuel Cells: Recent Advances and Challenges

Owing to the low price, chemical stability and good conductivity, carbon-based materials have been extensively applied as the anode in microbial fuel cells (MFCs). In this review, apart from the charge storage mechanism and anode requirements, the major work focuses on five categories of carbon-based anode materials (traditional carbon, porous carbon, nano-carbon, metal/carbon composite and polymer/carbon composite). The relationship is demonstrated in depth between the physicochemical properties of the anode surface/interface/bulk (porosity, surface area, hydrophilicity, partical size, charge, roughness, etc.) and the bioelectrochemical performances (electron transfer, electrolyte diffusion, capacitance, toxicity, start-up time, current, power density, voltage, etc.). An outlook for future work is also proposed.

Macromonomers as a Novel Way to Investigate and Tailor Silicon-Oxycarbide-Based Materials Obtained from Polymeric Preceramic Precursors

It has been shown that bifunctional monomers (D units), which are used to increase the carbon content in silicon oxycarbide precursors, can form volatile oligomers, thus affecting the amount of carbon available during the transition into the final material in the annealing process. Additionally, an uneven distribution of carbon-rich mers may lead to the formation of a free-carbon phase, instead of the incorporation of carbon atoms into the silicon matrix. In this study, a novel two-step approach was utilized. Firstly, a macromonomer containing a number of structural units with precise structure was synthesized, which was later polycondensed into a ceramic precursor. Chlorodimethylsilane modified 2,4,6,8-tetramethylcyclotetrasiloxane was used as a silicon oxycarbide precursor monomer containing both T and D structural units (i.e., silicon atoms bonded to three and two oxygen atoms, respectively), with well-defined interconnections between structural units. Such a macromonomer prevents the formation of small siloxane rings, and has a very limited number of possible combinations of structural units neighboring each silicon atom. This, after investigation using IR, XRD, TG and elemental analysis, gave insight into the effect of “anchoring” silicon atoms bonded to two methyl groups, as well as the impact of their distribution in comparison to the materials obtained using simple monomers containing a single silicon atom (structural unit).

Up-Cycling of Iron-Rich Inorganic Waste in Functional Glass-Ceramics

The intensive mechanical stirring of suspensions of recycled glass and inorganic waste powders in ‘weakly alkaline’ aqueous solutions (e.g., 2.5–3 NaOH), followed by viscous flow sintering at 800–1000 °C, easily yields highly porous glass-ceramic foams. The firing determines just the consolidation of powders with concurrent incorporation of pollutants from iron-rich waste, such as fly ash from coal combustion (FA). Engineered mixtures allow for the obtainment of chemically stable foams from treatments in air. Treatments in nitrogen are even more significant since they extend the conditions for stabilization and promote novel functionalities. In addition, the change in the atmosphere favors the formation of magnetite (Fe3O4), in turn enabling ultra-high dielectric permittivity and semiconductivity. Such a condition was further evidenced by preliminary tests on recycled glass combined with residues from the Bayer processing of aluminum ores or red mud (RM).

A new silicon oxycarbide based gas diffusion layer for zinc-air batteries

Rational material designs play a vital role in the gas diffusion layer (GDL) by increasing the oxygen diffusion rate and, consequently, facilitating a longer cycle life for metal-air batteries. In this work, a new porous conductive ceramic membrane has been developed as a cathodic GDL for zinc-air battery (ZAB). The bilayered structure with a thickness of 390 μm and an open porosity of 55% is derived from a preceramic precursor with the help of the freeze tape casting technique. The hydrophobic behaviour of the GDL is proved by the water contact angle of 137.5° after the coating of polytetrafluoroethylene (PTFE). The electrical conductivity of 5.59 * 10^-3 S/cm is reached using graphite and MWCNT as filler materials. Tested in a ZAB system, the as-prepared GDL coated with commercial Pt-Ru/C catalyst shows an excellent cycle life over 200 cycles and complete discharge over 48 h by consuming oxygen from the atmosphere, which is comparable to commercial electrodes. The as-prepared electrode exhibits excellent ZAB performance due to the symmetric sponge-like structure, which facilitates the oxygen exchange rate and offers a short path for the oxygen ion/-electron kinetics. Thus, this work highlights the importance of a simple manufacturing process that significantly influences advanced ZAB enhancement.

Improved bio-electricity production in bio-electrochemical reactor for wastewater treatment using biomass carbon derived from sludge supported carbon felt anode

Microbial fuel cell (MFC), a promising bio-electrochemical reactor could decompose organics in wastewater by redox processes of electro-active microorganism in anode and produce bio-energy, and the total MFC performance could mainly rely on electrochemical performance anode. Here, biomass carbon derived from municipal sludge was employed as low-cost and high-performance bio-anode for enhancing bioelectricity generation and wastewater treatment in MFC simultaneously. The electrochemical tests demonstrated that the large electrochemical active surface area, strong conductivity, and good biocompatibility in sludge carbon (SC) electrode resulted in higher power density (615.2 mW m^-2) and lower power loss (5.4%) than those of none carbon (NC) electrode in long term operation. After 30-cycle of continuous running, the low loss of chemical oxygen demand (COD) removal was achieved up to 5.2%, which was smaller than that of NC electrode (14.1%), indicating that the MFC with SC anode could effectively treat wastewater and keep stable redox processes in anode electrode. After the formation of biofilm, the charge transfer resistance of SC electrode (16.38 Ω) was 72.4% lower than that of NC electrode (59.35 Ω). High-throughput analysis of biofilm exhibit Proteobacteria was the dominant electro-active bacteria, and the modification of SC could slightly change the bacterial community. Therefore, resource utilization of natural wastes provided the novel concept of anode catalyst fabrication for MFC in enhancing electron transfer, power output and wastewater decomposition.

Microbial fuel cell for nutrient recovery and electricity generation from municipal wastewater under different ammonium concentrations

In the present study, a dual-compartment microbial fuel cell (MFC) was constructed and continuously operated under different influent concentrations of ammonium-nitrogen (5-40 mg/L). The impacts of ammonium on organics removal, energy output and nutrient recovery were investigated. Experimental results demonstrated that this MFC reactor achieved a CDO removal efficiency of greater than 85%. Moreover, excess ammonium concentration in the feed solution compromises the generation of electricity. Simultaneously, the recovery rate of phosphate achieved in the MFC was insignificantly influenced at the wider influent ammonium concentration. In contrast, a high concentration of ammonium may not be beneficial for its recovery.